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#1 Posted : Friday, September 23, 2022 6:57:40 PM(UTC)

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1. Types and applications of motor overheating protection.
The commonly used overheating protection and temperature measuring components of small and medium-sized three-phase asynchronous motors can be roughly divided into two categories:
One is a constant value temperature sensing element, such as thermistor and thermal switch; The other category is thermocouple and platinum thermoresistor.
There is also a moisture-proof heating belt for protecting motors operating in moist environments. These temperature sensing elements are embedded in the corresponding positions inside the motor.
Such as: embedded in the motor winding or motor bearings before and after, can directly reflect the actual temperature of the motor winding and bearing. Whether it is due to over voltage, under voltage, over current, lack of phase, or overload, blocked rotor and other faults, are shown by the temperature rise of the motor winding. When such signals are transmitted to the motor protector or temperature controller, the power supply of the motor can be cut off immediately to protect the motor.

2. The application of thermal switch motor local overtemperature protection is usually used is 17AM thermal switch.
When making the motor, it is embedded in the coil of the end winding of the motor, bound and fixed, soaked in paint and dried together with the coil, and its lead is led out with the motor lead and connected to the specified terminal post in the motor junction box.
When the coil temperature of the motor reaches the operating temperature of the thermal switch, the thermal switch can disconnect the power supply of the controller, so that the main circuit of the motor is disconnected, so as to protect the motor.
Electric motors with different insulation levels can choose different temperature thermal switches.

3.The application of thermistor motor protection is usually used in PTC thermistor.
PTC thermistor has small volume, small heat capacity and fast reaction speed. It is not only suitable for the undervoltage, overvoltage and overload protection of the motor, but also suitable for the lack of phase starting protection of the motor, but must be equipped with a special motor protector (such as GRB) when in use. When the motor is manufactured, the PTC thermistor is embedded inside the motor coil.
The three-phase electric machine selects three series thermistors, which are embedded in the three-phase coils of the motor A, B and C in turn. After pressing and binding, the wires are soaked with the coils, and the leads are connected to the junction box. When the temperature of the motor coil is close to the insulation level temperature, the PTC thermistor resistance value increases, this signal is transmitted to the GRB motor overheating protector, the protector will disconnect the motor circuit according to this signal, so as to protect the motor. If the motor is not equipped with PTC thermistor, you can open the end cover of the motor, stick the PTC thermistor on the coil with AB glue, and connect the lead to the junction box, and then use the thermistor special protector, but its control temperature should drop by 20℃ (because it is not embedded in the coil).
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