The supplier of the energy feedback unit of the frequency converter reminds you that when it comes to the protection function of the frequency converter, it is of course related to some fault protection that occurs in the frequency converter. In practical applications, it usually refers to the protection function of the transmission system including the frequency converter, such as line protection, frequency converter self-protection, motor protection, mechanical load protection, etc.
Integrated protection device inside the frequency converter
(1) Motor overload protection
The basic characteristic of electric motor thermal overload is that the actual temperature rise exceeds the rated temperature rise. Therefore, the purpose of overload protection for electric motors is also to ensure that they can operate normally and not burn out due to overheating.
When an electric motor is running, its lost power (mainly copper loss) is converted into heat energy, causing the temperature of the motor to rise. The heating process of an electric motor belongs to the transitional process of thermal equilibrium, and its basic law is similar to the common law of exponential curve rising (or falling). Its physical significance lies in the fact that as the temperature of the electric motor increases, it must dissipate heat to the surrounding area. The larger the temperature rise, the faster the heat dissipation. Therefore, the temperature rise cannot rise linearly, but rather slows down as it rises; When the heat generated by the motor is balanced with the dissipated heat, the temperature rise at this time is the rated temperature rise.
The manufacturing standards for asynchronous motors define different types of levels based on the maximum allowable temperature rise, namely Class A 105 ℃, Class E 120 ℃, Class B 130 ℃, Class F 155 ℃, and Class H 180 ℃.
Motor thermal overload refers to the excessive mechanical load on the motor shaft, causing the operating current of the motor to exceed the rated value and resulting in a temperature rise that also exceeds the rated value. The main characteristics of motor overload are:
① The increase in current is not significant. Because in the selection and design of electric motors, the maximum operating current of the load is generally fully considered, and the design is based on the maximum temperature rise of the motor. For certain variable loads and intermittent loads, short-term overload is allowed. Therefore, under normal circumstances, the amplitude of overload current is not very large.
② In general, the rate of change of current di/dt is small and rises slowly.
(2) Short circuit protection at the output end of the frequency converter
If there is a phase to phase short circuit at the output end of the frequency converter (motor terminal or the line between the frequency converter and the motor), the frequency converter will detect the short circuit fault and cut off the circuit within a few milliseconds to ensure the safety of the frequency converter and motor equipment.
(3) Other protective devices
① Electronic component overheating protection: If the temperature exceeds the set threshold, the sensor placed on the heat dissipation device will stop the frequency converter from working, preventing damage to electronic components caused by overheating.
② Instantaneous line voltage drop protection: This protection function can prevent faults in control circuits and motors, as well as prevent overcurrent caused by line voltage recovery.
③ Overvoltage protection for power supply lines: This protection function prevents damage to components.
④ Phase loss protection: Phase loss will cause a significant increase in current.
(4) Operation of integrated protection device
If there is a malfunction, the above protective device will stop the frequency converter, allowing the motor to stop freely, and the power will be cut off by the internally integrated relay.