Investigation on Impulse Characteristic of Full-Scale Grounding Grid in Substation

Impulse performance of grounding grid is needed for lightning protection design of power system. This paper describes an impulse test facility established for the full-scale grounding grid (50 m long and 52.5 m wide) in a 110 kV substation. Test method is presented, including configuration of current injection and return point, measurement of potential rise and longitudinal current. Impulse test is carried out with 2.6/50 and 8/20 μs current waveform, and the maximum current amplitude is 4 kA. A Current Distribution, Electromagnetic fields, Grounding and Soil structure simulation for the tested grounding grid is also adopted. Impulse performance of full-scale grounding grid is affected by soil ionization and conductor inductance. There is steeper peak on the potential rise waveform near the injection point with shorter wave front current, which leads to more uneven potential rise distribution. Partial soil ionization could increase the current dispersing into the soil at partial area of the grounding grid, and the longitudinal current flowing to the next area decreases. These two factors pose a high potential difference hazard to the secondary equipment via the secondary cable.

I. Introduction

Impulse performance of grounding grid subjected to lightning stroke is important in lightning protection design for power system [1], [2]. With the injection of lightning current into grounding grid, large current and high potential rise could cause danger to people and equipment [3], [4]. Due to the soil ionization and conductor inductance, impulse performance of grounding grid is quite different from that under power frequency condition [5]–[7] . Impulse characteristic of grounding grid is mainly investigated based on numerical simulation and impulse test. There are many kinds of simulation model applied with the development of computer technology [8]–[10]. But the quality of simulation result is strongly dependent on the assumptions adopted, and the result needs to be verified by lots of test.