Motor thermal protection principle

Principle: When the electrical appliance is working normally, the bimetallic sheet is in a free state and the contacts are in a closed/disconnected state. When the temperature rises to the operating temperature value, the bimetallic component is heated to generate internal stress and quickly acts. Opening/closing the contacts, cutting/connecting the circuit, and thus playing a thermal protection role.

When the temperature drops to the reset temperature, the contact automatically closes/opens and returns to normal working state. Widely used in household electrical motors and equipment, such as washing machine motors, air conditioning fan motors, transformers, ballasts, electric heating appliances, etc.

From the perspective of motor operating conditions, the types of motor protectors can be divided into the following:

1. For single machine independent running motors with low requirements for working conditions, simple operation control, casual monitoring and management, and little impact on production due to shutdown, ordinary type protectors can be selected. Due to their simple structure, on-site installation, wiring, replacement, and operation are simple and convenient, with high cost-effectiveness.

2. For MCC systems that require high working conditions, safety and continuity are crucial, and have a high degree of automation that requires dedicated personnel to control, monitor, and manage. In MCC systems that require network monitoring, mid to high-end and fully functional motor protectors should be selected.

3. For explosion-proof motors, eccentricity caused by bearing wear may cause high temperature friction at the explosion-proof gap, creating an explosion hazard. Therefore, the wear status monitoring function should be selected. For large capacity high-pressure submersible pumps, due to the difficulty of inspection and maintenance, the wear status monitoring function should also be selected to avoid significant economic losses caused by sweeping accidents.

4. For protectors used in places with explosion-proof requirements, corresponding explosion-proof motor protectors should be selected according to the specific requirements of the application site to avoid safety accidents.

Working principle of motor protector

The function of the motor protector is to provide comprehensive protection and control for the motor. In the event of overcurrent, undercurrent, phase failure, locked rotor, short circuit, overvoltage, undervoltage, leakage, three-phase imbalance, overheating, grounding, bearing wear, eccentricity of the stator and rotor, and winding aging, it will alarm or protect and control the motor.

Due to various reasons such as unstable voltage, phase failure, and overcurrent, the motor is damaged, resulting in abnormal operation. Therefore, it is necessary to protect the motor, and a motor protector is available.

There are many types of protectors, such as phase failure protection, overcurrent and undercurrent protection, time protection, temperature protection, leakage protection, overheating protection, and many other protectors. Protectors are divided into mechanical protection and electronic protection, and the principle is to protect the motor in the event of various conditions, minimizing losses and even protecting human life safety.

1. The Important Significance of Motor Protectors in the National Economy and Energy Conservation Cause

Motor protectors are important components in power generation, power supply, and consumption systems. It is an energy-saving electromechanical product that spans multiple industries, has a large quantity and a wide range, and has significant energy-saving effects.

Almost permeate all fields of electricity consumption; It is an important guarantee for industrial, agricultural, and national defense construction, as well as for the normal production and safety of people's lives. It plays an irreplaceable and important role in the national economy and energy conservation cause.

2. Common types of motor protectors

2.1. Thermal relay: Ordinary small capacity AC motor, with good working conditions and no harsh working conditions such as frequent starting. Due to poor accuracy and reliability, it is not recommended to use.

2.2. Electronic type: Detects the three-phase current value, and sets the current value using a potentiometer knob or pull-out switch operation. The circuit generally adopts analog type and adopts inverse time or definite time working characteristics. The protection function includes fault protection such as overload, phase loss, and locked rotor. The fault type is displayed using an indicator light, and the operating power is displayed using a digital tube.