If the burnt-out coil of the motor meets the following two characteristics, it can be determined that it is a phase loss burnout.
① When the motor is connected in a star configuration, two phase coils burn out while one phase coil remains intact.
② When the motor is connected in a delta configuration, one phase coil burns out while the other two phase coils remain intact.
Causes of phase loss in oil pump motor
1. Power supply phase loss
Before connecting a three-phase power supply to an AC motor, if one or two phases of the power supply are missing (the power supply has a problem, and one of the fuses in the three-phase fuse has burned out), it can cause the oil pump motor to fail to start or to operate abnormally.
2. Loose terminals in the motor junction box
One phase of the three-phase stator winding of the oil pump motor is disconnected, resulting in a phase loss during motor operation.
3. Loose or broken connection at the joint.
A loose connection in the power supply line or a breakage caused by external force can also cause a phase loss in the motor.
4. Phase loss caused by control circuit
Contactors and relays in the control circuit may develop oxidation on their contacts after prolonged use, leading to poor contact or wear and tear on their operating mechanisms. These electrical components may malfunction due to the impact of the motor's starting current (typically 5-7 times the rated current), vibrations from the equipment, or jamming or malfunction of the moving parts, resulting in a phase loss in the stator winding.
5. Insulation aging
After a considerable period of operation, the insulation of the stator windings of an oil pump motor may age (when the ambient temperature during motor operation is too high for an extended period, the power supply voltage is too high, or the load is too large), causing phase-to-phase or turn-to-turn short circuits in the motor stator windings, and one or more phases of the motor stator windings may also disconnect.
Solution to phase loss in oil pump motor
1) The coils of three relays or contactors are connected in a Y0 configuration to monitor the phase voltage of the three phases. The normally open contacts of the three relays are connected in series and then connected in series into the contactor coil circuit of the motor. In this way, if all three phases are normal, all three relays will be energized, all three normally open contacts will be closed, and the contactor coil circuit of the motor can work normally. If a phase is missing, at least one relay will not be energized, the contactor coil circuit of the motor will be disconnected, the contactor will not be able to be energized, or it will be forcibly disconnected, thus providing phase loss protection.
2) Currently, there are many types of dedicated phase loss protection relays in China. The principle is similar to that described above, which can simplify your wiring and reduce the space occupied in the control cabinet.
3) Use a smart motor protector, which is small in size and has multiple functions. In addition to phase loss protection, it can also have instantaneous overcurrent protection, overcurrent protection, excessive starting time protection, unbalanced current protection, etc.
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