Self-powered electrical measuring system isolated from electrical perturbances

Claim 1

A self-powered electrical measuring system for measuring current in a high-voltage circuit, said system comprising: current measuring means for sensing a current flowing in a conductor and producing a voltage signal proportional to the magnitude of said current, said current measuring means being a Rogowski coil disposed about said conductor, said coil producing said output signal in terms of about a few mv per Amp. and in accordance with the following formula: ##EQU2## where: E is the voltage, N is the number of turns (about 1000), A the section of the coil, R the radius of the coil, I the current, and T the time, electronic conditioning circuit means for conditioning said signal for transmission by optical link means to a remote receiver operating at ground potential and which is totally isolated from the high voltage circuit, said electronic conditioning circuit means having a modulator circuit for receiving said signal from said Rogowski coil and modulating same for transmission by a transmitter circuit connected thereto, said transmitter circuit generating a composite modulated signal over said optical link means, a floating supply means for deriving a supply voltage from the conductor for feeding said electronic conditioning circuit means, said floating supply means having a tapping coil with a magnetic core disposed about said conductor for tapping, by magnetic inductance caused by current flow in said conductor, sufficient voltage to feed said electronic conditioning circuit means; said tapping coil having a sufficient number of turns to generate said sufficient voltage even at low current flow in said conductor, said magnetic core having a selected dimension so as to saturate during high current surges such as occurs during a short-circuit condition, said system being located within a module is a toroidal shape metal housing disposed about said conductor and shielding said system from environmental electrical perturbances, a vacuum chamber is provided within said metal housing and has a fixed contact therein secured to a high-voltage line, an axially movable conductive contact rod is displaceably supported in sealing engagement with said vacuum chamber and as a portion extending exteriorly of said chamber, said toroidal shape metal housing being disposed about a portion of said contact rod exteriorly of said chamber with said Rogowski coil and tapping coil positioned thereabout.