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Working principle of thermal relay

  The main function of the thermal relay is to protect the electric motor or other electrical equipment, electrical line of the overload protection.

  Motor in operation process, such as in the process of driving the production machinery, if the machine is not normal, or the circuit is overloaded, so that the motor is overloaded, the motor speed will be reduced, the winding current will increase, so that the electric motor of the winding temperature rise. If the overload current is not large and the time is short, the motor winding is not more than the allowable temperature rise. But if the overload time, overload current, the motor winding temperature rise will exceed the allowable value, so that the motor winding aging, shorten the life of the motor, even if the motor winding burned. So, this kind of overload is the motor can not afford. Thermal relay is the use of the principle of thermal effect of electric current in the motor can not withstand the overload of the motor circuit to provide protection for motor overload protection.

  When the motor is overload protected by thermal relay, the stator winding of the motor is connected in series with the stator winding of the motor. The thermal relay is connected in series with the control circuit of the AC contactor. When the motor is working normally, the electric current of the electric motor is rated current of the motor, and the heat element is heated, and the double metal piece is heated, so that the push rod is in contact with the people in the shape of the rod. The normally closed contact is closed, the AC contactor to maintain normal operation of the motor to pull.

Keywords:Active power filter,Active filter, Power quality,Harmonic control,APF
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