Matters needing attention: The motor is more likely to burn the windings than in the past. Due to the continuous development of insulation technology, the design of the motor requires both increased output and reduced volume, so that the thermal capacity of the new motor is getting smaller and smaller, and the overload capacity is increasing. The weaker it is; and due to the improvement of production automation, the motor is required to operate in various modes such as frequent starting, braking, forward and reverse rotation, and variable load, which puts forward higher requirements for the motor protection device. In addition, the application of electric motors is wider. Often work in extremely harsh environments, such as humidity, high temperature, dust, corrosion and other occasions. Coupled with the irregularities in motor manufacturing and omissions in equipment management. All of these cause today's motors to be more easily damaged than in the past, especially faults such as overload, short circuit, phase loss, and sweeping that occur most frequently
The protection effect of traditional protection devices is not ideal. The traditional motor protection devices are mainly 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, so it is not advisable to use the fuse alone to protect the motor. Thermal relay is the most widely used motor overload protection device, but thermal relay has low sensitivity, large error, poor stability, and unreliable protection. This is also the case. Although many equipments are equipped with thermal relays, the phenomenon that the motor is damaged and affects the normal production is still widespread. The traditional protection device has no products that can realize the mechanical wear monitoring of the motor and the eccentricity monitoring of the stator and rotor.
The motor protector has now been developed from the mechanical type in the past to the electronic type and intelligent type, with high sensitivity, high reliability, multiple functions and convenient debugging. It can directly display the current, voltage, temperature and other parameters of the motor, and the types of faults after the protection action are clear at a glance, which greatly facilitates the judgment of faults, is conducive to fault handling on the production site and shortens the recovery time. In addition, the motor eccentricity detection technology based on the air gap magnetic field of the motor makes it possible to monitor the motor wear state online. The curve shows the change trend of the value reflecting the eccentricity degree of the motor, and records the change of the value within two years. Bearing faults can be detected early. Do early detection and early treatment to avoid sweeping accidents.
The purpose of selecting the motor protection device is not only to enable the motor to fully exert its overload capacity, but also to avoid damage, and to improve the reliability of the electric drive system and the continuity of production. When the protection requirements can be met, the simplest protection device is considered first. When the simple protection device cannot meet the requirements, or when higher requirements are placed on the protection function and characteristics, the application of the complex protection device is considered to achieve economical and Unity of reliability. The specific function selection should be based on the comprehensive consideration of the value of the motor itself, the load situation, the quality of the environment, the importance of the motor, and whether the withdrawal from operation will have a serious impact on the production system, and strive to be economical and reasonable.
