Principle and Debugging of Compressor Phase Sequence Protection | Fault Protection for Phase Loss, Reverse Phase, and Voltage Imbalance
The three-phase compressor motor must be equipped with a phase sequence protector to identify power reverse phase, phase loss, and three-phase voltage imbalance. In case of a fault, the contactor should be locked to prevent the motor from reversing and damaging the oil pump.
The semi closed piston compressor oil pump relies on the forward rotation of the motor to drive. When the motor rotates in reverse, the oil pump stops supplying oil. Running continuously for 30 minutes without lubrication will cause the bearing to lock and pull the cylinder.
The default configuration for three-phase semi enclosed units with a capacity of more than 3 horsepower in Xiteluo is the phase sequence protection module. Single phase low-power models do not have an oil pump and generally do not have phase sequence protection devices.
The three-phase voltage imbalance exceeds 5%, the motor winding heats up unevenly, and the local temperature rises above the normal value of 15K. The insulation aging rate of the winding significantly accelerates after long-term operation.
The phase sequence protector is only a protective device and cannot repair power supply problems. Repeatedly reporting phase sequence faults is mostly caused by virtual connections in the circuit, uneven transformer loads, and poor contact of the neutral line.
The stability of overseas power grids varies greatly, with voltage fluctuations and three-phase imbalances occurring frequently in remote construction sites in Africa and Southeast Asia. Phase sequence protection is the first line of electrical defense for compressors.
Many electricians directly short-circuit the phase sequence protection and forcibly start the machine during debugging, which can operate for a short period of time. Once there is a phase loss or reversal, the compressor will burn out directly, and the maintenance cost will be extremely high.
Screw refrigeration compressors also rely on forward rotation. When the rotor rotates in reverse, it not only has no compression capacity, but also the oil separation and return structure fails, causing a large amount of refrigeration oil to rush into the system and block the heat exchanger.
After the wiring of the phase sequence protector is completed, it is necessary to cut off the power and exchange two phase wires for simulation testing to confirm that the protector can reliably cut off the circuit and avoid protection failure.
Maintenance inspections require regular measurement of three-phase current. If the difference in three-phase current exceeds 10% of the rated current, it is necessary to investigate issues with the line joints, circuit breaker contacts, and power supply transformers.
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FAQ
What is the most direct harm of piston engine reverse rotation? The oil pump reverses and stops supplying oil, and the bearings lack lubrication to pull the cylinder.
2. What is the safe upper limit of three-phase voltage imbalance? Try to keep the imbalance within 5%.
Can phase sequence protection solve the problem of voltage imbalance? It can only trigger an alarm and shut down, and cannot repair the power supply.
4. Can the phase sequence protection be short circuited during startup? Short circuiting is strictly prohibited as it can easily cause irreversible damage to the compressor.
What happens when the screw machine reverses? No cooling is generated, the oil return system fails, and there is severe oil leakage.
Which compressors generally do not have phase sequence protection? Single phase low-power oil-free model.
7. How to verify if the phase sequence protector is functioning properly? Swap two phase lines to test if the shutdown is locked.
