The function of the motor protector is to provide comprehensive protection control for the motor. Overcurrent, undercurrent, phase failure, stall, short circuit, over voltage, under voltage, leakage, three-phase unbalance, overheating, grounding, bearing wear, When the rotor is eccentric, the winding is aged to give an alarm or protection control.
Common types of motor protectors
1. Thermal relay: ordinary small-capacity AC motor, working condition is good, there is no occasion of severe working conditions such as frequent starting; due to poor precision, reliability cannot be guaranteed, it is not recommended.
2. Electronic type: detection of three-phase current value, set the current value using potentiometer or pull code switch, the circuit is generally analog, using anti-time or time-limited operating characteristics. The protection functions include overload, phase loss, stall, etc. The fault type is displayed by an indicator light, and the running power is displayed by a digital tube.
3. Intelligent type: The three-phase current value is detected, and the protector uses the single-chip microcomputer to realize the intelligent comprehensive protection of the motor, integrating protection, measurement, communication and display. The setting current is digitally set and operated by the operation panel button. The user can modify various parameters on the spot according to the specific conditions of the motor. The digital tube can be used as the display window or the large-screen liquid crystal display can support multiple communication protocols. Such as ModBUS, ProfiBUS, etc., the price is relatively high, used for more important occasions; high-voltage motor protection uses intelligent protection devices.
4. Thermal protection type: The thermal component is embedded in the motor, and the protection is good according to the temperature of the motor winding. However, when the motor capacity is large, it needs to be used together with the current monitoring type to avoid the temperature rising sharply when the motor is blocked. The motor winding is damaged due to the hysteresis of the temperature measuring element.
5. Magnetic field temperature detection type: buried in the motor magnetic field detection coil and temperature measurement components, according to the internal rotating magnetic field changes and temperature changes in the motor protection, the main functions include overload, stall, phase loss, overheat protection and wear monitoring The protection function is perfect, and the disadvantage is that the magnetic field detecting coil and the temperature sensor need to be installed inside the motor.
