The function of the motor protector (also known as the motor protector) is to fully protect the motor. When the motor has overtime start, overcurrent, undercurrent, open phase, locked rotor, short circuit, overvoltage, undervoltage, leakage (grounding), Three-phase imbalance, overheating, bearing wear, stator and rotor eccentricity, external fault, automatic start after power on, and inverse time limit, alarm or protection device.
【working principle】
The motor is damaged due to electrical reasons such as overload, phase loss, inter-layer short-circuit and line-to-line short-circuit, ground leakage of the coil, and instantaneous overvoltage inflow, or due to mechanical reasons, such as locked rotor, motor rotating body encounters When it is solid, heat conduction occurs due to bearing wear or lack of lubricating oil, which damages the motor.Due to abnormal operation or stoppage or damage, it will cause production loss or the manpower loss during the stop time cannot be compared with the replacement cost of the motor itself. The loss is huge, then we need to protect the motor effectively to ensure the normal production run.
Three-phase motor protector
For electrical faults, whether it is over-current or over-voltage, the main reason is that the current increases instantaneously and exceeds the load current value of the motor and causes damage..According to this principle, the motor protector protects the motor by monitoring the current value change of the two-phase (three-phase) circuit of the motor. For overvoltage and low voltage, it protects the motor by detecting the voltage change between the motor phases..
Its basic principle and working process:
The sensor linearly reflects the current change of the motor to the sampling port of the protector. After rectification and filtering, it is converted into a DC voltage signal proportional to the motor current and sent to the corresponding part for comparison processing with the given protection parameters. Then it is processed by the single chip microcomputer loop to push the power loop to make the relay act.
When the current of the motor increases due to the overload of the driving part, the voltage signal obtained from the current sensor will increase. When this voltage value is greater than the setting value of the protector, the overload circuit works, and the RC delay circuit undergoes a corresponding (adjustable) delay. When the output relay is activated, the contactor cuts off the main circuit.The working principle of the motor protector of the functional part such as undervoltage and phase loss protection is basically the same.
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