A few aspects concerning the thermal connection of ZnO based varistors

The most efficient surge-arresters in use today are based on ZnO varistors. All electronic devices and power lines are using varistors in order to protect extremely sensitive devices and consumers against any type of overvoltage, mainly lightning strokes or induced overvoltages, both on power supply lines as well as on data lines. The heat produced inside the varistor is basically incontrollable, during a heavy duty permanent regime or after an extremely violent shock. That´s why, finding an efficient method to control heat dissipation or a technical solution to improve the thermal behavior by enlarging the safety stability reserve is very important. The new configuration proposed in this paper consists in two disc varistors electrically connected in parallel with an additional brass common electrode used for heat exchange between the varistors through conduction. This paper presents the finite-element model used for the direct control of heat dissipation and exchange, as well as some experimental results. The thermal behavior of two single varistors in parallel is compared with the new configuration (varistors in parallel with heat exchange), after applying a standard electric shock. Experimental results are shown in order to confirm this solution.