Precautions for motor protector
Motors are more likely to burn windings than in the past, due to the continuous development of insulation technology, the design of the motor requires both increased output and reduced size, so that the thermal capacity of the new motor is getting smaller and the overload capacity is getting weaker; Furthermore, due to the increase in the degree of production automation, the motors are required to run frequently in a variety of ways such as frequent starting, braking, forward and reverse rotation, and variable load, which puts forward higher requirements for motor protection devices. 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 the omissions in equipment management. All of these have caused today's motors to be more prone to damage than in the past, especially with the highest frequency of faults such as overload, short circuit, phase loss, and bore sweeping.
The protection effect of the traditional protection device is not very satisfactory. The traditional motor protection device is mainly based on 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. The fact is exactly the same. Although many devices are equipped with thermal relays, the phenomenon of damage to the motor that affects normal production is still widespread. The traditional protection device does not have products that can monitor the mechanical wear of the motor and the eccentricity of the stator and rotor.
The motor protector has now been developed from the mechanical type in the past to an electronic and intelligent type (such as NDD3B (JD-5B) Motor protector), with high sensitivity, high reliability, multiple functions, and convenient debugging. It can directly display the current, voltage, temperature and other parameters of the motor. After the protection is activated, the type of fault is clear at a glance, which greatly facilitates the judgment of the fault, and is conducive to the fault handling at 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 status online. The curve shows the change trend of the value reflecting the motor eccentricity, and the change of the value over a period of two years can be recorded to detect bearing faults early. Achieve early detection and early treatment to avoid the occurrence of sweeping accidents.
The purpose of selecting the motor protection device is to enable the motor to give full play to its overload capacity, avoid damage, and to improve the reliability of the electric drive system and the continuity of production. In the case of meeting the protection requirements, consider the simplest protection device first. When the simple protection device cannot meet the requirements, or when higher requirements are put forward for the protection function and characteristics, the application of complex protection devices is considered to be economical and economical. Unity of reliability. The specific function selection should be based on comprehensive consideration of the value of the motor itself, load conditions, environmental quality, the importance of the motor, whether the withdrawal of operation will cause a serious impact on the production system and other factors, and strive to be economically reasonable.
The ideal motor protector is not the most functional, nor the so-called most advanced, but the most practical. So what is practical? Practical should meet the factors of reliability, economy, convenience, etc., and have a high performance-price ratio. So what is reliability? Reliability should first meet the reliability of functions, such as overcurrent and phase failure functions must be able to reliably act on various occasions, processes, and overcurrent and phase failures that occur in various ways. Secondly, its own reliability (since the protector is to protect others, especially with high reliability) must have adaptability, stability and durability to various harsh environments. Economical: Adopt advanced design, reasonable structure, specialized and large-scale 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.