Electrolytic cell shunting switch - with parallel connected varistor as energy absorber to prevent contact burn-up

摘要

Bridge-over switches for use in short-circuiting electrolytic cells during necessary routine maintenance work are normally designed as low-voltage vacuum switches or gas-blast circuit breakers. At least one voltage-dependent resistor in a low-inductivity arrangement is connected in parallel to the switch to act as an energy absorber. The circuit breaker (2) is pref. closed during any maintenance work on the elctrolyte cell (1). The burn-up of the contacts during the switch opening is pref. eliminated by connecting a varistor (3) in parallel as an energy absorber. The pref. type is a zinc oxide varistor in a low-inductivity circuit which is designed to carry the working current below the arc voltage of the circuit breaker and absorbs only a residual current of a few ampere during normal working. Another alternative is one or more heavy-current diodes. The opening of such a switch at the end of the service work produces a high-intensity d.c. arc which would cause a rapid burn-up of the switch contacts if no counter measures were taken.