WRR-240 WRR-241 WRR-242 WRR-243 WRR-320 B thermocouples
WRR-240 WRR-241 WRR-242 WRR-243 WRR-320 B thermocouples, the failure mode of the varistor is usually short circuit. In order to prevent the varistor's failure from causing a short circuit in the power supply and causing fire, a temperature fuse or a thermal disconnection mechanism can be connected in series on each varistor. The temperature fuse should have good thermal coupling with the varistor. When the varistor fails (high-impedance short circuit), the heat generated by it will fuse the temperature fuse, thereby separating the failed varistor from the circuit and ensuring the equipment. Security. When a high power frequency temporarily acts on the varistor, it may cause the varistor to short-circuit short-circuit (low-impedance short-circuit) momentarily, and the temperature fuse is too late to fuse and may catch fire. To avoid this phenomenon, an additional shock-resistant power-frequency fuse can be connected in series on each varistor (single-use power-frequency fuses may not blow when aging fails). The varistor can also be used in series with the ceramic gas discharge tube. The ceramic gas discharge tube does not conduct during normal operation. There is no leakage current from the varistor, which can greatly extend the service life. When the surge is affected, the ceramic gas discharge tube strikes first. Through, and then the surge voltage is limited by the varistor, the total residual voltage is the sum of the two, slightly increased (tens of volts); after the impact has passed, because the varistor limits the current, the discharge tube cannot maintain conduction When the arc is extinguished, it returns to the normal working state. When the varistor short circuit fails, the ceramic gas discharge tube will quickly fail due to a large power frequency current, but most of its failure modes are open circuits, so it is not easy. Cause a fire.