Abstract: A series capacitor bank for connection into an electric power supply network is provided with overvoltage protective equipment having two branches connected in parallel with the capacitor bank. The first branch comprises a first zinc oxide varistor in series with a linear resistor and the second branch comprises a varistor with a higher "knee" voltage than the first zinc oxide varistor. The resistance of the linear resistor is preferably of the same order of magnitude as the absolute value of the impedance of the capacitor bank at the operating frequency of the power supply network. The "knee" voltage of the second varistor is at least 1.15 times (and preferably not more than 2.0 times) the "knee" voltage of the first varistor.

Abstract: A linear resistor is serially connected to a voltage-dependent metal oxide varistor and the series-connected resistor elements are connected in parallel with the series capacitor of a high voltage network to provide an overvoltage protection circuit for the series capacitor. A spark gap is also connected in parallel with the series-connected resistor elements in case of overload thereof. The voltage across the linear resistor triggers device for firing the spark gap when the voltage across the linear resistor exceeds a predetermined voltage. The resistance of the linear resistor and that of the varistor is dimensioned such that the predetermined voltage constitutes the smaller part of the voltage across the capacitor.

Abstract: A protective device for a capacitor bank is coupled to a cross-connection between equipotential points in two sub-banks forming the bank. Current or voltage surges, indicative of a capacitor failure are counted and when a threshold level is exceeded, an alarm may be energized.

Abstract: Series capacitor blanks are inserted in high-voltage alternating current network systems in order to improve the stability of the system. Such capacitor banks are provided with a shunt-circuit for short-circuiting the capacitors if the voltage across them increases above a predetermined value at which the capacitors may be damaged or destroyed. When, in the event of a disturbance in the network, said shunt-circuit has short-circuited the capacitors, the stabilizing ability of the capacitors is gone. In order to avoid this, the capacitor bank is provided with a further shunt circuit including non-linear resistors, said resistors having a very high resistance as long as the voltage across the capacitor bank is lower than a predetermined value. Said value is higher than the noraml operating voltage of the capacitors but lower than the voltage at which the first shunt circuit short-circuits the capacitor bank.