Single-Wire Time Domain Reflectometry Technique (SW-TDR): Detecting Faults in Power System Grounding Electrodes

Abstract

The performance of electrical power systems relies on a healthy and properly functioning grounding network. Buried vertical electrodes are the pillars of a grounding system. This paper presents a Time Domain Reflectometry (TDR) technique based on surface wave propagation along a single wire to detect a fault. In SW-TDR, a fast rise-time pulse is injected onto the single conductor grounding electrode primarily exciting transverse magnetic (TM) mode surface wave propagation. The surface wave propagates along the electrode and is reflected at any impedance mismatch such as a fault in the electrode. The mismatch location and severity of the fault can be identified using the reflected signal waveform. Expressions for the fields of the surface wave supported by a single electrode in a lossy media is presented. Full wave electromagnetic simulation is used to evaluate the wide-band input impedance and then FFT is applied to determine the TDR response. Simulation results show that SW-TDR can identify a break-point or even partial corrosion of a grounding electrode for a wide range of soil conductivity for a system bandwidth of 200 MHz. A surface wave launcher design is also presented which enables the SW-TDR to be implemented without disconnecting the electrode from the grounding grid. A scale model experiment demonstrates the feasibility of the SW-TDR approach. Measurements show detection capabilities are similar to those obtained by simulation.

Keywords

• Grounding electrode corrosion
• fault detection
• fault location
• surface wave propagation
• single conductor transmission line
• sommerfeld surface wave time