High voltage measuring circuit coupled to the capacitive grounding tap bushing of an HV device

A high voltage measuring circuit for broadband measurement of transient signals occurring in high voltage apparatus, said measuring circuit being housed in a shielded housing, said measuring circuit having an input sensing circuit for connection to a capacitive grounded tap bushing of a high voltage apparatus, said sensing circuit having an electrical shielded connection connected to an output circuit, said measuring circuit having means to generate output signals which are replicas of the high voltage transient signals appearing on said tap bushing, said measuring circuit having a broadband which extends over a frequency band of from about 1 Hz to 1 MHz and has a signal level higher than background noise, said input sensing circuit having an input current transformer, said current transformer having a primary winding connected to the said capacitive grounded tap busing and to a bushing flange, said transformer having a sufficient number of turns in its secondary winding to maintain a constant transformation ratio up to about 3 MHz, said secondary winding of said current transformer having its output integrated by a passive integrator and an active integrator acting respectively in the low and high frequency spectrum of said frequency band and ensuring a constant ratio of the input and output signals of said frequency band of the said measuring circuit.