Protective circuit for series capacitor banks

Claim 1

A protective circuit used in a series capacitor bank in a high voltage network, said circuit comprising: a voltage-dependent resistor connected in parallel with said capacitor bank, a spark gap circuit means for shunting the latter in case of overload thereof, said circuit means including at least two-series-connected spark gaps each provided with control impedances, an overload detector for said resistor, a pulse transformer for generating a high voltage pulse for triggering said spark gap means in case of resistor overload, said transformer having a low voltage winding and a high voltage winding, an auxiliary capacitor adapted to be charged during overload operation of the protective circuit, a switching means, said low voltage transformer winding being connected to said auxiliary capacitor through said switching means for charging said auxiliary capacitor upon closing of said switching means, said switching means being open during normal operation and being controlled by said overload detector in such a way that it closes in response to the resistor overload condition for triggering said spark gap means, said high voltage traneformer winding being connected in series with a resistor means across one of said spark gaps and its control impedance, said resistor means including a metal oxide varistor, and said transformer being so connected within the circuit that said generated high voltage pulse is in opposition to the voltage across the capacitor bank.