Electrical Shock Hazard Protection System

Abstract

ABSTRACT A new electrical shock hazard protection system actually predicts impending shock hazard and provides advance warning or shutdown of electrical equipment to protect deck handlers and divers working near electrical power cables. The increasing use of electrical diver support equipment, tethered vehicles, and high power remote subsea equipment has increased the need for a failsafe shock hazard protection system. At the same time, the higher voltages, higher power, and longer cable lengths now being used make it more difficult to get good protection without a high incidence of false alarms. With the new approach, it is no longer necessary to tolerate more false alarms to get better sensitivity. This new system is immune to false alarms from changes in submerged cable length, temperature, and electrical load Characteristics including balance and transients. It also gives an alarm for almost any type of malfunction within the protective system itself. On its first application in the ocean, this system operated hundreds of hours without false alarms. It then gave an alarm when it detected damage to the jacket of a cable between canisters on the remote vehicle. It subsequently shut off power when it detected further breakdown of the insulation around the conductors inside the jacket at the point of damage. Even though this ground fault occurred in an interconnect cable on a remote vehicle, the detection system at the 'surface sensed the condition immediately. Future applications for this device include use on any electrical equipment in the marine environment. Applications to high-voltage and highpower remote vehicles are emphasized in this paper. INTRODUCTION Picture yourself on a steel deck with seawater washing around your ankles while you try to manhandle an umbilical cable carrying 2300V electrical power. One of your foremost concerns is bound to be the integrity of the insulation in the cable. Designers of electrical equipment for use in this environment should be equally concerned, especially since techniques are now available to continuously test the insulation and predict shock hazards, while the equipment is running, without impacting normal operation. The use of undersea electrical instrumentation and power equipment is rapidly growing in response to economic and safety demands of the expanding offshore industry. This is true for both manned and remotely controlled systems including underwater welding equipment, sophisticated manipulator bells, submersibles which are tethered to allow greatly increased mission time, and high-powered remotely-controlled vehicles such as trenchers. In the last few years, the power level has gone from 1kW to 2,000 kW; cable lengths from a few hundred feet to several thousand feet, and the transmission voltages are increasing to accommodate the higher power levels--from 24V to 120V to 480V to 2400V to 6600V. Each such extension increases the hazard to human life. Undersea power cables, particularly working cables used in the equipments outlined above, are indeed vulnerable.