1 Motor protection types and applications

    Commonly used in small and medium-sized three-phase asynchronous motor overheating protection and temperature measurement devices can be broadly divided into two categories: one is the setting temperature sensing element, such as thermistor and thermal switch; other thermocouples and platinum thermal resistance. There is also a tropical moisture plus, used to protect the motor running in a damp environment. These temperature sensing element is embedded in the corresponding position on the interior of the motor. Such as: embedded in the motor winding or motor on the front and rear bearings, and directly reflects the actual temperature of the motor windings and bearings. Whether as a result of over-voltage, under-voltage, over-current, phase, or overload stall failure are manifested through the motor winding temperature rise. Such signals are passed to the motor protection or temperature control device can be immediately cut off the power to the motor, the motor protection.

    2 thermal switch

    The motor the local over-temperature protection commonly used the MK1 thermal switch. In the manufacture of motor embedded in the motor end windings of the coil, lashing together with the coil dipping drying; leads, the leads with the motor leads connected to the motor terminal box of the specified terminal. Coil temperature rise of the motor is running the operating temperature of the thermal switch, thermal switch will be able to disconnect the power to the controller, so that the motor is disconnected from the main circuit, in order to protect the motor. The different motor insulation class can be used the different temperature thermal switches.

    3 thermistor application

    Commonly used motor protection PTC thermistor. PTC thermistor small size, heat capacity, fast response, applies not only to the motor undervoltage, overvoltage and overload protection, but also for the open phase of the motor starter protection, but must be used with a dedicated motor protection (GRB).

    PTC thermistor embedded in the inside of the motor coil in the motor manufacturing. Three-phase motor thermistor selected three series are in turn embedded in the motor A, B, C three-phase coil compression banding together with the coil dipping, the lead wire to the junction box. When the motor coil temperature close to the temperature of the insulation class, the PTC thermistor resistance increased; This signal is sent to the GRB motor overheating protection, the protection based on this signal to the motor circuit is disconnected, thereby protecting the motor.

    If the motor is not equipped with PTC thermistor, motor door is open, the PTC thermistor AB glue on the coil, and cited the lead connected to the junction box, matched thermistor special protection, but its control the temperature to drop to 20 ° C (because it is not embedded within the coil).