What are the repair methods of motor winding fault?

The winding is an integral part of the motor. How to maintain the motor winding if it is prone to aging, moisture, heat and corrosion after long-term use? The following is the maintenance method of motor winding fault compiled by Zhishi Bian Xiao, hoping to help you.

Repair method of motor winding fault 1. Winding grounding

Refers to the grounding caused by insulation damage between winding and iron core or bushing.

1, failure phenomenon

The shell is charged, the control circuit is out of control, and the winding is short-circuited and heated, which leads to the motor not operating normally.

2. the reason

The winding is damp, which reduces the insulation resistance; Long-term overload operation of motor; Harmful gas corrosion; Metal foreign bodies invade the winding and damage the insulation; When rewinding the stator winding, the insulation is damaged and touches the iron core; The winding end contacts the base of the end cover; Friction between stator and rotor leads to insulation burn; Lead insulation damage and shell collision; Overvoltage (such as lightning strike) leads to insulation breakdown.

3. Inspection method

(1) observation method. Visually inspect the insulation of winding ends and slots, and observe whether there are any signs of damage and blackening, and if there are any, it is the grounding point.

(2) Multimeter inspection method. Check with a low-resistance multimeter. If the reading is small, it will be grounded.

(3) Megger method. According to different grades, choose different megohmmeters to measure the insulation resistance of each group of resistors. If the reading is zero, it means that the winding is grounded. However, it is necessary to judge the motor insulation from damp or accidental breakdown by experience. Generally speaking, where is the pointer? 0? When it swings irregularly, it can be considered as having a certain resistance value.

(4) Test lamp method. If the test light is on, it means that the winding is grounded. If sparks or smoke are found somewhere, it is the winding grounding fault point. If the light is dimmed, there is a ground fault in the insulation. If the light is off, but sparks appear when the test bar is grounded, it means that the winding has not yet broken down, but it is seriously wet. Hardwood can also be struck at the edge of the shell, hitting a place, indicating that the current is off, and that place is the grounding point.

(5) Current burn-through method. When a voltage regulating transformer is connected to the power supply, the grounding point will heat up rapidly, and the place where insulation smokes is the grounding point. It is especially important to note that the small motor should not exceed twice the rated current for less than half a minute; The large motor is 20%-50% of the rated current or gradually increase the current, and the power will be cut off as soon as the grounding point smokes.

(6) Grouping elimination method. For the grounding point in the core wire and serious combustion, the burning copper wire fuses with the core wire. The method adopted is to divide the grounded one-phase winding into two halves, and so on, and finally find out the grounding point.

In addition, there are high voltage test method, magnetic needle exploration method and power frequency vibration method. I won't introduce it here.

4. Processing method

(1) If the winding is grounded due to moisture, it should be dried first. When cooled to about 6070℃, the insulating paint should be poured first and then dried.

(2) When the winding end insulation is damaged, re-insulate it on the ground, paint it, and then dry it.

(3) When the winding grounding point is in the slot, the winding should be rewound or some winding elements should be replaced.

Finally, different megohmmeters are used for measurement to meet the technical requirements.

Second, the winding short circuit

Insulation damage is caused by excessive motor current, excessive power supply voltage change, single-phase operation, mechanical collision, poor manufacturing and other reasons, including turn-to-turn short circuit, winding short circuit, inter-pole short circuit, winding phase-to-phase short circuit and so on.

1. Fault phenomenon

The uneven distribution of ion magnetic field and unbalanced three-phase current aggravate the vibration and noise of the motor during operation. In severe cases, the motor can't be started, but a large short-circuit current is generated in the short-circuit coil, which leads to the rapid heating and burning of the coil.

2. the reason

The motor is overloaded for a long time, which makes the insulation aging lose its insulation function; Insulation damage caused by wire embedding; The winding is damp, which reduces the insulation resistance and leads to insulation breakdown; During the molding process, the insulating materials at the ends and between layers are not filled or damaged correctly; The insulation of the end connection wire is damaged; Insulation breakdown caused by overvoltage or lightning strike; Friction between rotor and stator winding ends leads to insulation damage; Foreign metal objects fall into the motor, resulting in excessive oil pollution.

3. Inspection method

(1) external observation method. Observe whether the junction box and winding end are burnt, and the winding still has dark brown and odor after overheating.

(2) Temperature detection method. Run at no-load for 20 minutes (stop immediately if any abnormality is found), and touch with the back of your hand whether all parts of the winding exceed the normal temperature.

(3) charged experimental method. When measuring with ammeter, if a certain phase current is too large, it means that there is a short circuit in this phase.

(4) Bridge inspection. When measuring the DC resistance of each winding, the general difference should not exceed 5%. If it exceeds 5%, the phase with small resistance has a short circuit fault.

(5) Short circuit detector method. If the winding is short-circuited, the steel plate will vibrate.

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

(7) Pressure drop method. After the three windings are connected in series, low-voltage safe alternating current is applied, and the group with small reading is found to have short circuit fault.

(8) Current methods. When the motor is running at no load, measure the three-phase current first, and then measure the two-phase comparison when it is changed. If it does not change with the change of power supply, the single-phase winding with large current is short-circuited.

4. Short circuit treatment method

(1) The short circuit point is at the end. The short-circuit points can be separated by insulating materials, or the insulated wires can be repackaged, repainted and dried again.

(2) The short circuit is in the wire slot. After softening, find out the short circuit point for repair, put it back in the tank, and then paint it to dry.

(3) For each phase winding with short-circuit turns less than112, when the turns are connected in series, the short circuit is completely cut off, and the conductive parts are connected to form a closed loop for emergency use.

(4) When the number of turns at the winding short-circuit point exceeds112, all windings shall be dismantled and rewound.

The reason of inter-turn short circuit of motor winding is 1. The motor is seriously corroded by toxic and harmful gases in the place of use, and the winding insulation decreases after corrosion, resulting in turn-to-turn short circuit or grounding.

2. The use site is wet, the dust is serious, the oil pollution invades and accumulates on the winding for a long time, which leads to the winding insulation reduction and the winding insulation damage, resulting in its own short circuit fault.

3. During the maintenance of the motor drawout rotor, the winding was accidentally damaged by the drawout rotor, and the insulation of the winding was not properly repaired after the damage, and then the turn-to-turn short circuit or winding grounding occurred.

4. The insulation of the motor that has not been used for a long time decreases due to poor storage, or the motor that has been put into use without necessary inspection and test after long-distance transportation may also cause the turn-to-turn short circuit fault of the motor.

5. During wire embedding operation, the motor manufacturer accidentally scraped the outer insulation of the electromagnetic wire or melted solder fell into the winding, resulting in the latent fault of the winding, and suddenly the turn-to-turn short circuit fault occurred after running for a period of time.

6. Excessive grid power or lightning overvoltage intrudes into motor windings from overhead lines, resulting in insulation breakdown, etc.

Local repair process of winding turn-to-turn short circuit 1. Check and find the short circuit point. Detect the phase-to-phase, turn-to-turn and grounding fault points of motor windings respectively, and find out the winding fault points. In general, the winding of motors above 160KW is made of flat copper wire with glass fiber color, and the short-circuit current at the fault point is very large, which is several times of the normal working current. So the fault point can be seen intuitively. If you can't see it intuitively, you can use a double-arm bridge to detect it.

2. Take out the short-circuit coil by heating. After finding out the fault point, put the closed electric furnace plate on the core of the fault point for heating. The power of electric furnace plate is above 2KW. According to the power of the motor and the length of the iron core, it is decided to use several heating electric furnace plates for heating.

The heating time depends on the size of the motor, as long as the temperature reaches the point where the slot wedge of the motor can be pulled out after softening. After pulling out the slot wedge, take out the winding insulation paper separately with a special slot cleaning shovel, and then take out the winding flat copper wire coil with short circuit between turns. As long as the temperature is properly controlled, it is easier to take out the old wire part.

3. Clean the ditch. After the faulty flat copper wire is taken out, the original insulating material of the groove is removed in the hot state. The metal melting point of iron core breakdown caused by turn-to-turn short circuit can be removed with an electrician's chisel tool, and then deburred with an angular grinding wheel or a file until smooth.

4. Weld the new coil. The turn-to-turn short circuit point of flat copper wire is in the straight part of the slot or at the two ports of the magnetic slot. The welding points of the new copper flat wire replaced locally are all on the prismatic straight lines at both ends. If multiple wires are damaged and replaced, the welding points should be separated by a certain distance to form trapezoidal welding.

Before welding, file the welding points of the welded copper flat wire into a groove butt joint with a flat file, and weld with gas welding. It is best to choose a small gas welding torch and use a welding wire with high silver content for welding. When welding, separate the winding coils with heat-resistant asbestos board to avoid burning the winding. After welding, use a flat file to file the burr or excess metal at the welding place to the size of flat copper wire.

5. Insulation treatment and embedding.

The flat copper wire formed by welding is covered with two layers of glass ribbon. Add 0.5 mm thick glass fiber slats between turns or phases. The trench insulation adopts 0.35mm DMD composite insulation material. The flat copper wire at the replacement part is colored with glass fiber, coated with 1032# insulating paint, and then properly heated to be non-sticky and embedded in the groove. The groove is made of glass fiber slats with a thickness of 2mm.

6. Try it before drying and painting.

After the insulation between phases, turns and ground is qualified, the varnish shall be subjected to pressure test before drying. The withstand voltage of the test is 2UN+ 1000 volts, and the test time is 1 minute. Phase-to-phase and grounding withstand voltage shall be conducted once each.

The stator parts are dried. Our self-made drying box, the drying temperature is 100℃, and after four hours of constant temperature, the whole winding is dipped in paint, and the model of insulating paint is 1032#. More varnish should be poured on the local repair parts, and it must be soaked thoroughly. After painting, secondary drying is carried out. Dry at 100℃ for four hours. After drying, after the motor is cooled, at room temperature, the withstand voltage test after painting is carried out again. The withstand voltage is 2UN+1 000V1min. After the withstand voltage test, the insulation to ground and interphase can reach 150M? Above.

7. Complete the machine test after assembly.

(1) After assembly, test the insulation resistance between phases and ground of the motor. Tested with a 500-volt megohmmeter, the insulation can reach more than 150 megohmmeter.

(2) No-load running test. In order to ensure the safety of initial operation after local repair, we use a three-phase voltage regulator to gradually increase from low voltage to full voltage. At the same time, the balance value of three-phase current is tested. After no-load rated voltage operation is not less than 1 hour and there is no abnormal phenomenon, do the second overpressure operation test. Excess rated voltage 10%, no-load running time 1 min. Pay attention to the operation.

(3) Do rated current test under no load. When the motor is at a low potential, clamp the shaft head of the motor with a pipe wrench so that it cannot rotate, and then slowly raise the voltage. Pay attention to observe that the three-phase ammeter stops boosting when it reaches the rated current, and record the rated three-phase current value.

(4) After the test of the whole machine is completed, use a 500-volt megohmmeter to test the insulation values between phases and ground.

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