Magnetic starters are designed for remote start and stop of electric motors, reverse control and other manipulations. The task also includes the protection of equipment from overloads in the presence of protection in the circuit. Starters with the correct calculation of the connected load can work for months and even years without any intervention, costs and investments. But like any electrical equipment, they have malfunctions and breakdowns, which means that the list of work with this equipment includes maintenance and repair.

All these works are performed at different times. It depends on many factors, the main one being the intensity of the magnetic starter. For example, emery in a workshop: if it is made for short but frequent starts, the closing and opening of the main contacts occurs more often, and the electric arc leaves traces on the main contacts. More power of the connected electric motor - more powerful arc.

As a result, the contact heel burns. This, in turn, violates their tight fit and heating begins, which will increase over time. And the result can be deplorable if for some reason the protection does not work. Both coils and engines are burning. This can be avoided by performing maintenance.

First, you need to turn off the electric motor and hang a poster “Do not turn on! People are working!”, and then take the necessary measures to prevent erroneous or accidental switching on of the service area of ​​work (according to the rules).

You can pull out the inserts (fuses) in the switch cabinet. It is necessary to do this, since one poster is not enough - there are cases when the poster is in its place, but they do not notice it and try to turn on the equipment. Then you need to remove the cover of the starter, sweep away the dust with a brush and immediately remove it with a vacuum cleaner. For these purposes, I use the old "Rocket". You can do this in two ways: “suck off” or “blow out”, the result will be equally positive.

Next, you need to get to the main contacts, this is done in different ways depending on the design of the model. It is necessary to remove the main contacts and thoroughly clean and polish them with a crow (do not use a needle file or abrasive materials). Being inside the starter, it is necessary to measure the insulation resistance between the entire electrical part and the housing, which must be at least 10 MΩ. After completing these steps, you can put everything in its place, check the tightness of all bolts and screws, sweep away any remaining dust and close the cover.

Repair of the magnetic starter is carried out in case of replacement of the coil, auxiliary contacts, thermal relay, main contacts or other parts of the device.

As a rule, the contacts of the thermal relay and auxiliary contacts do not require frequent maintenance, as they are located in the control circuit, where the currents are small.

When repairing, if possible, it is advisable to check and test the thermal relay at the stand.

All these works take a little time, and if this is done on time, then the magnetic starters of your site will serve you faithfully for a long time. Magnetic starters are rather unpretentious equipment. A word of advice: put Grover washers on all screw connections, this is an essential element in electrical connections. You need to finish working with the starter by washing the case.

And the contactors are checked and adjusted according to the following program: external inspection, adjustment of the magnetic system; adjustment of the contact system, checking the insulation resistance of current-carrying parts.

During an external inspection of contactors and magnetic starters, first of all, they pay attention to the condition of the main and interlocking contacts, the magnetic system, check the presence of all parts of the contactor: a non-magnetic gasket for a DC contactor, mounting bolts, nuts, washers, a short-circuited coil for AC contactors, arcing cameras.

The ease of movement of the contactor is checked by closing it by hand. The course of the magnetic system should be smooth, without shocks and jamming.

When current flows through the coil, the AC contactor should make only a slight noise. A strong hum of the contactor may indicate improper attachment of the armature or core, damage to the shorted coil around the core, or a loose fit of the armature to the core of the electromagnet. To eliminate excessive buzz, tighten the screws securing the armature and core.

The tightness of the armature to the core is checked as follows. A sheet of paper is placed between the armature and the core and the contactor is closed by hand. The contact area should be at least 70% of the cross section of the magnetic circuit; with a smaller contact area, the defect is eliminated by the correct installation of the core and armature. When a common gap is formed, the surface is scraped along the layers of sheet steel of the magnetic system.

As the DC contactor operates, abrasion of the non-magnetic gasket may occur, which reduces the gap and promotes sticking of the armature to the core, therefore, with significant wear, the gasket is replaced with a new one.

The contact system is the most critical part of the contactors of magnetic starters, so special attention should be paid to its condition. In the closed state, the contacts should touch each other with their lower parts, forming a linear contact across the entire width of the contact without gaps. The presence of sagging or solidified pieces of metal on the contact surface increases the contact resistance (and, consequently, the loss in contacts) by more than 10 times. Therefore, if sagging is found, it is necessary to remove them with a file. Grinding with sandpaper and lubrication of the contact surface is not allowed.

In addition, in especially critical contactors and magnetic starters, the initial and final pressing forces of the main contacts are determined. Initial pressing - the force created by the contact spring at the moment of contact of the contacts. It characterizes the elasticity of the spring. The final pressing force characterizes the pressure on the contacts when the contactor is fully engaged and the contacts are not worn. The initial and final pressing forces are determined using a dynamometer.

The insulation resistance of the current-carrying parts of contactors and magnetic starters is checked with a megohmmeter for 500 or 1000 V. The insulation resistance value of the coil should not be lower than 0.5 MΩ.

In addition to the above works, the following may be included:

a) checking the absence of short-circuited turns in the coil,

b) checking contactors by repeated switching on and off,

c) setting up magnetic starters.

DISASSEMBLY OF THE CONTACTOR

The electromagnetic contactor MK-310B is disassembled in the following sequence:

They remove the arc chute, and on the MK-15-01 partitions and inspect their condition.

Disconnect flexible shunts and connecting cable. Check their integrity and soldering of the tip to the wire. Remove the fixed contact, the lever with the moving contact. They remove the blockage, clean all parts and inspect their integrity, rails, springs and spring holders. Check the threaded holes in the slats. Remove the springs from the contactor.

Remove the arc quenching coil, after loosening its conclusions.

Inspect the insulating rack and, if necessary, remove and replace with another. Unscrew the bolts, fixing the vertical wall, remove it. Remove the closing and holding coils.

They check the serviceability of the anchor, yoke and their fastenings, in case of a malfunction, they remove it from the contactor.

REPAIR OF ELECTROMAGNETIC CONTACTORS

Repair of electromagnetic contactors during current repairs is carried out with their complete disassembly. It is convenient to produce it on special stands with air supply and 50V direct current for testing repaired devices. On such a stand, each contactor is installed in a socket, which allows you to quickly fix the rack and freely rotate the device in a horizontal plane during disassembly and assembly. Before disassembly, the contactors are blown with compressed air, the arc chute is removed and the components and parts are inspected to determine the scope of repair. All parts are cleaned of dirt, disassembled and inspected, making sure that there are no cracks.

The horn of the arc extinguishing system is cleaned of melting and soot with a metal brush or emery cloth. The profile of the horn is checked according to the template and, in case of large melting or cracks, is restored by gas welding. After the arc horn has cooled down, the welding seam is cleaned with a file.

Contacts with slight wear or burns are cleaned with a velvet or personal file, trying to remove the smallest possible layer of metal and not change the contact profile. After stripping, wipe the contacts with a rag. Places of resistance to contact with the horn are served with solder. Contacts worn out above acceptable limits can be restored. In this case, worn contacts after cleaning and measurements are welded with copper by gas welding. The contacts are preheated with a gas burner, after which their working surfaces are welded. The welded contacts are tapped with a hammer and processed to harden them. Contact profile dimensions are controlled by templates.

The extinguishing coil is checked for damage to the surface insulation, for the reliability of the soldering of cable lugs; measure the active resistance of the winding and the insulation resistance between the winding and the poles, which must be at least 10 MΩ. If the insulation resistance is low, the coil is dried in an oven at a temperature of 100-110°C or the core insulating sleeve is replaced. The cross-sectional area of ​​the wire and the number of turns of the arcing coil must comply with the technical requirements of the drawing. If this condition is not met, there may be an incorrect direction of the magnetic blowing of the electric arc, which leads to severe burns of the arcing horns and contacts. The arcing coil of the contactor with cracks in the coils is replaced. When installing a new coil, the contact terminal is welded with brass, having previously fitted the mating surfaces well to each other. After that, the junction with the turns is insulated in a half-roof with two layers of varnished cloth and insulating tape. The turns of the coil are painted over, if necessary, with oil-bitumen varnish BT-99. The turns should not touch each other and come closer than 2 mm to the arc horn.

The switching coil of the contactor is washed with gasoline and inspected for loosening of the output clamps, the outer insulation and the condition of the frame are checked. To identify possible wire breaks, measure the active resistance of the coil with a megohmmeter. It should not deviate from the established value by more than 8% up or 5% down. The resistance of the coil, increased beyond the permissible value, will indicate a possible internal breakage of the winding or a deterioration in contact between the core of the winding output and the tip. Coils with reduced insulation resistance are impregnated.

Repair of coils with their complete disassembly is carried out in the presence of wire breaks or interturn short circuits in them. If the cover insulation of the coils is damaged, then during the repair they are limited only to changing the insulation. Coils are allowed to recover two breaks in the winding. The ends of the winding wires in the places of the break are cleaned, bunched and soldered with POS-40 solder.

Coils with coil melting of more than 3% of their cross-sectional area or with tire cracks are subject to repair. Burnouts, melting or cracks are cleaned and boiled with brass by gas welding. With deeper burns, the coils are replaced. Coils that have been repaired are impregnated in varnish. The damaged braid of the leads is sealed with rubberized adhesive tape.

The anchor of the magnetic circuit, the core is washed from dirt and, if necessary, galvanized. Bushings with developed holes in the contact holder, the anchors are pressed out and new ones are installed. Axles and rollers are cleaned of dirt, opal, burn marks, galvanized and lubricated before setting.

arc chute

The arc chute removed from the contactor is blown with compressed air, cleaned of soot, burns and metal splashes and disassembled. Asbestos-cement walls, partitions and gratings are cleaned in a steel blast or installation. Walls with a thickness of less than 4 mm, with chips, cracks and burnouts with a depth of more than 25% of their thickness are replaced. Places of deeper cracks and burnouts are cut, carefully cleaned with a file, coarse-grained sanding paper or processed in a sandblasting chamber, cleaned of dust and sand and sealed with special putty or epoxy resin.

As a putty, asbestos-cement powder diluted with liquid glass, or a mixture of equal parts of gypsum powder and asbestos fiber on alkaline varnish, is used. The putty is applied so that its level is slightly higher than the surface to be repaired, as it shrinks as it hardens. The putty on liquid glass is dried at a temperature of 25-30°C, and the alkali putty is dried in a drying oven at a temperature of 70-80°C for 7-8 hours.

Through burns and cracks can be eliminated with special mastic. The putty is applied immediately after its manufacture, since it quickly begins the polymerization process and after 30-40 minutes. it is already hardening. Before applying the mastic, the area to be repaired is thoroughly degreased with acetone or gasoline. After final processing, to increase moisture resistance, asbestos-cement walls and partitions are impregnated with linseed oil. After making sure that all parts are in good condition, the camera is assembled.

Insulating strips and base panels, levers, racks must have a clean glossy surface or be painted with GF-92-KhK enamel.

Surface insulation that has cracks, chips, burns or damage up to half of its thickness is removed completely or partially. Small burnouts are cleaned with a file and polished with fine glass paper. The area to be repaired is washed with gasoline and enamelled twice.

The springs are removed, washed and checked for basic dimensions. Springs with traces of rust are galvanized with subsequent dehydration. Stretched or sagging, but not mechanically damaged springs are restored. To do this, the spring is released, heated to a temperature of 920-980°C, compressed or stretched to the drawing dimensions and hardened to give the necessary elasticity. The end screws of the spring must have a flat horizontal surface. Springs with cracks and not corresponding to the characteristic are replaced.

Swivel joints.

They must ensure free movement of the parts to be joined without jamming and not have increased play.

For repair, the swivel joint is disassembled. Faulty axles and rollers are not repaired, but replaced with new ones. The developed holes are welded and drilled to the drawing size or to a larger diameter, followed by the installation of bushings with the corresponding inner and outer diameters.

Before assembly, the rubbing surfaces of the hinge joints are coated with grease, and after assembly, the clearance in the hinge is controlled.

After repair of all components and parts, the contactor is assembled in reverse disassembly of the sequence.

A magnetic emitter (MF) is a complex permutation device that is much easier and many times faster to restore than to replace with new equipment. From this article, the reader will learn how to check the starter coil on their own.

How to check the starter and its components

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A magnetic starter consists of a coil (its most important part), a core (fixed element) and an armature (moving element). In addition, as in any mechanism of the electrical system, the starter has contacts.

Contacts

So, in any electrical equipment, moving components primarily fail. In MP, contacts become such components. Soot, dross and deposits are sure to collect on contact surfaces and cause sparking and other problems. They arise not only due to the humidity of the environment, but also due to the occurrence of various electrochemical processes.

To check the starter bobbin, it is first recommended to inspect the contacts, clean them of accumulated soot and dirt. You can use a file or sandpaper for this, but you need to carry out the cleaning procedure carefully so as not to leave scratches on the contacts.

The next step is to adjust the contacts. It is necessary with the help of thin plastic tapes and a dynamic meter to set the correct gap, clamp the contacts. Plastic strips in this case will imitate contact. The dynamometer, on the other hand, performs the function of a force meter - as soon as it reaches 700 g, the plate is removed.

Common starter failures include:

• The occurrence of a layer of corrosion at the junction of the movable part of the starter with the fixed one;
• Cracking of a short-circuited (KRTZ) coil;
• Wrong position of armature and core;
• Excessive tension of contacts, etc.

As mentioned above, contacts and their damage are a separate type of fault. They are usually divided into the following:

1. The appearance of pollution of various properties, which are eliminated by wiping with gasoline or alcohol. If the deposits are convex and hard, then they are cleaned with a file.
2. Erosion of contacts, when they are partially or 70 percent destroyed. In this case, only replacement with new elements helps.
3. Contact springs fail. This is also not "cured" by repair. Contacts need to be replaced.

Coil or bobbin

First of all, the starter coil is inspected for cracks. When found, you need to take some cold welding and fill the space with a thin and small spatula. It is recommended to strengthen the insulation by gluing a medical plaster over the cold welding.

If an MKZ (interturn short circuit) is detected in the coil, then the turns must be removed to the point of short circuit. This is done simply by unwinding the wiring. You can notice the place of the closure by the damaged enamel on the coil. The cable is cut close to the fault, stripped and soldered.

Wiring

A short circuit that occurs when the contacts are dirty can cause an arc. It can quite easily be transferred to the magnetic circuit. Corrosion is added to pollution. To clean the surface of the magnetic circuit, you need to take a rag, moisten it with gasoline or acetone, and thoroughly clean it from dirt. Large layers of corrosion are removed with sandpaper - polished.

There are other difficulties in the operation of the starter:

• Damage to CRTZ coils;
• Loosening of the screw fasteners fixing the anchor-core pair.

KRTZ turns are an obligatory component of the fixed part of the starter, they are located at the ends of the core. They are made from soft metal. For KRTZ turns, a special type of grooves is provided in which they are placed. In addition, the turns can also deteriorate inside the coil, which actually magnetizes the core.

It is clear that problems with the clamps can be eliminated by tightening weak fasteners. And as for the KRTZ turns, only a replacement will help.

Read more about various starter and coil malfunctions in the table

Fault type	Cause	elimination
No output voltage	Movable contacts do not touch fixed contacts due to contamination or deterioration	Disassemble the device, check the contacts
Starter does not work	Jamming of the internal mechanism due to contamination or damage	Check and eliminate the jam, clean the device
Burning of the terminals for connecting wires to starters	Weak fixation of the core	Replacing a starter or a removable part, checking contacts for new devices
Overheating or oxidation of wire terminals	Weak fixation of clamps	Dismantle fasteners, clean and reassemble
The starter does not turn on (no voltage on the coil)	Broken chain or something else	Check control circuit
	Weak pressing in clamps or contacts	Adjust contacts, tighten clamps
The starter does not turn on (there is voltage on the coil)	The starter is jammed when moisture freezes in the gaps	Disassemble starter and assemble

How the starter works

The principle of operation of the starter is simple. To use the starter, you must first apply voltage to the coil of the device. When turned on, it will consume an insignificant voltage in the range of 10-80 watts.

After the coil turns on, it acts on the fixed part of the starter, magnetizes it. This contributes to the movement of the armature, which closes the contacts. As a result, the circuit closes, and the voltage goes throughout the circuit.

To turn off the device, it is enough to de-energize the coil. If no current is supplied to it, then the moving part of the mechanism will return back, the contacts will open.

To protect the coil and the entire starter from overloads and various emergency situations, it is customary to install a relay between the device and the motor. However, if it is a thermal relay, then it will not be able to protect the starter from a short circuit.

In fact, the starter is a modified contactor with a wide range of different functions. It allows not only to use a generator or other electric motor, but also to reverse, protect the motor from overloads, maintain control circuits, etc.

As for the coil of the device, it can have a different type of design. It all depends on voltage and current.

In most electric drive control circuits, contactors are used to turn on motors, as well as magnetic and non-contact (thyristor) starters. With their help, remote and automatic switching on and off of the drive motor, starting and adjusting resistances, switching off emergency sections of the network, turning on brake electromagnets and other auxiliary devices is carried out.

Contactors and starters are most often completed by manufacturers together with control and protection equipment in special blocks, panels, boards and control stations according to design schemes and are delivered to the consumer checked and adjusted. Often, magnetic starters are supplied for installation in bulk, then the design scheme is mounted completely on site.

Contactor-relay equipment supplied for installation, in most cases, needs to be pre-checked and mechanically adjusted, since during transportation the fasteners can loosen, and during long-term storage, corrosion can form, causing seizing of moving systems and violating the conductivity of the contact surfaces.

During the initial adjustment of the devices at the installation site, they are checked by external inspection: compliance with the type of device and the parameters of the retracting coil to the project or real loads, the absence of preservative lubricant and transport fasteners, the presence of all parts of the magnetic system and return springs; the state of flexible connections, the presence and condition of spark arresters, the presence of a non-magnetic gasket or a short-circuited coil and their condition, the presence of fixing bolts, nuts, flat and spring washers and the quality of fastening; integrity of support prisms or bearings; the condition of the main and auxiliary contacts and their springs. In addition, manually check: no jamming of the mobile system; simultaneous closing and opening of the main contacts; the presence and size of the failures of the main and auxiliary contacts; correct operation of auxiliary contacts; the density of the magnetic cores. The correct operation of the contacts and the stiffness of the springs are evaluated during testing and adjustment by comparison with other contactors of this type (in case of emergency, according to catalog data). When closing and opening, one contact must slide relative to the other (rolling).

The dimensions of the solutions and dips are indicated in the special tables of the manufacturer. If the measured and factory data do not match, additional adjustment of the contacts is performed.

The insulation of contactors, coils, contactor-relay and other equipment is checked when monitoring the insulation of secondary switching circuits of the entire control circuit and power circuits of the installation. Separately, the devices are turned off only if it is necessary to find a section with low insulation.

Next, the operation of the apparatus is tested by supplying an operating current to its coil. At the same time, the health of the coil, the correct installation of the springs, the free movement of the moving part, the correctness of the gaps are checked for DC contactors, and the behavior of the magnetic system for AC contactors. If the vibration of the magnetic system is significant and the armature is buzzing, check the attachment of the armature when turned on, the presence of distortions. In case of insufficient diligence or distortions, additional mechanical adjustment is performed, and, if necessary, grinding of the poles. Next, they control the operation of the circuit, the clarity of turning on and off the devices at a rated and reduced turn-on voltage of up to 0.9 Unom., Off to 0.8 Unom. on operating current buses. If, at a reduced voltage, the clarity of turning on the devices decreases or they do not work, check and adjust the pull-in and drop-out voltage of contactors or magnetic starters according to the diagrams shown in fig. 2, a, b.

The most common malfunctions of starters and contactors are:

- vibration of the magnetic circuit of starters and contactors of alternating current, caused by the absence of a short-circuited coil, pollution of the planes of electromagnets, or loose surfaces of electromagnets;

- increased heating of the coils of starters or contactors, which is explained by the low economic resistance of DC contactors and the increased gap of the middle rod of contactors and AC starters;

- burning, deep corrosion of the contacts, which is explained by the non-simultaneity of their contact, insufficient initial pressing of the contacts, their vibration when touched.