How to check the three-phase electric motor. How to check the three-phase engine tester. Total Asolation Status Assessment

The electric motor is the main component of any modern household electrical engineering, whether it is a refrigerator, a vacuum cleaner or another unit used in the household. In the event of an exit of any instrument, in the first place, it is necessary to establish the cause of the breakage. To find out if the engine is in serviceability, it must be checked. To carry the device in the workshop for this is optional, it is enough to have an ordinary tester. After reading this article, you will learn how to check the electric motor multimeter, and you can cope with this task yourself.

What electromotors can be checked by a multimeter?

There are different modifications of electrical engines, and the list of their possible faults is quite large. Most problems can be diagnosed using the usual multimeter, even if you are not a specialist in this area.

Modern electric motors are divided into several species that are listed below:

Asynchronous, three phases, with a short-circuited rotor. This type of electrical power units is the most popular thanks to a simple device that provides easy diagnostics.
Asynchronous condenser, with one or two phases and a short-circuited rotor. Such a power plant is usually equipped with household appliances, powered by a regular network by 220V, most common in modern homes.
Asynchronous, equipped with a phase rotor. This equipment has a more powerful starting point than the motors with a short-circuited rotor, and therefore it is used as a drive in large power devices (lifts, cranes, power plants).
Collector, DC. Such engines are widely used in cars, where they play the role of actuators and pumps, as well as windows and janitors.
Collector, alternating current. These motors are equipped with manual power tools.

The first stage of any diagnostics is a visual inspection. Even the burnt windings or broken parts of the engine are visible to the naked look, it is clear that further check is meaningless, and the unit must be taken to the workshop. But often inspection is not enough to identify malfunctions, and then more thorough check is required.

Repair of asynchronous engines

The most common asynchronous power units for two and three phases are most common. The order of their diagnosis is not exactly the same, so it should be stopped in more detail.

Three-phase motor

There are two types of faults of electrical units, and regardless of their complexity: the presence of contact in the wrong place or its absence.

The composition of the three-phase motor operating from alternating current includes three coils that can be connected in the form of a triangle or stars. There are three factors that determine the performance of this power plant:

The correctness of the winding.
The quality of isolation.
Reliability of contacts.

The hull closure is usually checked with a megommeter, but if it is not, you can do the usual tester, putting the maximum resistance value for megaoms on it. It is not necessary to talk about the high accuracy of measurements in this case, but it is possible to obtain approximate data.

Before measuring resistance, make sure that the engine is not connected to the power grid, otherwise the multimeter will be in disrepair. Then you need to make a calibration by putting the arrow to zero (the probes should be closed). Check the serviceability of the tester and the correctness of the settings, briefly touching in one probe of the other, each time before measuring the resistance.

Attach one dipstick to the electromotor housing and make sure that the contact is available. After that, remove the instrument readings, touching the engine with the second probe. If data within the norm, connect the second probe with the output of each phase alternately. A high resistance rate (500-1000 and more MOM) indicates good isolation.

How to check the insulation of the windings is shown in this video:

Then you need to make sure that all three windings are intact. You can check this by calling the ends that go into the box outputs of the electric motor. If any winding is discovered, the diagnostics should be stopped before troubleshooting.

The next checkpoint is the definition of short-circuited turns. Quite often, this can be seen when visual inspection, but if the externally winding looks fine, then you can establish a short circuit fact for unequal consumption of electric cooker.

Two-phase electric engineb

The diagnosis of force aggregates of this type is somewhat different from the above procedure. When checking the motor equipped with two coils and powered by a regular power grid, its windings need to be squeeze with an ohmmeter. The resistance indicator of the working winding must be 50% less than that of the launcher.

Resistance to the case must be measured - in the normal case, it should be very large, as in the previous case. Low resistance indicator indicates the need to rewind the stator. Of course, to obtain accurate data, such measurements are better carried out with a megommeter, but this possibility is rare at home.

Check collector electric motors

Having understood with the diagnosis of asynchronous motors, we turn to the question of how to ring the electric motor multimeter, if the power unit refers to the collector type, and what are the features of such checks.

To correctly check the performance of these engines using a multimeter, you need to act in the following order:

Turn on the tester on OM and in pairwise measure the resistance of collector lamellas. Normally, this data should not be different.
Measure the resistance rate by attaching one probe device to the anchor housing, and the other to the collector. This indicator should be very high, strive for infinity.
Check the stator on the integrity of the winding.
Measure the resistance, applying one probe to the stator body, and the other to the conclusions. The higher the resulting indicator, the better.

Check the motor using a multimeter to the inter-touch closure will not work. To do this, use a special apparatus, with the help of an anchor check.

Details Checking the engine power tools is shown in this video:

Features of checking electric motors with additional elements

Often, electrical power plants are equipped with additional components designed to protect the equipment or optimizing its operation. The most common elements embedded in the engine are:

The usual multimeter is usually enough to diagnose most problems that may occur in electric motors. If the cause of the fault, this device is not possible, the test is performed using high-precision and expensive devices that are available from specialists.

This material contains all the necessary information on how to properly check the motor multimeter in living conditions. When you exit any electrical engineering, the most important thing is to ring the motor winding to eliminate its malfunction, since the power plant has the highest cost compared to other elements.

Single-phase engines are low power machines. In the magnetic circuit breeding of single-phase engines there is a two-phase winding, which consists of the main and starting winding.

The most common engines of this type can be divided into two groups: single-phase engines with launcheling and engines with a working capacitor.

In the first type engines, the launcher turns on through the capacitor only at the time of start-up and after the engine developed the normal speed of rotation, it turns off from the network, after which the engine continues to work with one working winding. The capacitance of the condenser is usually indicated on the engine plate plate and depends on its design.

At single-phase asynchronous engines with a working capacitor, the auxiliary winding is enabled constantly through the capacitor. The magnitude of the working capacity of the capacitor is determined by the design of the engine.

If an auxiliary winding of a single-phase motor starting, its connection will occur only at the start time. If the auxiliary winding is a condenser, its connection will occur through a condenser. And it remains enabled during the engine operation.

In most cases, launcher and working windings of single-phase engines are different and in the cross section of the wire and by the number of turns. A single-phase engine working winding always has a larger cross section, and therefore its resistance will be less.

A winding that has less resistance is a worker.

If the engine has 4 output, then measuring resistance to between them, it is possible to determine the smallest resistance of the working winding, and the larger resistance in the start-up.

Connect everything is quite simple. 220V fed to thick wires. And one tip of the launcher, one of the workers, does not matter what direction does not depend on this. Also, from how you insert the plug into the outlet. Rotation will change, from connecting the startup, namely, changing the ends of the launcher.

In the case when the engine has 3 outputs, measurements will look as follows, for example - 10 ohms, 25 ohms, 15 ohms. By measurements, it is necessary to find a tip, from which testimony, with two others, will be 15 ohms and 10 ohms. It will be one of the network wires. The tip with the 10th Ohmami, this is also a network and third 15 ohms will be started, it connects to the second network via the condenser. In this case, to change the direction of rotation, you need to get to the winding scheme.

The case when measurements for example are shown 10 ohms, 10 ohms, 20 ohms. Also is one of the varieties of windings. For example, in some washing machines and not only. In such cases, the working and starting windings are the same (according to the design of three-phase windings). In this case, it does not matter which winding will perform the role of a working, and which launcher. Connection is also made through the condenser.

The adjustment of asynchronous engines is performed in the following volume:

Visual inspection;

Check mechanical part;

Measurement of insulation resistance of windings relative to the housing and between windings;

Measurement of resistance of windings DC;

Test windings with increased voltage of industrial frequency;

Trial Start.

An external inspection of an asynchronous engine starts from a shield.

The following data should be on the shield:

Name or trademark of the manufacturer,

Type and factory number,

Nominal data (power, voltage, current, speed, winding rate, efficiency coefficient, power factor),

Year of issue,

Mass and GOST to the engine.

At the beginning of work is mandatory. Then check the condition of the outer surface of the engine, its bearing nodes, the output end of the shaft, fan, and the state of the terminal conclusions.

If the three-phase motor does not have composite and partitioned windings on the stator, then the conclusions are denoted according to the table. 1, and in the presence of such windings - the conclusions indicate the same letters as simple windings, but with additional numbers ahead of the capital letters. For ahead, letters put numbers indicating the number of poles of this section.

Table 1

table 2

Note: Clements with Numbering P - are connected to the network, C - free, s - shorten

Marking of multi-speed motors and methods for their inclusion at different speeds can be explained using Table. 2.

With an external inspection of an asynchronous engine, it is necessary to pay special attention to the condition of the conclusions and output ends, in which various insulation disorders are often found, while measuring the distance between the current-time parts and the housing. It should be large enough so that no floors around the surface occurred. No less important is the elevation of the shaft in the axial direction, which according to the standards should not exceed 2 mm (1 mm in one direction) for engines up to 40 kW.

The magnitude of the air gap is of great importance, since it has a significant effect on the characteristics of asynchronous motors, so after repairs or in the event of unsatisfactory operation of the engine, the air clearance is measured in four diametrically opposite points. Clauses should be the same throughout the circumference and should not be different in any of these four points more than 10% of the average.

Asynchronous engines of a number of machine tools, such as threaded and shredded, are particular requirements in terms of beating and vibrations. The test of the shaft and vibration of electrical machines has a great influence of processing accuracy and the state of rotating parts of the machine. Especially great vibration and vibration when the motor shaft is hooked.

The beating is the deviation from the specified (correct) mutual arrangement of the surfaces of rotating or fluctuating parts of the type of rotation bodies. Distinguish radial and ending beats.

For all vehicles of the beyon, it is undesirable, because at the same time the normal operation of bearing nodes and cars in general are disturbed. Using a clockwise indicator that allows you to measure beating from 0.01 mm to 10 mm. When measuring the shaft beating, the indicator tip be rests into the shaft rotating at low speed. Upon deflection of the arrows of the hourly indicator, judge the value of the beyon, which should not exceed the values \u200b\u200bspecified in the technical conditions on the machine or engine.

The insulation of the electrical machine is an important indicator, since the durability and reliability of the machine depends on its condition. According to GOST resistance to the insulation of windings in the IOM Electrical Machines should be no less

where U n-nominee winding voltage, in; P H is the rated power of the machine, kW.

The insulation resistance is measured before the test start of the engine, and then during operation periodically, in addition, control after long interruptions in operation and after each emergency shutdown of the drive.

The insulation resistance of the windings relative to the body and between the windings is measured during cold windings and in the heated state, at a temperature of windings equal to the temperature of the nominal mode, immediately before checking the electrical strength of the winding isolation.

If the engine and end of each phase are displayed in the engine, then the insulation resistance is measured separately for each phase relative to the housing and between the windings. Multi-speed engines insulation resistance is checked for each winding separately.

For measurements of electric motors insulation resistance voltage up to 1000 V is used by 500 and 1000 V.

Measurement is carried out as follows, the "Screen" megommeter clamp is attached to the machine body, and the second clamp flexible wire with reliable insulation is attached to the winding output. The ends of the conductors must be embedded in the handle from the insulating material with a metal pin, pointed at the end to ensure reliable contact.

The megommeter knob is rotated with a frequency of approximately 2 rev / s. Small power engines have a small capacity, so the device arrow is set to a position corresponding to the insulation resistance of the machine winding.

For new machines, the insulation resistance, as practice has shown, fluctuates at a temperature of 20 ° С in the range from 5 to 100 mΩ. The uninterrupted small power and voltage engines to 1000 V do not make specific requirements for the value of R. From the practice there are cases when the engines having resistance less than 0.5 MΩ were introduced into operation, their insulation resistance was improved and in the future they worked correctly.

The decrease in the insulation resistance during operation is caused by surface humidity, contamination of the surface of the insulation of conductive dust, penetration into the thickness of moisture insulation, chemical decomposition of isolation. To clarify the reasons for reducing the insulation resistance, it is necessary to measure with a double bridge, for example, P-316, at two current directions in the controlled chain. Under different measurements, the most likely cause is the penetration of moisture into the thickness of the insulation.

Specifically the question of the inclusion of an asynchronous engine to work It should be solved only after testing the windings with increased voltage. The inclusion of an engine having a small insulation resistance value is allowed without testing with increased voltage only in exceptional cases when the question is solved that it is more profitable: to undergo danger of the engine or to allow simple expensive equipment.

During the operation of the engine are possible insulation damage, leading to a decrease in its electrical strength below acceptable norms. According to the GOST test of the electrical strength of the insulation of the windings in relation to the body and among themselves, it is produced by the engine disconnected from the network for 1 minute the test voltage, the value of which should be at least the magnitude given in Table. 3.

Table 3.

Increased voltage is fed by one of the phases, and the remaining phases are attached to the engine housing. If the windings are connected inside the engine in a star or a triangle, then the insulation test between the winding and the housing is carried out simultaneously for the entire winding. When performing tests, the voltage cannot be applied instantly. The test starts with 1/3 of the test voltage, then gradually raise the voltage to the test, and the raising time from half to the complete test voltage should be at least 10 s.

Complete voltage is kept for 1 min, after which it is smoothly reduced to 1 / 3Uis and disconnect the test installation. The test results are considered satisfactory if there was no breakdown of insulation or overlaps on the insulation surface during the test, while the instruments did not observe sharp shocks, indicating partial insulation damage.

If the test occurred when testing, they find it and repair the winding. The breakdown site can be found by repeated voltage application with the subsequent observation of the appearance of sparks, smoke, or easy crackling when sincere, invisible outside.

Measurement of DC winding resistance, which is carried out to clarify the technical data of the schema elements, makes it possible in some cases to determine the presence of short-circuited turns. The temperature of the windings during the measurement should not differ from the surrounding more than 5 ° C.

Measurements are performed using a single or double bridge, according to the method of an ammeter-voltmeter or a micrommeter method. Resistance values \u200b\u200bshould not differ from the average by more than 20%.

According to GOST when measuring the windings resistance, each resistance must be measured 3 times. When measuring the resistance of the winding according to the method of ammeter-voltmeter Each resistance must be measured at three different current values. For the actual amount of resistance, the arithmetic average of three dimensions takes.

The voltmeter ammeter method (Fig. 1) is used in cases where there is no significant measurement accuracy. Measurement by an ammeter-voltmeter is based on the Ohm Lab:

where R X-measured resistance, Ohms; U is a voltmeter reading, in; I - an ammeter reading, A.

The accuracy of measurement at the same time is determined by the total error of the instruments. So, if an ammeter accuracy class is 0.5%, and a voltmeter is 1%, then the total error will be 1.5%.

In order for an ammeter-voltmeter method to give more accurate results, you must comply with the following conditions:

1. The accuracy of measurement largely depends on the reliability of contacts, so the contacts are recommended before measuring;

2. The DC source must be a network or a well-charged battery with a voltage of 4-6 V in order to avoid the effect of the voltage drop at the source;

3. The edge count must be made simultaneously.

Measuring resistance with bridges is mainly used in cases where it is necessary to obtain greater measurement accuracy. Accuracy reaches 0.001%. The limits of the bridge measurements range from 10-5 to 106 ohms.

The microgrammeter is measured with a large number of measurements, such as transitional resistances of contacts, interrupical connections.

Fig. 1. Scheme of measuring the resistance of the windings of DCOs according to the method of ammeter-voltmeter

Fig. 2. Scheme measurement of the resistance of the winding of an asynchronous engine stator connected to a star (A) and in a triangle (b)

Measurements are carried out quickly, as there is no need for adjusting the device. Resistance to the DC winding for engines up to 10 kW is measured no earlier than 5 hours at the end of its operation, and for engines more than 10 kW - at least 8 hours with a fixed rotor. If the engine's stator has all the six ends of the windings, the measurement is carried out on the winding of each phase separately.

With the internal connection of the windings in the star, the resistance of two successively connected phases is measured in pairwise (Fig. 2, a). In this case, the resistance of each phase

With an internal connection to the triangle, the resistance between each pair of the output ends of linear clamps is measured (Fig. 2, b). Considering that the resistance of all phases is equal, the resistance of each phase is determined:

For multi-speed engines, similar measurements are carried out for each winding or for each section.

Checking the correctness of the AC machine windings. Sometimes, especially after repairs, the aqueous ends of an asynchronous motor turn out to be uncrharked, the need to determine the starts and the ends of the windings arise. The most common two ways to determine.

According to the first method, first determine the ends of the windings of individual phases. Then collect the scheme according to rice. 3, a. The "plus" of the source attach to the beginning of one of the phases, "minus" - by the end.

C1, C2, C3 for the beginning of phases 1, 2, 3, and C4, C5, C6 - 3, 5, 6. At the time of turning on the current in the windings of other phases (2-3), the electromotive force with the polarity is induced. Minus "on the basis of C2 and C3 and Plus at the ends of C5 and C6. At the time of turning off the current in phase 1, the polarity at the ends of the phases 2 and 3 is opposite to the polarity when they are turned on.

After labeling phase 1, the DC source is attached to phase 3 if the arrow of the Millivoltmeter or the galvanometer deviates to the same side, then all the ends of the windings are installed correctly.

To determine the starts and ends according to the second method, the engine windings in a star or triangle (Fig. 3, b) are connected, and a single-phase reduced voltage is supplied to the phase 2. In this case, between the ends C1 and C2, as well as the C2 H C3, there is a voltage, somewhat more subordinate, and between the ends C1 and C3, the voltage is zero. If the ends of the phases 1 and 3 are incorrectly included, the voltage between the ends C1 and C2, C2 and C3 will be less than the subordinate. After mutual determination of the marking of the first two phases, the third phases are similar.

Initial inclusion of an asynchronous engine. To clarify the complete operation of the engine, it is experiencing it in idle mode and under load. Previously check the state of the mechanical parts, filling with lubricant bearings.

The ease of the engine is checked by turning the shaft manually, and the cod, a grincping and such sounds should be heard, indicating the contact of the rotor and the stator, as well as the fan and the casing, then check the correct direction of the rotation, for this, the engine is turned on short time.

The duration of the first inclusion is 1-2 s. At the same time, the magnitude of the start current is observed. A short-term start of the engine is advisable to repeat 2-3 times, gradually increasing the power duration, after which the engine can be turned on for a longer period. During the operation of the engine at idle, the adjuster must be verified in good condition of the running parts: the absence of vibrations, current impetus, the absence of bearing heating.

With satisfactory results of test starts, the engine is included in conjunction with the mechanical part or subjected to a special stand test. The engine check time ranges from 5 to 8 hours, while monitoring the temperature of the main nodes and windings of the machine, the power factor, the state of lubrication of the nodes.

Types of electric motors

The most common electric motors are;

Asynchronous three-phase motor with a short-circuited rotor

Asynchronous three-phase motor with a short-circuited rotor. Three engine windings are laid in the stator grooves;
- Asynchronous single-phase motor with a short-circuited rotor. Basically, its use finds in household electrical engineering in vacuum cleaners, washing machines, hoods, fans, air conditioners;
- DC collector engines are installed in the electrical equipment of the car (fans, windows, pumps);
- Collective AC motor finds use in electrical instruments. Such instruments include electric drills, grinders, perforators, meat grinders;
- an asynchronous motor with a phase rotor has a rather powerful starting point. Therefore, such engines are installed in the drives of lifts, cranes, elevators.

Measurement of insulation resistance windings

To check the engine to insulation resistance, electricians use a test voltage with a test voltage of 500 V or 1000 V. This device measures the insulation resistance of the windings of engines calculated for the operating voltage 220 V or 380 V.

For electric motors with a nominal voltage of 12V, 24V use the tester, since the insulation of these windings is not designed to test under high voltage 500 in the megommeter. Usually, the test voltage is specified in the passport to the electric motor when measuring the insulation resistances of coils.

Insulation resistance is usually checked by a megommeter

Before measuring insulation resistance, you need to get acquainted with the circuit of connecting the motor, since some of the stars of the windings are connected by the midpoint to the engine case. If the windings have one or more connection points, a "triangle", "star", single-phase motor with a launcher and working winding, then the insulation is checked between any point of connection of the windings and the case.

If the insulation resistance is significantly less than 20 minutes, the windings are disconnected and check each separately. For an integer engine, the insulation resistance between the coils and the metal case should be not lower than 20 minutes. If the electric motor worked or stored in raw materials, then the insulation resistance may be below 20 mΩ.

Then the electric motor is disassembled and dried several hours by a 100 W, placed in the stator body. When measuring the insulation resistance by a multimeter, the measurement limit is set to the maximum resistance, on the megoma.

How to ring the electric motor to break the windings and interstetic closure

Mixed closure in windings can be checked by a multimeter on Omah. If there are three windings, then it is enough to compare their resistance. The difference in the resistance of the same winding indicates the intersless closure. An intersless closure of single-phase engines is more difficult to determine, as there are only different windings - it is a starting and working winding that has a smaller resistance.

Compare them is not possible. To identify the interstitious closure of three-phase windings and single-phase engines can be measuring ticks, comparing currents of windings with their passport data. With interstitious closure in the windings, their rated current increases, and the value of the starting moment decreases, the engine is hardly started or not started, but only buzzing.

Checking the electric motor for breakdown and intersensional closure of windings

Measure the resistance of the windings of powerful electric motors by a multimeter will not work, because the cross-section of the wires is large and the resistance of the windings is within the tenths of the fraction of Ohm. Determine the resistance difference, with such values \u200b\u200bof the multimeter, is not possible. In this case, the operation of the electric motor is better to check with current ticks.

If there is no possibility to connect the electric motor to the network, the resistance of the windings can be found in an indirect method. Collect the serial chain from the battery to 12V voltage with a 20 ohm retail. With the help of a multimeter (ammeter), the current of 0.5 - 1 A. The collected fixture is connected to the inspected winding and the voltage drop is measured.

Overlooking the electric motor for an insulation resistance

A smaller drop in the voltage on the coil will indicate an inter-touch closure. If you want to know the winding resistance, it is calculated by the formula R \u003d u / i. The malfunction of the electric motor can also be identified visually on the disassembled stator or the smell of burner isolation. If visually detected the place of the cliff, it can be eliminated, soldering jumper, isolate well and put.

The resistance of the windings of three-phase engines is carried out without removing the jumpers in the schemes of the "Star" windings and triangle. The resistance of the coils of collector electric motor valves of constant and alternating voltage is also checked by a multimeter. And with a large power of their power, the check is carried out using the battery tool - the retake, as described above.

Resistance to the windings of these engines is checked separately on the stator and rotor. On the rotor it is better to check the resistance directly on the brushes, scrolling the rotor. In this case, you can define a loose fit of the brushes to the rotor slats. Eliminate the nap and irregularities on the collector lamella, their grinding on the lathe.

It is difficult for manually this operation, you can not eliminate this malfunction, and sparking brushes will only increase. The grooves between the slats will also be cleaned. In the windings of electric motors, a fuse can be installed, a thermal relay. In the presence of a heat relay, it checks its contacts and, if necessary, clean them.

To find out the cause of the electric motor malfunction, it will just just examine it, you need to check it carefully. You can quickly do it with an ohmmeter, but there are other ways to check. About how to check the electric motor, we will tell below.

First, the test begins with a thorough inspection. If there are certain defects of the device, it may fail much before the deadline. Defects may appear due to improper operation of the engine or its overload. These include the following:

broken stands or mounting holes;
paint in the middle of the engine darkened due to overheating;
the presence of dirt and other extraneous particles inside the electric motor.

Also, inspection includes checking marking on the electric motor. It is applied to the metal nameplatewhich is attached outside the engine. The marking plate contains important information on the technical characteristics of this instrument. As a rule, these are parameters such as:

information about engine manufacturers;
model name;
serial number;
the number of rotor revolutions per minute;
the power of the device;
motor connection diagram to one or another voltages;
diagram of obtaining one or another speed and direction of movement;
voltage - requirements in terms of voltage and phase;
sizes and type of housing;
description of the type of stator.

The stator on the electric motor can be:

closed;
blown through the fan;
splash protection and other types.

After examining the device, you can start it to check and do it you need from the engine bearings. Very often malfunctions of the electric motor occur due to their breakdown. They are needed for the rotor smoothly and fluently moving in the stator. Bearings are located at both ends of the rotor in special niches.

For electric motors, such types of bearings are most often used as:

brass;
ball bearings.

Some need to equip with lubricant fittings, and some are already lubricated in the production process.

Check bearings are needed as follows:

place the engine on the hard surface and place one hand on its top;
specify the rotor with the second hand;
try to hear scratching sounds, friction and non-uniformity of movement - all this signals the device malfunction. A good rotor moves calmly and evenly;
we check the longitudinal backlash of the rotor, for this it is necessary to stop the axis from the stator. The backlash is allowed to maximize up to 3 mm, but not more.

If there are problems with bearings, the electric motor works noisily, they themselves overheat, which can lead to the exit of the device.

The next stage of check is checking the winding of the electric motor for short circuit on his body. Most often, the household engine will not work with a closed winding, because the fuse will burn or the protection system will work. The latter is characteristic of ungrounded devices designed for a voltage of 380 volts.

Ommeter is used to check the resistance. To check with its help the winding of the electric motor in this way:

we install an ohmmeter into resistance measurement mode;
properties connect to the necessary sockets (as a rule, to the general jack of "OM");
select the scale with the highest multiplier (for example, R * 1000, etc.);
install the arrow on zero, while the probes should touch each other;
we find a screw for grounding the electric motor (most often it has a hex head and painted in green). Instead of a screw, any metal part of the housing can be approached, on which you can scrape the paint for better contact with the metal;
to this place we press the diploma of the ohmmeter, and the second probe is pressed in turns to each electric contact of the engine;
ideally the arrow of the measuring device must deviate slightly From the highest resistance indicator.

In the course of work, see that your hands do not touch the probe, otherwise the indicators will be incorrect. The resistance value should be shown in millions of OM or MOM. If you have a digital ohmmeter, in some of them there is no possibility of installing the device to zero, for such ohmmeters, the zero stap should be skipped.

Also when checking the windings, see that they are not short-lived or torn off. Some simple single-phase or three-phase electric motors are checked by switching the mesmer's range to the lowest, then the arrow becomes zero and the resistance is measured between the wires.

To make sure that each of the windings is measured, you need to refer to the engine scheme.

If an ohmmeter shows a highly low resistance value, it means that it is either such, or you touched the device to the appliance. And if the value is too high, then this indicates the availability of problems with the windings of the electric motor, for example, about the break. With a high resistance of the windings, the engine will not work all, or their system regulator will come out. The latter most often concerns three-phase engines.

Checking other details and other potential problems

Be sure to check the starting capacitor, which is needed to start some models of electric motors. Basically, these capacitors are equipped with a protective metal cover inside the engine. And to check the condenser you need to remove it. Such an inspection can detect such signs of troubleshooting as:

oil leakage from the condenser;
the presence of holes in the case;
expanded condenser case;
unpleasant odors.

The condenser is also checked with an ohmmeter. The props of the condenser should be touched, and the resistance level must first be small, and then gradually increase As you charge the capacitor with a voltage from the batteries. If the resistance is not growing or the condenser is short-circuited, then, most likely, it is time to change it.

Before re-checking the condenser needs to be discharged.

Go to the next engine checking step: the back of the crankcase, where bearings are installed. In this place a number of electric motors equipped with centrifugal switcheswhich switches the starting capacitors or chains to determine the number of revolutions per minute. You also need to check the contacts of the relay for carrying things. In addition, they should be cleaned with fat and dirt. The mechanism of the switch is checked by means of a screwdriver, the spring must normally work normally.

In this article, I want to talk about how to detect a malfunction in the power supply chain of a three-phase engine and how to check the engine itself.

Let's start in order.

1. The first thing you need to do is check the availability of voltage on the circuit breaker (AB) or magnetic starter, i.e. Does the voltage from the electrical panel? You can check the voltage using the voltmeter or where there is a voltmeter. I do not advise you to use the voltage indicator, because You define the presence of input voltage, and no zero.

2. Check the automatic switch and magnetic starter itself For goodness. Measure the voltage at the input contacts of both devices, and then on the output (the machine must be enabled and the "Start" button must be pressed), which goes to the electric motor. If it is faulty (no voltage), then replace it with a similar voltage (220 or 380V) and for current strength (A). If there is no voltage on the output contacts of the magnetic starter, then the contact plates are most likely burned out. If there is an opportunity, then replace them if not, then replace the entire starter to the same.

Fault: Magnetic Starter does not work

Check the presence of the voltage on the contacts of the starter coil. It should be remembered that the coils are 220V and 380V.
If there is no voltage, then replace the coil or starter. If the voltage is supplied, then you need to "ring" the coil on the integrity of the winding. This can be done with the help of electrical test (buzzer) or electrical equipment.
Check the serviceability and integrity of the "Start" and "Stop" buttons.

Buttons Connection Scheme:

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3. Check the integrity of the electric pipeline (cable) going to the electric motor.

You can check the integrity of the wire using the electrothelter bunder or. You can also check with a control lamp or a voltmeter. Turn off the machine (AB), disconnect the wires from the electric motor. Then turn on the machine and check the presence of voltage on the wires. Caution, work under voltage!

If there is a chance that there has happened a short circuit in the cable (spike and wire break), then you need to check the wires on the closure. Turn off the machine, disconnect the wires from the electric motor. With the help of electrical test (buzzer) or electrical finish, we check the wire turns to the closure.

4. Check the integrity of the windings of the electric motor itself.

Turn off the power supply (automatic).
It is better to disconnect the feeding wires from the electric motor.
With the help of electrical test (buzzer) or electrical equipment, we check the integrity of the stator winding.
With the help of the same devices, we determine the presence of either the absence of a "breakdown" on the electric motor housing. One probe device - on the housing, the other - on the contact of the output of the winding of the electric motor. If the buzzer was dismissed, and the arrow was rejected on Brechunka, then there was a "test" on the electric motor body - the "Khan" engine.

Check the integrity of the stator windings of the electric motor can also be using a bevel light. But this is only when there are no other devices. Disconnect the machine, disconnect the two powered phase wires, we leave one. Turn on the machine, check the presence of voltage on all output contacts of the windings. If all the windings of the electric motor are whole, then the test light will glow.

Caution, work under voltage!

With the help of a multimeter and several devices, not particularly dealing in the principle of operation of electric motors, you can check:

Test insulation windings

Regardless of the design, the electric motor must be verified using a megommeter on the insulation test between windings and a housing. Checks using one multimeter alone may not be enough to identify insulation damage, so high voltage is used.

Megommeter for measuring insulation resistance

In the passport of the electric motor, the voltage must be indicated for testing the insulation of windings for electrical strength. For engines connected to the network 220 or 380 V, 500 or 1000 volts are used when they are checked, but for non-source, you can use the network voltage.

Asynchronous motor passport

Insulation of winding wires of low-voltage engines is not designed to withstand such overvoltages, so when checking should be checked with passport data. Sometimes some electric motors output windings connected by the star can be connected to the housing, so you should carefully study the connection of the taps, making the check.

Check windings for opening and intervatite closure

To ring the windings on the opening, you need to switch the multimeter to the module mode. You can identify the intervatite closure by comparing the winding resistance with passport data or with measurements of symmetric windings of the engine of the engine.

It must be remembered that in powerful electric motors, the cross-section of the windings of the windings is quite large, so their resistance will be close to zero, and such accuracy of measurements in the tenths of Ohm, ordinary testers do not provide.

Therefore, it is necessary to assemble the measuring device from the battery and the rheostat, (approximately 20 ohms) exhibiting the current 0.5-1a. Measure the voltage drop on the resistor connected sequentially into the battery circuit and the measured winding.

For reconciliation with passport data, you can calculate resistance by the formula, but, it is possible not to do this - if the identity of the windings is required, then there will be a coincidence of the voltage drop in all measured outputs.

Measurements can be made any multimeter

Mastech MY61 58954 Digital Multimeter

Below are algorithms for checking electric motors, in which the necessary working condition is the symmetry of the windings.

Check asynchronous three-phase engines with a short-circuited rotor

In such engines, only stator windings can be ringing, the electromagnetic field of which in the closed spice rotor rods, the currents that create a magnetic field interacting with the stator field, can be called.

Malfunctions in rotors of these electric motors are extremely rare, and special equipment is necessary to identify them.

Engine rotor

To check the three-phase motor, you need to remove the terminal cover - there are terminals for connecting windings that can be connected by the type "Star"

or "triangle".

The call can be done, without even removing the jumpers -

it is enough to measure the resistance between phase terminals - all three of the testimony of the ohmmeter should coincide.

If the readings are lost, it will be necessary to disconnect the windings and check them separately. If the estimated resistance in one of the windings is less than that of the rest, this indicates the presence of an intervatite closure, and the electric motor must be rewound.

Checking condenser engines

To check the single-phase asynchronous motor with a short-circuited rotor, by analogy with a three-phase motor, only stator windings must be called.

But single-phase (two-phase) electric motors have only two windings - working and starting.

The resistance of the working winding is always less than that of the launcher

Thus, measuring resistance, you can identify the conclusions if the plate with the scheme and the notation shook or lost.

Often, such engines operating and starting windings are connected inside the housing, and a total output is made on the connection point.

The belongings of the conclusions are identified as follows - the sum of the resistance measured from the overall discharge must correspond to the total resistance of the windings.

Checking collector engines

Since the collector electric motors of the AC and DC are similar to the design, the transverse algorithm will be the same.

First, check the stator winding (in DC motors it can be replaced with a magnet). Then they check rotary windings, the resistance of which should be equally, touched upon by the leaps of the collector's brushes, or opposite contact conclusions.

It is more convenient to check the rotor windings on the brush outputs, scrolling the shaft, seeking the brushes to contact only one pair of contacts - in this way you can reveal a burning in some contact sites.

To check the rotor windings, you need to find conclusions from the data of the rings, and make sure the coincidence of the measured resistance. Often such engines are equipped with a mechanical system for disconnecting the rotor windings when the revolutions set, so the lack of contact may be due to breakage in this mechanism.

Stator windings are checked as an ordinary three-phase engine.

Measuring the insulation resistance of windings relative to the machine body and between the windings is made in order to verify the state of insulation and the suitability of the machine to conduct subsequent tests. It is recommended to measure:

in a practically cold state of the test machine - before its testing on the relevant program;

regardless of the temperature of the windings - before and after testing the insulation of windings on electrical strength relative to the machine body and between the windings of alternating voltage.

Measuring the insulation resistance of the windings should be carried out: at rated winding voltage up to 500 in inclusive - a megoometer by 500 V; With a rated voltage of winding over 500 V - a megaommeter at least 1000 V. When measuring the insulation resistance of windings with a nominal voltage over 6000 V, having a significant container with respect to the body, it is recommended to use a 2-2500V megaommeter with a motor drive or a static straightening scheme AC voltage.

Measurement of insulation resistance relative to the machine housing and between windings should be made alternately for each chain having separate conclusions, with electrical connection of all other chains with the machine housing.

Measurement of the insulation resistance of three-phase current windings, tightly conjugate in a star or triangle, is made for the entire winding with respect to the case.

Isolated windings and protective capacitors, as well as other devices, permanently connected to the machine housing, during the measurement of resistance of their insulation must be disconnected from the machine housing.

Measuring the insulation resistance of windings with direct water cooling should be made by a megaommeter having internal shielding; At the same time, the megohmmeter clamp connected to the screen should be attached to the catchment collectors, which should not have a metallic connection with the external power supply system by distillate.

Upon completion of the measurement of the insulation resistance of each chain, it should be discharged by its electrical connection with a grounded body housing. For windings on the nominal voltage of 3000 V and above, the duration of the connection with the case must be:

for machines with a capacity of up to 1000 kW (sq · a) - at least 15 s;

for machines with a capacity of more than 1000 kW (sq · a) - at least 1 min.

When using a 2,500 megaommeter in the duration of the connection with the housing should be at least 3 minutes, regardless of the power of the machine.

Measuring the insulation resistance of the laid resistance thermal converters should be carried out by a megaommeter of 500 V.

Measuring the insulation resistance of insulated bearings and oil seals The shaft relative to the body should be carried out at an ambient temperature with a voltage of at least 1000 V.

Table 2.

Table 3.

Table 4.

Isolation resistance R from is the main indicator of the state of insulation of the stator and the rotor of the electric motor.

Simultaneously with the measurement of the insulation resistance of the stator winding, the absorption coefficient is determined. Measurement of the rotor insulation resistance is carried out in synchronous electric motors and electric motors with a phase rotor to the voltage of 3Q and above or more than 1 MW. The resistance of the isolation of the rotor must be no lower 0.2m.

The absorption coefficient is mandatory to determine only for electric motors with a voltage above 3kV or a power of Bol e.1MW.

Prepare measurement tools:

Check the battery or battery level for the MIC-2500 megommeter.

Set the value of the test voltage.

In the case of using the ESCU202 arrow instrument, set it horizontally.

For ES0202, set the required measurement limit, the instrument scale and the value of the test voltage of the megommeter.

Check the performance of the megommeter. To do this, it is necessary to close the measuring probe and start rotating the generator handle at a speed of 120¸140 revolutions per minute. The appliance arrow must show "0". To break the measuring probes and start rotating the generator handle at a speed of 120 °40 revolutions per minute. The appliance arrow should show "10 4 MΩ."

Before measuring, you must open the introductory device of the electric motor (Born), wipe the insulators from dust and pollution and connect the megaometer according to the schema shown in the figure.

Picture. Measurement of the insulation resistance of the electric motor windings.

Figure A shows the megaommeter connection diagram to the test motor, which has windings are connected to a star or a triangle inside the housing and it is impossible to disconnect in Born. In this case, the megaommeter connects to any clamp of the stator of the electric motor and the insulation resistance is measured in the entire winding immediately relative to the case.

In the figure, the measurement of the insulation resistance is made at the electric motor for each of the parts of the winding separately, while the other parts of the winding (which are not currently processed) are shred and connected to the ground.

When measuring the insulation resistance, the megoometer readings are made every
15 seconds and the result is considered to be resistant after 60 seconds after the start of measurement, and the ratio of the readings R 60 / R 15 is considered an absorption coefficient.

For electric motors with a rated voltage of 0.4kV (electric motors up to 1000V), a single measurement of insulation by a megaommeter by 2500V is equal to the high-voltage test.

At synchronous electric motors, when measuring the insulation resistance of the stator windings (stator winding), it is necessary to navigate and ground the rotor winding. This must be done to eliminate the possibility of damage to the isolation of the rotor.

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