The function of a motor protector is to provide comprehensive protection and control for the motor. It provides alarms or protective control when the motor experiences overcurrent, undercurrent, phase loss, locked rotor, short circuit, overvoltage, undervoltage, leakage, three-phase imbalance, overheating, grounding, bearing wear, stator and rotor eccentricity, or winding aging.
Motor Protection Tips
1. Why are modern motors more prone to burning out their windings than those of the past?
Due to continuous advancements in insulation technology, motor design now demands both increased output and reduced size, resulting in smaller heat capacity and weaker overload capacity in new motors. Furthermore, increased automation in production requires motors to operate under frequent starting, braking, forward and reverse rotation, and load variations, placing higher demands on motor protection devices. Additionally, motors are now used in a wider range of harsh environments, such as humid, high-temperature, dusty, and corrosive conditions. Coupled with non-standard manufacturing and repair practices and oversights in equipment management, all these factors contribute to the increased susceptibility to damage in modern motors compared to the past, with overload, short circuit, phase loss, and rotor rubbing being the most frequent faults.
2. Why are the protective effects of traditional protection devices not ideal?
Traditional motor protection devices mainly consist of fuses and thermal relays. Fuses are primarily used for short-circuit protection, and the selection of the fuse current must consider the motor's starting current; therefore, using fuses alone to protect motors is not advisable. Thermal relays are the most widely used motor overload protection devices, but they suffer from low sensitivity, large errors, and poor stability, making their protection unreliable. Indeed, despite the widespread installation of thermal relays in many devices, motor damage affecting normal production remains common. Furthermore, traditional protection devices currently lack the capability to monitor mechanical wear and stator/rotor eccentricity in motors.
4. What is the current state of development of motor protectors?
Currently, motor protectors have evolved from mechanical types to electronic and intelligent types, offering high sensitivity, high reliability, multiple functions, and convenient debugging. They can directly display parameters such as motor current, voltage, and temperature, and the type of fault after protection action is immediately apparent, greatly facilitating fault diagnosis and improving on-site fault handling and reducing production recovery time. Furthermore, the technology of detecting motor eccentricity based on the motor's air gap magnetic field makes online monitoring of motor wear possible. By displaying the changing trend of the motor's eccentricity value as a curve and recording the change over two years, bearing faults can be detected early, enabling timely intervention and preventing rotor rubbing accidents.
5. What are the principles for selecting a protector?
The purpose of selecting motor protection devices is to enable the motor to fully utilize its overload capacity while preventing damage, and to improve the reliability of the electric drive system and the continuity of production. When protection requirements are met, the simplest protection device should be considered first. Only when the simple device fails to meet the requirements, or when higher demands are placed on protection functions and characteristics, should a more complex protection device be considered, achieving a balance between economy and reliability. The specific functional selection should be based on a comprehensive consideration of factors such as the motor's value, load conditions, environmental conditions, the motor's importance, and whether its shutdown would severely impact the production system, striving for economic rationality.
6. What is the ideal motor protector?
An ideal motor protector is not one with the most functions, nor the most advanced technology, but rather the most practical. What does practicality mean? Practicality should meet factors such as reliability, economy, and convenience, offering a high performance-to-price ratio. What does reliability mean? First, it must meet functional reliability requirements. For example, overcurrent and phase loss protection functions must reliably operate in various situations, processes, and methods of overcurrent and phase loss. Second, it must be inherently reliable (since the protector is protecting others, it should possess particularly high reliability), exhibiting adaptability, stability, and durability in various harsh environments. Economy: Advanced design, a rational structure, and specialized, large-scale production reduce product costs, bringing users significant economic benefits. Convenience: Installation, use, adjustment, and wiring must be as simple and convenient as possible.
