Protection of the hottest explosion-proof safe mot

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Protection of explosion-proof safety motor

in order to ensure the safe operation of explosion-proof safety motor, the allowable limit temperature should be specified first. Obviously, the allowable limit temperature depends not only on the insulation material grade of the motor itself, but also on the ignition temperature of explosive gas. Generally, the protection device is required to ensure that the temperature of the motor as a graphene industry research and development demonstration base does not exceed the allowable temperature under the following three fault conditions:

(1) overload or rotor locked rotor

(2) the temperature of liquid cooling medium increases or the flow decreases

(3) winding failure or short circuit

there are two common protection methods:

(1) indirect temperature protection usually adopts thermal relay, which may cause safety problems when the operating temperature rises. Iec79-7 stipulates that when the total investment of the rotor is 500million yuan, the minimum time te from the hot state to the temperature reaching the specified allowable temperature is 5 seconds. In order to protect the starting current of the motor before it is disconnected after te, the tripping device should be selected according to the rated current of the motor, and the device should be set. The required time delay should be determined according to the type of thermal relay. If the motor starts for a long time, it may trip during the starting process, so we must try to avoid this kind of wrong action. Generally, the measures of shorting the protective device during starting can be taken to meet this requirement

(2) direct temperature protection uses the temperature sensor and temperature relay embedded in the winding to realize direct temperature protection, which can overcome the disadvantage that the thermal relay is difficult to fully simulate the heating characteristics of the motor

in addition, the protective device composed of semiconductor thermistor (PTC) which can recall the experimental curve after the experiment with positive resistance temperature coefficient is also effective

direct temperature control and monitoring can reliably protect the motor, and it is also very economical. If the comprehensive protection mode of direct temperature monitoring and indirect temperature protection is adopted, the protection is more effective

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