Ground fault detector and shutdown system

Claim 1

A ground fault detection and power shutoff system for underwater AC power transmission which provides protection to divers from underwater electrical shock hazards, comprising: a. an insulated pair of electrical power transmission lines which supply AC power from a source to an insulated underwater load; b. an isolation transformer having a primary and a secondary winding; said secondary winding connected to the input to said insulated pair of power transmission lines; c. a triac connected across the secondary winding of said isolation transformer operable to function as a low resistance path for discharging any stored energy in the load circuit; d. circuit breaker means connected between said source of AC power and the primary winding of said isolation transformer; said circuit breaker means being operable to interrupt the flow of AC power through said pair of transmission lines; e. an insulation resistance monitor circuit including DC supply means for providing a DC output and voltage comparator means; said DC supply means having a positive side of its DC output connected to both of said pair of transmission lines at the secondary winding side of said isolation transformer and to said voltage comparator and a negative side of its DC output connected to ground means; said ground means including any of transmission line ground conductor and shielding, load ground conductor and shielding, and seawater; f. said voltage comparator means being connected to said circuit breaker means and being operable to generate a trip signal for quickly shutting off said circuit breaker means to interrupt the flow of AC power through said transmission lines when there is ground fault due to a drop below a predetermined value in the insulation resistance of any insulation in the system which results in a DC current flow in said insulation resistance monitor circuit means exceeding a predetermined level.