Electricity quality. Power quality requirements. Requirements for the reliability of power supply and quality of electricity Quality of electricity in the project what to write

Quality of electrical energy

Introduction

electrical energy voltage

Electric energy as a commodity is used in all spheres of human life, has a set of specific properties and is directly involved in the creation of other types of products, affecting their quality. The concept of quality of electric energy (QE) differs from the concept of quality of other types of products. Each power receiver is designed to operate at certain parameters of electrical energy: nominal frequency, voltage, current, etc., therefore, for its normal operation, the required CE must be provided. Thus, the quality of electrical energy is determined by the totality of its characteristics, under which power receivers (EP) can operate normally and perform their functions.

CE at the place of production does not guarantee its quality at the place of consumption. The CE before and after switching on the EA at the point of its connection to the electrical network can be different. CE is also characterized by the term "electromagnetic compatibility". Electromagnetic compatibility is understood as the ability of an EA to function normally in its electromagnetic environment (in the electrical network to which it is connected), without creating unacceptable electromagnetic interference for other EAs operating in the same environment.

The problem of electromagnetic compatibility of industrial ED with the supply network has arisen in connection with the widespread use of powerful valve converters, arc steel-smelting furnaces, welding installations, which, for all their economy and technological efficiency, have a negative impact on the CE.

Household EPs, as well as industrial ones, must also have electromagnetic compatibility with other EPs included in the common power grid, not reduce the efficiency of their work and not worsen the SCE.

CE in industry is evaluated by technical and economic indicators, which take into account damage due to damage to materials and equipment, disruption of the technological process, deterioration in the quality of products, and a decrease in labor productivity - the so-called technological damage. In addition, there is electromagnetic damage from low-quality electricity, which is characterized by an increase in electricity losses, failure of electrical equipment, disruption of automation, telemechanics, communications, electronic equipment, etc.

KE is closely related to the reliability of power supply, since the normal mode of power supply to consumers is such a mode in which consumers receive electricity uninterruptedly, in an amount agreed in advance with the power supply organization, and of a normalized quality. Article 542 of the Civil Code of the Russian Federation obliges to supply electricity, the quality of which meets the requirements of state standards and other mandatory rules or energy supply contracts.

In accordance with the Law of the Russian Federation "On the Protection of Consumer Rights" (Article 7) and the Decree of the Government of Russia dated August 13, 1997 No. 1013, electrical energy is subject to mandatory certification in terms of electricity quality indicators established by GOST 13109-97 "Quality standards for electrical energy in general purpose power supply systems. This means that each energy supplying organization, along with a license for the production, transmission and distribution of electricity, must obtain a certificate certifying that the quality of the energy it supplies meets the requirements of GOST 13109-97.

1. The main provisions of the state standard for the quality of electrical energy

GOST 13109-97 "Normals for the quality of electrical energy in general-purpose power supply systems" (hereinafter referred to as GOST) establishes indicators and standards for the quality of electricity in electrical networks of general-purpose power supply systems of three-phase and single-phase alternating current with a frequency of 50 Hz at points to which electrical networks are connected. owned by various consumers of electrical energy, or receivers of electrical energy (points of common connection). GOST 13109-97 is an interstate standard and has been in force in the Russian Federation since January 1, 1999.

The CE limits set by the standard are the EMC levels for conducted EMI in general power systems. Subject to the established PQ standards, the electromagnetic compatibility of electrical networks of power supply organizations and electrical networks of consumers of electrical energy or electric power is ensured.

The standard does not establish requirements for PQ in electrical networks for special purposes (contact, traction, communications), mobile installations (aircraft, trains, ships), etc.

Conductive electromagnetic interference in the power supply system - electromagnetic interference propagating through the elements of the electrical network.

Point of general connection - a point of a general-purpose electrical network, electrically closest to the networks of the considered consumer of electrical energy, to which the electrical networks of other consumers are connected or can be connected.

The standard does not establish CE norms for modes caused by force majeure (exceptional weather conditions, natural disasters, etc.).

GOST 13109-97 is the first standard in the field of PQ, which states that the established norms are to be included in the technical specifications for the connection of consumers and in power supply contracts.

In order to ensure the standard standards at the points of general connection, consumers who are the culprits for the deterioration of the PQ are allowed to establish more stringent standards in the technical specifications for connection and in power supply contracts (with smaller ranges of changes in the corresponding PQ indicators) than those established in the standard.

The norms of the standard should be applied in the design and operation of electrical networks, in establishing the levels of noise immunity of the EP and the levels of electromagnetic interference introduced by these receivers into the electrical network to which they are connected.

2. Indicators of the quality of electrical energy

The standard establishes the following power quality indicators (PQI):

Steady voltage deviation;

range of voltage change;

flicker dose;

coefficient of the n-th harmonic component of the voltage;

frequency deviation;

voltage dip duration;

impulse voltage;

temporary overvoltage coefficient.

When determining the values ​​of some SCEs, the standard introduces the following auxiliary parameters of electrical energy:

Interval between voltage changes;

voltage dip depth;

the frequency of occurrence of voltage dips;

pulse duration at the level of 0.5 of its amplitude;

duration of temporary overvoltage.

Part of the PQ characterizes the steady-state operating modes of the electrical equipment of the power supply organization and consumers of EE and gives a quantitative assessment of the features of the technological process of production, transmission, distribution and consumption of EE by CE. These SCEs include: the steady-state voltage deviation, the distortion factor of the sinusoidal curve of the voltage, the coefficient of the n-th harmonic component of the voltage, the voltage asymmetry coefficient in the negative sequence, the voltage asymmetry coefficient in the zero sequence, the frequency deviation, the voltage change range.

The assessment of all SCEs related to voltage is made according to its current values.

To characterize the above indicators, the standard establishes numerical normal and maximum allowable values ​​of the SCE or norm.

Another part of the PQ characterizes short-term interference that occurs in the electrical network as a result of switching processes, thunderstorm atmospheric phenomena, the operation of protective equipment and automation, and in post-emergency modes. These include voltage dips and pulses, short-term overvoltages. For these SCEs, the standard does not establish acceptable numerical values. To quantify these SCEs, the amplitude, duration, frequency of their occurrence, and other characteristics established but not standardized by the standard should be measured. Statistical processing of these data makes it possible to calculate generalized indicators that characterize a specific electrical network in terms of the probability of short-term interference.

To assess the compliance of the SCE with the specified standards (with the exception of the duration of the voltage dip, impulse voltage and the coefficient of temporary overvoltage), the standard establishes a minimum calculation period of 24 hours.

Due to the random nature of the change in electrical loads, the requirement to comply with the PQ standards during all this time is practically unrealistic, therefore, the standard establishes the probability of exceeding the PQ standards. The measured SCEs should not go beyond the normally permissible values ​​with a probability of 0.95 for the estimated period of time established by the standard (this means that individual excesses of the normalized values ​​can be disregarded if their expected total duration is less than 5% for the specified period of time).

In other words, the CE according to the measured indicator complies with the requirements of the standard, if the total duration of the time for going beyond the normally permissible values ​​is no more than 5% of the set time period, i.e. 1 h 12 min, and for the maximum allowable values ​​- 0% of this period of time.

The standard indicates the likely culprits for the deterioration of the PQ. The frequency deviation is regulated by the power supply system and depends only on it. Separate EPs at industrial enterprises (and even more so at home) cannot influence this indicator, since their power is disproportionately small compared to the total power of generators of power plants of the energy system. Voltage fluctuations, asymmetry and non-sinusoidality of the voltage are mainly caused by the operation of individual powerful electric circuits at industrial enterprises, and only the magnitude of these SCEs depends on the power of the power supply system at the considered consumer connection point. Voltage deviations depend both on the level of voltage supplied by the power system to industrial enterprises, and on the operation of individual industrial EAs, especially those with a large consumption of reactive power. Therefore, PQ issues should be considered in direct connection with reactive power compensation issues. The duration of the voltage dip, the impulse voltage, the coefficient of temporary overvoltage, as already noted, are determined by the operating modes of the power system.

Table 2.1. the properties of electrical energy, their indicators characterizing and the most likely culprits for the deterioration of the CE are given.

Table 2.1. Properties of electrical energy, indicators and the most likely culprits for the deterioration of PQ

Properties of electrical energyPQ indicatorThe most likely culprits for the deterioration of PQVoltage deviationSustained voltage deviation Power supply organizationVoltage fluctuationsVoltage change range

Flicker dose Variable load consumerVoltage non-sinusoidal Voltage distortion factor

Coefficient of the nth harmonic component of the voltage Consumer with a non-linear load Unbalance of the three-phase voltage system Negative sequence voltage unbalance factor

Zero sequence voltage unbalance factor Unbalanced load consumer Frequency deviation Frequency deviation Power supply companyVoltage dipDuration of dip Power supply organizationImpulse voltageImpulse voltage Power supply companyTemporary overvoltageTemporary overvoltage factor Energy supply organization

The standard establishes the calculation methods and methods for determining the PQI and auxiliary parameters, the requirements for measurement errors and averaging intervals for the PQI, which should be implemented in PQ control devices when measuring indicators and processing them.

3. Characteristics of power quality indicators

Voltage deviation

Voltage deviations from nominal values ​​occur due to daily, seasonal and technological changes in the electrical load of consumers; changes in the power of compensating devices; voltage regulation by generators of power plants and substations of power systems; changes in the scheme and parameters of electrical networks.

The voltage deviation is determined by the difference between the effective U and the nominal voltage values, V:

The steady voltage deviation is, %:

where is the steady-state (effective) voltage value for the averaging interval (see clause 3.8).

In electrical networks of single-phase current, the effective voltage value is determined as the value of the voltage of the fundamental frequency without taking into account the higher harmonic components of the voltage, and in electrical networks of three-phase current - as the effective value of the direct sequence voltage of the fundamental frequency.

The standard normalizes voltage deviations at the outputs of electrical energy receivers. Normally permissible and maximum permissible values ​​of the steady-state voltage deviation are respectively ±5 and ±10% of the nominal voltage value and at the points of common connection of consumers of electrical energy should be established in power supply contracts for hours of minimum and maximum loads in the power system, taking into account the need to comply with the standards for outputs of electrical energy receivers in accordance with regulatory documents.

Voltage fluctuations

Voltage fluctuations are caused by a sharp change in the load in the section of the electrical network under consideration, for example, by switching on an asynchronous motor with a high starting current ratio, technological installations with a rapidly changing operating mode, accompanied by active and reactive power shocks - such as the drive of reversing rolling mills, arc steel furnaces, welding devices, etc.

Voltage fluctuations are characterized by two indicators:

dose of flicker.

The range of voltage change is calculated by the formula,%

where, are the values ​​of the extrema following one after another (or the extremum and the horizontal section) of the envelope of the rms voltage values, in accordance with Fig. 3.1.

Rice. 3.1. Voltage fluctuations

The frequency of repetition of voltage changes, (1/s, 1/min) is determined by the expression:

where m is the number of voltage changes over time T;

T is the measurement time interval taken equal to 10 min.

If two voltage changes occur with an interval of less than 30 ms, then they are considered as one.

The time interval between voltage changes is:

The assessment of the admissibility of the range of voltage changes (voltage fluctuations) is carried out using the curves of the dependence of the permissible range of oscillations on the frequency of repetition of voltage changes or the time interval between subsequent voltage changes.

The CE at the point of common connection with periodic voltage fluctuations having the shape of a meander (rectangular) (see Fig. 3.2) is considered to comply with the requirements of the standard if the measured value of the range of voltage changes does not exceed the values ​​determined from the curves of Fig. 3.2 for the corresponding frequency of repetition of voltage changes, or the interval between voltage changes.

Rice. 3.2. Voltage fluctuations of arbitrary shape (a) and meander-shaped (b)

The maximum allowable value of the sum of the steady-state voltage deviation δUU and the range of voltage changes δUt at the points of connection to electric networks with a voltage of 0.38 kV is ±10% of the rated voltage.

Flicker dose is a measure of a person's susceptibility to the effects of fluctuations in light output caused by voltage fluctuations in the supply network over a set period of time.

The standard establishes a short-term () and long-term flicker dose () (short-term is determined at an observation time interval of 10 minutes, long-term at an interval of 2 hours). The initial data for the calculation are flicker levels measured using a flickermeter - a device in which the sensitivity curve (amplitude-frequency characteristic) of the human eye is modeled. At present, the development of flickermeters for monitoring voltage fluctuations has begun in the Russian Federation.

The EC for the flicker dose complies with the requirements of the standard, if the short-term and long-term flicker doses, determined by measuring for 24 hours or by calculation, do not exceed the maximum permissible values: for a short-term flicker dose - 1.38 and for a long-term - 1.0 (with voltage fluctuations with a shape different from the meander).

The maximum allowable value for a short-term flicker dose at the points of general connection of electricity consumers with incandescent lamps in rooms where significant eye strain is required is 1.0, and for a long-term - 0.74, with voltage fluctuations with a shape different from the meander.

Non-sinusoidal voltage

In the process of generating, converting, distributing and consuming electricity, there are distortions in the shape of sinusoidal currents and voltages. The sources of distortion are synchronous generators of power plants, power transformers operating at elevated values ​​of magnetic induction in the core (with increased voltage at their terminals), AC-to-DC converters and EP with non-linear volt-ampere characteristics (or non-linear loads).

Distortions created by synchronous generators and power transformers are small and do not have a significant impact on the power supply system and on the operation of the ED. The main cause of distortions are valve converters, electric arc steel-smelting and ore-thermal furnaces, arc and resistance welding installations, frequency converters, induction furnaces, a number of electronic technical equipment (television receivers, PC), gas discharge lamps, etc. Electronic electricity receivers and gas discharge lamps are created with their own operation, a low level of harmonic distortion at the output, but the total number of such EDs is large.

It is known from the course of mathematics that any non-sinusoidal function (for example, see Fig. 3.3) that satisfies the Dirichlet condition can be represented as the sum of a constant value and an infinite series of sinusoidal quantities with multiple frequencies. Such sinusoidal components are called harmonic components or harmonics. A sinusoidal component whose period is equal to the period of a non-sinusoidal periodic quantity is called the fundamental or first harmonic. The remaining components of the sinusoid with frequencies from the second to the nth are called higher harmonics.

Rice. 3.3. Non-sinusoidal voltage

Voltage non-sinusoidality is characterized by the following indicators:

· the distortion factor of the sinusoidality of the voltage curve;

· coefficient of the n-th harmonic component of the voltage.

The distortion factor of the sinusoidality of the voltage curve is determined by the expression, %

where is the effective value of the n-th harmonic component of the voltage, V; is the order of the harmonic component of the voltage, is the order of the last of the harmonic components of the voltage taken into account, the standard sets N = 40;

The effective value of the voltage of the fundamental frequency, V.

It is allowed to determine by expression, %

where is the rated voltage of the network, V.

The coefficient of the n-th harmonic component of the voltage is, %

It is allowed to calculate by expression, %SRC= "publ_image/Image48.gif" align= "top"> (3.10)

For the calculation, it is necessary to determine the voltage level of the individual harmonics generated by the non-linear load.

The phase voltage of the harmonic at the design point of the network is found from the expression:

where is the effective value of the phase current of the nth harmonic;

Non-linear load voltage (if the calculated point coincides with the non-linear load connection point, then =);

Rated mains voltage;

Short circuit power at the point of connection of a non-linear load.

For the calculation, it is necessary to first determine the current of the corresponding harmonic, which depends not only on electrical parameters, but also on the type of non-linear load.

Normally permissible and maximum permissible values ​​at the point of common connection to electrical networks with different rated voltages are given in Table 3.1.

Table 3.1. Values ​​of the distortion factor of the sinusoidal voltage curve

Normally admissible values ​​at , kVMaximum permissible values ​​at , kV0.386 -2035110-3300.386 -2035110-3308.05.04.02.012.08.06.03.0

Voltage unbalance

The most common sources of voltage asymmetry in three-phase power supply systems are such consumers of electricity, the symmetrical multi-phase execution of which is either impossible or impractical for technical and economic reasons. Such installations include induction and arc electric furnaces, traction loads of railways made on alternating current, electric welding units, special single-phase loads, lighting installations.

Asymmetric voltage modes in electrical networks also occur in emergency situations - with a phase failure or asymmetric short circuits.

Voltage asymmetry is characterized by the presence in a three-phase electrical network of negative or zero sequence voltages, which are much smaller in magnitude than the corresponding components of the direct (main) sequence voltage.

The asymmetry of the three-phase voltage system occurs as a result of the imposition of a direct sequence of voltages of the negative sequence system on the system, which leads to changes in the absolute values ​​of phase and interphase voltages (Fig. 3.4.).

Rice. 3.4. Vector diagram of positive and negative sequence voltages

In addition to the unbalance caused by the voltage of the negative sequence system, there can be unbalance from the superimposition of the zero sequence system voltages on the positive sequence system. As a result of the displacement of the neutral of a three-phase system, asymmetry of phase voltages occurs while maintaining a symmetrical system of phase-to-phase voltages (Fig. 3.5.).

Rice. 3.5. Vector diagram of positive and zero sequence voltages

Voltage asymmetry is characterized by the following indicators:

· voltage unbalance factor in reverse sequence;

· coefficient of voltage asymmetry in the zero sequence.

The coefficient of voltage asymmetry in the reverse sequence is, %

where is the effective value of the negative sequence voltage of the fundamental frequency of the three-phase voltage system, V;

The effective value of the positive sequence voltage of the fundamental frequency, V.

It is allowed to calculate by expression,%:

where is the nominal value of the phase-to-phase voltage of the network, V.

The coefficient of voltage asymmetry in the zero sequence is, %:

where is the effective value of the voltage of the zero sequence of the main frequency of the three-phase voltage system, V.

It is allowed to calculate by the formula,%

where is the nominal value of the phase voltage, V.

The measurement of the voltage unbalance factor in the zero sequence is carried out in a four-wire network.

The relative error in determining and according to formulas (3.15) and (3.16) is numerically equal to the value of voltage deviations from.

Normally permissible and maximum permissible values ​​of the voltage asymmetry coefficient in reverse sequence at the point of common connection to electric networks are 2.0 and 4.0%.

The normalized values ​​of the zero sequence voltage asymmetry coefficient at the point of common connection to four-wire electrical networks with a rated voltage of 0.38 kV are also equal to 2.0 and 4.0%.

Frequency deviations

Frequency deviation - the difference between the actual and nominal values ​​of frequency, Hz

The standard sets the normal and maximum permissible values ​​for the frequency deviation equal to ± 0.2 Hz and ± 0.4 Hz, respectively.

voltage dip

Voltage dips include a sudden significant change in voltage at a point in the electrical network below the level of 0.9, followed by voltage recovery to the original or close to it level after a period of time from ten milliseconds to several tens of seconds (Fig. 3.6).

Rice. 3.6. voltage dip

The characteristic of the voltage dip is its duration - equal to:

where and are the initial and final moments of the voltage dip.

The voltage dip is also characterized by the voltage dip depth - the difference between the nominal voltage value and the minimum effective voltage value, expressed in units of voltage or as a percentage of its nominal value. The voltage dip is calculated by the expressions

The maximum allowable value of the voltage dip duration in electrical networks with voltage up to 20 kV inclusive is 30 s. The duration of the automatically eliminated voltage dip at any point of connection to the electrical networks is determined by the time delays of relay protection and automation.

Voltage impulse and temporary overvoltage

Distortion of the shape of the supply voltage curve can occur due to the appearance of high-frequency pulses during switching in the network, the operation of arresters, etc. Voltage pulse - a sharp change in voltage at a point in the electrical network, followed by the restoration of voltage to its original level or close to it. The magnitude of voltage distortion in this case is characterized by an indicator of impulse voltage (Fig. 3.7).

Rice. 3.7. Pulse voltage parameters

The impulse voltage in relative units is:

where is the value of the impulse voltage, V.

The amplitude of the pulse is the maximum instantaneous value of the voltage pulse. The pulse duration is the time interval between the initial moment of the voltage pulse and the moment the instantaneous value of the voltage is restored to its original level or close to it.

The indicator - impulse voltage is not standardized by the standard.

Temporary overvoltage - an increase in voltage at a point in the electrical network above 1.1 for more than 10 ms, occurring in power supply systems during switching or short circuits (Fig. 3.8.).

Rice. 3.8. Temporary overvoltage

A temporary overvoltage is characterized by a temporary overvoltage coefficient (): this is a value equal to the ratio of the maximum value of the envelope of the amplitude values ​​of the voltage during the existence of a temporary overvoltage to the amplitude of the rated voltage of the network.

The duration of a temporary overvoltage is the time interval between the initial moment of the occurrence of a temporary overvoltage and the moment of its disappearance.

The coefficient of temporary overvoltage is also not standardized by the standard.

The values ​​of the coefficient of temporary overvoltage at the points of connection of the general-purpose electrical network, depending on the duration of temporary overvoltages, do not exceed the values ​​given in Table 3.3.

Table 3.3. Dependence of the coefficient of temporary overvoltage on the duration of overvoltage

Duration of temporary overvoltages, sUp to 1Up to 20Up to 60Coefficient of temporary overvoltage, pu 1.471.311.15

On average, about 30 temporary overvoltages are possible at the connection point per year.

When the neutral conductor breaks in three-phase electrical networks with voltages up to 1 kV, operating with a solidly grounded neutral, temporary overvoltages occur between the phase and the ground. The level of such overvoltages with a significant asymmetry of phase loads can reach the values ​​of the phase-to-phase voltage, and the duration is several hours.

Statistical assessment of power quality indicators

Changes in the parameters of the electrical network, power and the nature of the load over time are the main reason for the change in the SCE. Thus, the SCE - the steady voltage deviation, the coefficients characterizing the non-sinusoidality and asymmetry of the voltage, the frequency deviation, the amplitude of the voltage change, etc. - are random quantities and their measurement and processing should be based on probabilistic-statistical methods. Therefore, as already noted, the standard establishes the SQE norms and stipulates the need to fulfill them within 95% of the time of each day (for normally acceptable values).

The most complete characterization of random variables is given by the laws of their distribution, which make it possible to find the probabilities of the occurrence of certain values ​​of the SCE. We will explain the use of probabilistic-statistical methods using the example of estimating voltage deviations.

Operating experience shows the presence of daily, weekly and longer cycles of voltage deviations in time. Statistical data confirm that the distribution law of voltage deviations in electrical networks can be most accurately described using the normal distribution law, which is used in the practice of PQ control.

The analytical description of the normal law is carried out using two parameters: the mathematical expectation of a random variable and the standard deviation from the mean. The equation for the distribution curve of voltage deviations from the nominal, corresponding to the normal distribution law, has the form:

Expression (3.25) is written for a continuous process of changing a random variable. To simplify the CE control devices, continuous random variables, which are the CEs, are replaced during control by discrete sequences of their values.

The most convenient form of presenting information about changes in a random variable is a histogram. Histogram - a graphical representation of the statistical series of the indicator under study, the change of which is random (Fig. 3.9.). In this case, the entire range of voltage deviations is divided into intervals of equal width (for example, 1.25%). Each interval is given a name - the value of voltage deviations corresponding to the middle of the interval, and the probability (frequency) of voltage deviations falling into this interval is found

where is the number of hits in the i-th interval;

The total number of measurements.

Rice. 3.9. Voltage deviation histogram

Based on the histogram, the answer is given: what is the quality of electricity at the control point. Such an assessment is made by the sum of the values ​​of falling into intervals that fit into the allowable range of voltage deviations. With the help of the histogram, the probability of voltage deviations beyond the normally permissible values ​​is also found. This allows you to judge the reasons for the low quality of voltage in the electrical network and choose measures to improve it.

Numerical characteristics and determined from the histogram are widely used to assess the voltage quality.

Mathematical expectation determines the average level of voltage deviations at the considered point of the network for a controlled period of time

where k is the number of histogram bins.

Dissipation of voltage deviations is characterized by dispersion. It is equal to the mathematical expectation of the square of deviations of a random variable from its mean value and is determined from the expression

The parameter is the standard deviation and characterizes the scatter of the histogram, i.e. spread of voltage deviations around the mathematical expectation. For most histograms of voltage deviations, the integral probability of falling into range 4 is 0.95. This means that in order to meet the requirements of the standard, the measured value must not exceed 1/4 of the width of the allowable range. So, if the allowable voltage deviation range, then it is necessary that it does not exceed 2.5%.

The standard establishes methods and techniques for determining the SCE and auxiliary parameters that implement the provisions of mathematical statistics and probability theory. For the measured discrete values ​​of the SQI, averaging intervals are set, presented in Table 3.4.

Table 3.4. Intervals for averaging the results of measurements of KE indicators

KE indexAveraging interval, sSteady voltage deviation Span of voltage change Flicker dose Coefficient of distortion of the sinusoidality of the voltage curve Coefficient of the n-th harmonic component of the voltage Coefficient of voltage asymmetry in the negative sequence Coefficient of voltage asymmetry in the zero sequence Frequency deviation Duration of the voltage dip Impulse voltage Temporary overvoltage factor60 - - 3 3 3 3 20 - - -

For the averaging intervals of various SQIs, the standard sets the number of observations (N) and, using the methodology set out in the standard, one or another SQI is determined. For example, calculate the value of the average voltage in volts, as a result of averaging N voltage observations over a time interval of 1 min using the formula:

where is the voltage value in the i-th observation, V.

The number of observations for 1 min in accordance with the standard should be at least 18. The value of the steady-state voltage deviation is calculated using the formula,%

The values ​​of the SCE accumulated over the minimum billing period are processed by the methods of mathematical statistics and the probabilities of their compliance with the norms of the standard are determined.

The methods for determining the SQE established by the standard are implemented in the hardware controls for the QE. The form of presentation of measurement processing results must also meet the requirements of the standard.

Table 3.5 summarizes the SCE standards.

Table 3.5. Electricity quality standards

EC indicator, units measurementsNorms KENNormally allowablemaximum allowableSteady voltage deviation, % ± 5± 10Voltage change range, % Curves 1,2 in fig. 3.2Dose of flicker, refers. unit: Short-term

Long -

1.0; 0.74 Voltage curve sinusoidal distortion factor, %According to the table

1According to the table

3.1 Coefficient of the n-th harmonic component of the voltage,% According to the table

2According to the table

3.2 Negative sequence voltage unbalance factor , %24Voltage unbalance factor by zero sequence , %24Frequency deviation , Hz± 0.2± 0.4Voltage dip duration , s-30Impulse voltage , kV--Coefficient of temporary overvoltage , refers. units:--

4. Influence of power quality on the operation of power receivers

Deviations of the PQI from the normalized values ​​worsen the operating conditions of electrical equipment of power supply organizations and consumers of electricity, can lead to significant losses both in industry and in the domestic sector, cause, as already noted, technological and electromagnetic damage.

Typical types of electrical receivers

From the electrical networks of general-purpose power supply systems, EPs for various purposes are fed, consider industrial and household EPs.

The most characteristic types of ED, widely used in enterprises of various industries, are electric motors and electric lighting installations. Electrothermal installations, as well as valve converters, which are used to convert alternating current to direct current, are widely used. Direct current in industrial enterprises is used to power DC motors, for electrolysis, in galvanic processes, for certain types of welding, etc.

Electric motors are used in drives of various production mechanisms. In installations that do not require speed control during operation, AC electric drives are used: asynchronous and synchronous electric motors.

The most economical field of application of asynchronous and synchronous electric motors, depending on the voltage, has been established. At voltages up to 1 kV and power up to 100 kW, it is more economical to use asynchronous motors, and over 100 kW - synchronous motors, at voltages up to 6 kV and power up to 300 kW - asynchronous motors, and above 300 kW - synchronous motors, at a voltage of 10 kV and power up to 400 kW - asynchronous motors, above 400 kW - synchronous.

The wide distribution of asynchronous motors is due to their simplicity in design and operation and relatively low cost.

Synchronous motors have a number of advantages over induction motors: they are usually used as reactive power sources, their torque is less dependent on the terminal voltage, and in many cases they are more efficient. At the same time, synchronous motors are more expensive and difficult to manufacture and operate.

Electric lighting installations with incandescent, fluorescent, arc, mercury, sodium, xenon lamps are used at all enterprises for indoor and outdoor lighting, for urban lighting, etc.

AC electric arc and resistance welding installations are a single-phase non-uniform and non-sinusoidal load with a low power factor: 0.3 for arc welding and 0.7 for contact welding. Welding transformers and low power devices are connected to a 380/220 V network, more powerful ones - to a 6 - 10 kV network.

Valve converters, due to the specifics of their regulation, are consumers of reactive power (the power factor of valve converters of rolling mills ranges from 0.3 to 0.8), which causes significant voltage deviations in the supply network; the non-sinusoidality coefficient during the operation of thyristor converters of rolling mills can reach a value of more than 30% on the 10 kV side of their supply voltage; valve converters do not affect the voltage symmetry due to the symmetry of their loads.

Electric welding installations can cause disruption of normal working conditions for other EAs. In particular, welding units, whose power currently reaches 1500 kW per unit, cause much larger voltage fluctuations in electrical networks than, for example, starting asynchronous motors with a squirrel-cage rotor. In addition, these voltage fluctuations occur for a long time and with a wide frequency range, including the most unpleasant range for electric lighting installations (about 10 Hz).

Electrothermal installations, depending on the method of heating, are divided into groups: arc furnaces, resistance furnaces of direct and indirect action, electronic melting furnaces, vacuum, slag remelting, induction furnaces. This group of EP also has an adverse effect on the supply network, for example, arc furnaces, which can have a power of up to 10 MW, are currently being built as single-phase. This leads to a violation of the symmetry of currents and voltages (the latter occurs due to voltage drops on the network resistances from currents of different sequences). In addition, arc furnaces, as well as valve installations, are non-linear EFs with low inertia. Therefore, they lead to non-sinusoidal currents, and, consequently, voltages.

The modern electrical load of an apartment (cottage) is characterized by a wide range of household EPs, which, according to their purpose and influence on the electrical network, can be divided into the following groups: passive consumers of active power (incandescent lamps, heating elements of irons, stoves, heaters); EP with asynchronous motors operating in a three-phase mode (drive of elevators, pumps - in the water supply and heating system, etc.); EP with asynchronous motors operating in a single-phase mode (drive of compressors of refrigerators, washing machines, etc.); EP with collector motors (drive of vacuum cleaners, electric drills, etc.); AC and DC welding units (for repair work in the workshop, etc.); rectifying devices (for charging batteries, etc.); radio-electronic equipment (TVs, computer equipment, etc.); high-frequency installations (microwave ovens, etc.); fluorescent lighting lamps.

The impact of each individual household EP is insignificant, while the totality of EP connected to the 0.4 kV buses of a transformer substation has a significant impact on the supply network.

Influence of voltage deviations

Voltage deviations have a significant impact on the operation of induction motors (IM), which are the most common receivers of electricity in industry.

Rice. 4.1. Mechanical characteristics of the motor at rated (M1) and reduced (M2) voltages

When the voltage changes, the mechanical characteristic of the AM changes - the dependence of its torque M on slip s or rotational speed (Fig. 4.1). With sufficient accuracy, we can assume that the torque of the motor is proportional to the square of the voltage at its terminals. With a decrease in voltage, the torque and speed of the motor rotor decreases, as its slip increases. The decrease in the rotational speed also depends on the law of change in the moment of resistance Mc (Mc is taken constant in Fig. 4.1) and on the engine load. The dependence of the motor rotor speed on voltage can be expressed:

where - synchronous speed;

Engine load factor;

Nominal voltage and slip values, respectively.

From formula (4.1) it can be seen that at low engine loads, the rotor speed will be greater than the rated speed (at rated engine load). In such cases, voltage drops do not lead to a decrease in the productivity of technological equipment, since the reduction in the engine speed below the nominal does not occur.

For motors running at full load, lowering the voltage results in a reduction in speed. If the performance of mechanisms depends on the engine speed, then it is recommended to maintain a voltage at the outputs of such engines that is not lower than the nominal voltage. With a significant decrease in the voltage at the outputs of motors operating at full load, the moment of resistance of the mechanism may exceed the torque, which leads to a “tipping” of the motor, i.e. to stop him. To avoid damage, the motor must be disconnected from the mains.

Reducing the voltage also worsens the conditions for starting the engine, since this reduces its starting torque.

Of practical interest is the dependence of the active and reactive power consumed by the motor on the voltage at its terminals.

In the case of a decrease in voltage at the motor terminals, the reactive power of magnetization decreases (by 2 - 3% with a decrease in voltage by 1%), with the same power consumption, the motor current increases, which causes overheating of the insulation.

If the motor runs for a long time at reduced voltage, then due to the accelerated wear of the insulation, the service life of the motor is reduced. Approximately the service life of insulation T can be determined by the formula:

where is the service life of the motor insulation at rated voltage and rated load; is a coefficient depending on the value and sign of the voltage deviation, as well as on the load factor of the motor and equal to:

at - 0.2< <0; (4.3);

at 0.2 ≥ > 0; (4.4)

Therefore, from the point of view of engine heating, negative voltage deviations within the considered limits are more dangerous.

A decrease in voltage also leads to a noticeable increase in reactive power lost in the leakage reactances of lines, transformers and AM.

An increase in voltage at the motor terminals leads to an increase in the reactive power consumed by them. At the same time, the specific consumption of reactive power increases with a decrease in the engine load factor. On average, for each percentage increase in voltage, the consumed reactive power increases by 3% or more (mainly due to an increase in the no-load current of the motor), which in turn leads to an increase in active power losses in the electrical network elements.

Incandescent lamps are characterized by nominal parameters: power consumption, luminous flux, luminous efficiency (equal to the ratio of the luminous flux emitted by the lamp to its power) and the average nominal service life. These indicators largely depend on the voltage at the terminals of incandescent lamps. With voltage deviations of 10%, these characteristics can be approximately described by the following empirical formulas:

Rice. 4.2. Dependences of the characteristics of incandescent lamps on voltage: 1 - power consumption, 2 - luminous flux, 3 - luminous efficiency, 4 - service life

From the curves in Figs. 4.2. it can be seen that with decreasing voltage, the luminous flux decreases most noticeably. When the voltage rises above the nominal value, the luminous flux F, the lamp power P and the light output h increase, but the service life of the lamps T sharply decreases and as a result they quickly burn out. At the same time, there is an overspending of electricity.

Voltage changes lead to corresponding changes in luminous flux and illumination, which ultimately affects labor productivity and human fatigue.

Fluorescent lamps are less sensitive to voltage fluctuations. With an increase in voltage, the power consumption and luminous flux increase, and with a decrease, they decrease, but not to the same extent as with incandescent lamps. At low voltage, the conditions for ignition of fluorescent lamps worsen, therefore, their service life, determined by the spraying of the oxide coating of the electrodes, is reduced both with negative and positive voltage deviations.

With voltage deviations of 10%, the service life of fluorescent lamps is reduced by an average of 20 - 25%. A significant disadvantage of fluorescent lamps is their consumption of reactive power, which increases with increasing voltage supplied to them.

Valve converters usually have an automatic DC control system by phase control. When the voltage in the network increases, the regulation angle automatically increases, and when the voltage decreases, it decreases. A 1% increase in voltage leads to an increase in the reactive power consumption of the converter by about 1-1.4%, which leads to a deterioration in the power factor. At the same time, other characteristics of valve converters improve with increasing voltage, and therefore it is beneficial to increase the voltage at their terminals within acceptable values.

Electric ovens are sensitive to voltage fluctuations. Lowering the voltage of electric arc furnaces, for example, by 7% leads to a lengthening of the steel melting process by 1.5 times. Increasing the voltage above 5% leads to excessive consumption of electricity.

Voltage deviations adversely affect the operation of electric welding machines: for example, for spot welding machines, a 15% change in voltage results in a 100% defective product.

Effect of voltage fluctuations

Lighting devices, especially incandescent lamps and electronic equipment, are among the EAs that are extremely sensitive to voltage fluctuations:

The standard defines the effect of voltage fluctuations on lighting installations that affect human vision. Flashing light sources (flicker effect) causes an unpleasant psychological effect, fatigue of vision and the body as a whole. This leads to a decrease in labor productivity, and in some cases to injuries.

The strongest impact on the human eye is caused by flashes with a frequency of 3-10 Hz, therefore, the allowable voltage fluctuations in this range are minimal - less than 0.5%.

With the same voltage fluctuations, the negative effect of incandescent lamps is manifested to a much greater extent than gas-discharge lamps. Voltage fluctuations greater than 10% can cause the discharge lamps to go out. Depending on the type of lamps, they are ignited after a few seconds and even minutes.

Voltage fluctuations disrupt normal operation and reduce the life of electronic equipment: radios, televisions, telephone and telegraph communications, computer equipment, x-ray installations, radio stations, television stations, etc.

With significant voltage fluctuations (more than 15%), the conditions for the normal operation of electric motors may be violated, the contacts of magnetic starters may fall off with a corresponding shutdown of running motors.

Voltage fluctuations with a range of 10 - 15% can lead to failure of capacitor banks, as well as valve converters.

The influence of voltage fluctuations on individual power receivers has not yet been studied enough. This complicates the technical and economic analysis in the design and operation of power supply systems with sharply variable loads.

Influence of voltage unbalance

Voltage asymmetry, as already noted, is most often caused by the presence of an asymmetric load. Asymmetric load currents flowing through the elements of the power supply system cause asymmetric voltage drops in them. As a result, an asymmetric voltage system appears on the outputs of the EA. Voltage deviations at the EA of the overloaded phase may exceed the normally permissible values, while voltage deviations at the EA of other phases will be within the normalized limits. In addition to the deterioration of the voltage regime of the EP in the asymmetric mode, the operating conditions of both the EP themselves and all network elements deteriorate significantly, the reliability of the operation of electrical equipment and the power supply system as a whole decreases.

The action of the asymmetric mode is qualitatively different compared to the symmetrical one for such common three-phase EDs as asynchronous motors. Of particular importance to them is the negative sequence voltage. The resistance of the negative sequence of electric motors is approximately equal to the resistance of a stalled motor and, therefore, 5 to 8 times less than the positive sequence resistance. Therefore, even a small voltage unbalance causes significant negative sequence currents. Negative sequence currents are superimposed on positive sequence currents and cause additional heating of the stator and rotor (especially the massive parts of the rotor), which leads to accelerated aging of the insulation and a decrease in the available motor power (decrease in motor efficiency). Thus, the service life of a fully loaded asynchronous motor operating at a voltage unbalance of 4% is reduced by 2 times. With a voltage unbalance of 5%, the available motor power is reduced by 5 - 10%.

With asymmetry of mains voltages in synchronous machines, along with the occurrence of additional losses of active power and heating of the stator and rotor, dangerous vibrations can occur as a result of the appearance of alternating torques and tangential forces pulsing at a double mains frequency. With significant asymmetry, vibration can be dangerous, and especially with insufficient strength and the presence of defects in welded joints. With current asymmetry not exceeding 30%, dangerous overvoltages in structural elements, as a rule, do not occur.

The rules for the technical operation of electrical networks and stations in the Russian Federation indicate that “long-term operation of generators and synchronous compensators with unequal phase currents is allowed if the current difference does not exceed 10% of the rated stator current for turbogenerators and 20% for hydrogenerators. In this case, the currents in the phases must not exceed the nominal values. If these conditions are not met, then special measures must be taken to reduce the asymmetry.”

In the case of reverse and zero sequence currents, the total currents in the individual phases of the network elements increase, which leads to an increase in active power losses and may be unacceptable from the point of view of heating. Zero sequence currents flow constantly through the ground electrodes. This additionally dries up and increases the resistance of grounding devices. This may be unacceptable from the point of view of the operation of relay protection, as well as due to the increased impact on low-frequency communication installations and railway blocking devices.

Voltage asymmetry significantly worsens the operating modes of multi-phase valve rectifiers: the ripple of the rectified voltage increases significantly, the operating conditions of the pulse-phase control system of thyristor converters worsen.

Capacitor units with voltage asymmetry are unevenly loaded with reactive power in phases, which makes it impossible to fully use the installed capacitor power. In addition, capacitor units in this case reinforce the already existing asymmetry, since the output of reactive power to the network in the phase with the lowest voltage will be less than in the other phases (proportional to the square of the voltage on the capacitor unit).

Voltage asymmetry also significantly affects single-phase EAs, if the phase voltages are unequal, then, for example, incandescent lamps connected to a phase with a higher voltage have a greater luminous flux, but a significantly shorter service life compared to lamps connected to a phase with a lower voltage . Voltage asymmetry complicates the operation of relay protection, leads to errors in the operation of electricity meters, etc.

Influence of non-sinusoidal voltage

EA with non-linear current-voltage characteristics consume non-sinusoidal currents from the network when a sinusoidal voltage is applied to their terminals. The currents of higher harmonics, passing through the elements of the network, create voltage drops in the resistances of these elements and, superimposed on the main voltage sinusoid, lead to distortions in the shape of the voltage curve in the nodes of the electrical network. In this regard, an EP with a nonlinear current-voltage characteristic is often called a source of higher harmonics.

The most serious CE violations in the electrical network occur during the operation of powerful controlled valve converters. In this case, the order of the higher harmonic components of current and voltage in the network is determined by the formula

where m is the number of rectification phases; is a sequential series of natural numbers (0,1,2…).

Depending on the rectification circuit, valve converters generate the following current harmonics into the network: with a 6-phase circuit - up to the 19th order; with a 12-phase circuit - up to the 25th order inclusive.

The distortion factor of the sinusoidality of the voltage curve in networks with electric arc steel-smelting and ore-thermal furnaces is determined mainly by the 2nd, 3rd, 4th, 5th, 7th harmonics.

The coefficient of distortion of the sinusoidality of the voltage curve of arc and resistance welding installations is mainly determined by the 5th, 7th, 11th, 13th harmonics.

The currents of the 3rd and 5th harmonics of discharge lamps are 10 and 3% of the current of the 1st harmonic. These currents coincide in phase in the corresponding linear wires of the network and, adding up in the neutral wire of the 380/220 V network, determine the current in it, which is almost equal to the current in the phase wire. Other harmonics for gas-discharge lamps can be neglected.

Studies of the magnetizing current curve of transformers connected to a sinusoidal voltage network showed that with a three-rod core and U / U winding connections; and /U; in the electrical network there are all odd harmonics, including harmonics that are multiples of three. Harmonics that are multiples of three are due to the asymmetry of the magnetizing currents in phases:

The effective value of the magnetizing current of the transformer:

Magnetizing currents form systems of positive and negative sequence currents, which are the same in absolute value for harmonics that are multiples of three. For other odd harmonics, negative sequence currents are about 0.25 positive sequence currents.

If a non-sinusoidal voltage is applied to the inputs of transformers, additional components of the higher harmonics of the current appear. GPP transformers give the 5th harmonic of a small magnitude.

In general, non-sinusoidal modes have the same disadvantages as asymmetric ones.

Higher harmonics of current and voltage cause additional losses of active power in all elements of the power supply system: in power lines, transformers, electrical machines, static capacitors, since the resistance of these elements depends on the frequency.

So, for example, the capacitance of capacitors installed in order to compensate for reactive power decreases with increasing frequency of the input voltage. Therefore, if there are higher harmonics in the mains voltage, then the resistance of the capacitors at these harmonics is much lower than at a frequency of 50 Hz. Because of this, in capacitors intended for reactive power compensation, even small higher harmonic voltages can cause significant harmonic currents. In enterprises with a large proportion of non-linear loads, capacitor banks do not work well. They are either switched off by overcurrent protection or fail in a short time due to swelling of the cans (or accelerated aging of the insulation). There are cases when, at enterprises with a developed cable network with a voltage of 6-10 kV, capacitor banks find themselves in the current resonance mode (or close to this mode) at the frequency of any of the harmonics, which leads to a dangerous current overload.

Higher harmonics cause:

· accelerated aging of the insulation of electrical machines, transformers, cables;

· deterioration of the power factor of the ED;

· deterioration or disruption of the operation of automation devices, telemechanics, computer equipment and other devices with electronic elements;

· measurement errors of induction electricity meters, which lead to incomplete accounting of consumed electricity;

· malfunction of the valve converters themselves at a high level of higher harmonic components.

· The presence of higher harmonics adversely affects the operation of not only consumer electrical equipment, but also electronic devices in power systems.

· For some installations (a system of pulse-phase control of valve converters, complete automation devices, etc.), the permissible values ​​of individual current (voltage) harmonics are indicated by the manufacturer in the product passport.

· The voltage curve supplied to the EP should not contain higher harmonics in the steady state of the power grid. It should be emphasized that under the operating conditions of the EA, the voltage non-sinusoidality manifests itself in conjunction with the actions of other influencing factors, and therefore it is necessary to consider the entire set of factors together.

Influence of frequency deviation

The stringent requirements of the standard for deviations in the frequency of the supply voltage are due to the significant influence of frequency on the operating modes of electrical equipment, the course of technological processes of production and, as a result, the technical and economic performance of industrial enterprises.

The electromagnetic component of the damage is due to an increase in active power losses in electrical networks and an increase in the consumption of active and reactive power. It is known that reducing the frequency by 1% increases losses in electrical networks by 2%.

The technological component of the damage is caused mainly by the underproduction by industrial enterprises of their products and the cost of additional time for the enterprise to complete the task. According to expert estimates, the value of technological damage is an order of magnitude higher than electromagnetic damage.

An analysis of the work of enterprises with a continuous production cycle showed that most of the main technological lines are equipped with mechanisms with constant and fan resistance torques, and asynchronous motors serve as their drives. The frequency of rotation of the motor rotors is proportional to the change in the frequency of the network, and the performance of production lines depends on the engine speed.

The degree of influence of frequency on the performance of a number of mechanisms can be expressed in terms of the active power they consume:

where a - coefficient of proportionality, depending on the type of mechanism; - network frequency; - exponent.

Depending on the values ​​of the exponent n, EP can be divided into the following groups:

1.mechanisms with a constant moment of resistance - piston pumps, compressors, machine tools, etc.; for them n=1;

2.mechanisms with a fan moment of resistance - centrifugal pumps, fans, smoke exhausters, etc.; for them n=3; at TPPs, CPPs, NPPs, these are usually the motors of feed water pumps, circulation pumps, smoke fans, oil pumps, etc.

.mechanisms for which n = 3.5-4 are centrifugal pumps operating with a large static head (back pressure), for example, boiler feed pumps.

EPs of the 2nd and 3rd groups, which are most affected by frequency, have adjustment capabilities, due to which the power they consume from the network remains practically unchanged.

The motors of auxiliary needs of power plants are most sensitive to frequency reduction. The decrease in frequency leads to a decrease in their productivity, which is accompanied by a decrease in the available power of generators and a further shortage of active power and a decrease in frequency (there is a frequency avalanche).

Such electronic devices as incandescent lamps, resistance furnaces, electric arc furnaces practically do not react to frequency changes.

Frequency deviations adversely affect the operation of electronic equipment: a frequency deviation of more than +0.1 Hz leads to brightness and geometric background distortions of the television image, frequency changes from 49.9 to 49.5 Hz entail an almost fourfold increase in the allowable range of the television signal to the background interference. Changing the frequency to 49.5 Hz requires a significant tightening of the requirements for the signal / background noise ratio in all parts of the television path - from the equipment of the hardware-studio complex to the television receiver, the implementation of which is associated with significant material costs.

In addition, the reduced frequency in the electrical network also affects the service life of equipment containing elements with steel (electric motors, transformers, reactors with a steel magnetic circuit), due to an increase in the magnetization current in such devices and additional heating of steel cores.

To prevent system-wide accidents caused by frequency reduction, special devices for automatic frequency unloading (AFD) are provided, which cut off some of the less responsible consumers. After the power shortage has been eliminated, for example, after switching on the backup sources, special frequency automatic reclosing devices (CHAR) turn on the disconnected consumers and the normal operation of the system is restored.

Maintaining a normal frequency that meets the requirements of the standard is a technical, not a scientific problem, the main way to solve it is to introduce generating capacities in order to create power reserves in the networks of power supply organizations.

Influence of electromagnetic interference

In general-purpose power supply systems, electronic and microelectronic control systems, microprocessors and computers are widely used, which led to a decrease in the level of noise immunity of EP control systems and a sharp increase in the number of their failures. The main cause of failures is the impact of electromagnetic transient interference that occurs during electromagnetic transients both in power grids, and in urban and industrial electrical networks. The duration of transient processes ranges from several periods of industrial frequency current to several seconds, and the effective interference frequency band can reach tens of megahertz.

Electromagnetic crosstalk, accompanied by voltage dips, occurs mainly during single-phase short circuits of overhead lines due to insulation flashing. These damages either self-destruct or are eliminated during a short-term disconnection followed by automatic reclosing (AR). In addition, the cause of voltage dips are phase-to-phase short circuits resulting from atmospheric phenomena, as well as disconnection of supply lines and capacitors. The number of voltage dips with a depth of up to 20% reaches 55 - 60% in distribution networks. Over 60% of machine shutdowns are due to voltage dips with a depth of more than 20%.

The cause of electromagnetic transient interference in general-purpose power supply systems can be overvoltages that occur during single-phase earth faults, when switching banks of capacitors and resonant filters, when disconnecting unloaded cable lines and transformers, while switching contacts of switches and other switching equipment, in open-phase modes operation of the electrical network due to various reasons leading to ferroresonance phenomena. The susceptibility of electronic equipment and computers to surges depends both on the frequency response of the ED and on the frequency response of electromagnetic interference.

An increase in the power of power systems and the number of overhead lines used to improve the reliability of power supply to industrial enterprises leads to a decrease in the reliability of the functioning of complex electronic control systems and an increase in the number of failures of noise-sensitive ED.

As already noted, with the values ​​of all SCEs for voltage different from the normalized ones, accelerated aging of the insulation of electrical equipment occurs, as a result, the intensity of failure flows increases over time. So, if the mains voltage curve is not sinusoidal, even with the resonant tuning of the arc extinguishers, the current of higher harmonics passes through the place of the earth fault, and the cable can burn through at the place of the first damage. In this case, as experience shows, two or more accidents due to overvoltages can occur simultaneously.

At low PQ, there is an interdependence of element failures, for example, when the negative effect of non-linear, asymmetric and shock loads is compensated with the help of appropriate corrective devices when one or another device is turned off. Thus, the failure of a high-speed static compensator causes asymmetry, voltage fluctuations and harmonics, which were previously compensated, which, in turn, is fraught with the occurrence of false alarms of relay protection, emergency failure of some types of electrical equipment and other similar negative consequences. Failures in the channels of information transmission through power circuits in the presence of harmonics lead to the submission of incorrect commands to control the switching equipment. Thus, PQ significantly affects the reliability of power supply, since the accident rate in networks with low PQ is higher than in the case when PQ is within acceptable limits.

5. Quality control of electrical energy

.1 Main tasks and types of power quality control

The main tasks of PQ control are:

Verification of compliance with the requirements of the standard in terms of operational control of the PQ in general-purpose electrical networks;

Checking the compliance of the actual values ​​​​of the SQI at the network interface in terms of balance sheet belonging to the values ​​\u200b\u200bfixed in the power supply agreement

Development of technical conditions for the connection of the consumer in terms of CE;

Verification of the fulfillment of contractual conditions in terms of PQ with the determination of the allowable calculated and actual contributions of the consumer to the deterioration of PQ;

Development of technical and organizational measures to ensure CE;

Determination of discounts (surcharges) to EE tariffs for its quality;

Electrical energy certification;

Search for the "culprit" of the distortions of the SCE.

Depending on the goals to be solved during the control and analysis of CE, measurements of the CE can take four forms:

· diagnostic control;

· inspection control;

· operational control;

· commercial accounting.

PQ diagnostic control - the main purpose of diagnostic control at the interface between the electrical networks of the consumer and the power supply organization is to detect the "culprit" of the deterioration of the PQ, determine the permissible contribution to the violation of the requirements of the standard for each SQI, include them in the power supply contract, normalize the PQ.

Diagnostic control should be carried out when issuing and verifying the fulfillment of technical specifications for connecting a consumer to an electrical network, when monitoring contractual conditions for power supply, and also in cases where it is necessary to determine the share contribution to the deterioration of the PQ of a group of consumers connected to a common power center. Diagnostic control should be periodic and include short-term (no more than one week) measurements of PQE. During diagnostic control, both normalized and non-normalized SCEs are measured, as well as currents and their harmonic and symmetrical components and their corresponding power flows.

If the results of the PQ diagnostic control confirm the “guilty” of the consumer in violating the PQ standards, then the main task of the power supply organization together with the consumer is to develop and evaluate the possibilities and timing of measures to normalize the PQ. For the period prior to the implementation of these measures, on-line control and commercial accounting of PQ should be applied at the interface between the electrical networks of the consumer and the power supply organization.

At the next stages of PQ diagnostic measurements, the control points should be the buses of regional substations, to which the cable lines of consumers are connected. These points are also of interest for monitoring the correct operation of transformer on-load tap-changers, for collecting statistics and fixing voltage dips and temporary overvoltages in the electrical network. Thus, the operation of already existing means of ensuring CE is controlled: synchronous compensators, banks of static capacitors and transformers with on-load tap-changers that provide specified ranges of voltage deviations, as well as the operation of protection and automation equipment in the electrical network.

PQ inspection control is carried out by certification bodies to obtain information on the state of certified electricity in the electric networks of the power supply organization, on compliance with the conditions and rules for applying the certificate, in order to confirm that the PQ continues to comply with the established requirements during the validity period of the certificate.

Operational control of the PQ is necessary under operating conditions at the points of the electrical network where voltage distortions exist and cannot be eliminated in the short term. Operational control is necessary at the points of connection of traction substations of railway and urban electrified transport, substations of enterprises with EP with non-linear characteristics. The results of operational control should be sent via communication channels to the control points of the electrical network of the power supply organization and the power supply system of the industrial enterprise.

Commercial metering of the PCE - should be carried out at the interface between the electrical networks of the consumer and the energy supply organization, and based on its results, discounts (surcharges) to electricity tariffs for its quality are determined.

The legal and methodological basis for ensuring the commercial accounting of PV in electrical networks is the Civil Code of the Russian Federation (CC RF), part 2, GOST 13109 - 97, Instructions on the procedure for payments for electrical and thermal energy (No. 449 of December 28, 1993 of the Ministry of Justice of the Russian Federation ).

Commercial metering of the PV should be continuously carried out at the metering points of the consumed electricity as a means of economic impact on the culprit of the deterioration of the PV. For these purposes, devices should be used that combine the functions of electricity metering and measuring its quality. The presence in one device of the functions of electricity metering and PQE control will allow to combine operational control and commercial metering of PQ, while common communication channels and means of processing, displaying and documenting ASKUE information can be used.

PQ commercial metering devices must register the relative time of exceeding the normal and maximum allowable SQI values ​​at the electricity control point for the billing period, which determine the tariff premiums for the perpetrators of the PQ deterioration.

.2 Standard requirements for power quality control

Control over compliance with the requirements of the standard by power supply organizations and consumers of electrical energy should be carried out by supervisory authorities and accredited testing laboratories for PQ.

PQ control at the points of general connection of consumers of electrical energy to general-purpose systems is carried out by energy supply organizations (control points are selected in accordance with regulatory documents). Frequency of measurements of SQE:

for a steady voltage deviation - at least twice a year, depending on seasonal changes in loads in the distribution network of the power center, and if there is automatic counter voltage regulation in the power center, at least once a year;

for the rest of the PCE - at least once every two years, with the network scheme and its elements unchanged and a slight change in the nature of the consumer's electrical loads that worsen the PQ.

Electricity consumers that worsen the PQ should carry out control at the points of their own networks, closest to the points of common connection of these networks to the general-purpose electric network, as well as at the outputs of electrical energy receivers that distort the PQ.

The frequency of PQ control is established by the consumer of electric energy in agreement with the energy supply organization.

The control of the CE supplied by traction substations of alternating current to electric networks with a voltage of 6 - 35 kV should be carried out:

· for electrical networks 6 - 35 kV, administered by power systems, at the points of connection of these networks to traction substations;

· for electrical networks 6 - 35 kV, not under the authority of power systems, at points selected by agreement between traction substations and consumers of electricity, and for newly built and reconstructed (with replacement of transformers) traction substations - at the points of connection of consumers of electrical energy to these networks.

5.3 Discounts and surcharges on the electricity quality tariff

In paragraph 1 of Art. 542 part 2 of the Civil Code of the Russian Federation establishes: "the quality of the energy supplied by the energy supply organization must comply with the requirements established by state standards and other mandatory rules, or provided for by the energy supply agreement."

To ensure the norms of the standard at the points of common connection, it is allowed to establish in power supply contracts with consumers - the "culprits" of the deterioration of the CE, more stringent standards (with smaller ranges of changes in the corresponding CE indicators) than those established in the standard, which consumers are required to maintain at the interface of the balance belonging of electrical networks.

In case of violation by the energy supply organization of the requirements for CE, the subscriber has the right to prove the amount of damage and recover it from the energy supply organization in accordance with the rules of Art. 547 of the Civil Code of the Russian Federation. At the same time, given that the subscriber still used energy of inadequate quality, he must pay for it, but at a proportionately reduced price (clause 2, article 542 of the Civil Code of the Russian Federation).

Obviously, violations can be mutual and for different SCEs. The party responsible for the reduction of the PQ is determined in accordance with the Rules for the Application of Discounts and Surcharges to Electricity Quality Tariffs.

The instruction on the procedure for payments for electricity and heat in section 4 "Discounts (surcharges) to the tariff for electricity quality" establishes penalties for the culprit of the deterioration of the PQ.

The mechanism of penalties established by the Instruction does not apply to all SCEs, but to those numerical values, the norms of which are in the standard:

steady voltage deviation;

the distortion factor of the sinusoidality of the voltage curve;

voltage unbalance factor in reverse sequence;

coefficient of voltage asymmetry in the zero sequence;

frequency deviation;

range of voltage change.

Of the listed SCEs, the distortion coefficient of the sinusoidality of the voltage curve and the coefficients of the harmonic components of the voltage reflect the same phenomenon - non-sinusoidality. Moreover, it reflects all the harmonics in total, and - each of the 40 harmonics separately. Therefore, the Instructions apply discounts (surcharges) for the total impact (coefficient), in addition, it must be taken into account that discounts (surcharges) for individual SCEs are added up. Therefore, the indicator is not included in the Instruction. The duration of the voltage dip is also not included in the discounts (surcharges), since the amount of sanctions for the listed SCEs depends on the total duration of the supply of low-quality electrical energy per month, and in terms of voltage dips, the duration of one dip is normalized without rationing their number.

Discounts (surcharges) for the quality of electrical energy are applied in settlements with all consumers.

The value of the discount (surcharge) depends on:

from the number of SCEs for which there is a violation of the norms of the standard at the point of electricity metering during the billing period;

from the relative time of exceeding the normal and maximum allowable values ​​of the SQI at the point of electricity control during the billing period.

The specific value of the discount (surcharge), depending on the degree of violation of these factors, can be from 0.2 to 10% of the electricity tariff.

Payment under the tariff with a discount (surcharge) for CE is made for the entire volume of electric energy supplied (consumed) during the billing period. If the energy supply organization is guilty of the violation, the penalty is implemented in the form of a discount from the tariff, if the consumer is guilty, in the form of a surcharge.

For unacceptable voltage and frequency deviations, the unilateral responsibility of the power supply organization is provided. For voltage deviation, the power supply organization is responsible to the consumer if the subscriber does not exceed the technical limits of consumption and generation of reactive power.

Responsibility for violation of the norms for the remaining four SCEs rests with the culprit of the deterioration of the CE. The culprit is determined on the basis of a comparison of the allowable contribution included in the contract to the value of the considered SCE at the control point with the actual contribution determined by measurements.

Literature

1. GOST 13109-97 "Quality standards for electrical energy in general-purpose power supply systems."

Guidelines for monitoring and analyzing the quality of electricity in general-purpose power supply systems (RD 34.15.501 - 88).

Zhezhelenko I.V. Power quality indicators and their control at industrial enterprises. M.: Energoatomizdat, 1986. 168 p.

Ivanov V.S., Sokolov V.I. Modes of consumption and quality of electricity in power supply systems of industrial enterprises. M.: Energoatomizdat, 1987. 336 p.

Goryunov I.T., Mozgalev V.S., Dubinsky E.V., Bogdanov V.A., Kartashev I.I., Ponomarenko I.S. Basic principles of building a system for monitoring, analyzing and managing the quality of electricity. Power stations, 1998, No. 12.

Rules for applying discounts and surcharges to electricity quality tariffs (approved by Glavgosenergonadzor on May 14, 1991).

Petrov V.M., Shcherbakov E.F., Petrova M.V. On the influence of household electrical receivers on the operation of related electrical devices. Industrial Energy, 1998, No. 4.

Levin M.S., Muradyan A.E., Syrykh N.N. The quality of electricity in the networks of rural areas. M.: Energy, 1975. 224 p.

Kudrin B.I., Prokopchik V.V. Power supply of industrial enterprises. Minsk: Higher school, 1988. 357 p.

Instructions on the procedure for payments for electrical and thermal energy (registration No. 449 of December 28, 1993 of the Ministry of Justice of the Russian Federation).

Golovkin P.I. Energy system and consumers of electric energy M.: Energy, 1973. 168 p.

Mozgalev V.S., Bogdanov V.A., Kartashev I.I., Ponomarenko I.S., Syromyatnikov S.Yu. Evaluation of the efficiency of power quality control in EPS. Power stations, 1999, No. 1.

MINISTRY OF SCIENCE AND EDUCATION OF UKRAINE

STATE HIGHER EDUCATIONAL INSTITUTION

DONETSK NATIONAL TECHNICAL UNIVERSITY

Research work

on the topic: "Quality of electricity"

Completed st.gr. ________________________ date signature Checked by ________________________ date signature

Donetsk, 2011

This work contains: 27 pages, 7 figures, 1 table, 6 sources. The object of the research work is: the quality of electricity in the power supply systems of Ukraine. The purpose of the work: to get acquainted with the factors affecting the quality of electricity, ways of its regulation; find out how automatic regulation of power quality is carried out; determine how the quality of electricity will affect its cost. In the work, power supply and power consumption systems of various designs are investigated, the main problems of these systems are identified, which can lead to a decrease in the quality of electricity. ELECTRICITY, POWER QUALITY, VOLTAGE ASYMMETRY, OVERVOLTAGE, AUTOMATED CONTROL, ELECTRICAL SYSTEM.

1. Power quality indicators………………………………………………4 1.1 Voltage fluctuation………………………………………………………6 1.2 Voltage fluctuation…… …………………………………………….8 1.2.1 Influence of voltage fluctuations on the operation of electrical equipment…………………………………………………………. ..8 1.2.2 Measures to reduce voltage fluctuations……………….9 1.3 Voltage unbalance………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………….10 ……………………………………………………… 11 1.3.2 Measures to reduce voltage unbalance………… 12 1.4 Voltage non-sinusoidality…………………………………… …..12 1.4.1 Influence of voltage non-sinusoidality on the operation of electrical equipment………………………………………………………….13 1.4.2 Measures to reduce voltage non-sinusoidality ..14 1.5 Frequency deviation 15 ………………………….........16 2. Automated power quality control…………..16 2.1 Basic requirements for models of electrical systems containing distributed mixed sources of voltage distortion………… ..17 2.2 Methodology for determining the actual impact of the consumer on the PQ...19 3. Calculations for electricity depending on its quality……………….22 Literature…………………………………………… …………………………...26

1 POWER QUALITY INDICATORS

Electrical appliances and equipment are designed to operate in a specific electromagnetic environment. The electromagnetic environment is considered to be the power supply system and the electrical apparatus and equipment connected to it, connected inductively and creating to some extent interference that negatively affects each other's work. With the possibility of normal operation of the equipment in the existing electromagnetic environment, one speaks of the electromagnetic compatibility of technical means. Uniform requirements for the electromagnetic environment are fixed by standards, which allows you to create equipment and guarantee its performance in conditions that meet these requirements. The standards establish permissible levels of interference in the electrical network, which characterize the quality of electricity and are called power quality indicators (PQIs). With the evolutionary change in technology, the requirements for the electromagnetic environment also change, naturally in the direction of tightening. So our power quality standard, GOST 13109 of 1967, was revised in 1987 with the development of semiconductor technology, and revised in 1997 with the development of microprocessor technology. Indicators of the quality of electrical energy, methods for their assessment and norms are determined by the Interstate Standard: “Electric Energy. Compatibility of technical means is electromagnetic. Standards for the quality of electrical energy in general-purpose power supply systems” GOST 13109-97. Table 1.1 - Rationing of power quality indicators

	Name of PCE	Most likely cause
Voltage deviation
	steady state voltage deviation	consumer load schedule
Voltage fluctuations
	voltage swing	fluctuating load consumer
	flicker dose
Voltage unbalance in a three-phase system
	negative sequence voltage unbalance factor	consumer with unbalanced load
	zero sequence voltage unbalance factor
Non-sinusoidal voltage waveform
	voltage sine wave distortion factor	consumer with non-linear load
	coefficient of the nth harmonic voltage component
	frequency deviation	network features, climatic conditions or natural phenomena
	dip duration
	impulse voltage
	temporary overvoltage factor

Most of the phenomena that occur in electrical networks and degrade the quality of electrical energy occur due to the peculiarities of the joint operation of power consumers and the electrical network. Seven SCEs are mainly due to voltage losses (drops) in the section of the electrical network, from which neighboring consumers are powered. Voltage losses in the section of the electrical network (k) are determined by the expression: ΔU k \u003d (P k R k + Q k X k) / U nom Here, the active (R) and reactive (X) resistance of the k-th section of the network are practically constant , and the active (P) and reactive (Q) power flowing through the k-th section of the network are variable, and the nature of these changes affects the formation of electromagnetic interference:

With a slow change in the load in accordance with its schedule - voltage deviation; With a sharply changing nature of the load - voltage fluctuations; With an asymmetric distribution of the load over the phases of the electrical network - voltage asymmetry in a three-phase system; With a non-linear load - non-sinusoidal shape of the voltage curve.

In relation to these phenomena, consumers of electrical energy have the opportunity to influence its quality in one way or another. Everything else that worsens the quality of electrical energy depends on the characteristics of the network, climatic conditions or natural phenomena. Therefore, the consumer of electrical energy does not have the opportunity to influence this, he can only protect his equipment with special means, for example, high-speed protection devices or uninterrupted power supply devices (UPS). 1.1 Voltage deviation. Voltage deviation - the difference between the actual voltage in the steady state operation of the power supply system and its nominal value. Voltage deviation at one point or another in the network occurs under the influence of load changes in accordance with its schedule.

Influence of voltage deviation on the operation of electrical equipment:

Technological installations:

With a decrease in voltage, the technological process deteriorates significantly, and its duration increases. Consequently, the cost of production increases. With an increase in voltage, the service life of the equipment decreases, and the likelihood of accidents increases. With significant voltage deviations, the technological process is disrupted.

Lighting:

The service life of lighting lamps is reduced, so at a voltage of 1.1 U nom, the service life of incandescent lamps is reduced by 4 times. At a voltage of 0.9 U nom, the luminous flux of incandescent lamps is reduced by 40% and fluorescent lamps by 15%. voltage value less than 0.9 U nom fluorescent lamps flicker, and at 0.8 U nom they simply do not light up.

Electric drive:

When the voltage at the terminals of the asynchronous motor is reduced by 15%, the torque is reduced by 25%. The engine may not start or stop.

With a decrease in voltage, the current consumed from the network increases, which leads to heating of the windings and a decrease in the life of the motor. With long-term operation at a voltage of 0.9 U nom, the service life of the motor is halved. With an increase in voltage by 1%, the reactive power consumed by the motor increases by 3 ... 7%. The efficiency of the drive and network is reduced.

The generalized load node of electrical networks (load on average) is:
- 10% of the specific load (for example, in Moscow this is the metro - ~ 11%);
-30% lighting and more;
- 60% asynchronous motors. Therefore, GOST 13109-97 sets the normal and maximum permissible values ​​of the steady-state voltage deviation at the terminals of power consumers within the limits, respectively, δUy norm = ± 5% and δUy pre = ± 10% of the rated network voltage. These requirements can be met in two ways: by reducing voltage losses and by regulating the voltage. ΔU = (P R + Q X) / U CPU (TC) Reducing voltage losses (ΔU) is achieved:

The choice of cross-section of the conductors of power lines (≡ R) according to the conditions of voltage losses. The use of longitudinal capacitive compensation of the reactive resistance of the line (X). However, this is dangerous due to an increase in short-circuit currents at X→0. Reactive power compensation (Q) to reduce its transmission through the mains, using capacitor banks and synchronous electric motors operating in overexcitation mode.

In addition to reducing voltage losses, reactive power compensation is an effective energy saving measure, providing a reduction in electricity losses in electrical networks.

Voltage regulationU:

In the power center, voltage regulation (U CPU) is carried out using transformers equipped with a device for automatic regulation of the transformation ratio depending on the load - regulation under load (OLTC). ~ 10% of transformers are equipped with such devices. The regulation range is ± 16% with a resolution of 1.78%. with disconnection from the network. Adjustment range ± 5% with a resolution of 2.5%.

Responsibility for maintaining tension within the limits established by GOST 13109-97, is assigned to the energy supply organization.

Indeed, the first (R) and second (X) methods are chosen when designing the network and cannot be changed in the future. The third (Q) and fifth (U TP) methods are good for regulating during seasonal changes in network load, but it is necessary to manage the operating modes of consumer compensating equipment centrally, depending on the operating mode of the entire network, that is, the power supply organization. The fourth way - voltage regulation in the power center (U CPU), allows the power supply organization to actively regulate the voltage in accordance with the load schedule of the network. GOST 13109-97 establishes the permissible values ​​​​of the steady-state voltage deviation at the terminals of the electrical receiver. And the limits of voltage change at the point of connection of the consumer should be calculated taking into account the voltage drop from this point to the power receiver and indicated in the power supply contract. 1.2 Voltage fluctuations Voltage fluctuations are rapidly changing voltage fluctuations lasting from half a cycle to several seconds. Voltage fluctuations occur under the influence of a rapidly changing network load. The sources of voltage fluctuations are powerful power consumers with a pulsed, sharply variable nature of active and reactive power consumption: arc and induction furnaces; electric welding machines; electric motors at startup.

The quickest way would be to call the networks and find out exactly what they need.
Personally, I xs what needs to be done, but I'll try to guess:

Option one: there is GOST 32144-2013 (entered into force on 07/01/2014) "Quality standards for electrical energy in general-purpose power supply systems" where you will find quality standards and tolerances and the term itself:
3.1.38 quality of electrical energy (QE): The degree of compliance of the characteristics of electric energy at a given point of the electrical system with a set of normalized indicators of QE.
Actually, if you have done all the calculations and you do not have consumers that worsen the quality of electricity, then in the "Ensure the quality of electricity" section, simply indicate these calculations and the absence of the need to install "devices for compensating and regulating reactive power in electrical networks".

Option two: to the resolution (No. 861 of December 27, 2004) in the annex on what the specifications should contain: "Technical conditions for connection to electric networks (for individuals for the purpose of technological connection of power receiving devices, the maximum power of which is up to 15 kW inclusive (taking into account power receiving devices previously connected at this point of connection) and which are used for domestic and other needs not related to business activities) "there is paragraph 10:
10. The network organization carries out
(requirements are indicated for strengthening the existing electrical network in connection with the connection
new capacities (construction of new power lines, substations, increase in the cross-section of wires and cables,
replacement or increase in the power of transformers, expansion of switchgear, equipment modernization, reconstruction
power grid facilities, installation of voltage regulation devices to ensure the reliability and quality of electrical energy,
as well as, by agreement of the Parties, other obligations to fulfill the technical specifications provided for in clause 25_1 of the Rules for Technological Connection
power receivers of electric energy consumers, electric energy production facilities, as well as electric grid facilities owned by grid organizations and other persons, to electric networks)

You can indicate in the section in the "Ensure the quality of electricity" section that, according to the regulation for consumers up to 15 kW, the quality is provided by the network organization.

Option three: If the contract is between adjacent grid organizations, then:
(Decree of the Government of the Russian Federation No. 861 of December 27, 2004, III. The procedure for concluding and executing contracts between grid organizations) p 38. An agreement between related grid organizations must contain the following essential conditions:

f) organizational and technical measures agreed with the subject of operational dispatch control in the electric power industry for the installation of devices for compensating and regulating reactive power in electric networks that are the objects of dispatching of the corresponding subject of operational dispatch control in the electric power industry, within the territory of the subject of the Russian Federation or other specified by the specified subject territories that are aimed at ensuring a balance of consumption of active and reactive power within the boundaries of the balance sheet of power receiving devices of consumers of electrical energy (subject to compliance by producers and consumers of electrical energy (power) with the requirements for the quality of electrical energy for reactive power) (the sub-clause was additionally included from March 27, 2010 year by Decree of the Government of the Russian Federation of March 3, 2010 N 117);

g) the obligations of the parties to comply with the required parameters of the reliability of power supply and the quality of electrical energy, the modes of consumption of electrical energy, including maintaining the ratio of consumption of active and reactive power at the level established by the legislation of the Russian Federation and the requirements of the subject of operational dispatch control in the electric power industry, as well as to comply with the established the subject of operational dispatch control in the electric power industry of compensation levels and reactive power control ranges (the sub-clause was additionally included from March 27, 2010 by Decree of the Government of the Russian Federation of March 3, 2010 N 117);

those. you must specify the equipment installed to bring the quality of electricity back to normal.

something like that, but not the fact that this information will help you.

hombre, Faced a similar issue on the quality of e / e. The network organization wrote comments on the external power supply project that something like "... determine a set of technical measures for quality control of electric power, excluding their deviation from the norm. values ​​in accordance with GOST 32144-2013 ..."

So the question is, how can this set of measures be determined in the project of external and internal power supply? How to evaluate the parameters of power quality in the project in order to decide whether additional device or not?

Okay, according to voltage losses, I calculated whether to compensate for reactive power or not, I also calculated - what about the other parameters of the quality of e / energy (their assessment) in the power supply project?
The project is a production base, Rrazr. according to TU 100kW. In my case, I do it only on external networks from the PTS of the network organization to RP-0.4kV prod. bases, i.e. I do not do intranets and on-site networks

In general, I prescribe in the PZ, just in case, that such as "the planned electrical receivers and electrical consumers do not worsen the quality parameters of electricity below the standards established by GOST ...." But today I received such comments

One more question, they wrote comments on the compensation of react. power and bringing tgf no more than 0.1.

As I understand it, if connected power according to specifications is less than 150 kW, then the requirements for cosf from the power supply. there can be no organization and reactive power compensation can not be done (the basis is the Order of the Ministry of Industry and Energy of the Russian Federation of February 22, 2007 N 49)

Tell me the best way to answer

If I'm wrong about something, please correct me.

In the text part of the power supply project, it is necessary to describe the power receivers indicating the category of power supply required for them and a description of the measures to ensure this category.

Requirements for the reliability of power supply.

All consumers of electrical energy are divided into 3 categories of power supply reliability in accordance with Ch. 1.2 PUE.

First category- in normal modes, they must be supplied with electricity from two independent mutually redundant power sources, and interruption of their power supply in the event of a power failure from one of the power sources can only be allowed for the period of automatic power restoration. (see also the first special category).

These categories of power supply are defined in the regulatory documents regarding each individual type of equipment or object (building, structure, mechanism). The technical conditions issued by the grid organization determine the category of power supply provided by the grid organization, for its part. Based on local regulatory documents, which define the category of reliability of a particular type of power receiver, a comparison is made. If the category of power supply according to specifications is lower than required in the regulatory documents, then it is necessary to provide for measures to ensure the required category by installing additional sources of electrical energy - batteries, diesel generators.

In connection with the replacement of GOST 13109-97 with GOST 32144-2013. Standards for the quality of electrical energy in general-purpose power supply systems and the introduction of GOST R 50571.5.52-2011 (IEC 60364-5-52:2009) Low-voltage electrical installations. Selection and installation of electrical equipment. the requirements for designers to voltage losses in electrical networks, as well as to the calculation of voltage losses, have changed.

Here is an example of a paragraph from the Explanatory Note:

Fire and burglar alarm devices, fire warning system, fire-fighting devices, VZU, emergency lighting are classified as Category I. Provided by ATS, UPS

To ensure the second category of reliability at the site, a quarantine facility is used single transformer substation with two cables entering the building from the transformer substation and DGU.

Power receivers of the first category in normal modes must be supplied with electricity from two independent mutually redundant power sources, and a break in their power supply in the event of a power failure from one of the power sources can only be allowed for the period of automatic power restoration. In this regard, emergency lighting fixtures are used with emergency power supplies. Also, emergency power units are built into the microclimate control panels and fire alarm devices and fire alarm systems.

2.1. Power quality indicators and their regulation

For a long time, the development of the energy sector in our country was accompanied by an underestimation, and often by ignoring the problems of the quality of electrical energy, which led to a massive excitation of the electromagnetic compatibility of electrical networks, consumers and power systems. Electromagnetic compatibility is defined as the ability of an electrical device to function satisfactorily in an electromagnetic environment to which other devices also belong. The quality of electrical energy is deteriorating from year to year, while the requirements for its improvement are increasing. Now a difficult situation has arisen, when many technological processes, for example, biotechnology, automatic lines, computer, vacuum, microprocessor technology, remote control, electrical measuring systems, etc. with the existing quality of electrical energy, they cannot work reliably (without disturbances).

After all, the time has come when electrical energy (EE) must be considered as a commodity, which, under any management system, is characterized by certain (specific) indicators, the list and values ​​of which determine its consumer quality.

Power quality (KE) there is a corresponding set of its parameters that describe the features of the EE transmission process for its use under normal operating conditions, determine the continuity of the power supply (the absence of long or short interruptions in the power supply) and characterize the supply voltage (value, asymmetry, frequency, waveform). Two more remarks must be added before this definition.

First: KE as a whole is expressed by the degree of satisfaction of the consumer with the conditions of power supply, which is important from a practical point of view.

Secondly: KE depends not only on the conditions of power supply, but also on the characteristics of the electrical equipment that is used (its criticality to electromagnetic obstacles (EMF), as well as the possibility of their generation) and operating practices. The last remark determines the fact that not only supplying organizations, but also consumers of electricity and manufacturers of electrical equipment should be responsible for KE.

The International Electrotechnical Commission (IEC) develops and approves KE standards of three types: defining ones, which contain a description of the electromagnetic environment, terminology, instructions for limiting the equal generation of EMF and for measuring and testing means for determining power quality indicators (PQU), recommendations for the manufacture of electrical equipment; general norms, which give the permissible levels of EMP that are generated or their permissible levels in electrical networks for domestic or industrial purposes; detailed (subject) norms, which contain requirements for individual products and are attached from the point of view of KE.

The main organization in Europe that coordinates work on standardization in electrical engineering, electronics and related fields of knowledge is MEK. It is also necessary to name such international organizations as the Committee on Large Electric Systems and the Union of Manufacturers and Distributors of EE. CENELEC is an influential regional organization that deals with normalization in the field of EC for the countries of the European Union (EU). There are a number of international professional organizations and national committees that develop national standards for KE, as a rule, based on the MEK standards. The adoption of norms occurs mainly by the method of expert assessments, by voting.

The normalization of PKE values ​​is one of the main issues of the KE problem. The PKE system is formed by quantitative characteristics of slow (deviation) and fast (oscillation) changes in the effective voltage value, its shape and symmetry in a three-phase system, as well as frequency changes. The personnel of the energy services of enterprises cannot influence the level of frequency in the network. The exception is cases of power supply from autonomous sources, which are relatively rare in practice. Therefore, in the future, only issues that relate to KE by voltage are considered.

The principles of normalization of PKE voltage are based on technical and economic prerequisites and are as follows:

PKE voltages have an energy value, that is, they characterize the power (energy), the distortion of the voltage curve, the degree of negative effect of this energy on electrical equipment, and the efficiency of technological processes is compared with the values ​​of the indicated PKE distortions;

The maximum permissible values ​​of PKE are selected from technical and economic considerations;

PKE are normalized with a given reliability over a certain time interval to obtain specific values ​​that allow comparison.

The PKE system, which is based on these prerequisites, can be applied from design work. It makes it possible to carry out mass metrological support for EC control using relatively simple and inexpensive devices, as well as to implement measures and technical means for EC normalization.

In Ukraine, since January 1, 2000, the interstate standard GOST 13109-97 “Standards for the quality of electrical energy in general-purpose power supply systems” has been put into effect. The standard establishes indicators and norms of KE in electrical networks of general-purpose power supply systems of replaceable three-phase and single-phase current with a frequency of 50 Hz at nodes to which electrical networks that are owned by different EE consumers or EE receivers (at common connection nodes) are connected. If these standards are observed, electromagnetic compatibility of electrical networks of general-purpose power supply systems and electrical networks of EE consumers (EE receivers) is ensured.

The norms established by the specified standard are mandatory in all modes of operation of general-purpose power supply systems, except for modes that are due to the following:

Exceptional weather conditions and natural disasters (hurricane, flood, earthquake, etc.);

Unforeseen situations that are caused by the actions of a party that is not an energy supply organization and consumer of IT (fire, explosion, military action, etc.);

Conditions that are regulated by government authorities, as well as those related to the elimination of consequences caused by exceptional weather conditions and unforeseen circumstances.

The norms established by this standard are to be included in the technical specifications for the connection of EE consumers and in contracts for the use of EE between electricity suppliers and consumers. According to GOST 13109-97, KE indicators are:

Stable voltage deviation dU y;

The range of voltage change dUt;

Flicker dose Pt;

The distortion factor of the sinusoidal voltage curve KU;

Coefficient of the nth harmonic voltage component KU (n) ;

Voltage unbalance factor in reverse sequence K 2U ;

Zero sequence voltage unbalance factor K 0U ;

Frequency deviation (f;

Voltage dip duration Dtn;

Impulse voltage U imp;

Temporary overvoltage factor K perU .

It should be noted that two types of norms for KE are considered - normally permissible and maximum permissible. The assessment of the compliance of the PKE with the specified standards is carried out during the billing period, which is equal to 24 hours.

Most of the phenomena that are observed in electrical networks and degrade the quality of electrical energy occur due to the peculiarities of the general operation of electrical receivers and the electrical network, their electromagnetic compatibility. Seven PKEs are mainly due to voltage losses (drops) in the section of the electrical network from which consumers are powered.

The voltage loss in the section of the electrical network is determined by the expression:

The active (R) and reactive (X) resistance of the network sections indicated here are assumed to be constant, and the active (P) and reactive (Q) powers that are transmitted through the network section are replaceable. The nature of these changes, moreover, can be different, which prompts different definitions of voltage losses:

With a slow change in load according to its schedule - voltage deviation;

With a sharply changing nature of the load - voltage fluctuation;

With an asymmetric distribution of the load over the phases of the electrical network - voltage unbalance in a three-phase system;

With a non-linear load - non-sinusoidal load curve.

From those phenomena that the consumer of electrical energy cannot influence, he can only protect his equipment with special means, for example, high-speed protection devices or guaranteed power supplies.

Responsibility for maintaining the voltage within the limits established by GOST 13109-97 relies on the power supply organization.

Voltage deviation (HV) – discrepancy between the actual voltage in a stable mode of operation of the power supply system and its nominal value. The indicated deviation is characterized by the indicator of stable HV dU y.

The voltage deviation at one or another point of the network occurs, as already noted, under the influence of a slow change in load according to its schedule.

GOST 13109 - 97 establishes permissible values ​​of constant voltage deviation on the terminals of the electrical receiver. And the limits of voltage change at the point of connection of the consumer should be determined taking into account the voltage drop from the specified point to the power receiver and indicated in the power supply contract.

Voltage fluctuations (VV) - voltage deviation that occurs in the interval from half a cycle to several seconds.

The sources of voltage fluctuations are powerful electrical receivers with a pulsed, sharply changing nature of active and reactive energy consumption: arc and induction furnaces; electric welding machines; electric motors in starting modes, etc. KN is characterized by the following indicators:

The range of voltage change dUt;

The dose of flicker Pt.

flicker – this is a subjective perception by a person of fluctuations in the luminous flux of artificial lighting sources, which are caused by voltage fluctuations in the electrical network that feeds these sources.

Flicker dose - a measure of a person's susceptibility to the action of a flicker over a specified period of time. Flicker Perception Time - the minimum period of time for subjective perception by a person of flicker caused by voltage fluctuations of a certain shape.

The short-term flicker dose is determined over an observation time interval that does not exceed 10 minutes. The long-term flicker dose is determined over an observation time interval of 2 hours.

Non-sinusoidal voltage - distortion of the sinusoidal shape of the voltage curve.

Electrical receivers with a non-linear current-voltage characteristic consume current, the shape of which is different from the sinusoidal curve. And the flow of such a current through the elements of the electrical network creates a voltage drop on them that is different from sinusoidal. This is the reason for the curvature of the sinusoidal shape of the voltage curve.

Fig 2.1. Non-sinusoidal voltage

The sinusoidality of the voltage is characterized by the following indicators:

The coefficient of curvature of the sinusoidality of the voltage curve K U ;

The coefficient of the n-th harmonic component of the voltage K U (n) .

Voltage unbalance - unbalance of a three-phase voltage system.

Voltage asymmetry occurs only in a three-phase network under the influence of an uneven distribution of loads over its phases. GOST 13109 - 97 indicates a consumer with an asymmetric load as a reliable source of the one responsible for the voltage asymmetry.

Sources of voltage asymmetry are: arc steel-smelting furnaces, traction substations of alternating current, electric welding machines, single-phase electrothermal installations and other single-phase, two-phase and asymmetric three-phase consumers of electricity, in particular households.

So the total load of individual enterprises contains 85 ... 90% of the asymmetric load. And the coefficient of voltage asymmetry in the zero sequence (K 0U) of one 9-surface house can be 20%, which on the buses of a transformer substation (point of common connection) can exceed the allowable 2%.

Fig 2.2. Voltage unbalance

Voltage asymmetry is characterized by the following indicators:

Voltage unbalance factor in reverse sequence K 2U ;

Voltage asymmetry coefficient in the zero sequence K 0U.

Frequency deviation - deviation of the actual frequency of the replacement voltage (f fac) from the nominal value (f nom) in the constant mode of operation of the power supply system.

The frequency deviation of the alternating current voltage in electrical networks is characterized by the frequency deviation indicator (f.

Voltage dip - a sudden and significant decrease in voltage (less than 90% U nom) lasting from several periods to several tens of seconds with further restoration of voltage.

The causes of voltage dips are the operation of automation protection equipment when lightning surges, short-circuit currents (short circuits) are turned off, as well as in case of erroneous protection trips or as a result of erroneous actions of operational personnel.

GOST 13109-97 does not standardize the voltage dip, it limits its duration to 30 seconds. True, there are practically no voltage dips lasting 30 seconds - the voltage is not restored.

The voltage dip is characterized by the voltage dip duration indicator Dtn . .

Voltage pulse - a sharp increase in voltage lasting less than 10 milliseconds.

Surge overvoltages occur during thunderstorms and when switching equipment (transformers, motors, capacitors, cables), in particular, when short-circuit currents are turned off. The magnitude of the overvoltage pulse depends on many conditions, but is always significant and can reach many hundreds of thousands of volts.

GOST 13109-97 provides reference values ​​of surge voltage during switching for different types of networks.

Fig.2.3. voltage pulse

The voltage impulse is characterized by the impulse voltage U imp.

Temporary overvoltage - a sudden and significant increase in voltage (more than 110% Unom) lasting more than 10 milliseconds.

Temporary overvoltages occur when equipment is switched (switching, short-term) and during short circuits to earth (long-term).

Switching surges occur when unloading long high voltage power lines. Continuous overvoltages occur in networks with compensated neutral, four-wire networks when the neutral wire breaks, and in networks with isolated neutral in case of a single-phase short circuit to ground (in networks of 6-10-35 kV, continuous operation is allowed in this mode). In these cases, the undamaged phase-to-ground voltage (line-to-line voltage) may rise to the line-to-line (line-to-line) voltage.

Temporary overvoltage is characterized by the coefficient of temporary overvoltage K per.U.

The norms of the given PKE are provided in tables 2.1. If the change in HV and the frequency deviation is random, then the requirements of GOST 13109-97 apply to those that have an integral reliability of at least 95% during the calculation period.

Table 2.1. – Norms of KE indicators and possible reasons for their decrease

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Symbol	KE indicator, unit of measurement	KE norms GOST 13109-97		More likely reason
		normally admissible	maximum allowable
Voltage deviation
δuy	Sustainable VN, %	±5	±10
Voltage fluctuation
δut	Range of voltage change, %	-	curves 1.2 in fig. 2.1
	Flicker dose, visible one: short-term prolonged
Voltage sinusoidality
Ku	The coefficient of curvature of the sinusoidal voltage,%	according to table 2.1.2	according to table 2.1.2
Ku(n)	Coefficient of n-th harmonic voltage component, %	according to table 2.1.3	according to table 2.1.3
Voltage unbalance in a three-phase system
K 2 u	Voltage asymmetry coefficient in reverse sequence, %	2	4
K 0 u	Zero sequence voltage unbalance factor, %	2	4
Other
Df	Frequency deviation, Hz	±0.2