Common types of motor protectors
1. Thermal relay: ordinary small-capacity AC motor, good working conditions, no frequent working conditions, etc. Due to poor precision, lack of phase loss protection function, reliability cannot be guaranteed, it is not recommended.
2, motor protector: detection of three-phase current value, set the current value using potentiometer knob or pull code switch operation, the circuit is generally analog, using anti-time limit operating characteristics. Protection functions include overload, phase loss, three-phase unbalance, and other fault protection. The fault type is displayed by indicator light. For example, the UL-E2 series is such a motor protector.
3. Comprehensive intelligent type: The three-phase current value is detected, and the motor protector uses the single-chip microcomputer to realize the intelligent comprehensive protection of the motor, integrating protection, measurement and display. The setting current is digitally set and operated by the operation panel button. The user can modify the various parameters on the spot according to their actual use requirements and protection conditions. The digital tube is used as the display window, or the large screen LCD display price is relative. Higher, for more important occasions, the current high-voltage motor protection is intelligent.
4. Thermal protection type: The thermal element is embedded in the motor, protected according to the temperature of the motor, protected generally, and has temperature hysteresis. However, when the motor capacity is large, it needs to be used together with the current monitoring type to avoid the motor stalling. The temperature rises sharply, and the motor winding is damaged due to the hysteresis of the temperature measuring element.
5. Magnetic field temperature detection type: The magnetic field detection coil and temperature probe are embedded in the motor, and the protection is based on the change of the internal rotating magnetic field of the motor and the change of temperature. 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, which is difficult to use in a complicated field environment, and is currently only suitable for laboratory use.
Selection of motor protector type under motor working conditions
1. For the working conditions are not high, the operation control is simple, the monitoring and management are relatively random, and the single-machine independent operation motor with little impact on the production is stopped. The ordinary type protector can be used. Because the ordinary type protector has a simple structure, the wiring is installed on the site. It is simple, convenient, and cost-effective.
2, for the working conditions are very high, safety and continuity are critical, and the degree of automation is high, and requires special personnel to control, monitor, manage, MCC system that needs network monitoring, should choose medium-to-high-end, full-featured Motor protector.
3. For explosion-proof motors, eccentricity due to bearing wear may cause high temperature friction at the explosion-proof gap and cause explosion hazard. The wear status monitoring function should be selected. For large-capacity high-pressure submersible pumps, due to the difficulty in inspection and maintenance, the wear status monitoring function should also be selected to avoid major economic losses caused by broom accidents.
4. For motor protectors in places with explosion-proof requirements, according to the specific requirements of the application site, the corresponding explosion-proof protectors should be selected to avoid safety accidents.
