Motor protector's role is to protect the overall motor and the motor overload, phase lack, blocking, short circuit, overvoltage, undervoltage, leakage, three-phase unbalance, overheating, bearing wear, rotor eccentricity, give alarm or protective device.
First, the basic principles of motor protective device selection
At present, there is no unified standard for motor protection products on the market. Manufacturers in order to satisfy different users use demand derived a series of products, variety and bring a lot of inconvenience to the selection of the majority of users, the user in the selection should fully consider the actual needs of motor protection, reasonable selection of the protection function and the protection way, in order to achieve a good protective effect, to improve the reliability of the equipment, reduce the unplanned shutdown, reduce the loss of the accident.
Two, the basic method of motor protector selection
(a) the conditions relating to selection:
Selection of motor protector of motor protector and the two how reasonable matching relationship. Here are a few and protection related conditions and factors, and to provide reference for the user selection.
1, motor aspects: first understand the model specifications, motor function characteristics, protection type, rated voltage, rated current, rated power, power frequency, insulation grade, etc.. The content of the basic can give users how to correctly use and maintenance and selection of protective device provides a reference.
2, environmental conditions: mainly refers to the room temperature, high temperature, cold, corrosion, vibration, wind and sand, elevation, electromagnetic pollution, etc..
3, motor uses: mainly refers to drag the mechanical equipment requirements characteristics, such as wind, water pump, air compressor, lathe, oil field pumping unit, such as different load mechanical characteristics.
4, control system: control mode is manual, automatic, local control, remote control, stand-alone operation, production line centralized control, etc.. Start mode: direct, step-down, star delta, frequency sensitive rheostat, inverter, soft start and start-up mode.
5, other aspects: the user to the field production monitoring management is more casual or rigorous, non normal shutdown of the production of the impact of the severity of the.
And the selection of motor protector has certain correlation factors, there are many, such as the installation position, power, and distribution system with; also to consider whether to buy the new configuration of motor protection, or to protect the motor upgrade, or improve on the protection of the motor accident; also consider motor protection way to change the difficulty and the degree of influence on production; according to the actual working conditions considering the protector of the selection and adjustment.
(two) the common types of motor protectors
1, thermal relay: Ordinary small capacity AC motor, good working conditions, there is no frequent start and other harsh conditions, due to poor accuracy, reliability can not be guaranteed, do not recommend the use of.
2, electronic type: detection of three-phase current value, the current value of the adjustment of the potentiometer knob or pull the code switch operation, the circuit is generally used analog, the use of anti time limit or time limit. Protection functions include overload, lack of phase, blocking and other fault protection, fault type using the indicator light shows that the operation of the digital tube display.
3, intelligent: detection of three-phase current value, the protection of the use of single-chip microcomputer to achieve intelligent motor integrated protection, protection, measurement, communication, display as a whole. Setting current using digital set, through the operation panel buttons to operate, users can according to their actual use requirements and protection at the scene by itself, and the various parameters modification of setting, the use of digital tube as display window, or using large screen LCD display, can support a variety of communication protocols, such as for and process field bus, are relatively expensive, for important occasions, at present protection of high voltage motor are used intelligent.
4, thermal protection: in motor embedded heating element, according to the temperature of the motor protection, the protective effect of good, but motor capacity is large, and with the use of current monitoring, to avoid motor locked rotor temperature rise sharply, because of the lagging of the measuring element, resulting in damage to the motor winding.
5, magnetic field temperature test type: magnetic field detection coil and a temperature probe is buried in the motor and changes according to the change of the motor rotating magnetic field and temperature protection, the main functions include overload, locked rotor, lack of phase, overheat protection and wear monitoring, perfect protection function, the disadvantage is the magnetic field detection coil and a temperature sensor is installed in the interior of the motor.
(three) the choice of motor protector type under the working conditions of motor
1, for working condition requirements is not high, simple operation and control, monitoring and management more casual, stop of had little effect on production of single motor operation, the use of ordinary type protector, because ordinary type protector has the advantages of simple structure, in the field installation and wiring, replacing, simple operation, convenient and has high performance price ratio.
2, for work requirement is very high, safety and continuity is the key, and high degree of automation, and need someone to control, monitoring and management, monitoring network of MCC system should be used in high-grade, function than the whole of the protector.
3, for the explosion-proof motor, due to bearing wear caused by eccentric, may lead to the explosion of clearance at high temperature friction, resulting in explosion hazard, should choose the wear condition monitoring function. For large capacity high pressure submersible pump, due to the difficulty of inspection and maintenance, it should also choose the wear condition monitoring function, to avoid the occurrence of sweeping bore accident caused significant
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