Why are electric motors more likely to burn out now than in the past?

Why are electric motors more likely to burn out now than in the past?

1. 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 getting weaker and weaker; due to the improvement of the degree of production automation , the motor is required to operate in frequent starting, braking, forward and reverse rotation, and variable load modes, which puts forward higher requirements for the motor protection device. In addition, the motor has a wider application area and often works in extremely harsh environments, such as humidity, high temperature, dust, corrosion and other occasions. In addition, there are irregularities in motor repair and omission in equipment management. All of this makes today’s motors more prone to damage than in the past.

Why is the protection effect of traditional protection devices not ideal?

2. The traditional motor protection devices are mainly fuses and thermal relays. Fuse is the earliest and simplest protection device to use. In fact, the fuse is mainly used to protect the power supply line and reduce the expansion of the fault range in the event of a short-circuit fault. It is unscientific to think that the fuse can protect the motor from short-circuit or overload. Don’t know, this is more likely to cause the motor to damage the motor due to phase failure. Thermal relays are the most widely used motor overload protection devices. However, the thermal relay has a single function, low sensitivity, large error and poor stability, which have been recognized by the majority of electrical workers. All these defects make the motor protection unreliable. This is also the case; although many equipments are equipped with thermal relays, the phenomenon of motor damage affecting normal production is still common.

The principle of protector selection?

3. 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. At the same time, when choosing a protection device, several contradictory factors must be considered, namely reliability, economy, simple structure, convenient operation and maintenance, etc. When the protection requirements can be met, the simplest protection device is considered first. Only when the simple protection device cannot meet the requirements, or when higher requirements are placed on the protection characteristics, the application of the complex protection device is considered.

The ideal motor protector?

4. The ideal motor protector is not the most functional, nor the so-called most advanced, but should be the most practical. So why is it practical? Practical should meet the reliability, economy, convenience and other factors, with a high cost performance. So what is reliable? Reliability should first meet the reliability of functions, such as overcurrent and phase failure functions, which must act reliably for overcurrent and phase failures that occur in various occasions, processes, and methods. Secondly, its own reliability (since the protector is to protect others, it should have high reliability in particular) must have adaptability, stability and durability to various harsh environments. Economy: 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 at least similar to thermal relays in terms of installation, use, adjustment, wiring, etc., as simple and convenient as possible. Because of this, relevant experts have long predicted that in order to simplify the electronic motor protection device, a design scheme without a power supply transformer (passive) should be designed and adopted, and a semiconductor (such as a thyristor) should be used to replace the electromagnetic actuator with contacts. element. In this way, it is possible to manufacture a protective device consisting of a minimum number of components. We know that active sources will inevitably lead to unreliability. One requires working power for normal operation, and when the other is out of phase, it will definitely lose working power. This is an insurmountable contradiction. In addition, it needs to be powered on for a long time, and it is easily affected by grid voltage fluctuations and large current shocks, and its own failure rate will be greatly increased. Therefore, the motor protection industry regards active and passive as the milestones of technological progress. As a user, passive products should also be considered first when choosing. The development status of motor protection.

At present, the motor protector has been developed from the mechanical type in the past to an electronic type and an intelligent type, which can directly display the current, voltage, temperature and other parameters of the motor, with high sensitivity, high reliability, multiple functions, convenient debugging, and clear fault types after the protection action. , which not only reduces the damage of the motor, but also greatly facilitates the judgment of the fault, which is conducive to the fault handling of the production site and shortens the recovery time. In addition, the motor eccentricity detection technology using the motor air-gap magnetic field makes it possible to monitor the motor wear state online. The curve shows the change trend of the motor eccentricity, and can early detect bearing wear and inner circle, outer circle and other faults. Early detection, early treatment, to avoid sweeping accidents.