“High-Impedance Fault Detection” Revisited: Why the Term Has Lost Its Meaning and Should be Abandoned

“High-impedance fault” is a commonly used term in power system literature with a decades-long history. While the term may be commonly used, it is not used consistently. This is especially true when one considers the disparity between usage in academic and industry contexts. In academic literature, the term is seldom defined explicitly, but appears to mean something like, “faults that are hard to detect.” When the authors informally survey practitioners, a common answer to the question, “What is a high-impedance fault?” resembles, “It is a fault with a high impedance.” While this is correct by way of tautology, it is unhelpful as a functional matter. Few practitioners or academics include multiple varieties of power system events that occur on operational circuits which might reasonably be called a high impedance fault, nor do they consider distinct and often differing characteristics of such events. Said differently, “high-impedance fault” is not a homogeneous class of events which can be considered uniformly, but a diverse set of power system conditions which share some characteristics and diverge substantially in others. This paper draws on over 40 years of practical experience and research in electrical characterization of normal and abnormal power system transients performed at the Power System Automation Laboratory at Texas A&M University to argue that the term “high-impedance fault” itself has become an impediment to developing techniques and technologies for detecting and mitigating a wide class of power system events which do not reliably operate conventional overcurrent protection devices.