Ratings of working and starting windings. How to check an electric motor with a multimeter: step-by-step instructions and recommendations

How to test an electric motor with a multimeter: step-by-step summary and tips

The question often arises of how to check an electric motor after failure, also after repair, if it does not turn. There are several methods for this: external inspection, a special shield, “testing” the windings with a multimeter. The latter method is more economical and versatile, but it does not always give correct results. For most constants, the winding resistance is virtually zero. Therefore, you will need an additional circuit for measurements.

Motor design

To quickly learn how check the electric motor, you need to clearly understand the structure of the main parts. HOW TO CHECK How to ring a three-phase motor with a tester. All motors are based on two parts of the structure: the rotor and the stator. The 1st component always rotates under the influence of the electric field, the 2nd component is motionless and just creates this vortex flow.

To realize how check the electric motor, you will need to disassemble it with your own hands at least once. Different manufacturers have different designs, but the diagnostic principle electrical part remains constant for now. There is a gap between the rotor and stator, in which small iron shavings can accumulate when the housing is depressurized.

When bearings wear out, they can produce excessive current characteristics, as a result of which the protection will be knocked out. How to test a motor with a multimeter. When dealing with the question of how to check an electric motor, one should not forget about mechanical damage to the moving parts and the parts where the contacts are located.

Difficulties in diagnosis

Before check electric motor with a multimeter, you should carry out an external inspection of the housing, cooling impeller, check the temperature by touching your hand iron surfaces. A heated case indicates an increased current due to problems with the mechanical part.

Switching equipment

To start the rotation of the windings, a board or relay is used. To begin to understand the question of how to check the winding of an electric motor, you need to disconnect the supply circuit. The elements of the control board can “ring” through it, which will introduce an error in the measurements. With the wires folded back, you can measure the incoming voltage to be sure of serviceability electrical diagram.

In home appliance engines, a design with a starting winding is often used, the resistance of which exceeds the value of the operating inductance. When taking measurements, take into account the fact that there may be current-collecting brushes. Carbon deposits often appear at the point of contact with the rotor; after cleaning it, it is necessary to restore the reliability of the brushes during rotation.

Washing machines use compact motors with one working winding. The whole essence of diagnostics comes down to measuring its resistance. The current is measured less frequently, but by reading the lines at various speeds, conclusions can be drawn about the serviceability of the motor.

Diagnostic details electrical part

How to ring an electric motor

Three-phase asynchronous electric motor, examination tester. In practice it is enough check electric motor

Location of three-phase motor contacts and winding continuity

We consider the location of the ends of the windings three phase motor, determine whether they are connected correctly.

Let's look at how to check the serviceability of an electric motor. Three-phase asynchronous motor Electric meter three-phase How to check. Three-phase that the motor is not connected to How to check the insulation of the windings is shown. First of all, inspect the contact connections. If there are no visible damages, then open the junction of the wires with the engine and disconnect them. It is advisable to determine the type of motor. If it is a collector type, then there are lamellas or sections where the brushes attach.

Diagnostics of asynchronous motors

Industrial washing machines can use powerful three-phase electric motors. Their rotor is often made in the form of stacked plates with a magnetic core. Phase windings are often stationary and located in the stator.
It is much easier to check such a motor with a multimeter. Use an ohmmeter to measure the resistance of each winding. It should be the same. Do not forget to check the breakdown on the case by measuring the resistance on the case. However, it is more reliable to check the insulation with a megohmmeter.

Answering the question of how to check the windings of an electric motor tester, it should be noted that “phase imbalance” in an asynchronous motor is not allowed. The resistance difference should not exceed one ohm. Otherwise, the current at the smaller inductance increases, which leads to burning of the winding.

If the DC motor

These motors have very low winding resistance and measurements are carried out using two instruments. At the same time, take readings from the ammeter and voltmeter. A 4-6 V battery is selected as the source. How to check the lambda probe with a tester or. The resulting value is determined by the formula R = U/I.

Check all available resistance of the armature windings, measure the values between the collector plates. All multimeter readings must be equal. From this comparison, we can draw conclusions on how to check the armature of an electric motor.

The difference in resistance readings between adjacent collector plates is allowed no more than 10%. How to check a lambda probe with a 4-wire tester. When the design provides an equalizing winding, the operation of the motor will be normal with a difference in values of 30%. Multimeter readings do not always give an accurate forecast of the engine condition washing machine. Additionally, an analysis of the operation of the motor on a calibration stand is often required.

Checking the Direct Drive Motor

If we consider the question of how to check the electric motor of a washing machine, then we should take into account the type of connection of the drum to the shaft. The type of design of the electrical part depends on this. A multimeter is used to test the windings and draw conclusions about their integrity.

The performance check is carried out after replacing the Hall sensor. This is what fails in most cases. After checking the windings if they are intact experienced craftsmen It is recommended to connect the motor directly to a 220 V network. As a result, uniform rotation is observed; to change its direction, you can re-plug the plug into the socket, turning it with other contacts.

This simple method helps identify a common problem. However, the presence of rotation does not guarantee normal operation in all modes that differ during spinning and rinsing.

Diagnostic sequence

First of all, it is recommended to immediately pay attention to the condition of the brushes and wiring. Carbon deposits on live parts indicate abnormal operating conditions of the engine. The current collectors themselves must be smooth, without chips or cracks. Scratches also lead to sparking, which is detrimental to the motor windings.

U washing machines The rotor often warps, causing the lamellas to chip or break. The control board constantly monitors the rotor position through a Hall sensor or tachogenerator, adding or decreasing the voltage applied to the working winding. This results in strong noise during rotation, sparking, and disruption of operating modes during spinning.

This phenomenon can only be noticed during the spin cycle, and the washing cycle is stable. How to check a lambda probe with a multimeter tester. Diagnosis of machine operation does not always go through condition analysis electrical part. Mechanics may be the cause of malfunction. No load engine It can spin quite evenly and pick up speed steadily.

If he still knocks out the defense?

After the measurements have been taken, in the event of floating faults, it is not recommended to connect to the network for testing. Place the motor on a hard surface and put How to check the winding. You can permanently damage the motor without knowing there is a problem. A technician will tell you how to check the winding of an electric motor with a multimeter. service center by phone. Under his guidance, it will be easier to determine the type of design and procedure for diagnosing a faulty washing machine.

Today we will discuss how to test an electric motor with a multimeter. An indicator screwdriver is suitable for those who know how to use it. One caveat: with the help of a tester, we will evaluate the parameters and distinguish the starting winding from the working winding by the resistance value (in the first case, the value will be twice as high). The indicator screwdriver is miniature, convenient, you will acquire the ability to use it, and if necessary, pay 30 rubles to find a new one.

Electric motor device

There are plenty of varieties of engines. Composed of a moving part - the rotor - a stationary part - the stator. First of all, let's see where the copper wire is wound. There are three possible answers:

The coils are only on the rotor.
The coils are only on the stator.
There is winding on the moving and fixed parts.

For the rest call asynchronous electric motor will be no more difficult than a collector one. And vice versa. The difference is limited to the principle of operation, without affecting the methodology for assessing the performance of the structure. To correctly ring the electric motor, stop disassembling the features.

Electric motor rotor

In this and the next subtitle we will teach you how to ring a three-phase electric motor. If there are coils (regardless of the number) on the rotor, look at the design of the current collector. There are at least two possible answers.

Graphite brushes

We see the rotor drum, equipped with pronounced sections. The current collectors are graphite brushes. The engine is commutator. You need to ring all sections. The outputs of the coils are opposite sections of the circle.

We take the tester and begin to evaluate the resistance one by one: in each case the answer (in ohms) is the same, plus minus the error. When fixing a break, cleaning the drum does not help. The fact of infinite resistance or short circuit indicates: the coil has burned out. In some engines, the coil resistance is close to zero.

They told me what to do in this case. Take a normal Krona 12 volt, connect the rotor coil in series with a low resistance (20 Ohm). Using a tester, measure the voltage drop across the coil, additional resistor, using the proportion, calculate the value (R1/R2 = U1/U2). Please note: the resistor is high-precision (E48 series or higher) so that the calculations have a small error. It is possible to measure relatively small resistances.

Please note: the current reaches 0.5 A at 7 W. Instead of a battery, it is better to take a computer power supply or battery.

Continuous rings

The current collector is made in the form of one or several continuous rings. Indicates eloquently: a synchronous motor (number of phases according to the number of sections), or an asynchronous motor with a wound rotor. Actually, we don’t care about this, because we were planning to ring the electric motor with a tester and were too lazy to determine the purpose of the device. We look at the number of rings: the number falls within the range of 1 – 3. The latter means: the motor is three-phase. We start calling.

The windings are connected in a star, resulting in equal resistance between each two contacts. If you have equipment on hand to create a voltage of 500 V, you should test the electric motor with a megger on the housing. The standard insulation value is 20 MΩ. Please note: windings may not withstand the test. With a 12 volt motor, such actions should not be taken. As a result, with a fully functional rotor, equal resistance between the contacts will be obtained. If a short circuit to the frame is detected, check whether the technical solution is to create a system with a solidly grounded neutral.

It's time to mention that for such a system the power supply method is typical for voltages below 1 kV. However, with resonance compensation (if it is possible to find a motor in nature), something similar can be used. Using the marked nameplate you can quickly resolve the issue (neutral output to the housing).

The commutator brushes are often located perpendicular to the surface of the drum, while they are pressed against the current collectors at a certain angle. The question arises: where is the neutral? Doesn't go to the body - don't use it in the circuit. Often found at voltages above 3 kV. Here the neutral is isolated, the currents flow through the phase, where in in this case a zero (or negative value) is present.

In high-voltage circuits, the common wire can be grounded through an arc suppression reactor. When one phase is short-circuited to ground, a parallel circuit is formed between the capacitance of the line and the inductance of the reactor. Actually, the type of impedance gave the name to the device (imaginary, reactive part of the resistance). At industrial frequency, the circuit resistance is close to infinity; as a result, the break is blocked until the repair team arrives.

The rotor is often called an armature.

Motor stator

After calling the motor rotor, work on the stator. A detail of a simpler design. If we have a generator in front of us, part of the windings is exciting, in general case you just need to find the resistance of each. Windings can only start single-phase circuits. The coil resistance will be higher. Let's say there are three contacts, then the distribution between them is as follows:

The common wire of both windings, where the zero (ground) is supplied.
Phase input of the working coil.
The end of the starting winding, where 230 volts is supplied, bypassing the capacitor.

The distinction is made by the value of resistance: between the phase inputs the rating is greater, therefore, the remaining end is the neutral wire. Further division is carried out as indicated above. The resistance of the starting coil is greatest (the difference between zero and this contact), the remaining ends indicate the working winding. The value of the active part of the impedance is reduced, reducing heat losses. Please note: there are also models of electric motors for 230 volts, where both windings are considered working. The difference in resistance between them is small (less than two times).

For three-phase motors, the stator windings are made of different numbers of poles, but are always equivalent. Strict symmetry is professed. The merger is carried out according to a star scheme. In high-power commutator motors, additional (additional) ones can be placed between the poles of the main coil. They are wound in one layer, therefore they demonstrate greater resistance. Designed to compensate for armature reactive power. It is clear that the number of additional poles is equal to the number of main ones. The difference is limited by geometric dimensions.

The core of the additional poles is made with an overlap (laminated structure) to reduce eddy currents. Similar to the rotor, it will not be enough to test the three-phase electric motor with a multimeter; you should also measure the insulation of the housing (typical value 20 MOhm).

Additional engine design

Often the composition of engines is replete additional elements, optimizing work, performing a protective or other function. This includes varistors. The resistors connecting each brush to the body close a spark when the voltage rises sharply. Extinguishing is in progress. Phenomena such as a circular fire on the collector lead to premature equipment failure.

The phenomenon is observed as a result of the occurrence of back-EMF. The generation mechanism is quite simple: when the current changes in the conductor, a force is formed that counteracts the process. During the transition to the next section, the phenomenon causes the emergence of a potential difference between the brush and the non-working part of the commutator. At voltages above 35 volts, the process causes ionization of the air in the gap, which is observed in the form of a spark. At the same time, the noise characteristics of the equipment deteriorate.

This phenomenon, however, is used to monitor the constancy of the shaft speed commutator motor. The level of sparking is determined by the number of revolutions. If the parameter deviates from the nominal value, the thyristor circuit changes the voltage cutoff angle in the desired direction to return the shaft speed to the nominal one. Such electronic boards are often found in household food processors or meat grinders. The engine composition is as follows:

Electric motor

Thermal fuses. The response temperature is selected to protect the insulation from burnout and destruction. The fuse is mounted on the motor housing with a steel shackle, or is hidden under the insulation of the windings. In the latter case, the leads stick out; you can easily check them with a multimeter. It’s easier to see, with the help of a tester and an indicator screwdriver, which pins of the connector the protection circuit goes to. In normal condition, the thermal fuse produces a short circuit.
Temperature relays are installed instead of frequency fuses. Normally open or closed. The latter type is most often used. The brand is written on the body; you can find the corresponding type of element on the Internet. Then act according to the information found (type, resistance, response temperature, position of contacts at the initial moment of time).
Speed sensors and tachometers are often installed on washing machine engines. In the first case there are three conclusions, in the second – two. The operating principle of Hall sensors is based on changing the potential difference in the transverse direction of a plate through which a weak electric current flows. Accordingly, the two outer terminals serve to supply power and should produce a short circuit (small resistance), while the output can only be tested under the influence of a magnetic field in operating mode. To do this, you need to supply power according to the electrical wiring. We recommend downloading the technical information (data sheet) for the Hall sensor present in the electric motor. Other options have been thought of. You can measure the power with a tester while the washing machine is turned on. We believe readers understand the danger of manipulation. It would be better to remove the electric motor and supply power separately, only to the Hall sensor. Then it all depends on the design. If there is a permanent magnet on the rotor, it is enough to simply rotate the axis by hand so that pulses appear at the output of the Hall sensor (detected by the tester). Otherwise, you will need to remove the sensor. Enlisting help permanent magnet, functionality is checked. A Hall sensor as part of an electric motor is usually used to control the rotation speed.

Now readers know how to test an electric motor with a multimeter, the review ends. The number of specific devices can be continued ad infinitum. The main thing is to ring the winding of the electric motor; the motor usually costs more than other parts. We don’t take the case when a Hall sensor costs 4,000 rubles. We are sure that readers will be able to add recommendations. But get into the situation - it is impossible to grasp the immensity... within one overview.

Hello, dear readers and guests of the Electrician's Notes website.

I am often asked how one can distinguish the working winding from the starting winding in single-phase motors when there are no markings on the wires.

Each time you have to explain in detail what and how. And today I decided to write a whole article about this.

As an example, I’ll take a single-phase electric motor KD-25-U4, 220 (V), 1350 (rpm):

KD - capacitor motor
25 - power 25 (W)
U4 - climatic version

Here is his appearance.

As you can see, there are no markings (color and numbers) on the wires. On the engine tag you can see what markings the wires should have:

working (C1-C2) - red wires
starting (B1-B2) - blue wires

First of all, I will show you how to determine the working and starting windings of a single-phase motor, and then I will assemble a circuit diagram for its connection. But this will be the subject of the next article. Before you start reading this article, I recommend that you read:.

So let's get started.

1. Wire cross-section

Visually check the cross-section of the conductors. A pair of wires with a larger cross-section belong to the working winding. And vice versa. Wires with a smaller cross-section are classified as starting wires.

Then we take the multimeter probes and measure the resistance between any two wires.

If there is no reading on the display, then you need to take another wire and measure again. Now the measured resistance value is 300 (ohms).

We found the conclusions of one winding. Now we connect the multimeter probes to the remaining pair of wires and measure the second winding. It turned out to be 129 (Ohm).

We conclude: the first winding is the starting winding, the second is the working winding.

In order not to get confused in the wires when connecting the motor in the future, we will prepare tags (“cambrides”) for marking. Usually, as tags, I use either a PVC insulating tube or a silicone tube (Silicone Rubber) of the diameter I need. In this example, I used a silicone tube with a diameter of 3 (mm).

According to new GOSTs, the windings of a single-phase motor are designated as follows:

(U1-U2) - working
(Z1-Z2) - launcher

The KD-25-U4 engine, taken as an example, still has the same digital markings as before:

(C1-C2) - working
(B1-B2) - launcher

To avoid any discrepancies between the wire markings and the diagram shown on the engine tag, I left the old markings.

I put tags on the wires. This is what happened.

For reference: Many people are mistaken when they say that the rotation of the motor can be changed by rearranging the power plug (changing the poles of the supply voltage). This is not right!!! To change the direction of rotation, you need to swap the ends of the starting or working windings. That's the only way!!!

We considered the case when 4 wires are connected to the terminal block of a single-phase motor. And it also happens that only 3 wires are connected to the terminal block.

In this case, the working and starting windings are connected not in the terminal block of the electric motor, but inside its housing.

What to do in this case?

We do everything the same way. We measure the resistance between each wire. Let's mentally label them as 1, 2 and 3.

Here's what I got:

(1-2) - 301 (Ohm)
(1-3) - 431 (Ohm)
(2-3) - 129 (Ohm)

From this we draw the following conclusion:

(1-2) - starting winding
(2-3) - working winding
(1-3) - starting and working windings are connected in series (301 + 129 = 431 Ohm)

For reference: With this connection of the windings, reversing a single-phase motor is also possible. If you really want, you can open the motor housing, find the junction of the starting and working windings, disconnect this connection and bring out 4 wires into the terminal block, as in the first case. But if your single-phase motor is capacitor-based, as in my case with the KD-25, then it.

P.S. That's all. If you have questions about the material in the article, ask them in the comments. Thank you for your attention.

How to check the condition of an electric motor winding

At first glance, the winding looks like a piece of wire wound in a specific way and there is nothing particularly broken in it. But it has features:

serious selection of homogeneous material along the entire length;

clear calibration of shape and cross-section;

industrial application of a layer of varnish with the highest insulating qualities;

strong contact connections.

If any of these requirements are violated at any point in the wire, then the conditions for the passage of electronic current change and the engine begins to operate with reduced power or stops altogether.

To check one winding of a three-phase motor, you need to disconnect it from other circuits. Which electric motors can be tested with a multimeter? Three-phase how to check insulation. In all electric motors they can be assembled according to one of two schemes:

The ends of the windings are usually brought out to terminal blocks and are marked with the signs “H” (start) and “K” (end). How to test a motor with a multimeter. From time to time, individual connections may be hidden inside the case, and other designation methods, for example, numbers, are used for pins.

A three-phase motor uses windings on the stator with similar electronic features and equal resistance. If, when measured with an ohmmeter, they show different values, then this is a reason to seriously think about the reasons for the scattering of readings.

How do winding faults manifest?

It is not possible to visually assess the quality of the windings due to the limited access to them. In practice, their electronic properties are inspected, taking into account that all winding faults appear:

a break, when the integrity of the wire is disrupted and the passage of electronic current through it is prevented;

a small short circuit that occurs when the insulation layer between the input and output turns is broken, characterized by the exclusion of the winding from operation with shunting of the ends;

interturn short circuit, when the insulation is broken between one or several nearby turns, which are thereby put out of operation. The current passes through the winding, bypassing the short-circuited turns, without overcoming their electronic resistance and without creating a certain amount of work;

breakdown of insulation between the winding and the stator or rotor housing.

Checking the winding for a wire break

This type of fault is determined by measuring the insulation resistance with an ohmmeter. The device will show a huge resistance - ∞, which takes into account the section of air space formed by the rupture.

Checking the winding for a short circuit

Engine, inside electronic circuit which has a short circuit, is switched off by protection from the power supply. But, even with a quick shutdown using this method, the location of the short circuit is clearly visible visually due to the consequences of exposure to high temperatures with pronounced soot or traces of melting of metals.

Electronic methods for determining winding resistance with an ohmmeter yield a very small value, very close to zero. Indeed, virtually the entire length of the wire is excluded from the measurement due to random shunting of the input ends.

Checking the winding for an interturn short circuit

This is a more hidden and difficult to detect malfunction. To identify it, you can use several methods.

Ohmmeter method

The device operates on a constant current and measures only the active resistance of the conductor. The winding, when operating due to turns, creates a significantly large inductive component.

When closing the 1st turn, and their total number can be several hundred, it is very difficult to see a change in the active resistance. After all, it varies within a few percent of the total value, and even less.

How to ring an electric motor

Three-phase asynchronous electric motor, tester check. In practice quite check electric motor

Location of three-phase motor contacts and winding continuity

Considering the placement of the ends of the windings three phase motor, we determine whether they are connected correctly.

You can try to accurately calibrate the device and closely measure the resistance of all windings, comparing the results. But the difference in readings even in this case will not always be visible.

More accurate results can be obtained by the bridge method of measuring active resistance, but this is usually a laboratory method that is difficult for most electricians to access.

Measurement of current consumption in phases

When an interturn short circuit occurs, the ratio of currents in the windings changes, causing excess heating of the stator. A working motor has similar currents. Therefore, their direct measurement in an operating circuit under load more accurately reflects the real picture of the technical condition.

AC measurements

Find the total resistance of the winding taking into account the inductive component in full working diagram may not always be the case. To do this, you will have to remove the cover from the terminal box and cut into the wiring.

With the motor taken out of operation, you can use a step-down transformer with a voltmeter and ammeter for measurement. The current can be limited by a current-limiting resistor or rheostat of the appropriate rating.

When taking measurements, the winding is located inside the magnetic core, and the rotor or stator can be removed. There will be no balance of electrical flows, for which the engine is designed. About how to check the engine and whether it can be checked with a multimeter? And as possible. Therefore, a reduced voltage is used and the current values are controlled, which should not exceed the nominal values.

The voltage drop measured across the winding, divided by the current, will give the impedance value according to Ohm's law. It remains to be compared with the features of other windings.

The same circuit allows you to determine the current-voltage properties of the windings. You just need to take measurements at various currents and write them down in tabular form or build graphs. If, when compared with similar windings, there are no serious deviations, then there is no interturn short circuit.

Ball in stator

The method is based on the development of a rotating electric field by serviceable windings. How to check an electric motor with a multimeter step by step. To do this, they are supplied with a three-phase symmetrical voltage, but certainly of a reduced value. For this purpose, three similar step-down transformers are usually used, operating in each phase of the power circuit.

To limit current loads on the windings, the experiment is carried out for a short period of time.

A small metal ball from a ball bearing is introduced into the rotating magnetic field of the stator immediately after turning on the voltage. If the windings are in good condition, the ball rolls synchronously along the inner surface of the magnetic circuit.

When one of the windings has an interturn short circuit, the ball will hang at the fault location.

During the test, the current in the windings must not exceed the rated value and it should be taken into account that the ball freely jumps out of the body at the speed of a slingshot.

Electrical check of winding polarity

Stator windings may not have markings for the start and end of the terminals and this will make correct assembly more difficult.

In practice, 2 methods are used to find polarity:

1. using a low-power source of constant current and a sensitive ammeter showing the direction of the current;

2. by using a step-down transformer and a voltmeter.

In both options, the stator is considered as a magnetic circuit with windings, operating similarly to a voltage transformer.

Checking polarity using a battery and an ammeter

On the outer surface of the stator, six wires lead out three separate windings, the beginnings and ends of which need to be found.

Using an ohmmeter, they call and mark the terminals related to each winding, for example, with the numbers 1, 2, 3. Then they randomly mark the beginning and end of any of the windings. An ammeter with an arrow in the center of the scale, capable of indicating the direction of the current, is connected to one of the remaining windings.

The minus batteries are aggressively connected to the end of the selected winding, and the plus batteries are briefly touched to its beginning and immediately break the circuit.

When a current pulse is applied to the first winding, it is transformed by electrical induction into a second circuit closed through an ammeter, repeating the original shape. In this case, if the polarity of the windings is guessed correctly, then the ammeter needle will deviate to the right when the pulse begins and move to the left when the circuit opens.

If the needle behaves differently, then the polarity is simply confused. All that remains is to mark the terminals of the 2nd winding.

Another 3rd winding is checked in a similar way.

Checking polarity using a step-down transformer and voltmeter

Here, too, first call the windings with an ohmmeter, determining the pins that relate to them.

Then the ends of the first selected winding are randomly marked for connection to a step-down voltage transformer, for example, 12 volts.

The two remaining windings are randomly twisted at one point with 2 leads, and the remaining pair is connected to a voltmeter and power is supplied to the transformer. Its output voltage is transformed into other windings with the same value, since they have an equal number of turns.

Due to the alternate connection of the 2nd and third windings, the voltage vectors will add up, and their sum will be shown by a voltmeter. How to check the parking sensor with a multimeter (tester. In our case, if the direction of the windings coincides given value will be 24 volts, and with different polarities - 0.

All that remains is to mark all the ends and perform a control freeze.

The article gives general order actions when checking the technical condition of some random motor without certain technical features. They may change in each individual case. See them in the documentation for your equipment.

/ 27.07.2018

How to check an electric motor

A malfunction can be detected when the tool body is heated unevenly. When you touch your hand, you feel a temperature difference in different places housings. In this case, the tool must be disassembled and checked with a tester and other methods.

If a short circuit occurs in the stator turns and troubleshooting, first of all we inspect the turns and terminals. As a rule, when a short circuit occurs, the current passing through the windings increases and overheating occurs.

A greater short circuit of turns occurs in the stator windings and the insulation layer is damaged. Therefore, we begin identifying faults by conducting a visual inspection. If no burns or damaged insulation are found, then proceed to the next step.

The cause of the breakdown may be a malfunction of the voltage regulator, which occurs when the excitation currents increase. To detect the problem, the brushes are checked; they must be ground evenly and free of chips and damage. Then you should check using a light bulb and 2 batteries.

Application of a multimeter

Now we need to check the possibility of a break in the stator windings. On the multimeter scale, set the switch to the resistance measurement sector. Without knowing the measurement value, we set the maximum value for your device. We check the functionality of the tester.

We touch each other with our probes. The arrow of the device should show 0. We carry out the work by touching the terminals of the windings. When an infinite value is shown on the multimeter scale, the winding is faulty and the stator should be rewound.

We check the possibility of a short circuit to the housing. Such a malfunction will cause a decrease in the power of the angle grinder, the possibility of electric shock and an increase in temperature during operation. The work is carried out according to the same scheme. Turn on the resistance measurement on the scale.

We place the red probe on the winding terminal, and attach the black probe to the stator housing. If the winding is short-circuited to the housing, the resistance value on the tester scale will be less than on a working one. This malfunction requires rewinding of the stator windings.

It's time to take measurements and check whether there is an interturn short circuit in the stator winding. To do this, the resistance value on each winding is measured. We determine the zero point of the windings by measuring the resistance for each of them. When the device shows the lowest winding resistance, it should be changed.

Checking the motor windings

An electronic rotor tester is a standard digital multimeter. Before you begin testing the circuit, you should check the multimeter and its readiness for use. The switch is set to measure resistance and the probes touch each other. The device should show zeros. Set the maximum measurement value and check:

This completes the rotor check. It is worth recalling the main stages of fault determination once again. Before checking, the angle grinder or any other device should be de-energized. Before taking measurements, you should visually inspect the housings, insulation and the absence of carbon deposits on the stator and rotor.

It is necessary to clean the contact surfaces from blockages with dust and dirt. Contamination causes an increase in current when the motor loses power.

When disassembling the instrument for the first time, write down all your steps. This will allow you to have a hint next time, avoiding the appearance unnecessary details during assembly. If the brush extends beyond the edge of the brush holder by less than 5 mm, such brushes should be replaced. You can check the interturn short circuit with an electronic tester, that is, a multimeter.

Checking the electric motor by external inspection

A full inspection can be carried out only after disassembling the electric motor, but do not rush to disassemble it right away.

All work is carried out only after turning off the power supply, checking that it is not present on the electric motor and taking measures to prevent its spontaneous or erroneous activation. If the device is plugged into a power outlet, then simply remove the plug from it.

If there are capacitors in the circuit. then their conclusions must be deflated.

Check before disassembling:

Play in bearings. Read this article on how to check and replace bearings.
Check the paint coverage on the body. Burnt or peeling paint in places indicates that the engine is heating up in these places. Pay special attention to the location of the bearings.
Check the motor mounting feet and the shaft together with its connection to the mechanism. Cracks or broken legs must be welded.

After disassembling according to these instructions, you need to check:

Part of the winding may burn out and an interturn short circuit will occur (in the picture on the left), or the entire winding (in the right picture). Despite the fact that in the first case the motor will work and overheat, it is still necessary to rewind the windings in any case.

How to ring an asynchronous electric motor

If nothing is revealed during an external examination, then it is necessary to continue checking using electrical measurements.

How to test an electric motor with a multimeter

The most common electrical measuring instrument in the household is the multimeter. With its help, you can check the integrity of the winding and the absence of a breakdown on the housing.

In 220 Volt engines. It is necessary to ring the starting and working windings. Moreover, the starting resistance will be 1.5 times greater than that of the working one. For some electric motors, the starting and running windings will have a common third terminal. Read more about this here.

For example. The motor from an old washing machine has three terminals. The greatest resistance will be between two points, which includes 2 windings, for example 50 Ohms. If we take the remaining third end, then this will be the common end. If you measure between it and the 2nd end of the starting winding, you will get a value of about 30-35 Ohms, and if between it and the 2nd end of the working winding, about 15 Ohms.

In 380 Volt motors connected according to a star or delta circuit, it will be necessary to disassemble the circuit and ring each of the three windings separately. Their resistance should be the same from 2 to 15 Ohms with deviations of no more than 5 percent.

It is imperative to ring all the windings among themselves and on the housing. If the resistance is not infinitely high, then there is a breakdown of the windings between themselves or to the housing. Such motors must be rewinded.

How to check the insulation resistance of electric motor windings

Unfortunately, you cannot check the insulation resistance of the electric motor windings with a multimeter; for this you need a 1000-volt megohmmeter with a separate power source. The device is expensive, but every electrician at work who has to connect or repair electric motors has it.

When measuring, one wire from the megohmmeter is connected to the body in an unpainted place, and the second in turn to each terminal of the winding. After this, measure the insulation resistance between all windings. If the value is less than 0.5 Megohm, the engine must be dried.

Be careful. to avoid defeat electric shock Do not touch the test clamps while taking measurements.

All measurements are carried out only on de-energized equipment and last for at least 2-3 minutes.

How to find turn-to-turn short circuit

The most difficult thing is to find an interturn short circuit. in which only part of the turns of one winding is connected to each other. It is not always detected during external inspection, therefore, for these purposes, an inductance meter is used for 380 Volt engines. All three windings must have same value. With an interturn short circuit, the inductance of the damaged winding will be minimal.

When I was in practice 16 years ago at a factory, electricians used a ball bearing with a diameter of about 10 millimeters to search for interturn short circuits in an asynchronous motor with a power of 10 Kilowatt. They took out the rotor and connected 3 phases through 3 step-down transformers to the stator windings. If everything is in order, the ball moves in a circle on the stator, and if there is an interturn short circuit, it is magnetized to the place where it occurs. The check should be short-term and be careful the ball may fly out!

I have been working as an electrician for a long time and check for an interturn short circuit if only a 380 V motor starts to get very hot after 15-30 minutes of operation. But before disassembling, with the motor turned on, I check the amount of current it consumes in all three phases. It should be the same with a slight correction for measurement errors.

Interturn short circuit of the electric motor

Causes of interturn short circuit

If you have read previous articles, then you know that inter-turn short circuit of an electric motor accounts for 40% of electric motor malfunctions. There may be several reasons for an interturn short circuit.

Electric motor overload - the load on the electrical installation exceeds the norm, as a result of which the stator windings heat up and the insulation of the windings is destroyed, which leads to an interturn short circuit. Loading may occur due to improper operation of the equipment. The rated load can be determined from the electrical installation data sheet or read on the electric motor plate. Overload can also occur due to mechanical damage to the electric motor itself. Seized or dry bearings can also cause interturn “shortness”.

The possibility of a factory defect in the windings cannot be ruled out, and if the electric motor was rewound in a handicraft workshop, then there is a high probability that the “mezhvitnyak” is already knocking on your door.

Also, improper operation and storage of the electric motor can cause moisture to get inside the motor; damp windings are also a very common cause of interturn short circuits.

As a rule, with such a short circuit, the electric motor is no longer alive, and will work for a very short time. I think that’s enough of analyzing the reasons, let’s move on to the question “how to determine an interturn short circuit.”

Search for interturn short circuit.

Determining the interturn short circuit is not too difficult, and there are several handy methods for this.

If during operation of the electric motor some part of the stator heats up more than the entire engine, then you should think about stopping it and accurately diagnosing it.

Ordinary current clamps will also help determine the short circuit; we measure the load on each phase in turn and if on one of them it is greater than on the others, then this is a sign that there may be a winding inter-turn. But it should be taken into account that there may be a phase imbalance at the substation in order to verify the incoming voltage with a voltmeter.

You can ring the windings with a tester. To do this, we call each winding separately and compare the obtained resistance results. This method may not work if only a couple of turns are closed, then the discrepancy will be minimal.

It would not be superfluous to test the electric motor with a megger in search of a short circuit to the housing; we apply one probe to the motor housing, and the second to the output of the windings in turn.

If you still have doubts, then you will have to disassemble the electric motor. Having removed the covers and rotor, we visually examine the windings. It is likely that you will see a burnt part.

Well, the most accurate way to check the interturn circuit is to check using a three-phase step-down transformer (36-42 volts) and a bearing ball.

We supply three phases from a step-down transformer to the starter of the disassembled electric motor. With a little acceleration we throw the ball there, if the ball starts to run in a circle inside the stator, then everything is in order. If, after making a couple of revolutions, it sticks to one place, then there is an interturn short circuit.

Instead of a ball, you can use a plate from transformer iron, we apply it inside the stator to the iron and in the place where the interturn it starts to rattle, and where everything is fine the plate will be magnetized.

Be sure to use all of the above methods with a grounded electric motor and strictly using a step-down transformer.

Testing with a ball and a plate at a voltage of 380 volts is prohibited and is very dangerous for your life.

Winding insulation resistance measurement

To test a motor for insulation resistance, electricians use a megger with a test voltage of 500 V or 1000 V. This device measures the insulation resistance of motor windings designed for an operating voltage of 220 V or 380 V.

For electric motors with a rated voltage of 12V, 24V, a tester is used, since the insulation of these windings is not designed for testing under the high voltage of 500 V megger. Typically, the motor data sheet indicates the test voltage when measuring the insulation resistance of the coils.

Insulation resistance is usually checked with a megger

Before measuring the insulation resistance, you need to familiarize yourself with the connection diagram of the electric motor, since some star connections of the windings are connected at a midpoint to the motor housing. If the winding has one or more connection points, delta, star, single-phase motor with starting and running windings, then the insulation is checked between any connection point of the windings and the housing.

If the insulation resistance is significantly less than 20 MΩ, the windings are disconnected and each is checked separately. For a whole motor, the insulation resistance between the coils and metal body must be at least 20 Mohm. If the motor has been operated or stored in damp conditions, then the insulation resistance may be below 20 MΩ.

Then the electric motor is disassembled and dried for several hours with a 60 W incandescent lamp placed in the stator housing. When measuring insulation resistance with a multimeter, set the measurement limit to the maximum resistance, megohms.

How to test an electric motor for broken windings and interturn short circuits

Turn-to-turn short circuits in the windings can be checked with an ohm multimeter. If there are three windings, then it is enough to compare their resistance. The difference in the resistance of one winding indicates an interturn short circuit. The interturn short circuit of single-phase motors is more difficult to determine, since there are only different windings - this is the starting and operating winding, which has less resistance.

There is no way to compare them. You can detect the interturn short circuit of the windings of three-phase and single-phase motors using clamp meters, comparing the winding currents with their passport data. When there is an interturn short circuit in the windings, their rated current increases, and the starting torque decreases, the engine starts with difficulty or does not start at all, but only hums.

Checking the electric motor for open circuit and interturn short circuit of windings

It will not be possible to measure the resistance of the windings of powerful electric motors with a multimeter, because the cross-section of the wires is large and the resistance of the windings is within tenths of an ohm. It is not possible to determine the difference in resistance with such values using a multimeter. In this case, it is better to check the serviceability of the electric motor with a current clamp.

If it is not possible to connect the electric motor to the network, the resistance of the windings can be found by an indirect method. Collect series circuit from a 12V battery with a 20 ohm rheostat. Using a multimeter (ammeter), set the current with a rheostat to 0.5 - 1 A. The assembled device is connected to the winding being tested and the voltage drop is measured.

Testing the electric motor for open circuit and insulation resistance

A lower voltage drop across the coil will indicate an interturn short circuit. If you need to know the winding resistance, it is calculated using the formula R = U/I. A malfunction of the electric motor can also be determined visually, on a disassembled stator, or by the smell of burnt insulation. If a break point is visually detected, it can be eliminated by soldering a jumper, insulating it well and laying it down.

Measurement of the resistance of the windings of three-phase motors is carried out without removing jumpers on the star and delta winding connection diagrams. The resistance of the coils of DC and AC commutator motors is also checked with a multimeter. And if their power is high, the test is carried out using a battery-rheostat device, as indicated above.

The winding resistance of these motors is checked separately on the stator and rotor. On the rotor, it is better to check the resistance directly on the brushes by turning the rotor. In this case, it is possible to determine whether the brushes are not tightly attached to the rotor lamellas. Remove carbon deposits and irregularities on the collector lamellas by grinding them on a lathe.

It is difficult to do this operation manually; this malfunction may not be eliminated, and the sparking of the brushes will only increase. The grooves between the slats are also cleaned. A fuse or thermal relay can be installed in the windings of electric motors. If there is a thermal relay, check its contacts and clean them if necessary.

Basic electric motor malfunctions

Every year, gasoline engines are increasingly being replaced by electric motors installed in a new type of car called electric vehicles. However, like internal combustion engines, electric powertrains can break down, causing performance problems. vehicle. The majority of electric motor malfunctions occur due to severe wear of mechanism parts and aging of materials, which is reinforced by improper operation of such a vehicle. There can be many reasons for the appearance of characteristic problems, and we will now tell you about some (the most common) ones.

Causes of electric motor malfunction

All possible malfunctions of an electric vehicle engine can be divided into mechanical and electrical. The causes of mechanical problems include distortions of the electric motor housing and its individual parts, loosening of fastenings and damage to the surface of the constituent elements or their shape. Besides, common problem is overheating of the bearings, oil leakage from them and the appearance of abnormal operating noise. To the most typical malfunctions The electrical part is attributed to short circuits inside the windings of the electric motor, as well as between them, short circuits of the windings to the housing and breaks in the windings or in the external circuit, that is, in the supply wires and starting equipment.

As a result of the appearance of certain malfunctions, the following malfunctions may be observed in the operation of the vehicle: inability to start the motor, dangerous heating of the windings, abnormal rotation speed of the electric motor, unnatural noise (hum or knock), unequal current strength in individual phases.

Typical motor problems

Let's look at electric motor breakdowns in more detail, identifying their possible causes.

AC motor

Problem: when connected to the power supply, the electric motor does not develop the rated speed and makes unnatural sounds, and when the shaft is turned by hand, uneven operation is observed. The reason for this behavior is most likely a break in two phases when connecting the stator windings with a triangle, or a break when connecting a star.

If the engine rotor does not rotate, makes a strong hum and heats up above the permissible level, we can say with confidence that the stator phase is to blame. When the engine hums (especially when trying to start), and the rotor rotates at least slowly, the cause of the problem is often a break in the rotor phase.

It happens that with a rated load on the shaft, the electric motor operates stably, but its rotation speed is slightly lower than the rated one, and the current in one of the stator phases is increased. As a rule, this is a consequence of a phase failure when connecting the windings with a delta.

If at idle speed of the electric motor there is local overheating of the active steel of the stator, this means that due to damage to the inter-sheet insulation or burnout of the teeth due to damage to the winding, the sheets of the stator core are closed to each other.

When the stator winding overheats in certain places, when the engine cannot develop the rated torque and hums strongly, the cause of this phenomenon should be sought in a turn short circuit of one phase of the stator winding or an interphase short circuit in the windings.

If the entire electric motor overheats evenly, then the fan of the ventilation system is faulty, and overheating of the plain bearings with ring lubrication is due to one-sided attraction of the rotors (due to excessive wear of the liner) or poor fit of the shaft to the liner. When a rolling bearing overheats and produces abnormal noise, it is likely that the cause is contamination of the lubricant, excessive wear of the rolling elements and races, or inaccurate alignment of the unit shafts.

Knocking in the plain bearing and in the rolling bearing is explained by serious wear of the liner or destruction of the tracks and rolling elements, and increased vibration is a consequence of imbalance of the rotor due to interaction with pulleys and couplings, or the result of inaccurate alignment of the unit shafts and misalignment of the connecting coupling halves.

A DC electric motor may also have its own characteristic faults:

Under serious load, the machine’s armature may not rotate, and if you try to turn it by external force, the engine will run “staggered.” Reasons: poor contact or complete break in the excitation circuit, interturn or short circuits inside the independent excitation winding. Under conditions of rated values of the network voltage and excitation current, the armature rotation speed may be less or more than the established norm. In this case, the culprits for this situation are the brushes, shifted from the neutral position in the direction of rotation of the shaft or against it.

It may also be that the brushes of one sign spark a little stronger than the brushes of another sign. Perhaps the distances between the rows of brushes around the circumference of the commutator are not the same, or there is an interturn short circuit in the windings of one of the main or additional “pluses”. If the sparking of the brushes is also accompanied by blackening of the commutator plates, which are located at a certain distance from each other, then the culprit for this situation is most likely poor contact or a short circuit in the armature winding. Also, do not forget about the possibility of a break in the armature coil connected to the blackened plates.

In cases where only every second or third plate of the collector darkens, the cause of the malfunction may be a weakened compression of the collector or protruding micanite of the insulating tracks. Brushes can spark even with normal heating of the motor and a fully functional brush apparatus, which is explained by unacceptable wear of the commutator.

The reasons for increased sparking of brushes, overheating of the commutator and darkening of most of it are usually the insulation tracks (they say the commutator “beats”). When the motor armature rotates in different directions, the brushes also spark with different intensities. There is only one reason - the displacement of the brushes from the center.

If increased sparking of the brushes is observed on the commutator, then it is worth checking the tightness of their fit, as well as conducting diagnostics for the presence of defects in the working surface of the brushes. In addition, the reason may be uneven pressure of the brushes or their jamming in the brush holder. Naturally, if any of the listed problems are detected, it must be properly eliminated, but quite often only highly qualified specialists can do this.

Troubleshooting electric motor

Qualitative major renovation Electric motors can only be produced at specialized enterprises. During the current repair work disassembly in progress power unit and subsequent partial replacement of worn parts. Let's look at the order of performing all actions using the example of an asynchronous electric motor.

At the initial stage, using a screw puller, remove the pulley or coupling half from the electric motor pulley. After this, you need to unscrew the bolts securing the fan casing and remove it. Next, using the same screw puller, you need to unscrew the locking screw and remove the fan itself. If necessary, the same tool can be used to remove the bearings from the motor shaft, and then, by unscrewing the fastening bolts, remove their covers.

After this, unscrew the bolts securing the bearing shields and lightly hit the wooden spacer remove these shields. To avoid damaging the steel and windings, a cardboard spacer is placed in the air gap, onto which the rotor is lowered. Reassembling the electric motor is carried out in the reverse order.

After repair work is completed (the specifics depend on the nature of the breakdown), the electric motor should be tested. To do this, simply rotate the rotor by holding the pulley, and if the assembly is done correctly, the unit should rotate easily. If everything is normal, the motor is installed in place, connected to the network and checked for operation in idle mode, after which the motor is connected to the machine shaft and tested again. Let's look at options for troubleshooting an electric motor using the example of some typical breakdowns.

So, let's imagine that the motor does not start due to a lack of voltage in the network, the machine is turned off or the fuses are blown. The presence of voltage can be checked using a special device - an AC voltmeter with a 500 V scale, or using a low-voltage indicator. The problem can be resolved by replacing the blown fuses. Pay attention! If at least one fuse blows, the engine will make a characteristic hum.

A phase break in the stator winding can be detected using a megger, but before doing this, all ends of the motor windings must be freed. If a break is detected inside the winding phase, the motor will have to be sent to professional repair. The acceptable norm for reducing the voltage at the motor terminals when starting it is considered to be 30% of the nominal value, which is caused by losses in the network, insufficient power transformer or its overload.

If you notice a decrease in voltage at the electric motor terminals, you need to replace the supply transformer or increase the cross-section of the supply line wires. Lack of power supply contact in one of the stator windings (phase loss) causes an increase in current in the element windings and a decrease in the number of revolutions. If you leave the motor running on two windings, it will simply burn out.

In addition to the listed electrical problems, electric motors can also suffer from mechanical problems. Thus, excessive heating of the bearings is often caused by improper assembly of these parts, poor alignment of the motor, contamination of the bearings, or excessive wear of the balls and rollers.

In any case, before proceeding to direct action, you should conduct a complete diagnosis of the electric motor and the parts interacting with it. The inspection procedure begins with checking the battery, and if it is in good condition, then the next step is to check the power supply to the controller circuit (the computer that controls the rotation speed of the electric motor). It is quite possible that you will find a broken wire along the path from the battery to the board. The breakdown of an electronic board is not a frequent occurrence, but if there is even the slightest doubt about its serviceability, then it is better to immediately visually assess the condition of the part. If there has been strong heating of the board elements, you will immediately notice blackened and swollen areas with possible leaks.

In the case where the car owner has at least minimal knowledge in the field of electronics, he can independently check fuses, semiconductor parts (like diodes and transistors), all contacts, capacitances and soldering quality.

When the ECU output has operating voltage in the on state, then, as a rule, the cause of the malfunction should be sought in the electric motor itself. The complexity of repairing the unit depends on the specific malfunction and type of mechanism. So, when examining AC electric motors with rotary power, first of all, it is necessary to check the contact brushes, because they are most often the cause of breakdowns of motors of this type. After this, you should check the windings for breaks or short circuits. In the event of a break, the tester will not show any resistance value, and in the event of a short circuit, the resistance indicator will correspond to zero or one Ohm.

Having discovered a malfunction, it, of course, needs to be eliminated. This can be done either by repairing and replacing failed parts (for example, a brush), or by replacing the entire motor with a working analogue.

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Methods for diagnosing faults in asynchronous electric motors

The engine does not turn over when starting or its rotation speed is abnormal. The causes of this malfunction may be mechanical or electrical problems.

Electrical problems include: internal breaks in the stator or rotor windings, breaks in the supply network, disruption of normal connections in the starting equipment. If the stator winding breaks, a rotating magnetic field will not be created in it, and if there is a break in two phases of the rotor, there will be no current in the winding of the latter that interacts with the rotating field of the stator, and the engine will not be able to operate. If a winding break occurs while the motor is running, it may continue to operate at rated torque, but the rotation speed will be greatly reduced and the current will increase so much that without maximum protection, the stator or rotor winding may burn out.

If the motor windings are connected in a triangle and one of its phases is broken, the motor will begin to turn around, since its windings will be connected in an open triangle, in which a rotating magnetic field is formed, the current strength in the phases will be uneven, and the rotation speed will be lower than the nominal one. With this fault, the current in one of the phases in the case of the rated load of the motor will be 1.73 times greater than in the other two. When the motor has all six ends of its windings removed, a phase break is determined with a megohmmeter. The winding is disconnected and the resistance of each phase is measured.

The engine rotation speed at full load is lower than rated due to low mains voltage, poor contacts in the rotor winding, and also due to high resistance in the rotor circuit of a wound-rotor motor. With high resistance in the rotor circuit, the motor slip increases and its rotation speed decreases.

Resistance in the rotor circuit is increased by poor contacts in the rotor brush device, the starting rheostat, winding connections with slip rings, soldering of the frontal parts of the winding, as well as insufficient cross-section of cables and wires between the slip rings and the starting rheostat.

Poor contacts in the rotor winding can be identified if a voltage equal to 20-25% of the rated voltage is applied to the motor stator. The locked rotor is slowly turned by hand and the current strength in all three phases of the stator is checked. If the rotor is in good condition, then in all its positions the current strength in the stator is the same, and if there is a break or poor contact it will vary depending on the position of the rotor.

Poor contacts in the solders of the frontal parts of the phase rotor winding are determined by the voltage drop method. The method is based on increasing the voltage drop in places of poor-quality soldering. In this case, the voltage drop values are measured at all connections, after which the measurement results are compared. Solders are considered satisfactory if the voltage drop in them exceeds the voltage drop in solders with minimum values by no more than 10%.

Rotors with deep slots may also experience breakage of the rods due to mechanical overstressing of the material. The rupture of the rods in the groove part of the squirrel-cage rotor is determined as follows. The rotor is pushed out of the stator and several wooden wedges are driven into the gap between them so that the rotor cannot turn. A reduced voltage of no more than 0.25 Un is supplied to the stator. A steel plate is placed in turn on each groove of the protruding part of the rotor, which should overlap the two teeth of the rotor. If the rods are intact, the plate will be attracted to the rotor and rattle. If there is a gap, the attraction and rattling of the plate disappears.

The engine turns when the wound rotor circuit is open. The cause of the malfunction is a short circuit in the rotor winding. When turned on, the motor turns slowly, and its windings become very hot, since a large current is induced in the short-circuited turns by the rotating field of the stator. Short circuits occur between the clamps of the frontal parts, as well as between the rods when the insulation in the rotor winding is broken down or weakened.

This damage is determined by a thorough external inspection and measurement of the insulation resistance of the rotor winding. If damage cannot be detected during inspection, it is determined by uneven heating the rotor windings are felt by touch, for which the rotor is braked and a reduced voltage is applied to the stator.

Uniform heating of the entire engine above the permissible norm can result from prolonged overload and deterioration of cooling conditions. Increased heating causes premature wear of the winding insulation.

Local heating of the stator winding, which is usually accompanied by a strong hum, a decrease in the motor rotation speed and uneven currents in its phases, as well as the smell of overheated insulation. This malfunction can occur as a result of incorrect connection of the coils to each other in one of the phases, a short circuit of the winding to the housing in two places, a short circuit between two phases, a short circuit between the turns in one of the phases of the stator winding.

When there is a short circuit in the motor windings, the rotating magnetic field in the short-circuited circuit will induce e. d. s, which will create a large current, depending on the resistance of the closed circuit. A damaged winding can be found by the value of the measured resistance, while the damaged phase will have less resistance than the good ones. Resistance is measured using a bridge or ammeter-voltmeter method. The damaged phase can also be determined by measuring the current in the phases if a reduced voltage is supplied to the motor.

When connecting the windings in a star, the current in the damaged phase will be greater than in the others. If the windings are connected in a triangle, the line current in the two wires to which the damaged phase is connected will be greater than in the third wire. When determining the specified damage to an engine with squirrel cage rotor the latter may be braked or rotating, and in slip-wound rotor motors the rotor winding may be open-circuited. Damaged coils are determined by the voltage drop at their ends: on damaged coils the voltage drop will be less than on healthy ones.

Local heating of the active steel of the stator occurs due to burnout and melting of the steel during short circuits in the stator winding, as well as when the steel sheets are shorted due to the rotor touching the stator during engine operation or due to the destruction of insulation between individual sheets of steel. Signs of the rotor touching the stator are smoke, sparks and a burning smell; active steel in places of contact takes on the appearance of a polished surface; a humming sound appears, accompanied by engine vibration. The cause of contact is a violation of the normal gap between the rotor and stator as a result of wear of bearings, improper installation, large bending of the shaft, deformation of the stator or rotor steel, one-sided attraction of the rotor to the stator due to turn short circuits in the stator winding, strong vibration of the rotor, which determined with a probe.

Abnormal engine noise. A normally running engine produces a uniform hum, which is characteristic of all AC machines. An increase in humming and the appearance of abnormal noise in the engine may be a consequence of a weakening of the press-fit of the active steel, the packages of which will periodically be compressed and weakened under the influence of the magnetic flux. To eliminate the defect, it is necessary to repress the steel packages. Strong humming and noise in the machine can also be the result of an uneven gap between the rotor and stator.

Damage to the winding insulation can occur from prolonged overheating of the motor, moisture and contamination of the windings, metal dust and shavings getting on them, as well as as a result of natural aging of the insulation. Damage to the insulation can cause short circuits between phases and turns of individual winding coils, as well as short circuits of the windings to the motor housing.

Humidification of the windings occurs in the event of long breaks in the operation of the engine, when water or steam gets into it directly as a result of storing the engine in a damp, unheated room, etc.

Metal dust that gets inside the machine creates conductive bridges, which can gradually cause short circuits between the phases of the windings and to the housing. It is necessary to strictly observe the timing of inspections and scheduled preventive maintenance of engines.

The insulation resistance of motor windings with voltages up to 1000 V is not standardized; insulation is considered satisfactory with a resistance of 1000 ohms per 1 V of rated voltage, but not less than 0.5 MΩ at operating temperature windings

A short circuit of the winding to the motor body is detected with a megohmmeter, and the location of the short circuit is detected by “burning” the winding or by feeding it with direct current.

The “burning” method is that one end of the damaged phase of the winding is connected to the network, and the other to the housing. When current passes at the point where the winding is shorted to the housing, a “burn-through” is formed, smoke and the smell of burnt insulation appear.

The engine does not start as a result of blown fuses in the armature winding, breakage of the resistance winding in the starting rheostat, or broken contact in the supply wires. A break in the resistance winding in the starting rheostat is detected with a test lamp or megger.

Motor design

Difficulties in diagnosis

Switching equipment

Diagnostic details electrical part

How to ring an electric motor

Location of three-phase motor contacts and winding continuity

Diagnostics of asynchronous motors

If the DC motor

Checking the Direct Drive Motor

Diagnostic sequence

If he still knocks out the defense?

Electric motor device

Electric motor rotor

Graphite brushes

Continuous rings

Motor stator

Additional engine design

How to ring an electric motor

Location of three-phase motor contacts and winding continuity

How to check an electric motor

Application of a multimeter

Checking the motor windings

Checking the electric motor by external inspection

How to ring an asynchronous electric motor

How to test an electric motor with a multimeter

How to check the insulation resistance of electric motor windings

How to find turn-to-turn short circuit

Related Posts

Winding insulation resistance measurement

How to test an electric motor for broken windings and interturn short circuits

Basic electric motor malfunctions

Causes of electric motor malfunction

Typical motor problems

Troubleshooting electric motor

Methods for diagnosing faults in asynchronous electric motors