Abstract: A sensing circuit is disclosed for simultaneously and continuously monitoring the impedance of a trip coil of the type used to actuate synchronously operated circuit breakers, and the charge on a capacitor used to power the trip coil. The sensor comprises a circuit including the trip coil, the capacitor, a large resistance and a photo-diode connected together in series. A d.c. voltage is continuously applied across the capacitor, maintaining it charged and causing a constant direct current to flow through the other three components. The magnitude of the current will fall below a predetermined threshold value if either the capacitor voltage, which is proportional to the charge stored on the capacitor, falls below a certain level or the resistance of the trip coil rises above a certain level. The photo-diode produces a light signal representative of the current therethrough.

Abstract: A trigger system for chemical actuators, e.g. of the type used for high voltage isolation, is disclosed. A light source, preferably a laser, emits a powerful, highly concentrated pulse of light energy. The pulse is conveyed by fiber optics to a chemical explosive charge, which it detonates. Because the fiber optics used are excellent electrical insulators, it is possible to locate all of the trigger system except the output end of the fiber optics at ground potential, eliminating the need for shielding the trigger system against high-voltage noise.

Abstract: A method and apparatus for sensing the clearance of a fault current on an ac transmission line and providing a fault cleared signal for closing a current limiter bypass switch includes the technique of successively sensing half cycles of current magnitudes of the system after establishing a predetermined fault current threshold and producing a fault clear signal only when a signal indicating the threshold has been exceeded is followed by two subsequent signals indicating that the threshold has not been exceeded by the two half cycles of current.

Abstract: A fault current limiting resistor for high energy dissipation includes a frustro-conical support structure where the resistor wire is wound on the support structure in the form of a three dimensional spiral. This provides optimum voltage clearances even when the wire may sag due to thermal expansion.