Portable System for Measuring the Grounding Resistance of Transmission Line Towers Using Fast-Rising Current Pulses

Abstract

A new portable system for measuring the grounding resistance of transmission towers equipped with overhead ground wires (OHGWs) was developed. To predict the lightning performance of power lines, electric power companies until now measure the low-frequency grounding resistance. A new technique of processing the transient impedance time-dependency obtained by injects of a fast-rising pulse current into a tower base was developed. The technique allows the estimation of element values for a simple lumped RLC equivalent tower grounding circuit, suitable for use across a wide range of soil resistivity values. The tower grounding resistance value finally calculated from the obtained resistance value of the equivalent circuit, by accounting for the parallel-connected surge impedances of OHGWs. For the measuring system, a pulse generator based on inductive energy storage was designed. Since an inductive generator's current pulse shape is not distorted due to a reflection from the remote end of the current lead, therefore, the rather short potential and current leads of 50-meter long and short ground rods could be used. The pulse has 100 ns rising time and constant amplitude within the time of measurement interval, which is limited only by the arrival time of a current wave reflected from the nearest OHGW-connected tower. In the implemented prototype, the main instrumentation requirements for field measurements, such as low weight and dimensions, autonomous power, dust and moisture protection, usability, and easy maintenance, were taken into account. The general hardware structure, operational principles, and main technical specifications of the portable measuring system prototype are discussed in the paper along with the field test results.