1. The motor is easier to burn the winding than in the past. It is due to the continuous development of insulation technology. In the design of the motor, it is required to increase the output and reduce the volume, so that the heat capacity of the new motor is getting smaller and smaller, and the overload capacity is getting weaker; Moreover, due to the improvement of the degree of production automation, the motor is often required to operate frequently in various ways such as frequent starting, braking, forward and reverse rotation, and variable load, which puts higher requirements on the motor protection device. In addition, the application of the motor is wider. Often used in extremely harsh environments, such as humidity, high temperature, dust, corrosion and other occasions. Coupled with the irregularity of motor manufacturing, the omission of equipment management. All these have made the motor more easily damaged than in the past, especially overload, short circuit, phase gap, chamber sweeping and other faults occur most frequently.

2. The protection of traditional protection devices is not ideal. The traditional motor protection device is mainly composed of fuses and thermal relays. The fuse is mainly used for short-circuit protection. The selection of the fuse current needs to consider the starting current of the motor. Therefore, it is not advisable to use a fuse alone to protect the motor. Thermal relays are the most widely used motor overload protection devices, but thermal relays have low sensitivity, large errors, poor stability, and unreliable protection. This is also the case. Although many devices are equipped with thermal relays, the phenomenon that the motor is damaged and affects normal production is still widespread. Conventional protection devices have not yet been able to achieve mechanical wear monitoring of the motor and eccentricity monitoring of the stator and rotor.

3, Motor protector has been developed from mechanical type to electronic type and intelligent type, with high sensitivity, high reliability, many functions and convenient debugging. The current, voltage, temperature and other parameters of the motor can be directly displayed, and the types of faults after the protection action are clear at a glance, which greatly facilitates the judgment of the fault, is beneficial to the fault handling at the production site and shortens the recovery production time. In addition, according to the motor air gap magnetic field, the motor eccentricity detection technology makes the motor wear state online monitoring possible. The change trend of the value reflecting the degree of eccentricity of the motor is displayed by a curve, and the change of the value in two years is recorded. Bearing failure can be detected early, early detection, early treatment, and avoiding broom accidents.

4. The purpose of selecting the motor protection device is to enable the motor to fully exert the overload capability and avoid damage, and also improve the reliability and continuity of the electric drive system. The simplest protection device is first considered when the protection requirements are met. When a simple protection device fails to meet the requirements, or when higher requirements are placed on the protection function and characteristics, it is considered to apply a complicated protection device to achieve uniformity of economy and reliability. The specific function selection should be based on comprehensive consideration of the value of the motor itself, the load condition, the quality of the environment, the importance of the motor, whether the exit operation has serious impact on the production system, etc., and strive to be economic and reasonable.

4. The ideal motor protector is not the most functional, nor the so-called most advanced, but should be the most practical.
So what is practical?
Practical should meet the requirements of reliability, economy, convenience, etc., with a high performance-price ratio.

So what is reliable?
Reliable first of all should meet the reliability of the function, such as over current, phase failure function must be able to respond to various occasions, various processes, various ways of overcurrent, phase failure can be reliable.
Secondly, its own reliability (since the protector is to protect others, especially high reliability) must have adaptability and durability to various harsh environments.

Economical:
Adopt advanced design, reasonable structure, professional and large-scale production, reduce product cost, and bring high economic benefits to users.

Convenience:
It must be as simple and convenient as possible in terms of installation, use, adjustment, wiring, etc.