Protective circuit arrangement for a high-voltage capacitor bank

Claim 1

In a protective circuit arrangement for a high voltage capacitor bank, including at least two equal branches containing individual capacitors connected in parallel and on one side to a phase of the network system, a current measuring device being arranged in series with each of the branches for measuring the current therein, with the outputs of the current measuring devices provided to a differential protection device, the output of which is coupled to a monitor, an improved differential protection device comprising: a. a first differential protection relay having first and second inputs and an output; b. first and second highpass filters coupling the first and second inputs of said first differential protection relay to the current measuring devices in the two branches; c. a second differential protection relay having first and second inputs and an output; d. first and second lowpass filters coupling the first and second inputs of said second differential protection relay to said two current measuring devices; e. storage means coupled to the output of said first differential protection relay; f. an AND gate having as inputs the output of said storage means and the output of said second differential protection relay; g. time delay means having its input coupled to the output of said AND gate and providing an output which is delayed to appear a predetermined time after its input appears; and h. wherein the output of said first differential protective relay and the output of said time delay means are coupled to the monitor.