In our daily lives, we are constantly confronted with various electrical devices that greatly facilitate our activities. Almost all of them have in their design an engine that is powered by electricity to perform a specific job.
Sometimes, for various reasons, malfunctions arise in it. We have to determine its performance, to identify and fix the breakdown.
How is the electric motor
Immediately make a reservation that we will not resort to complex technical descriptions and formulas, but we will try to use simplified schemes and terminology. We also take into account that working with electric motors in electrical installations is dangerous. They are allowed trained, trained personnel.
Attention: Self-repair of the electric motor by unskilled workers can end tragically!
By mechanical design, any electric motor can be represented as consisting of only two parts:
1. permanently fixed, which is called the stator and is attached to the body of the machine, mechanism or held in hands, as on a drill, punch and similar devices,
2. mobile - a rotor performing a rotational motion transmitted to an actuator.
Both of these halves are completely separated from each other, but are in contact through bearings. Nowhere else and in any place do they come into purely mechanical contact. The rotor is inserted inside the stator and rotates completely freely in it.
This ability to rotate must be evaluated first of all when analyzing the operability of any electric machine.
To check rotation, you must:
1. completely remove the voltage from the power circuit,
2. Try to manually rotate the rotor.
The first action is a necessary requirement of safety rules, and the second is a technical test.
It is often difficult to evaluate rotation due to the connected drive. For example, the rotor of the engine of a working vacuum cleaner is quite easy to unwind with a movement of the hand. To rotate the shaft of the working punch, you will have to make an effort. To roll the shaft of the engine connected through a worm gearbox will not work at all due to the design features of this mechanism.
For these reasons, the rotor rotation in the stator is evaluated when the drive is disconnected and the quality of the bearings is analyzed. It can hinder movement:
wear of slip pads,
lack of lubrication in bearings or its improper use. For example, an ordinary solid oil, which is often filled with ball bearings, thickens in the cold and can cause poor engine starting,
dirt or foreign objects between the moving and stationary parts.
Noise during engine operation is created by faulty, broken bearings with increased play. For its quick assessment, it is enough to sway the rotor relative to the stationary part, creating variable loads in the vertical plane, and try to push and pull it along the axis. On many models, minor play is considered acceptable.
If the rotor rotates freely and the bearings work well, then it is necessary to look for a malfunction in the electromagnetic circuits.
For any engine to work, two conditions must be met:
1. on its winding (or windings in multiphase models) to bring the rated voltage,
2. The electrical and magnetic circuits must be operational.
Where to check motor voltage
Consider the first position on the example of the design of an electric drill with a collector motor.
If you insert a plug into a power outlet with a working voltage at a working drill, then this is not enough to start the engine. You will need to press the power button again.
Only then, the electric current from the plug through the cord through the triac control unit and the contacts of the pressed button will come to the brush unit located on the collector, and through it can get to the winding.
To summarize: to make a conclusion about the health of the drill motor is possible only after checking the voltage on the brushes of the collector assembly, and not on the contacts of the plug. The above example is a special case, but reveals the general principles of troubleshooting, typical for most electrical devices. Unfortunately, some electricians in a hurry neglect this position.
Types of electrical circuits of electric motors
Electric motors are designed to operate on direct or alternating current. Moreover, the latter are divided into:
synchronous, when the rotational speeds of the rotor speed and the stator electromagnetic field coincide,
asynchronous - with a lagging frequency.
They have different design features, but the general principles of operation, based on the effect of the rotating electromagnetic field of the stator on the rotor field, transmitting rotation to the drive.
They are made for use as coolers for computer devices, starters for cars, powerful diesel stations, combine harvesters, tanks and other tasks. The device of one of these simple models is shown in the picture.
The stator magnetic field in this design is created not by permanent magnets, but by two electromagnets collected on special cores - magnetic cores, around which coils with windings are located.
The magnetic field of the rotor is created by the current passing through the brushes of the collector assembly along the winding laid in the slots of the armature.
AC induction motors
The section of one of the models shown in the picture shows a certain similarity with the previously considered device. Design differences are in the implementation of the rotor in the form of a short-circuited winding (without direct supply of current from the electrical installation to it), called the "squirrel wheel" and the principles of arrangement of turns on the stator.
Synchronous AC Motors
Their windings of the stator coils are located at the same angle of displacement between themselves. Due to this, an electromagnetic field rotating at a certain speed is created.
A rotor electromagnet is placed inside this field, which, under the influence of applied magnetic forces, also begins to move with a frequency synchronous to the rotation speed of the applied force.
Thus, in all considered engine schemes are used:
1. windings of wires to enhance the magnetic fields of individual turns,
2. magnetic cores for creating paths of magnetic flux,
3. electromagnets or permanent magnets.
For individual designs of engines, called collector engines, a current transfer scheme is used from the stationary part to rotating parts through the brush holder assembly.
In all of these technical devices, various malfunctions can occur that affect the operation of a particular engine.
Since the magnetic circuit is created at the factory from plates of special steels assembled with high reliability, breakdowns of these elements are very rare, and even then under the influence of an aggressive environment that is not provided for by the operating conditions or due to unforeseen transcendent mechanical loads on the case.
Therefore, verification of the passage of magnetic fluxes is practically not carried out, and all attention in the event of a malfunction of the electric motors after evaluating the mechanics is drawn to the state of the electrical characteristics of the windings.
How to check the brush assembly of the commutator motor
Each collector plate is a contact connection of a certain part of the continuous winding of the armature and an electric current passes through its connection to the brush.
A working motor in this unit creates a minimum transient electrical resistance that does not have a practical effect on the quality of work and power output. The appearance of the plates is clean, and the gaps between them are not filled with anything.
Engines that have been subjected to severe loads have dirty manifold plates with traces of graphite dust that has accumulated in the grooves and impairs insulation properties.
The engine brushes are pressed against the plates by the force of the springs. Graphite gradually erases during operation. Its rod wears out in length, and the force of pressing the spring decreases. When the contact pressure is weakened, the transient electrical resistance increases, which causes sparking in the collector.
As a result, increased wear of the brushes and copper plates of the collector begins, which can cause engine damage.
Therefore, it is necessary to check the brush mechanism, inspect the cleanliness of the surfaces, the quality of the production of brushes, the working conditions of the springs, the absence of sparking and the appearance of circular fire during operation.
Contamination is removed with a soft cloth moistened with a solution of industrial alcohol. The gaps between the plates are cleaned with ravens from solid non-resinous wood species. The brushes are rubbed with a fine-grained emery cloth.
If potholes or burnt areas appear on the collector plates, the collector is machined and polished to a level at which all irregularities are eliminated.
A well-fitted brush assembly must not create sparks during operation.
How to check the insulation status of the windings relative to the housing
To detect a violation of the dielectric properties of the insulation relative to the stator and rotor, it is necessary to use a megaohmmeter specially designed for these purposes.
It is selected by the magnitude of the output power and voltage.
Initially, the measuring ends are connected to a common terminal of the terminals of the windings and the ground bolt of the housing. In an assembled motor, the electrical contact of the stator and rotor housings is created through metal bearings.
If the measurement shows normal insulation, then this is quite enough. Otherwise, all the windings are disconnected and a insulation violation is searched by measuring and inspecting individual circuits.
The reasons for the poor state of insulation can be different: from mechanical damage to the paint coating layer of wires to high humidity inside the case. Therefore, they must be precisely determined. In some cases, it is good enough to dry the windings, and in others it is necessary to look for places with scratches or scuffs to exclude leakage currents.
One of the most common cases is when voltage is applied to the sample, and it is “standing”, without any signs of “life”. It is not difficult to verify that the mechanical part of the engine is working - just turn its shaft by hand, and a couple of revolutions. If this can be done without any effort, then the product is in good condition. A small backlash (sometimes it is) for some types of electric motors is quite acceptable thing. But if it is significant, then this should already be considered as a deviation from the norm. In this case, complete engine serviceability (even in the absence of other defects) is not necessary.
Supply voltage check
If the mechanical part of the engine is serviceable, then you should proceed to testing the entire electrical circuit. The rated voltage must correspond to the value specified in the passport of the electric motor. This is what you need to make sure by making a measurement on its terminals (outputs). To do this, just remove the cover from the junction box. Why there?
Almost no electric motor is directly connected to the power source. There are always intermediate “links” in the chain. Even in the simplest scheme, there is at least 1 element - a button (toggle switch, AB or something similar). It is impossible to exclude the cable that connects the electric motor to the power source. Perhaps the product itself is normal, and does not start for a completely different reason (breakdown of the circuit breaker, MP, open circuit in the supply wire).
If the test showed that the voltage is supplied, and it meets the standard, then the conclusion is unequivocal - a malfunction in the electric motor.
You need to start with the fact that, as it does not seem strange, literally smell the electric motor. The easiest and most effective way to initially determine its malfunction. In most cases, with violations in the circuit, the temperature inside the case rises, which leads to partial melting of the compound. And this is always accompanied by a characteristic smell.
Darkening of the paint on the electric motor, especially on a separate segment, the appearance of dark sagging in the areas where the covers are attached at the ends of the case is a sure sign of excessive heating.
After removing the "caps" should inspect the inside of the motor from all sides. The melting of the compound will immediately be noticeable. If it “dripped” strongly enough, then you definitely have to deal with the repair of the product - it cannot be considered completely serviceable.
This applies to collector type models. The fact that they are in place does not yet indicate the serviceability of the electric motor. These interchangeable contacts have a certain wear limit, and its real value is visually not difficult to evaluate by their length. As a rule, the permissible output is if the “height” of the brush is at least 10 mm. Although for a particular product should be clarified. But in any case, if there is a suspicion of increased wear, it is better to replace them immediately.
To do this, they are excluded from the scheme. The technique depends on the type of electric motor. Conclusions can be unsoldered or “tilted” by loosening the fixing nuts. Otherwise, it is impossible to test them for integrity. The motor windings are connected into a common circuit (“star” or “triangle”), and testing them in the initial state is pointless - they will all “ring”. Even with a break in the event of a short circuit.
On winding integrity
In fact, each of them is a wire properly laid. All of them are connected in a circuit. Therefore, from the conclusions there should be only one “pair”. So you need to take any of them (after removing all the jumpers) and, alternately, using a multimeter, “ring” with the rest. If, while checking a specific output, the device constantly shows ∞ (when measuring resistance), then in this stator winding there is an internal break. Definitely - in repair.
The technique is identical, and it makes no sense to repeat the test. It is evaluated immediately, in parallel. It is only necessary to take into account that if some terminal “rings” with more than one wire, this means that there is a short circuit between the windings. The same thing - only in the workshop.
In principle, the same. The only difference is that when checking the insulation of the conductors, one probe of the tester is constantly on the motor housing (first you should clean a small “patch” from the paint), and the second is sequentially connected to all conclusions, in turn. If at least once the device shows zero resistance, then this conductor is "short." And in this case, repair is indispensable.
What to consider when checking the engine
- Testing with the "control" (bulb + battery) will not allow the engine to be fully tested. Therefore, it is impossible to unequivocally judge its serviceability with this method.
- There is another malfunction, although it is quite rare - inter-turn closure. It can only be determined using a special device. If after all the checks carried out the electric motor does not start or does not work correctly, then further testing should be entrusted to a professional in a specialized workshop. Verification of the winding resistance values (there are also such recommendations) is a waste of time. Deviations in 1 - 2 Ohm tester may not show (it is worth considering the permissible error in the measurements, depending on the class of the device).
- When choosing a service center (for further repairs), you should pay attention to the prices. Rewinding an electric motor is quite expensive. And if they ask a little for this service, there is something to think about. Several options - insufficient staff qualifications, a simplified procedure, the use of low-quality compound. But in any case, after rewinding, the engine will not last long.
And the last one. It is necessary to calculate what is more profitable - to restore the serviceability of the product or purchase a new one. It depends on the specifics of its operation, the intensity of use, the need for it at some point in time (urgent work, for example). Practice shows that after the electric engine has been in the workshop, in the “wrong hands”, it will not work for more than six months. Checked.
Well, what to do, it's up to you, dear reader. At least, you can already perform the simplest checks of the electric motor for serviceability yourself.
Before diagnosing, you should:
- Switch off the power to the unit. If the resistance measurement is carried out in a circuit connected to the mains, the device will fail.
- Calibrate the device, i.e. set the arrow to zero (the probes should be closed).
- Inspect the engine and find out if it is flooded, if there is a smell of burnt insulation or broken parts, etc.
Asynchronous, commutator, single-phase and three-phase motors are called by the same method, a small difference in the design does not play a special role, but there are nuances that must be taken into account.
The most common faults can be divided into two types:
- The presence of contact in a place where it should not be.
- Lack of contact in the place where it should be.
To begin, consider how to ring a 3-phase electric motor with a multimeter. It has three coils connected in a "triangle" or "star" pattern. Its performance is affected by the reliability of contacts, the quality of insulation and proper winding.
- To begin with, check the short to the case (keep in mind, the value will be approximate, since more sensitive instruments are required for accurate readings).
- Set the measurement values on the multimeter to maximum.
- Connect the probes to each other to make sure the settings are correct and the instrument is working.
- Connect one of the probes to the motor housing, if there is contact, attach the second probe to the housing and follow the readings.
- If there are no faults, alternately touch the probe to output each of the three phases.
- If the insulation is high-quality, the test should show a fairly high resistance (several hundred or thousand megohms).
It must be remembered that when measuring insulation resistance with a multimeter, the readings will be higher than permissible, since the EMF of the device does not exceed 9v. The engine works at 220 or 380v. According to Ohm's law, the value of resistance depends on the voltage, so make a discount on the difference.
Next, check the integrity of the windings by ringing the three ends included in the boron motor. In the presence of a break, a further check does not make sense, since first you need to eliminate this malfunction.
Then check the shorted turns. When connected with a “triangle”, the malfunction indicator will be a larger value at the ends A1 and A3. When connected with a star, the device shows an overestimated value in the A3 circuit.
Knowing how to ring an asynchronous electric motor with a multimeter, you will save time and money, because, perhaps, only minor malfunctions will be revealed, which you can easily fix yourself.
For a more serious and detailed diagnosis, other devices are required that are rarely used in everyday life because of their high cost.
If you could not find the damage with a multimeter, consult a specialist.
Checking the collector motor
Now let's move on to the above nuances, because the engines come in different types. How to ring a collector motor with a multimeter? The scheme for checking it is as follows:
- Turn on the unit per Ohm unit and measure the resistance of the collector lamellas in pairs.
- Then measure the resistance between the armature body and the collector.
- Check stator windings.
- Measure the resistance between the housing and the stator leads.
The inter-turn circuit is determined only by a special device. There is a way to measure the resistance of the armature. Remove the brushes from it and bring the voltage to the plates up to 6V, measure the voltage drop between them.
To test a single-phase motor, ring the operating and starting windings. The resistance of the first should be one and a half times lower than the second.
For example, take a single-phase motor with three terminals, used in washing machines (often the old model). If there is a very large resistance between the ends, then the coils are connected in series. It remains to find the midpoint and thus determine the ends of each of them individually.
Since electric motors are found in every home in household appliances - this is a refrigerator, a vacuum cleaner, and much more - and they break down periodically, it is simply necessary to know how to check a single-phase electric motor with a multimeter. If the breakdown is not too serious, it is impractical to bring the device to the repair shop. And you will have the opportunity to gain experience and gain skills by working with engines of different types and modifications.
Checking the operation of the electric motor
A used and even a new electric motor may have defects. Often, visual inspection is not enough to identify them, and verification of all nodes is required. In this article we will tell you how to check the efficiency of the electric motor yourself, without the help of specialists.
So, what are the steps involved in the verification process, and what should you pay special attention to?
When examining you should be alert for the following points:
- The stand or mounting holes are broken.
- There is dirt, soot, or other substances inside the engine.
- The paint in the middle of the unit has darkened (this is a sign of overheating).
These signs indicate that the engine was either frequently overloaded or operated in unsuitable conditions or without observing the rules.
A metal plate is attached to the outside of the engine, on which the following information about its characteristics is indicated:
- Manufacturer (company name).
- Type of hull (physical and landing dimensions).
- Serial number and model.
- The number of revolutions of the rotor per minute.
- Phase and voltage requirements.
- Connection diagram of the unit to different voltages in order to obtain the desired direction of rotation and speed.
- Current consumption
- Stator type (closed, fan-blown, splash-proof, etc.).
If the appearance of the engine is not suspicious, go on to check the bearings. They are located in niches at both ends of the shaft. Modern machines mainly use ball bearings or brass plain bearings.
The verification procedure is as follows: the unit is placed on a solid surface, the rotor is manually scrolled, while the free hand must be placed on the upper part of the housing.
Uniform, free and quiet rotation of the rotor indicates the health of the engine, and friction, uneven rotation and rattle - about malfunctions.
The permissible rotor play is 3 mm, but ideally it should tend to zero. To determine it, just pull and push the rotor out of the stator by the axis. Overheating of the bearings provokes breakdown of the entire unit, so you need to know how to check the electric motor and, first of all, the health of these parts.
The most common defect of the windings is a short circuit to the housing, which leads to the burning of the fuse. Products designed for 380V can also work with closed windings, since the circuit breaker is triggered, but it is better to avoid this.
To check the windings, you need an ohmmeter. The sequence of your actions should be as follows:
- An ohmmeter is set to resistance measurement mode.
- The probes connect to the Common and Ohm jacks.
- The scale with the highest multiplier is selected.
- The arrow is set to “0” (this item is skipped if you use a digital ohmmeter), while the probes touch each other.
- One of the probes of the device is pressed against the screw for grounding or another metal part of the housing.
- The second probe is connected to all electrical contacts of the machine in turn.
If the arrow of the ohmmeter only slightly deviates from the highest resistance, everything is in order with the motor winding. It is important to ensure that the probes do not touch their hands, as this will affect the accuracy of the measurements.
The next step is to check the windings for an open. Simple single and three phase motors used in industry and households are tested by switching the ohmmeter range to the lowest.
It is necessary to set the arrow to zero and re-measure the resistance between the wires of the unit. The value should be very low. If the device shows a high value, the probability of winding breakage is high.
In this case, the engine will either not work at all or the speed controller will fail.
For fully enclosed, air-cooled engines, the fan is located at the rear, behind a metal grill. Make sure that it is fixed securely and does not “hang out” when turned on. Dirt and debris in the openings of the grill prevent the free movement of air, and this contributes to overheating, but this problem is easily solved by cleaning.
You need to remove the metal cover on the outside of the case, under which there is a capacitor. Visual inspection may reveal the following problems:
- oil leak,
- deformed capacitor housing,
- the presence of holes in it,
- smell of smoke or burning.
For a more detailed check of the capacitor, an ohmmeter is also needed. When the probes and the terminals of the capacitor come into contact, the device must first show a low and then gradually increasing resistance value.
Such changes are due to the fact that a small voltage is supplied from the ohmmeter batteries to the capacitor, which charges it a little. The absence of an increase in the resistance value indicates a malfunction of the node.
If you try the test again, the capacitor should be completely discharged.
Centrifugal switches may be located in this part of the engine for connecting circuits or switching the starting capacitor. Relay contacts must be clean and not burnt. However, to clean them from grease and dirt is not difficult. The mechanism of the switch is checked with a screwdriver - if the spring works freely, then everything is in order.
Pay attention to the type of electric motor and its operating conditions. For work in damp rooms or where possible contact with water should be selected spray models. Open engines should not be installed in heavily soiled rooms. Make sure that the unit operates in the established mode without overloads and regularly check its components.
Knowing how to check the electric motor for serviceability, you can choose a defective and working instance and avoid many problems.
Symptom and sequence of checking the elements of the engine 9a and systems to identify the cause
Symptom Test sequence The cold engine does not start or starts with difficulty 1. Fuel pump 2. Wires and their connections, fuel pump power circuit 3. Fuel filter and fuel lines 4. Pressure disk of the air flow meter and / or distribution plunger of the fuel dispenser-distributor 5.
Position of the pressure disk of the air flow meter 6. Starting nozzle 7. Fuel supply pressure 8. Control pressure 9. Enrichment of the mixture when starting the engine 10. Enrichment of the mixture during engine warm-up 11. Ground and engine connections The engine does not start or does not start with difficulty. 1. Fuel pump 2.
Wires and their connections, fuel pump power circuit 3. Fuel filter and fuel lines 4. Air intake system leaks 5. Pressure disk of the air flow meter and / or the distribution plunger of the fuel dispenser-distributor 6. Position of the pressure disk of the air flow meter 7. Fuel supply pressure 8. Control pressure 9. Fuel system leaks 10.
Idling speed and CO content in exhaust gases 11. Enrichment of the mixture when starting the engine 12. Connections of the engine and the battery to ground. The engine is unstable idling during heating 1. Air intake system leaks2.
Pressure disk of the air flow meter and / or the distribution plunger of the fuel dispenser-distributor 3. Idle control 4. Leakage on the starting nozzle 5. Control pressure 6. Idling speed and CO content in the exhaust gas 7. Enrichment of the mixture during engine warm-up A warm engine is unstable ia idling
Air intake system leaks 2. Pressure disk of the air flow meter and / or the distribution plunger of the fuel dispenser-distributor 3. Idle control 4. Injector leak tightness 5. Control pressure 6. Idling speed and CO content in exhaust gases 7. Enrichment of the mixture during acceleration 8.
Throttle Idle Position Sensor Adjustment Backflashes in the intake manifold 1. Mixture enrichment when the engine warms up 2. Leakage in the vacuum system The engine does not have sufficient throttle response 1. Leakage in the air intake system 2. Pressure disk of the air flow meter and / or the distribution plunger of the fuel dispenser-distributor 3.
Throttle position full load sensor adjustment Flash in exhaust system 1. Start-up nozzle leakage 2. Enrichment of the mixture during engine warming 3. Leak in the fuel system 4. Idling speed and CO content in exhaust gases 5.
Idling controller Ignition misfires during engine load conditions 1. Fuel pump 2. Wires and their connections, fuel pump power circuit 3. Fuel filter and fuel wires 4. Fuel supply pressure 5. Control pressure 6. Enrichment of the mixture at full engine load The engine does not develop full power and does not have sufficient throttle response 1.
Fuel pump 2. Wires and their connections, fuel pump power circuit 3. Fuel filter and fuel lines 4. Fuel supply pressure 5. Control pressure 6. Throttle 7. Enrichment of the mixture at full load Flash in the cylinders after the ignition is turned off 1. Pressure disk of the air flow meter and / or distribution plunger of the fuel dispenser-distributor 2.
Position of the pressure disk of the air flow meter 3. Non-germicity of the starting nozzle 4. Idle regulator Increased fuel consumption 1. Launch nozzle non -hermegicity 2. Control pressure “Failure” of power during acceleration 1. Non-tightness of the air intake system2. Pressure disk of the air flow meter and / or the distribution plunger of the fuel dispenser-distributor 3.
Control pressure 4. Idling speed and CO content in exhaust gases Increased CO content in exhaust gases idling 1. Pressure disk of air flow meter and / or distribution plunger of fuel dispenser-distributor 2. Leakage on the starting nozzle 3. Managing Director 4.
Typical malfunctions of electric motors and methods for their elimination
The most common electrical faults are short short circuits inside the motor windings and between them, winding short circuits on the case, as well as breaks in the windings or in the external circuit (power wires and starting equipment).
As a result of these malfunctions of electric motors the following can occur: inability to start the electric motor, dangerous heating of its windings, abnormal motor speed, abnormal noise (humming and knocking), inequality of currents in separate phases.
Causes of a mechanical nature that cause a disruption in the normal operation of electric motors are most often observed in the incorrect operation of bearings: overheating of bearings, leakage of oil from them, and the appearance of abnormal noise.
The main types of malfunctions in electric motors and the reasons for their occurrence.
Asynchronous electric motor does not turn on (fuses blow or protection trips). The reason for this in slip ring motors may be the shorted position of the starting rheostat or slip rings. In the first case, it is necessary to bring the starting rheostat into the normal (starting) position, in the second case, raise the device shorting the contact rings.
It is also impossible to turn on the electric motor due to a short circuit in the stator circuit. It is possible to detect a short-circuited phase by touch on increased heating of the winding (feeling should be done by disconnecting the electric motor from the mains first), by the appearance of charred insulation, and by measurement.
If the stator phases are connected to a star, then the magnitude of the currents consumed from the network by the individual phases is measured. A phase having short-circuited turns will consume more current than undamaged phases.
When connecting individual phases into a triangle, the currents in two wires connected to the defective phase will have larger values than in the third, which connects only to undamaged phases. For measurements, a reduced voltage is used. When you turn on the asynchronous motor does not budge. The reason for this may be a break in one or two phases of the power circuit.
To determine the breakage point, first examine all the elements of the circuit supplying the electric motor (check the integrity of the fuses). If during an external examination it is not possible to detect a phase failure, then the necessary measurements are performed with a megger. Why the stator is previously disconnected from the mains.
If the stator windings are connected to a star, then one end of the megger is connected to the zero point of the star, after which the other ends of the winding alternately touch the second end of the megger. Присоединение мегомметра к концу исправной фазы даст нулевое показание, присоединение к фазе, имеющей обрыв, покажет большое сопротивление цепи, т. е. наличие в ней обрыва.
Если нулевая точка звезды недоступна, то двумя концами мегомметра касаются попарно всех выводов статора. Touching the megohmmeter to the ends of serviceable phases will show a zero value, touching the ends of two phases, one of which is defective, will show great resistance, that is, a break in one of these phases.
In the case of connecting the stator windings into a triangle, it is necessary to disconnect the winding at one point, and then check the integrity of each phase separately. A phase that has a break is sometimes detected by touch (it remains cold). If a break occurs in one of the phases of the stator during the operation of the electric motor, it will continue to work, but will begin to hum more strongly than under normal conditions.
Find the damaged phase as described above. When the induction motor is in operation, the stator windings become very hot. Such a phenomenon, accompanied by a strong buzz of the electric motor, is observed during a short circuit in any stator winding, as well as when the stator winding is double-closed to the housing.
Working asynchronous electric motor started to buzz. At the same time, its speed and power are reduced. The reason for the violation of the operating mode of the electric motor is a break in one phase.
When you turn on the DC motor, it does not budge. The cause of this can be blown fuses, an open in the power supply circuit, an open resistance in the starting rheostat.
First, they carefully inspect, then check with the help of a megger or a control lamp with a voltage of no higher than 36 V the integrity of these elements. If in this way it is not possible to determine the place of the cliff, proceed to check the integrity of the armature winding.
A break in the armature winding is most often observed at the junction of the collector with the winding sections. By measuring the voltage drop between the collector plates, they find the place of damage. Another cause of this phenomenon may be motor overload.
This can be checked by starting the motor idle, having previously disconnected it from the drive mechanism.
When turned on dc motor fuses blow or maximum protection trips.
The shorted position of the starting rheostat may be one of the reasons for this phenomenon. In this case, the rheostat is transferred to the normal starting position. This phenomenon can also be observed when the rheostat handle is pulled out too quickly; therefore, when the motor is turned on again, the rheostat is output more slowly.
When the motor is operating, increased bearing heating is observed. The cause of increased bearing heating may be an insufficient clearance between the shaft journal and the bearing shell, insufficient or excessive amount of oil in the bearing (check the oil level), oil contamination or the use of oil of inappropriate grades.
In the latter cases, the oil is replaced by first washing the bearing with gasoline. When starting up or during operation of the electric motor, sparks and smoke appear from the gap between the rotor and the stator. A possible cause of this phenomenon may be the impact of the rotor on the stator. This occurs when bearings are significantly triggered.
When the DC motor is operating, sparking is observed under the brushes. The reasons for this phenomenon can be improper selection of brushes, weak pressing them on the collector, insufficiently smooth surface of the collector and improper arrangement of brushes. In the latter case, it is necessary to move the brushes, placing them on a neutral line.
During operation of the electric motor, amplified vibration is observed, which may occur, for example, due to insufficient strength of fixing the electric motor to the foundation plate. If vibration is accompanied by overheating of the bearing, this indicates the presence of axial pressure on the bearing.
Malfunction Possible reason Remedy Brushes sparkle, some brushes and their fittings become very hot and burn Brushes poorly sanded Sanded brushes Brushes cannot move freely in the holder of the brush holder - the clearance is small Set the normal clearance between the brush and the clip O, 2 — O, 3 mm Contact rings and brushes are dirty or oily Clean the rings and brushes with gasoline and remove any dirt. Slip rings have an uneven surface Grind or polish slip rings Weakly pressed brushes to slip rings Adjust brush pressure Uneven current distribution between brushes Adjust brush pressure, check contact of traverse, conductors, brush holders Uniform overheating of stator active steel Mains voltage above rated Reduce voltage to nominal, increase ventilation Increased local heating of active steel at idle and rated voltage There are local faults between the individual active steel sheets. Remove burrs, short-circuit and treat sheets with insulating varnish Lost connection between tie bolts and active steel Restore the insulation of the coupling bolts The engine with a phase rotor does not develop a rated speed with a load Bad contact in rotor soldering Check all solder rotors. In the absence of malfunctions during an external inspection, rations are checked using the voltage drop method Rotor winding has poor contact with slip rings Check the contacts of the conductors at the places of their connection with the winding and slip rings Bad contact in the brush apparatus. Loose mechanism contacts for rotor short circuit Grind and adjust brush pressure Poor contact in the connections between the starting rheostat and slip rings Check the serviceability of the contacts at the points of connection of the connecting wires to the terminals of the rotor and starting rheostat An engine with a phase rotor moves without load - when the rotor circuit is open, and when starting with a load, it does not develop revolutions Short circuit between adjacent collars of the frontal joints or in the rotor winding Eliminate touching adjacent clamps The rotor winding in two places is grounded After determining the short-circuited part of the winding, replace the damaged coils with new ones. Squirrel cage motor does not move Fuses blown, circuit breaker defective, thermal relay tripped Troubleshoot When the engine starts, the contact rings overlap with an electric arc Contact rings and brush are dirty Carry out cleaning High humidity Provide additional insulation or replace the engine with another suitable environmental Open in rotor joints and in rheostat itself Check connection
Diagnostics of electrical equipment malfunctions
Diagnostics of electrical equipment malfunctions
A typical electric circuit may include a main electric element, various switches, relays, electric motors, fuses, fuse links or circuit breakers related to this element, wiring and contact sockets used to connect the main element to the battery and the body ground.
Before you start troubleshooting on any electrical circuit, carefully study the appropriate circuit in order to clearly understand its functional purpose.
The circle of troubleshooting is usually narrowed by gradually identifying and eliminating normally functioning elements of the same circuit.
In the event of the failure of several elements or circuits, the most likely cause of failure is a blown fuse or a violation of contact with the "ground" (different circuits in many cases can be shorted to one fuse or ground terminal).
Electrical failures are often explained by the simplest reasons, such as corrosion of the contacts of the connectors, failure of the fuse, blown fuse or damage to the relay. Visually check the condition of all fuses, wiring, and contact connectors of the circuit before proceeding to a more detailed check of the health of its components.
If you use diagnostic tools for troubleshooting, carefully plan (in accordance with the attached electrical diagrams) at which points in the circuit and in what sequence the device should be connected for the most effective troubleshooting.
The main diagnostic tools include an electric circuit tester or a voltmeter (you can also use a 12-volt test lamp with a set of connecting wires), an open circuit indicator (probe), including a lamp, its own power source and a set of connecting wires.
In addition, to start the engine from an external source (the battery of another car), you should always have a set of wires in the car equipped with crocodile clips and preferably with an electric circuit breaker.
They can be used to bypass and connect various elements of electrical equipment for circuit diagnostics.
As already mentioned, before you start checking the circuit with the diagnostic equipment, determine the location of its connection from the diagrams.
Supply Voltage Checks carried out in case of violation of the electrical circuit. Connect one of the wires of the circuit tester to the negative terminal of the battery or ensure good contact with the car body.
Connect the other wire of the tester to the connector pin of the circuit under test, preferably the one closest to the battery or fuse.
If the tester indicator lamp lights up, there is a supply voltage on this segment of the circuit, which confirms the serviceability of the circuit between this point in the circuit and the battery. Proceeding in the same way, examine the rest of the chain.
The detection of a supply voltage violation indicates a malfunction between this point in the circuit and the last of the previously tested ones (where the supply voltage was). In most cases, the cause of the failure is to loosen the connectors and damage the contacts themselves (oxidation).
Search for a short circuit. One of the methods for finding a short circuit is to remove the fuse and connect a probe lamp or voltmeter instead. There should be no voltage in the circuit. Twitch the wiring while observing the probe lamp.
If the lamp starts to blink, somewhere in this wiring harness there is a short to ground, possibly caused by grinding the wire insulation. A similar check can be carried out for each of the components of the electric circuit by turning on the corresponding switches.
Checking the reliability of contact with the "mass". Disconnect the battery and connect one of the wires of the probe lamp with an autonomous power source to a point with a known good ground contact. Connect the other lamp wire to the test harness or connector pin. If the lamp lights up, contact with "weight" is in order (and vice versa).
Check for open conducted to detect breaks in the electrical circuit. After turning off the power to the circuit, test it with a probe lamp with an independent power source. Connect the probe wires to both ends of the circuit. If the test lamp illuminates, there is no open circuit.
If the lamp does not light up, then this indicates the presence of an open circuit. Similarly, you can check the health of the switch by connecting the probe to its contacts.
When the switch is turned to the “ON” position, the probe lamp should light up.
Localization of the cliff.
When diagnosing a suspected break in a section of an electrical circuit, it is rather difficult to visually find the cause of the malfunction, since it can be difficult to visually check the terminals for corrosion or the quality of their contacts due to limited access to them (usually the terminals are closed by the connector body).
A sharp jerking of the body of the wiring harness pads on the sensor or the wiring harness itself in many cases leads to the restoration of contact. Do not forget about this when trying to localize the cause of the circuit failure, suspected of having an open. Unstable failures can result from oxidation of the terminals or poor contact quality.
Diagnosing faults in electrical circuits is not a difficult task, provided thatSharePinTweetSendSendSend