MONITORING DEVICE FOR THE CAPACITOR BATTERY OF A D-C FILTER CIRCUIT

摘要

A circuit for monitoring the capacitor battery of a filter circuit connected to a transmission line, the capacitor battery consisting of at least two parallel legs, each with a number of series-connected capacitors. A first signal is produced which corresponds to the total alternating current flowing through the capacitor battery. A second signal is produced which corresponds to the difference between the currents flowing through the respective parallel legs of the capacitor battery. The current difference signal is compared with a respective fraction of the total current signal. A fault indicator signal is produced if the difference between the difference current signal and the fractional total current signal exceeds a predetermined threshold value. Further circuitry is provided for correcting drift in the difference current signal, which may be caused by temperature variations or acceptable capacitor failures. Automatic ranging circuitry may be provided in embodiments of the invention in which the total capacitor battery current varies in amplitude over a large range.