A ground fault protection method for ungrounded systems

This paper presents a novel approach to simultaneous ground fault isolation for ungrounded power systems. The concept capitalizes on current differential and directional overcurrent designs by considering the second ground fault on the system to prevent a phase-to-phase-to-ground fault. Supplying uninterrupted power to consumers is important. Ungrounded power systems have an advantage of ride-through capability during single phase-to-ground faults. It is desirable and important, to trip only the appropriate breakers during faults. While an ungrounded power system can remain operational with a single phase-to-ground fault there are circumstances when a major portion of the distribution system shuts down upon a second ground fault on another phase resulting in a phase-to-phase-to-ground fault. A patent pending concept exploits prior art designs universally regardless of the various relay manufacturerspsila implementation methods. Combining prior art differential protection and ground fault detection the invention minimizes breaker tripping by addressing multiple ground faults.