company news about Did You Know That These Four Situations Will Cause Compressor Failure?

1. Insufficient cooling
Compressors with higher power are generally returned air cooled. The lower the evaporation temperature, the smaller the mass flow of the system tends to be. When the evaporation temperature is very low (beyond the manufacturer's specifications), the flow rate is not enough to cool the motor, and the motor will operate at a higher temperature. Air-cooled compressors (generally not more than 10HP) have little dependence on return air, but have clear requirements for compressor ambient temperature and cooling air volume.
Large refrigerant leaks can also reduce the mass flow of the system and affect the cooling of the motor. For example, the compressor exhaust temperature is too high to protect it.
Compressors are available in a safe operating range. The main safety considerations are the loading and cooling of the compressor and motor. Due to the different prices of compressors in different temperature zones, it was common for the domestic refrigeration industry to use compressors beyond the range in the past. The situation has improved markedly with the growth of expertise and the improvement of economic conditions.
2. The power supply is out of phase and the voltage is abnormal
Abnormal voltage and lack of phase can easily destroy any motor. The range of power supply voltage variation cannot exceed ±10% of the rated voltage. The voltage imbalance between the three phases should not exceed 5%. The high-power motor must be supplied independently to prevent low voltage caused by the start-up and operation of other high-power equipment on the same line. The motor power cord must be able to carry the rated current of the motor.
If the compressor is running when phase loss occurs, it will continue to operate but with a large load current. The motor windings will overheat quickly, and the compressor will normally be thermally protected. When the motor winding is cooled to the set temperature, the contactor will be closed, but the compressor will not start, and the stalled rotor will appear, and it will enter the dead cycle of "stalled-thermal protection-stalled".
In order to prevent the compressor from running out of phase, the compressor with three-phase power supply is provided with a phase sequence protector, and the phase sequence protector has two functions, one is to prevent the reverse operation of the compressor from the wrong phase sequence, and the other is to prevent the compressor from running out of phase.
The difference in the windings of modern motors is very small, and the difference in phase current when the power supply is balanced in three phases is negligible. Ideally, the phase voltages are always equal, and damage caused by overcurrent can be prevented by simply connecting a protector to either phase. In practice, it is difficult to ensure the balance of phase voltages. For example, the nominal 380V three-phase power supply, the voltages measured at the compressor terminal are 380V, 366V, and 400V, respectively, the average three-phase voltage is 382V, and the maximum deviation is 20V, so the voltage unbalance percentage is 5.2%.
As a result of voltage imbalance, the load current imbalance in normal operation is 4-10 times the percentage of voltage imbalance. In the previous example, a 5.2% unbalanced voltage could cause a 50% current unbalance.
3. AC contactor problem
AC contactor is one of the important components in the motor control circuit, and unreasonable selection can destroy the best compressor. It is extremely important to select the contactor correctly according to the load.
AC contactors must be able to meet demanding conditions such as fast cycling, continuous overload, and low voltage. They must have a large enough area to dissipate the heat generated by the load current, and the contact material must be chosen to prevent soldering in the event of high currents such as actuation or stalled rotors.
In order to be safe and reliable, the compressor contactor should be disconnected from the three-phase circuit at the same time. Copeland does not recommend disconnecting two-phase circuits.
The rated current of the contactor cannot be lower than the rated current on the nameplate of the compressor. The contactor with small specifications or poor quality cannot withstand the high current impact of compressor starting, stalled rotor and low voltage, and is prone to single-phase or multi-phase contact shaking, welding and even falling off, causing motor damage.
The contactor with jitter contacts frequently starts and stops the motor. Frequent start-up of the motor, huge starting current and heat generation will aggravate the aging of the winding insulation. Each time it starts, the magnetic torque causes the motor windings to move and rub against each other. If there are other factors (such as metal chips, lubricating oil with poor insulation, etc.), it is easy to cause short circuits between windings. Thermal protection systems are not designed to prevent such damage. In addition, jitter contactor coils are prone to failure. If the contact coil is damaged, it is prone to a single-phase state.
If the contactor is selected to be too small, the contacts cannot withstand arcing and high temperatures due to frequent start-stop cycles or unstable control loop voltages, and may weld or fall off the contact holder. The welded contacts will create a permanent single-phase state, allowing the overload protector to be continuously cycled on and off.
It should be particularly emphasized that after the contactor contact is welded, all controls (such as high and low pressure control, oil pressure control, defrost control, etc.) that rely on the contactor to disconnect the power supply circuit of the compressor will be invalid, and the compressor will be in an unprotected state. Therefore, when the motor burns out, the contactor must be inspected. Contactors are an important and often forgotten cause of motor damage.
After the AC contactor contacts are adhered to, the compressor will work regardless of whether the motherboard has an output or not, and it is inevitable that the compressor will be damaged if there is no protection for a long time. When replacing the compressor, we must find the cause of the compressor damage, and we must check whether the AC contactor is normal, whether there is phase loss and adhesion?
4. The compressor lacks oil
Lack of oil is one of the compressor failures that are easy to identify, when the compressor is short of oil, there is little or no oil in the crankcase, and it is easy to burn out the compressor.
The root cause of oil shortage is not how much oil runs to the compressor and how fast it is, but the poor oil return of the system. Installing an oil separator allows for fast oil return and extended compressor runtime without oil return. The evaporator and return lines must be designed with oil return in mind. Maintenance measures such as avoiding frequent start-ups, regular defrosting, timely replenishment of refrigerant, and timely replacement of worn piston components can also help with oil return.
The migration of the reflux and refrigerant will dilute the lubricating oil and is not conducive to the formation of oil film, the failure of the oil pump and the blockage of the oil circuit will affect the oil supply and oil pressure, resulting in the lack of oil on the friction surface, and the high temperature of the friction surface will promote the decomposition of the lubricating oil and make the lubricating oil lose its lubricating ability. Insufficient lubrication caused by these three problems also often leads to compressor damage.