Apr 01, 2016
Varistor considerations when using
Varistor failure modes are usually short, in order to prevent the varistor failure power short circuit caused the fire, can each pressure-sensitive resistor in series with a thermal fuse or heat from the body. Temperature fuse and varistor has good thermal coupling, when the varistor failure (high impedance circuit), its thermal fuse thermal fuse, so that the failure of the pressure-sensitive resistor and the circuit separation, ensuring the safety of equipment. When high frequency in temporary voltage varistor when the varistor instant breakdown short circuit (low impedance circuit), but before the temperature fuse fuse, and may cause a fire. To avoid this happening, in each of the varistor series on impact resistance of a power frequency fuses (single frequency fuse when the aging may not fuse). Also can put pressure sensitive resistance and ceramic gas discharge tube series using, normal work Shi ceramic gas discharge tube not guide pass, pressure sensitive resistance no leak current, can greatly extended using life; by waves Chung impact Shi, ceramic gas discharge tube first breakdown, then by pressure sensitive resistance limit waves Chung voltage, total of residual pressure for both of and, slightly has increases (dozens of v); impact past Hou, due to pressure sensitive resistance limit has current, discharge tube cannot maintained guide pass and out arc, recovery for normal work State; Dang pressure sensitive resistance short-circuit failure Hou, Ceramic gas discharge tube through a great deal of power current will quickly, but most of its failure modes are open and difficult to fire.
So, in our selection of varistor without error, according to the formula, should select the pressure sensitive 130V varistor voltage nominal voltage, according to the principle is not under, we should actually select the 14D151 model. Moreover, in terms of actual use, we should not direct the varistor and, according to the actual situation should be pressure-sensitive resistors with ceramic gas discharge tubes in series.