Safe Underwater Electrical Power.

The Civil Engineering Laboratory is developing a unique and improved ground fault detection and diver protection system that will allow safe electrical power transmission underwater. The system is designed to sense and shut down all electrical power on ground fault currents of 4.5 mA or more in 10 ms. The shutdown is performed in two steps: (1) first a signal initiated by a leakage to ground in the transmission cable or load trips the main power circuit breaker, and (2) a set of triacs are turned on which are connected to short the power lines. The circuit breaker is backed up by conventional fuses that would blow quickly from the short circuit current if the breaker should fail. This sequence of events is designed to occur in approximately 10 ms. The design of the system is adaptable to electric power transmission systems supplying up to 100 kW. The paper reviews electrical safety criteria relative to divers, describes the Civil Engineering Laboratory's protection concept, and presents laboratory test results from an experimental system protection a 30-kW underwater load. (Author)