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Analysis of compressor common faults -- motor burnout

Release date:2017-06-26 Author: Click:

Motor compressor (hereinafter referred to as compressor) failure can be divided into motor failure and mechanical failure (including crankshaft, connecting rod, piston, valve plate, cylinder head pad, etc.). Mechanical fault often makes the motor overload or even block, is one of the main reasons for motor damage.

Motor damage is mainly manifested by stator winding insulation failure (short circuit) and circuit breaking。 Stator winding damage is difficult to find in time, which may eventually cause winding burnout。 After the winding is burned, some phenomena or direct causes of burning are concealed, which makes it difficult to analyze afterwards and investigate the cause。

However, the operation of the motor can not be separated from the normal power input, reasonable motor load, good heat dissipation and winding insulation insulation protection. From this several aspects, it is not difficult to find the reason for the winding of the following six types: (1) abnormal load and locked rotor; (2) metal winding short circuit caused by chip; (3) contactor; (4) the power phase voltage abnormality; (5) insufficient cooling compressor (6); vacuum. In fact, multiple factors contribute to motor damage more commonly.

1. abnormal load and stall

The motor load includes the required load of the compressed gas and the load required to overcome the mechanical friction。 When the pressure ratio is too large or the pressure difference is too large, it will make the compression process more difficult; and the friction resistance caused by lubrication failure increases, and the motor blocking in extreme cases will greatly increase the motor load。

Lubrication failure and friction resistance increase are the primary causes of load anomalies. Liquid dilution, lubricating oil, lubricating oil overheating, lubricating oil, coking, deterioration, and lack of oil will destroy the normal lubrication, leading to lubrication failure. When the liquid is diluted, the lubricating oil affects the formation of the normal oil film on the friction surface, and even washes away the original oil film to increase friction and wear. Overheating of the compressor will cause the lubricating oil to become thinner at high temperature or even coking, which will affect the formation of the normal oil film. System return oil is not good, the compressor lack oil, naturally can not maintain normal lubrication. The crankshaft rotating speed, high speed rod piston, no friction surface oil film protection will be rapidly warming, local high temperature lubricating oil rapid evaporation or coking, make the lubrication more difficult, a few seconds can cause local severe wear. Lubrication failure, local wear, so that the crankshaft rotation requires greater torque. Small power compressor (such as refrigerator, air conditioner compressor) because the motor torque is small, lubrication failure often occurred after blockage (motor cannot rotate), and enter the "blocking thermal protection - blocking" dead cycle, the motor burned only a matter of time. While the power of semi closed compressor motor torque is large, local wear will not cause blockage, the motor power will be in a certain range with the load increases, causing more serious wear, and even cause the bite (cylinder piston card in the cylinder), connecting rod fracture and other serious damage.

The current (locked rotor current) during blocking is about 4-8 times the normal running current. At the start of the motor, the peak current can approach or reach the blocking current. Since the discharge resistance is proportional to the square of the current, the current at startup and blocking will cause the winding to heat up rapidly. Thermal protection protects the electrodes while blocking the rotor, but generally does not respond quickly, and does not prevent winding changes due to frequent starts. Frequent starting and abnormal load make the winding withstand high temperature test, which will reduce the insulation performance of enameled wire.

In addition, the required load of compressed gas will increase with the increase of compression ratio and pressure difference. Therefore, the use of high temperature compressor for low temperature, or the low temperature compressor for high temperature, will affect the motor load and heat dissipation, is inappropriate, will shorten the service life of the electrode.

If the insulation performance of the winding becomes worse, if there are other factors (such as metal chip, conductive circuit, acid lubricating oil, etc.), it will easily cause short circuit and damage.

After the motor is burnt, the damage of the winding is covered, which makes it difficult to analyze the fault。 However, the root cause of compressor motor damage will not disappear。 The abnormal load caused by poor lubrication or failure or blockage, lack of heat, will shorten the life of the winding winding; with a metal chip is provided for variable circuit; welding contactor will make the compressor protection cannot be performed; power motor that runs appear abnormal, will destroy any motor fundamentally; compressor vacuum, may cause internal post discharge。

Unfortunately, these adverse factors will lead to each other: abnormal load and high current blocking off contactor may lead to welding; arc welding or single contact will cause the phase imbalance or single phase; phase imbalance will cause heat; heat caused by a lack of wear; wear will have metal scraps。。。

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