Several common reasons for burning compressor windings

Common compressor failures mainly cover the following three types: one is the burning of the motor; the second is the liquid strike; and the third is the lack of oil caused by refrigeration oil.

Compressor failures can be divided into two categories: motor failure and mechanical failure, among which mechanical failures involve crankshaft, connecting rod, piston, valve plate, cylinder head gasket and other components. Mechanical failures often cause the motor to run overload and even cause blockage, which is one of the main reasons for motor damage.

The main manifestations of motor damage include damage to the insulating layer of the stator winding (short circuit) and circuit breaking. After the stator winding is damaged, it is often difficult to detect in time, which may eventually lead to the winding burn. After the winding is burned, some phenomena or direct causes will be covered up, making subsequent analysis and cause investigation difficult.

Comprehensive analysis from multiple aspects, there are six main reasons for winding burning:

Abnormal load and blockage;

Metal chips cause winding short circuit;

There is a problem with the contactor;

The power supply phase loss and voltage abnormality;

Inadequate cooling;

In fact, motor damage is often the result of a combination of factors, which is more common.

Factor 1: Abnormal load and blockage

The motor load includes the load required for compressed gas and the load required for overcoming mechanical friction. When the pressure ratio is too large or the pressure difference is too large, the compression process becomes more difficult; lubrication failure will lead to increased friction resistance, and in extreme cases, the motor will also be blocked, which will greatly increase the motor load. Among them, lubrication failure and friction resistance increase are the primary factors for abnormal loads.

Diluted lubricant oil, overheating of lubricant oil, coking and deteriorating lubricant, and oil shortage will destroy the normal lubricating state and lead to lubricating failure. Diluted lubricant by the return liquid will affect the formation of normal oil film on the friction surface, and will even wash away the original oil film, thereby increasing friction and wear.

Overheating of the compressor will cause the lubricant to become thinner or even coke at high temperatures, affecting the formation of normal oil film. If the oil return system is not smooth and the compressor lacks oil, it will naturally not be able to maintain normal lubrication. The crankshaft rotates at high speed, and the connecting rod piston and other components move at high speed. The friction surface without the protection of the oil film will heat up quickly. The local high temperature will cause the lubricating oil to evaporate or coke quickly, making lubrication of the part more difficult, and may cause local severe wear within a few seconds.

Power supply phase loss and voltage abnormality

Abnormal voltage and phase loss can easily destroy any motor.

The power supply voltage variation range cannot exceed ±10% of the rated voltage. The voltage imbalance between the three phases cannot exceed 5%. High-power motors must be powered independently to prevent low voltages when starting and running other high-power devices on the same line.

The motor power cord must be able to carry the motor's rated current. If the compressor is running when the phase is missing, it will continue to operate but will generate a large load current. The motor windings will overheat quickly, and under normal circumstances, the compressor is heat-protected.

When the motor winding cools to the set temperature, the contactor will close, but the compressor cannot start, and a blockage occurs, and an "blockage-heat protection-blockage" dead cycle occurs. The calculation method of the percentage of voltage imbalance is: the ratio of the maximum deviation value of the phase voltage to the average three-phase voltage and the average three-phase voltage.

Therefore, correctly installing and using the compressor and performing reasonable daily maintenance can prevent adverse factors from occurring. This is the fundamental way to avoid damage to the compressor motor.

Shanghai KUB Refrigeration Equipment Co., Ltd.

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