Today, the editor of the varistor manufacturer will tell you about 5 kinds of overheating protection technologies:

(1) Hot melt fuse technology. This technology is to install the low melting point metal protected by wax on the varistor through a certain process. When the leakage current of the varistor is too large and the temperature rises to a certain level, the low melting point metal is fused, thereby removing the varistor from the varistor. It is cut off in the circuit, which can effectively prevent the varistor from catching fire and burning. Thermal fuses, however, have reliability issues and only have a reliable lifespan of about 5 years in environments with intensive thermal cycling. In thermal cycling environments, thermal fuses need to be replaced periodically to maintain proper operation.

(2) Use the spring to pull the low melting point solder technology. This technology is the technology adopted by the voltage-limiting SPDs of the vast majority of lightning arrester manufacturers. A low-melting solder joint is added to the pin of the varistor, and then a spring is used to pull the solder joint. When the leakage current of the varistor is too large, when the temperature rises to a certain level, the solder of the solder joint is fused, and the solder joint is quickly separated under the tension of the spring, thereby cutting the varistor from the circuit, and at the same time, the alarm contact is linked to send out warning signal. Because the low melting point metal will flow and crack at the point of stress, the solder of the low melting point solder joint under the spring tension will also flow and crack, so the biggest problem with this kind of device is that the solder will age, causing the device to break for no reason open.

(3) Thermal fuse technology. This technology encapsulates the varistor and the thermal fuse in series, and uses thermal conduction to transfer the heat generated by the leakage current on the varistor to the thermal fuse. When the temperature rises to the set temperature of the thermal fuse, the thermal fuse is blown. The varistor is cut from the circuit. In addition to the same life and reliability problems of thermal fuses, the use of thermal fuses to protect varistors from overheating also has the following problems: long thermal conduction path, too slow response speed, heat is passed through a certain thermal conduction medium (filling material), The thermal fuse shell, the internal filling material of the thermal fuse, and then transferred to the melt of the thermal fuse, thus determine the slow response speed of the thermal fuse.

(4) Isolation technology. This technology packs the varistor in an airtight box, which is isolated from other circuits to prevent the spread of varistor smoke and flames. In the case of failure of various backup protections, isolation technology is also a simple and effective method, but it needs to occupy the equipment space of the university, and at the same time, it must also prevent smoke and flame from escaping from the opening of the box body. come out.

(5) Potting technology. In order to prevent smoke, fire and explosion of the varistor when it fails, some manufacturers use this technology to encapsulate the varistor. Carbon, the generation of carbon will maintain the arc, which will often lead to short circuit and blackening inside the equipment, and even lead to serious blackening of the entire equipment room. Experiments show that after the varistor is sheathed with a heat-shrinkable sleeve, due to the influence of the heat dissipation of the varistor, the maximum dissipation power of the varistor is reduced, which affects the power frequency voltage tolerance of the varistor. From another perspective, Affected heat dissipation will also accelerate the aging of the varistor and affect the service life of the varistor.