1、Brief

Common thermal protection components for medium-small size motor include PTC thermistor, PT100 temperature sensor and bimetallic temperature relay. Also include damp-proofing heater, for heating inside of motor in damp environment. These components are buried inside of motor, like windings, or bearings caps at DE and NDE sides.

If windings and bearings are caused higher temperature when motor is in higher voltage, lower voltage, over current, lack of phase or overload, this signal can be transferred to temperature control instrument of motor, then immediately the power supply is shut down, to protect the motor.

2、 PTC thermistor

It is a kind of resistance with Positive Temperature Coefficient. When the temperature is higher than the specified temperature (Curie temperature), the resistance will step rise as the rising temperature, it can reach 10—1000 times. It will also let relay act, together with the detecting of electronic circuit.

PTC has small size, small thermal capacity, rapid reaction. Put PTC inside of windings when making motor. Three phases motor select three series PTC, put them into the windings for phase U、V、W，vanished with windings after binding, lead the cables into t-box.

3、 Pt100 temperature sensor

Pt100 is platinic resistance sensor, the resistance is 0-100 ohms. It has simulated signal. It can detect the temperature of corresponding part through the relations between resistance and temperature. It can have high precision detect.

When detecting the temperature of windings, bind it on the end windings, varnish and dry it together with windings, lead the cables into the T/Box.

When detecting the temperature of bearings, drill and thread a hole on bearing house, then mount it, let the end surface of Pt100 touch outer ring of bearing, lead the cables into T/Box.

4、bimetallic temperature relay

It can be directly buried into the windings. When motor is overloaded the winding temperature reach close to the limited value, the bimetallic plates with two contactors bend because of heating, then shut down the circuit as the contactors are broken, to protect motor.

5、damp-proofing heater

In the damp environment, the heater starts to work when the motor is stopped, to heat the windings, to avoid the windings dampened. That can guarantee motor work in damp-proofing environment. Lead out of cables of heater together with cables of motor. The heater works when the motor stops working, the motor works when the heater stops working.