Motor winding fault analysis and processing method

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Motor winding fault analysis and processing method

The winding is an integral part of the motor. Aging, moisture, heat, erosion, foreign matter intrusion, and external force will cause damage to the windings. Motor overload, undervoltage, and overvoltage can also cause winding failures. Winding faults are generally divided into winding grounds, short circuits, open circuits, and wiring faults. Now explain the phenomenon of failure, the reasons for the cause and the inspection method.

Winding ground

Refers to grounding caused by damage to the windings and the core or to the insulation of the enclosure.

1, the phenomenon of failure

Enclosure electrification, control circuit out of control, winding short-circuit heat, resulting in the motor can not operate normally.

2, the reason

Insulation resistance decreases due to moisture in the windings; Long-term overload operation of the motor; Corrosion of harmful gases; Ingress of metal foreign materials into the windings to damage the insulation; Insulation damage to the stator winding when rewinding the iron cores; End caps of the windings touch the base; Insulation burns due to stator and rotor friction Leading line insulation damage collided with the shell; overvoltage (such as lightning) makes insulation breakdown.

3. Inspection method

(1) Observation method. Visually inspect the insulation at the ends of the windings and in the raceway for signs of damage and charring, and if so, the grounding point.

(2) Multimeter inspection method. Use a multimeter to check for low impedance and the reading is small, then ground.

(3) Megaohmmeter method. According to different levels, different megohmmeters are used to measure the insulation resistance of each group of resistors. If the reading is zero, it indicates that the winding is grounded, but it is determined by experience based on the experience that the insulation of the motor is damp or breakdown due to an accident. The pointer oscillates arbitrarily at "0" and it is assumed that it has a certain resistance value.

(4) Test light method. If the test light is on, it means that the winding is grounded. If a spark or smoke is found somewhere, it is a winding ground fault point. If the lamp is slightly bright, the insulation has a grounding breakdown. If the lamp does not light, but the test rod is also grounded when the spark, indicating that the winding has not yet penetrated, but severely damp. Hardwood can also be tapped on the edge of the shell's mouth, knocked to a place such as a light off, indicating that when the current off, then there is the ground point.

(5) Electric current burning method. With a voltage regulator transformer, after the power supply is connected, the grounding point will quickly heat up, and the insulation smoke will be the grounding point. Special attention should be paid to the fact that small motors must not exceed twice the rated current and the time should not exceed half a minute; large motors should be 20%-50% of the rated current or gradually increase the current, and should be powered off immediately when the grounding point is smoked.

(6) Group elimination method. For the grounding point inside the core and the burning is severe, the burned copper wire is fused with the iron core. The method used is to divide the grounded one-phase winding into two halves, and so on, and finally find the grounding point.

In addition, there are high-pressure test method, magnetic needle exploration method, industrial frequency vibration method, etc., which will not be introduced here.

4. Treatment method

(1) The grounding of windings caused by moisture should be dried first. When cooling to about 60-70°C, pour the insulation paint and dry it.

(2) When the insulation at the end of the winding is damaged, re-insert the insulation at the grounding, paint, and then dry.

(3) When the winding ground point is in the slot, the winding should be re-wound or some of the winding components should be replaced.

Finally, use different megohmmeters to measure and meet the technical requirements.

Winding short circuit

Due to excessive motor current, excessive power supply voltage fluctuations, single-phase operation, mechanical bumps, poor manufacturing, etc., insulation damage is caused, and the windings are short-circuited by windings, short-circuited between windings, short-circuit between windings, and short-circuit between windings.

1. Failure phenomenon

The magnetic field distribution of ions is not uniform, and the three-phase current is unbalanced, which makes the vibration and noise of the motor intensify. In severe cases, the motor cannot start, and a large short-circuit current is generated in the short-circuit coil, causing the coil to rapidly heat and burn.

2. Cause

Long-term overloading of the motor causes insulation aging to lose insulation; damage caused by inserting wires; insulation breakdown caused by windings dampening insulation resistance; damage to the ends and interlayer insulation material when not matted or shaped; insulation damage of the end connection wires Overvoltage or lightning strikes the insulation breakdown; rotor and stator winding ends rub against each other to cause insulation damage; metal foreign objects fall into the motor and there is too much oil.

3. Inspection method

(1) External observation method. Observe whether the junction box and the winding end are burnt. After the windings overheat, leave a dark brown color and smell.

(2) Temperature inspection method. No-load operation for 20 minutes (stop immediately when abnormality is found), touch the windings to check if the parts exceed the normal temperature.

(3) electricity test method. With ammeter measurement, if the current of a phase is too large, there is a short circuit in the phase.

(4) Bridge inspection. Measure the winding DC resistance, the general phase difference should not exceed 5% or more, if exceeds, then the resistance has a short circuit fault.

(5) Short-circuit detector method. If there is a short circuit in the measured winding, the steel plate will vibrate.

(6) Multimeter or Megohmmeter method. Measure the insulation resistance between any two phase windings. If the reading is very small or zero, it means that there is a short circuit between the two phases.

(7) Voltage drop method. After the three windings are connected in series, they are connected to low-voltage safe alternating current, and a small set of readings has a short-circuit fault.

(8) Current method. When the motor runs at no load, the three-phase current is measured first, and the two-phase measurement is replaced and compared. If the change does not change with the power supply, the one-phase winding with a large current has a short circuit.

4. Short-circuit processing method

(1) The short-circuit point is at the end. Insulating materials can be used to separate the short-circuit points, and the insulated wires can also be re-wrapped and then painted and re-dried.

(2) Short circuit in the slot. After it is softened, find the short-circuit point repair, put it back into the slot, and then paint and dry it.

(3) For each phase winding with less than 1/12 of the short circuit turns, cut off all the short-circuit lines when the number of turns is connected, and connect the conducting parts to form a closed circuit to supply them for emergency use.

(4) When the number of turns in the winding short-circuit point exceeds 1/12, the winding must be completely removed.

Winding open circuit

Due to poor welding or the use of corrosive flux, after welding, it may not be cleaned. It may result in pot welding or loosening. The wire may be burned when the wire is short-circuited or short-circuited or ground fault caused by mechanical stress or collision. When one or several wires in the wire are short-circuited, the other wires increase in temperature due to the increase of the current, causing the winding to heat and open circuit. It is generally divided into a phase winding end breakage, a turn-to-turn short circuit, a parallel branch circuit break, multiple conductors and a burnout, and a rotor break cage.

1. Failure phenomenon

The motor cannot start, the three-phase current is unbalanced, there is abnormal noise or vibration, and the temperature rise exceeds the allowable value or smoke.

2. Cause

(1) Break or create quality problems during inspection and maintenance.

(2) Wrong welding of each component of the winding, pole (phase) group, and wiring and lead wires such as the lead wire, long-term operation overheating and desoldering.

(3) The windings are damaged or broken due to mechanical and electromagnetic forces.

(4) The windings are seriously scorched or broken due to short circuit and grounding between turns.

3. Inspection method

(1) Observation method. Most of the breakpoints occur at the end of the winding, see if there is a fold, and if there is a break in the joint.

(2) Multimeter method. Using a resistance file, a "Y" type connection is made by connecting one bar to the center point of the "Y" shape, and the other one is connected to the first end of the three-phase winding in turn. The infinite one phase is the break point. After the short open connection of the delta connection method, each group of windings is measured separately. Infinity is the disconnection point.

(3) Test light method. The method is the same as before, and the unlit phase is an open circuit.

(4) Megaohmmeter method. A phase whose resistance tends to infinity (that is, not a zero value) is a trip point.

(5) Ammeter method. When the motor is running, the three-phase current is measured by the current meter. If the three-phase current is unbalanced and there is no short circuit phenomenon, the one-phase winding with smaller current has some short-circuit faults.

(6) Bridge method. When the resistance of one phase of the motor is greater than that of the other two phases, it indicates that the phase winding has partial open circuit faults;

(7) Current balance method. For "Y" type connection, the three-phase windings can be connected in parallel and the low-voltage and high-current alternating current can be connected. If the current difference in the three-phase winding is greater than 10%, the small current end is open circuit; for "△" For the type of connection, one contact of the stator winding is first opened, and then a low-voltage and large-current is passed through one by one, in which a phase with a small current is an open circuit.

(8) Broken cage detector inspection method. When checking, if the rotor is broken, the millivolt reading should be reduced.

4. Open circuit processing method

(1) When the circuit is broken at the end, it shall be firmly welded after being connected, covered with insulating material, put on the insulating tube, tied and then dried.

(2) Windings New windings should normally be replaced due to severe burn-out of windings due to interturn, phase-to-phase short circuits and grounding.

(3) Emergency handling is performed for the break point in the groove, which belongs to a small number of break points. A breakout point method is used to find the break point, and it is used after the winding is disconnected and the insulation is qualified.

(4) The caged cages can be repaired by welding, cold-bonding or strip change.

Wrong winding

Wrong winding results in an incomplete rotating magnetic field, resulting in difficult start-up, unbalanced three-phase current, and large noise. If it is not handled in time, it will burn the winding. There are mainly the following situations: One or more coils in a certain polar phase are embedded or connected head to tail incorrectly; the polar (phase) group is reversed; the winding of one phase is reversed; the windings of multiple parallel windings are connected incorrectly; "Y" wrong connection.

1, the phenomenon of failure

The motor cannot be started, the no-load current is too large or unbalanced, the temperature rise is too fast or there is severe vibration, there is a lot of noise, and the fuse is blown.

2, the reason

Misconnect the "△" type into "Y" type; one phase of the three phase winding is reversed during maintenance; the decompression start is inappropriate selection of tap position or internal wiring error; the winding connection is wrong when the new motor is offline; The motor failed to judge correctly.

3 maintenance methods

(1) Ball method. If the ball rotates and rolls along the inner circumferential surface of the stator, it means that it is correct, otherwise the winding will be miswired.

(2) Compass method. If the windings are not connected incorrectly, then in one phase winding, when the compass passes through the adjacent pole (phase) group, the polarity of the fingers should be reversed, and the polar (phase) groups of adjacent phases in the three phase windings are also On the contrary, if the polarity direction is constant, it indicates that there is a pole (phase) group reverse connection; if it is indefinite, there is a reversed coil in the phase group.

(3) Multimeter voltage method. According to the wiring diagram, if there is no indication on the two measured voltmeters, or if there is one reading and one reading at a time, it means that the windings are connected reversely.

(4) Common methods include dry battery method, milliammeter remanence method, and motor steering method.

4. Treatment method

(1) If a coil or coil group is connected reversely, the no-load current has a large imbalance and should be returned to the factory for repair.

(2) Leading line errors should be correctly judged before and after reconnection.

(3) The decompression start error should be checked against the wiring diagram or schematic diagram, and carefully re-wiring.

(4) After the new motor is disconnected or reconnected to the new winding and the wiring is wrong, it shall be sent to the factory for repair.

(5) When the stator windings are connected in opposite phase, the reversed phase current is particularly large. According to this characteristic, faults can be found and repaired.

(6) When the "Y" type is connected to a "△" type or the number of turns is insufficient, the no-load current is large and should be promptly corrected.

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