Stator fault of the hottest HV motor

2022-08-02
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High voltage motor stator fault

the high voltage motor in the small workshop of Shandong Shiheng Special Steel Group Co., Ltd. drives the rolling mill load. Due to the design of the workshop, the high voltage motor and the distribution cabinet are in the same room without isolation measures, resulting in a bad operating environment for the motor, high ambient temperature, a lot of dust, long-term overload operation of the motor, frequent water accumulation in the air duct, which seriously threatens the safe operation of the high voltage motor. As the company is short of spare parts for high-voltage motor, once the high-voltage motor is burned, it will bring huge losses to the workshop

1 common stator faults

(1) the motor starts frequently with load in a short time. The large starting current accelerates the insulation aging of the stator winding, resulting in insulation damage during the starting process. For example, other parts of the leakage detected by the sealed test container may burn out the motor

(2) motor lead insulation breakdown or lead cable head damage short circuit. The main reasons are that the selected lead is of low specification, poor quality (insulation eccentricity, low insulation withstand voltage), long operation time and frequent startup, resulting in high contact resistance at the lead connection and aging insulation failure. Most of the cable head failures are caused by lax manufacturing and maintenance, but if there are parts problems in the equipment measurement process, the relevant standards shall be implemented, the cable head mechanical damage is caused by rough operation, and the motor failure is caused by the poor operating environment (humidity, dust, etc.)

(3) due to the damage of the mechanical part of the load carried by the motor or the damage of the motor bearing (bearing bush), the motor is locked or overloaded to burn the motor

(4) there is a lot of dust at the installation position of the motor, resulting in a large amount of dust inside the motor, poor heat dissipation of the motor, which seriously causes friction between the motor stator and rotor, resulting in temperature rise and burning of the motor

(5) the voltage of the power supply system is low, the starting torque of the motor is small, and the motor cannot run. It is started for many times continuously, resulting in the motor over-current burning the motor:

(6) the circuit breaker of the high-voltage switchgear is not maintained in place, and the closing resistance is large, resulting in the asynchronous three-phase closing, and the operating overvoltage at the moment of closing, Cause insulation breakdown of motor winding and damage to motor:

(7) the iron core looseness causes the beneficial conditions for foreign trade export of China's plastic extruder to continue to increase. During operation, the silicon steel sheet protrudes, or burrs pierce the insulation layer, and the end binding is poor. Due to the vibration generated during the starting and running of the motor, the coil is relatively displaced, the motor noise is large, and the discharge phenomenon occurs. The mechanical strength of the winding is reduced, the insulation is invalid, and finally the insulation breakdown and short circuit of the motor are caused

(8) the motor relay protection was improperly set, and the protection was not adjusted in time during motor capacity expansion or transformation, especially the low-voltage zero sequence protection was not installed, and the protection setting was not calibrated and adjusted as required, resulting in small motor protection setting and continuous startup failure

(9) the motor starting time limit is improperly set (12 s set in this unit), causing the motor to burn out or fail to reach the rated speed

2 preventive measures

(1) avoid frequently starting the motor in a short time, and strictly implement the starting requirements for large and medium-sized motors. Generally, two continuous cold static starts are allowed, and the time interval shall not be less than 20 min. one hot static start is allowed. If it is necessary to start again, it shall be carried out after cooling to normal temperature. Hot state refers to the state when the heat energy has not dissipated after the motor is shut down

(2) use cables of appropriate specifications, and regularly check the insulation strength of cables and cable wiring

(3) insist on measuring the vibration of high-voltage motor bearing at least twice a day, and constantly monitor the temperature change of bearing (bearing bush)

(4) make full use of special research and development, and use the maintenance time to purge the interior of the motor with dry compressed air

(5) when the voltage of the power supply system is low and unstable, avoid frequently starting the motor

(6) clean the high-voltage switchgear at least twice a year, and invite the power company to adjust the synchronism of the circuit breaker

(7) the high-voltage motor shall be regularly overhauled and maintained, and the winding shall be used for on-site maintenance according to the service conditions. At the same time, the winding absorption ratio shall be measured, and the voltage withstand test and DC resistance measurement shall be conducted. The high-voltage motor shall be treated with silver welded joints

(8) according to the starting condition of motor, install heavy load and light load and set the time limit value of stator and rotor switch to achieve the best cooperation

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