In the operation of vacuum pump asynchronous motor, due to many reasons, there are often various failures, which affect the production. Therefore, it is very important to correctly use and maintain the operation of the motor, to understand the main phenomenon of motor failure, to limit the expansion of the fault, and to eliminate it in time.

1. Preparation before starting

Before starting a new motor or a motor that has not been operated for a long time, even if the insulation resistance of the winding to the frame and its three-phase winding is good, it must be dried. Because the measured insulation resistance can not indicate the turn to turn condition of the winding, even when the coil has a high insulation resistance to the ground and its phases, there may still be moisture inside the coil. If the motor is powered on without drying, the insulation will be damaged. Before starting the newly installed motor, the following conditions should be checked:

The garbage and dust shall be removed from the machine room.

Check the condition of dust filter and cooler (if not required).

Carefully check the accessible interior of the motor, check whether there are foreign matters inside the motor, and blow the interior with dry compressed air (no more than 200 kPa). If there is no compressed air, you can use the hand wind box to blow. To prevent damage to the coil insulation, do not use metal nozzles.

The motor needs to be dried.

Check whether the line voltage and frequency conform to the voltage value and frequency value shown on the motor nameplate (voltage charge difference is 1%, frequency charge difference is ± 1%); check whether all outlet terminals of the motor are correctly connected to the line according to the corresponding line connection method.

In a motor with a voltage of 220 / 380V, it is necessary to check whether the position of the connecting piece on the outlet end of the outlet box is correct. For 380V, it should be Y connection, 220V should be △ connection, correct connection piece.

Check that the nuts of the contact bolts and foot and bearing bolts are tightened and that they are mechanically secure.

If the motor is disassembled before installation, it is necessary to check whether the air gap between the stator and rotor is uniform with a feeler gauge. The deviation of air gap should not exceed 10% of the average value of one side air gap. When checking the sliding bearing, clean the bearing with kerosene, and wash the bearing in the oil until the oil is clear.

The lubricating oil of sliding shaft lubricated by oil ring shall be injected into bearing with turbine oil (for high-speed motor) or mechanical oil (for low-speed motor) to reach the specified oil level. No. 3 lithium grease is used for ball bearing and roller bearing, and special lithium grease (No. 1 lithium grease and 3% molybdenum disulfide) is used for two pole motor.

Check whether the bearing assembly is good, rotate both ends of the motor shaft, whether the rotor rotates freely and the sound is normal. When using sliding bearing, the axial flow of the rotor is within the range of 2-3mm on each side. Check the brush device on the collector ring and the brush lifting operating mechanism. The pressure on the brush working face is about 15 ~ 20KPa. Check whether the brush conductive wires on the collector ring collide with each other. Check whether all surfaces of all brushes are close to collector ring, and check protection and signal instruments (signal oil meter and thermocouple, etc.). Check the grounding condition of motor base and cable shell lead.

Check the insulation resistance of the motor with a megameter, and the measured value shall not be lower than the value obtained by the following formula.

2. Inspection in use

2.1 motor

During the use of motor, attention should be paid to its cleaning, especially the cleaning of coil. No matter the inside and outside of the motor, it is not allowed to get dirty, and there is no water and oil falling into the motor.

According to the site conditions, the interior of the motor should be carefully inspected regularly. Blow the dust away with compressed air. Dust should be blown out from the inside of the motor, not from one part to another. The collector ring, brush and wire should be clean. Small metal objects, broken wires, etc., should not be stacked next to the motor to avoid falling into the interior of the motor.

2.2 bearings

Oil leakage of sliding bearing is not allowed, because oil drop on collector ring and coil will affect conductivity and damage insulation. After running for a week, pour out the lubricating oil, wash the bearing with kerosene, and then inject new lubricating oil.

2.3 brush and collector ring

The collector ring should have a good polished surface, and the brush should be close to the collector ring. If necessary, the graphite brush can be ground with glass sandpaper, and the copper graphite brush can be ground with sandpaper. During grinding, the abrasive paper or glass sand paper is cut into narrow strips, and placed between the collector ring surface and the brush, which is close to the collector ring surface (ARC), and should be pulled along the rotation direction of the motor. At the same time, the electric brush can only be pressed by the spring on the brush holder, not by hand.

2.4 air gap

In order to ensure the uniformity of the air gap of the motor and avoid the rotor touching the stator, the air gap must be checked regularly (on both sides of the motor).

2.5 bolts

The tension of all bolts must be checked frequently, and special attention should be paid to the bolts fixing the insulating part and rotating part.

2.6 ventilation

The cooling air should be clean and the relative humidity of the environment should not be greater than 70%. For th type motor, the relative temperature is less than 95%, because dust will block the air duct and contaminate the winding, so as to reduce the air volume and insulation resistance, overheat the motor and reduce its working safety.

2.7 dust filter

If pipe ventilation is used, pay attention to whether the cooling air is clean, whether the dust filter is blocked, and whether all connections are tight. The dust filter should be cleaned regularly, and the lark glue liquid oil should be replaced for the lark glue liquid air dust filter (the coke dust filter needs to change the coke.

3. Common faults of AC motor and its treatment

The faults of AC motor are various. The same fault may be different, and the same phenomenon may be caused by different reasons. Only by grasping the essence through the phenomenon can we judge accurately and suit the remedy to the case.

Faults can be divided into two categories: mechanical and electromagnetic: the former, such as chamber sweeping (the outer circle of the rotor rubs against the inner circle of the stator) and bearing wear, while the latter mainly occurs on the winding. The principle of inspection is first the outside and then the inside, and the first mechanical and then electromagnetic.

To judge the fault, we should first understand the situation of the fault, especially the change before and after the fault. Observe whether the motor has abnormal conditions, such as whether the end cover cover, fan, end cover and casing are loose, cracked and damaged, whether the air path is blocked, whether the rotating shaft is bent, whether there is special smell, and whether it is the smell of burning insulation paint or the smell of melting and evaporation of lubricating grease, or others. Turn the rotor by hand and listen to the friction of foreign matters or the rubbing sound of stator and rotor core. If the motor can still be started, pay attention to whether there is abnormal sound during starting and running. Touch each part of the motor by hand to check whether there is local overheating (such as the temperature near the bearing chamber is hotter than other parts) and vibration.

The winding damage of three-phase asynchronous motor is caused by phase loss. The so-called phase loss operation refers to that one phase of the motor in operation is cut off suddenly, and the motor is still working. Due to the excessive current, the winding is bound to be burned. When phase loss occurs, the sound of the motor is very abnormal. If it is found, the power supply should be cut off immediately for inspection.

In addition, winding short-circuit fault is more common, winding short-circuit can be divided into one phase winding to ground short-circuit, namely grounding, two-phase winding phase to phase short-circuit and one-phase winding itself inter turn short-circuit.

When the insulation between the winding resistance and the iron core is damaged, the grounding fault will occur. Due to the high current, the grounding winding may be burnt out or the fuse of the fuse will be blown, and then the phase loss operation will be caused. If the casing is not reliably grounded in advance, the electric shock accident may be caused by the shell being charged. It is not difficult to determine the ground fault by megger or series lamp. In addition to insulation damage, phase to phase short circuit can also be caused by metal foreign matters (such as iron chips, aluminum chips, screws, wire heads, solder beans, etc.) inside the motor. Turn to turn short circuit is a short connection between the conductors of a phase winding itself, so the effective turns of the winding are reduced and the current is too large. Turn to turn short circuit can be checked by using transformer principle.