Analysis of fault locating signals for high-impedance grounded systems

Abstract

High-resistance grounding and ungrounded power systems have many advantages, including continuous operation after a ground fault. However, locating ground faults is inherently difficult and is a major disadvantage with these systems. The problem stems from the lack of a good signal, such as a large fault current, that points to the fault. Classical search methods use injected locating signals, but they have shortcomings with intermittent faults, multiple "same-phase" faults, and closed-loop/mesh power networks. New location methods attempt to overcome these previous problems by providing signals that can be used during system operation and with microprocessor-based detectors. This paper explores some of the key technical issues surrounding locating signals. Of concern are the signal flows through the power network including the uniqueness of the signal path. Other issues that are addressed are signal levels and power requirement, network impedances, and the impact of grounding capacitances and grounding resistances that divert the locating signal.