EN
Overcurrent relays are used to act when the current in the loop crosses the set value. Thermal relays are usually used for overload maintenance of motors to avoid motor overload; thermal relays are maintenance appliances used for overload maintenance of motors or other electrical equipment and electrical circuits. .
In the practice work of the motor, such as dragging the production machinery in the process of work, if the machinery presents abnormal conditions or the circuit is abnormal and the electric timing is overloaded, the motor speed will decrease, the current in the winding will increase, and the winding temperature of the motor will be increased. increase. If the overload current is not large and the overload time is short, the motor winding does not cross the allowable temperature rise, and this overload is allowable. However, if the overload time is long and the overload current is large, the temperature rise of the motor windings will exceed the allowable value, which will cause the motor windings to age, shorten the service life of the motor, and even burn the motor windings in severe conditions. Therefore, this kind of overload is unacceptable for the motor. The thermal relay is to use the principle of the thermal effect of the current to block the motor circuit when the motor is overloaded, and to supply the motor with maintenance appliances for overload maintenance.
When using the thermal relay to maintain the motor overload, connect the thermal element in series with the stator winding of the motor, connect the normally closed contact of the thermal relay in series with the control circuit of the electromagnetic coil of the touch device, and dispatch the setting current dispatch knob to make people The font-shaped lever is at a proper distance from the push rod. When the motor is in normal operation, the current passing through the heating element is the extra current of the motor. The heating element heats up, and the bimetallic sheet bends after being heated, so that the push rod just touches the herringbone shifting lever, but can not advance the hearing-shaped shifting lever. The normally closed contact is in the closed state, the communication toucher insists on pulling and closing, and the motor operates normally.
If the motor presents an overload condition, the current in the winding increases, and the increase in the current in the thermal relay element causes the temperature of the bimetal to rise higher, and the degree of tortuosity increases. Push the ear-shaped lever, and the herringbone lever pushes the normally closed contact. , The contactor is disconnected and the circuit of the coil of the communication touch device is disconnected, so that the touch device is released and the power supply of the motor is blocked, and the motor is parked for maintenance.
It can be seen that the thermal relay usually directly disconnects the control circuit of the touch device to disconnect the main circuit.
Over-current relay: used for motors or other electrical equipment, when the current crosses the set value (pull-in) Block the main circuit or announce the signal.
