New Revealing of High-Impedance Fault Testing On Normally Loaded Distribution Feeders

High-impedance faults (HIFs) do not generate fault current sufficient for conventional overcurrent protection but can still ignite fires. Generally, these faults range from a few milliamperes to a few amperes. With the increasing focus on wildfire mitigation, reliable detection of HIFs to prevent wildfires is the industry’s top priority but still poses the biggest challenge to it. To gain more insight on HIFs, further support the research effort, and verify existing HIF detection algorithms, PG&E conducted staged HIF tests on distribution feeders with live load at various locations. The testing revealed some unique aspects of HIFs, including the following:

• Involving the actual ground fault current return path from fault to substation ground during staged testing is the most accurate way to study HIFs. • Downed conductors do not necessarily generate drastic bouncing (sometimes none at all) to create varying arcing signatures. Some existing algorithms are based on this assumption. • The faults were staged on two operational feeders with normal load. Such testing results in a realistic, more accurate fault current signature for testing protection algorithms without overfitting. • The initial stage of vegetation contact is often purely a high-resistance fault with varying resistance and no visible arcing that generates sub-ampere range fault current over tens of minutes before the vegetation experiences arcing over its surface. The initial contact stage is critical to detecting faults to prevent wildfires because once the carbonized vegetation starts arcing and burning, it becomes difficult to contain the fire.

This paper presents the related test data to demonstrate and support the above-mentioned phenomena. Using the information gained during the testing, we propose a new algorithm to detect the early stage of vegetation contact causing HIFs for a three-wire, unigrounded system.