Ground Fault Detection and Localization for Low Voltage Alternating Current (LVAC) Shipboard Distribution Systems

Hepburn and Sons LLC proposes to design a ground fault detection system for 440VAC three phase radial Navy shipboard power distribution, while teaming with their partner Florida State University, Center for Advanced Power Systems (FSU CAPS). Existing Navy ground fault detection systems can detect and locate single line to ground faults on a given phase, but a second ground fault on a separate phase causes a line-to-line fault which trips breakers and removes power from downstream loads. Quickly detecting, locating, and resolving an initial single ground fault can mitigate the risk of double faults and loss of power to mission critical equipment. The ground fault detection and localization system will function for both permanent and non-permanent fault cases, particularly for USN Shipboard 440VAC three phase radial power distribution either grounded or ungrounded. The low voltage alternating current interface standard, MIL-STD-1399-300-1, provides further characteristics. For ungrounded and high resistance grounded power systems, a single line to ground fault is permissible on one of the three phases enabling continued operation. Without the benefit of simplified fault localization of a solidly grounded power system which trips upon a single ground fault, it is critical to quickly identify the faulted piece of Navy equipment or at least identify the shipboard compartment containing the fault. The Hepburn and FSU CAPS team proposes a noise pattern analysis approach to ground fault protection which yields the benefit of passive localization. This approach mitigates an interference issue that comes with conventional protection strategies involving disruptive signal injection as well as manual disconnect hunting of fault localization by trial and error. The methodology is based upon a patent presenting an autonomous fault location approach differentiating fault location by signal oscillatory characteristics (US Patent 8067942 B2, “Method for locating phase to ground faults in DC distribution systems”). In the presence of power electronic switching devices (converter, etc.), this noise pattern analysis-based fault localization does not require signal injection, but passively monitors a naturally occurring ringing circuit which is altered by a given fault case location. In the absence of such sources of continually occurring switching transients separate injection of a small amount of signal noise may be required. The team is building upon extensive previous work and intellectual property. The developed approach is applicable to the LVAC radial system of this topic, addressing the same challenge for a different system. While taking advantage of the team’s recent developments of a noise pattern analysis methodology, various fault protection methodologies will be investigated and considered through an analysis of alternative approaches, to thoroughly explore the optimal system solution.