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Types and selection methods of motor protectors

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.

First, common types
1. Thermal relay: ordinary small-capacity AC motor, good working conditions, no frequent working conditions, etc., due to poor precision, reliability can not be guaranteed, it is not recommended.
2. Electronic type: Detect three-phase current value. The setting current value is operated by potentiometer knob or dial switch. The circuit is generally analog, with anti-time or time-limited operating characteristics. The protection function includes fault protection such as overload, phase loss, and stalling. The fault type is displayed by indicator light, and the running power is displayed by 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 the various parameters on the spot according to the actual use requirements and protection conditions. The digital tube can be used as the display window or the large screen liquid crystal display can be used. Support a variety of communication protocols, such as ModBUS, ProfiBUS, etc., the price is relatively high, for more important occasions, today’s high-voltage motor protection is intelligent.

4. Thermal protection type: The thermal element is embedded in the motor and protected according to the temperature of the motor. The protection effect is good, but when the motor capacity is large, it needs to be used together with the current monitoring type to avoid the temperature rise sharply when the motor is blocked. The hysteresis of the temperature measuring element causes damage to the motor windings.

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 a magnetic field detecting coil and a temperature sensor are installed inside the motor.

Second, the selection method

1. Basic principle: Users should fully consider the actual needs of motor protection when selecting the type, and reasonably choose the protection function and protection mode to achieve good protection effect, improve equipment operation reliability, reduce unplanned parking, and reduce accident loss. .

2. Basic method:

(), motor: First understand the model specifications, motor function characteristics, protection type, rated voltage, rated current, rated power, power frequency, insulation level, etc. These contents basically provide a reference for users to correctly use and maintain and select the protector.

(2) Environmental conditions: mainly refers to normal temperature, high temperature, high cold, corrosion degree, vibration, sand, altitude, electromagnetic pollution, etc.

(3), motor use: mainly refers to the characteristics of the drag mechanical equipment, such as fans, pumps, air compressors, lathes, oil field pumping units and other different mechanical characteristics.

(4) Control system: The control mode includes manual, automatic, local control, remote control, stand-alone operation, and centralized control of the production line. The starting mode includes direct, buck, star triangle, frequency sensitive varistor, inverter, soft start and other starting methods.

(5) Other aspects: The user’s on-site production monitoring management is relatively random or rigorous, and the severity of the impact of abnormal shutdown on production.5b10f8d3351c2


Post time: Sep-20-2018
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