With the rise in the use of underground cables across different electric grids, the need for accurate and dependable fault location identification of underground transmission and distribution systems is paramount to ensuring that the advantages of Underground (UG) lines are maintained. Notable advantages offered by UG cables include increased resilience and reliability against adverse events, improved public safety in cases of accidents, and arc-flash-induced wildfire mitigation. However, they are accompanied by a set of challenges in their modeling, protection, and fault location estimation, stemming from their special electrical characteristics. Namely, higher shunt capacitances, lower series inductances, large charging currents, and non-linear zero sequence impedances.The most reliable fault locating methods include the double-ended traveling-wave (DE-TW) and the double-ended impedance-based (DE-Z) method. The DE-TW method requires the first TW arrival time to the two local and remote terminals. The DE-Z method uses metered voltages and current from both terminals to perform its fault location calculations. Both methods utilize two relays at different ends of the protected line to communicate through a direct fiber-optic channel or a C37.94 encoding digital channel. Based on filed data, the general convention is that impedance-based fault location is accurate for overhead transmission lines and short underground cables. However, due to the complex electrical behavior of UG cables, especially the nonlinear zero-sequence impedance, accuracy of the DE-Z method becomes more limited in long underground lines. Traveling-wave fault location is much more immune to the hard-to-predict characteristics of UG cables due to its high frequency wave detection, so long as the cable’s propagation velocity is correctly calculated, which is used in the fault locating calculations. The DE-TW method’s robustness aids in detecting more accurate fault locations, especially in long underground cables and hybrid lines consisting of overhead and underground sections. The aim of this research is to set up a hardware-in-the-loop (HIL) test to study the extent to which different fault and XLPE cable characteristics affect the accuracy of the DE-TW and DE-Z fault locating methods. These fault characteristics include the fault type, fault location, fault resistance, and fault inception angle (fault-point-on-wave). The cable characteristics include cable core transposition and bonding/grounding of the cable sheath.
