The detection element of the thermal relay is a bimetallic strip. Due to overcurrent impacts such as starting current and overload, it is easy to cause fatigue effects on the bimetallic strip, causing the scale value to shift, and the action is unstable, which is difficult to find at the production site. Eventually cause overload and no action. However, the electronic motor protector uses a current transformer as the detection element, so there is no heat generation problem, and its operation stability has a qualitative leap compared with the thermal relay.
The more advanced electronic integrated motor protector (motor protector), the detection element generally adopts current transformer, and a core-through structure has appeared. The self-piercing motor integrated protector (motor protector) came out, because it has many advantages compared with the thermal relay, it has aroused great interest in the electrical industry.
The core-through structure is not only convenient to use, and completely isolated from the main circuit, it will not affect the main circuit, but also improves its own reliability. At the same time, the problem of heating of the terminal is completely solved, and the interchangeability is good. But at present, generally only large-size motor comprehensive protectors (motor protectors) at home and abroad use the core-through type, while small-size motors can only use the wiring type.
The electronic integrated motor protector (motor protector) solves the problem of the single function of the thermal relay, and newly creates the disadvantage of requiring a working power supply. Although the requirements of electronic circuit amplification and driving need working power supply are reasonable, the application of integrated motor protector (motor protector) brings a series of problems, such as the user must look for the power supply terminal before using it, and understand the power supply Many inconveniences such as voltage level. In addition, because the integrated motor protector (motor protector) needs to work continuously, the failure rate is also high due to factors such as grid voltage fluctuations, interference, and self-heating.