Nine common reasons for compressor damage

2024-07-26

The motor of semi-hermetic piston compressors is in direct contact with the refrigerant and refrigeration oil, and operates under a certain pressure and temperature for a long time. The working environment of fluorine-resistant motors is relatively harsh. Moreover, during the operation and maintenance of the unit, if it is used and maintained improperly, it often causes the motor to burn out, making the system unable to work properly. And for previously repaired units, their motors are still prone to burnout. The main reasons for this type of burnout failure of refrigeration compressor motors are as follows.

Nine common reasons for compressor damage

Low supply voltage
When starting and operating at a low supply voltage, the current passing through the motor is very large, causing the thermal relay to open and close frequently, eventually leading to the melting and adhesion of the contacts, resulting in the failure of the thermal relay. Under the action of a large current, the winding binding wire of the motor is burned out, and the outer insulation layer of the electromagnetic wire is burned, causing some windings to short circuit and abnormal winding resistance. Low supply voltage, insufficient power supply capacity, other high-power electrical appliances on the power supply line, too thin or faulty power supply line diameter selection may all cause refrigeration compressor failures.
Motor power control circuit failure
Power switches and contactors are important components of the compressor motor control circuit. Unreasonable selection and lack of maintenance can damage the best refrigeration compressor. It is extremely important to correctly select switches and contactors according to the load.

It should be particularly emphasized that if the contactor contacts are welded together, all controls (such as high and low pressure control, oil pressure control, defrost control, etc.) that rely on the contactor to disconnect the compressor power circuit will fail completely, and the refrigeration compressor will be in an unprotected state. Therefore, when the motor burns out, it is essential to inspect the contactor, as the contactor is an often overlooked but important reason for motor burnout.

Unbalanced three-phase current causing motor failure
Abnormal voltage and phase loss can easily destroy the motor. The imbalance of three-phase voltage shall not exceed 5%. Unbalanced three-phase voltage can cause unbalanced three-phase current of the motor. One phase (or two phases) has excessive current, causing the winding to heat up first and breakdown or burn out, and the current of other windings will also rise sharply and burn out. During the operation of the motor, the current value of any one phase and the average value of the three-phase current shall not exceed 10%. The result of voltage imbalance, the percentage point of unbalanced voltage during normal operation can cause 4-10 times the current imbalance of its percentage point.
Abnormal load and locked rotor
The compressor motor load includes the load required to compress the gas and the load required to overcome mechanical friction. Excessive compression ratio and excessive pressure difference can make the compression process more difficult. The increase in friction caused by lubrication failure and the locked rotor of the motor in extreme cases greatly increase the load of the motor.

The torque of the motor of high-power semi-hermetic compressors is very large. Local wear generally does not cause locked rotor, but the motor output power will increase within a certain range as the load increases, resulting in more serious wear and even severe damage such as cylinder seizure and connecting rod fracture. The current during locked rotor (locked rotor current) is approximately 4-7 times the normal working current. Thermal protection can protect the motor during locked rotor, but it generally does not respond quickly (PTC is slightly faster) to prevent the winding temperature change caused by locked rotor, thereby reducing the insulation performance of the enameled wire.

Poor oil return in the refrigeration system
Due to poor oil return in the refrigeration system, the compressor will be short of oil and unable to deliver sufficient refrigeration oil to each lubrication part, increasing the friction at each lubrication part (bushing, piston). This can cause the piston and crankshaft to seize within a short period of time, causing a sharp increase in the current of the compressor motor and subsequently burning out the motor coil.

The reasons for poor oil return are diverse, such as: no oil return bend, liquid return, blocked throttle valve, blocked oil return hole, inappropriate hole size, or system overload operation, as well as leakage causing system oil shortage.

High water content in the refrigeration system
As the coils of the refrigeration compressor motor are soaked in the refrigerant and refrigeration oil for a long time, when the water content in the refrigeration system increases, water reacts with the refrigeration oil and refrigerant to produce acidic substances, which can corrode the insulation layer of the motor winding coil under certain temperature and pressure. In addition, a high water content in the refrigeration system will cause the insulation resistance of the winding coil to decrease. Under the influence of electromagnetic force, mechanical force and temperature, chemical reactions occur, causing cracking, brittleness and other aging phenomena in the insulation layer of the coil, thereby causing interphase or turn-to-turn breakdown and short circuit of the motor winding coil and ultimately causing the motor to burn out.

The sources of water in the refrigeration system include excessive water content in the refrigerant and refrigeration oil, which is brought in during filling; when the refrigeration system is opened for maintenance, it is exposed to the air for a long time and absorbs water from the air; after maintenance, the refrigerant and refrigeration oil are filled without sufficient drying and timely replacement of the desiccant of the filter.

Operation with lack of refrigerant
Due to long-term operation with a lack of refrigerant, the temperature of the compressor cylinder becomes higher and higher, and the expansion deformation becomes larger and larger, resulting in hard friction between the cylinder and the piston. The temperature also becomes higher and higher, causing carbonization of the refrigeration oil, resulting in blackening of the inner cavity and piston. In severe cases, the piston may be pulled, knocked or seized. This causes a large current in the motor, and the continuous large current can burn out the motor winding.
Vacuum operation
Due to vacuum operation, the temperature of the compressor cylinder rises rapidly, and the winding coil of the refrigeration compressor motor heats up, causing tiny bubbles to form in the insulation of the coil. At this time, the outside of the winding is in a high vacuum, which easily causes the bubbles to expand and the insulation layer to fall off, causing motor failure. The winding coil of the motor will be damaged in about two minutes of vacuum operation, making the compressor unable to operate normally.

The reasons for the vacuum operation of the compressor are generally that the power is turned on without opening the valve, the compressor is used to vacuum the pipeline system directly, or the operation is carried out without opening the low-pressure valve.

Foreign matter entering the compressor
Due to the entry of foreign matter into the compression chamber of the compressor, cracks occur during the reciprocating motion of the piston and cylinder, increasing the friction. Foreign matter moves at high speed in the cylinder, damaging the suction and exhaust valve plates. The temperature rise of the cylinder elongates the groove of the piston, causes knocking or seizure, causing motor failure. The metal debris mixed in the winding is the culprit for short circuits and low ground insulation resistance.

The failures of semi-hermetic refrigeration compressor motors are related to the manufacturing, installation, use and maintenance of the motors. Their burnout is generally the result of the combined action of multiple factors. If attention is paid to the methods during installation, repair and maintenance, the possibility of burnout failure will be greatly reduced. To avoid the quickly repeated burnout of the repaired compressor motor, the cause of the failure must be resolved, and no new failure factors should be introduced during the repair. Therefore, the correct installation and use of refrigeration compressors, as well as reasonable daily maintenance, can prevent the occurrence of unfavorable factors and are the fundamental methods to avoid damage to the refrigeration compressor motor.