(1) Hot fuse technology. The technology is to install the low melting point metal protected by wax on the varistor through a certain process, when the leakage flow of the varistor is large and the temperature rises to a certain extent, the low melting point metal is fused, so as to cut the varistor from the circuit, which can effectively prevent the varistor from burning. However, hot melt fuses have reliability problems and only have a reliable life of about 5 years in an environment with enhanced thermal cycling. In a thermal cycle environment, hot melt fuses need to be replaced regularly to maintain normal operation.
     (2) The use of spring to pull the low melting point solder technology. This technology is the current technology used by most of the voltage limiting SPD of lightning protection device manufacturers, adding a low melting point solder solder at the pin of the varistor, and then using a spring to pull this welding point, when the leakage current of the varistor is large, the temperature rises to a certain extent, the solder of the welding point is blown off, and the welding point is quickly separated under the pull of the spring. Thus, the varistor is cut out from the circuit, and the alarm contact is linked to send an alarm signal. Because the low-melting metal will flow and crack at the point of force, the solder at the low-melting solder joints in the spring tension will also flow and crack, so the biggest problem with this device is that the solder will age, causing the device to break without reason.
     (3) Temperature fuse technology. The technology package the varistor and temperature fuse in series together, using heat conduction to leakage current on the varistor heat conduction temperature fuse, when the temperature rises to the set temperature of the temperature fuse, the temperature fuse is blown, the varistor is cut out of the circuit. In addition to the same life and reliability problems of temperature fuses, the use of temperature fuses for overheating protection of varistors also has the following problems: The heat conduction path is long, the response speed is too slow, the heat is passed through a certain heat conduction medium (filling material), the temperature fuse housing, the internal filling material of the temperature fuse, and then transmitted to the melt of the temperature insurance, so it determines the response speed of the temperature fuse.
     (4) Isolation technology. The technology encloses the varistor in a closed box that is isolated from other circuits to prevent the spread of varistor smoke and flame. In the case of various backup protection failure, isolation technology is also a simple and effective method, but it needs to occupy a large amount of equipment space, but also to prevent smoke and flame from the box lead holes.
     (5) potting technology. In order to prevent the varistor from smoking, fire and explosion when it fails, some manufacturers use the technology to seal the varistor, but because the varistor will pull the arc inside the failure, resulting in the failure of the sealing material, and the production of carbon, the production of carbon will maintain the arc, which often leads to short circuit and blackening inside the equipment, and even lead to serious blackening of the entire equipment room. The experiment shows that after the varistor is covered with heat shrink sleeve, the heat dissipation of the varistor is affected, and the maximum power dissipation is reduced, which affects the power frequency voltage tolerance of the varistor. From another point of view, the heat dissipation is affected, which will also accelerate the aging of the varistor and affect the service life of the varistor.