Due to the continuous development of insulation technology, compared with the past, motors are easier to burn windings. The design of motors requires both increased output power and reduced size. Therefore, the thermal capacity of the new motor is getting smaller and the overload capacity is getting higher and higher. . In addition, due to the increase in the degree of production automation, the motor is required to frequently operate in a variety of ways, such as frequent starting, braking, forward and reverse rotation and variable load, which proposes a motor protection device higher requirement. In addition, the application range of the motor is wider. Usually work in extremely harsh environments, such as humidity, high temperature, dust, corrosion and other occasions. Coupled with violations in motor manufacturing and omissions in equipment management. All these make today's motors more susceptible to damage than in the past, especially in the case of the highest frequency of failures, such as overload, short circuit, phase loss, and hole scanning.
The protective effect of traditional protective devices is not very satisfactory. Traditional motor protection devices are mainly based on fuses and thermal relays. The fuse is mainly used for short-circuit protection. The selection of fuse current needs to consider the starting current of the motor, so it is recommended not to use a 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. The facts are exactly the same. Although many devices are equipped with thermal relays, motor damage that affects normal production is still common. There is no traditional protection device that can monitor the mechanical wear of the motor and the eccentricity of the stator and rotor.
The motor protector has developed from the mechanical type in the past to the electronic type and intelligent type. It has the characteristics of high sensitivity, high reliability, multi-function and convenient debugging. It can directly display the current, voltage, temperature and other parameters of the motor. After the protection is activated, the fault type is clear at a glance, which greatly facilitates the judgment of the fault, facilitates the fault handling at the production site, and shortens the recovery time. In addition, the motor eccentricity detection technology based on the motor air gap magnetic field makes it possible to monitor the motor wear status online. The curve shows the change trend of the value reflecting the motor eccentricity, and can record the value change during the two-year period, and early detection of bearing faults. Find out as soon as possible and carry out early treatment to avoid sweeping accidents.
The purpose of selecting a motor protection device is to enable the motor to give full play to its overload capacity, avoid damage, and improve the reliability of the electric drive system and the continuity of production. In the case of meeting the protection requirements, please consider the simplest protection equipment first. When simple protection devices cannot meet the requirements, or when higher requirements for protection functions and characteristics are put forward, the application of complex protection devices is considered economical and economical. Unity of reliability. The selection of specific functions should comprehensively consider the value of the motor itself, load conditions, environmental quality, the importance of the motor, whether the shutdown will have a serious impact on the production system and other factors, and strive to be economically reasonable.
The ideal motor protector is not the most complete, nor the so-called most advanced, but the most practical. So what is practical? Practicability should satisfy factors such as reliability, economy, convenience, etc., and have a high cost performance. So what is reliability? Reliability should first meet the reliability of the function. For example, the overcurrent and phase fault functions must be able to reliably function in various occasions, processes, and overcurrent and phase faults that occur in various ways. Secondly, its own reliability (because the protector can protect others, especially with high reliability), must have adaptability, stability and durability to various harsh environments. Economy: Adopt advanced design, reasonable structure, specialized mass production, reduce product cost, and bring extremely high economic benefits to users. Convenience: It must be as simple and convenient as possible in terms of installation, use, adjustment and wiring.