1. Overview of thermal protection management of electric motors

Thermal protection components of traditional three-phase asynchronous motors of different sizes can be divided into categories such as PTC thermistor, temperature sensor PT100 and bimetal temperature relay.Explosion proofMotorA type of motor that can be used in flammable and explosive plants, and it does not generate sparks during operation.Explosion-proof motors are mainly used in coal mines, oil and gas, petrochemical and chemical industries.In addition, it is also widely used in sectors such as textiles, metallurgy, city gas, transportation, grain and oil processing, papermaking, and medicine.Frequency conversion speed motorA general term for motors driven by frequency converters.In fact, the motor designed for the frequency converter is a special frequency conversion motor. The motor can achieve different speeds and torques under the drive of the frequency converter to adapt to the changes in the demand of the load.The motor is an electromagnetic device that realizes the conversion or transmission of electric energy according to the law of electromagnetic induction.There is also a tropical humid environment, which is used to heat the interior of the motor.The temperature protection element is embedded in the corresponding position inside the motor, such as the motor winding or the front bearing cover of the motor. When the motor winding or bearing temperature is too high due to overvoltage, undervoltage, overcurrent, phase or overload fault, such The signal is sent to the motor temperature control instrument, which can immediately cut off the power supply and realize the motor protection.

2. PTC thermistor

PTC thermistor is a kind of positive temperature influence coefficient for semiconductor passing resistance. When the temperature (Curie temperature) specified by the country is exceeded, its resistance value can increase step by step with the increase of ambient temperature, up to 10-1000 Times.When in use, it is equipped with electronic control circuit technology to detect, and then make the relay act.

The PTC thermistor is small in size, small in heat capacity, and fast in response.In the motor manufacturing process, the PTC thermistor is embedded in the motor winding.The three-phase motor uses three series of thermistors, which are embedded in the three-phase windings U, V, and W of the motor in turn.

Pt100 temperature sensor

Pt100 platinum RTD sensor, which has a resistance of 0°C to 100 ohms. The PT100 temperature sensor is an analog signal to measure the corresponding part of the motor temperature by the corresponding relationship between the resistance temperature.The resistance of the signal conversion ASIC can be measured with higher accuracy.

When measuring and controlling the temperature of the winding, it is embedded in the winding end of the winding for fixing, and it can be dipped and dried together with the winding to lead the lead into the network junction box.

When measuring the bearing temperature, punch a hole (through) in the motor bearing chamber and twist the corresponding thread, and then install it firmly so that the end surface of the sensor touches the outer ring of the bearing, and the wire is led into the junction box.

4. Temperature control relay with bimetallic strip

The bimetallic temperature relay can be directly embedded in the motor winding.When the temperature of the winding rises close to the limit value when the motor is overloaded, the bimetallic strip with a pair of contacts is heated and bends, so that the contacts are disconnected and the circuit is cut off, realizing the temperature protection of the motor.

5. Moisture-proof heating belt

In a humid environment, when the motor stops working, the moisture-proof heating belt starts to work, and the motor windings are heated, thereby preventing the motor windings from condensation due to moisture and ensuring the normal operation of the motor in a humid environment.The heating strip and the motor lead are connected together.When the motor is energized, the heating belt is powered off; when the motor is powered off, the heating belt is energized and heated.