Research on Field Test of Impulse Grounding Impedance for Small Substation

In this paper, application of a portable instrument to obtain impulse grounding impedance (IGI) characteristics for grounding grid of small substation is introduced. The test currents of 8/20 µs, 10/350 µs and 30/80 µs were chosen as the injection signal sources to the grounding grid respectively with simultaneous measurement of the response transient voltage waveshapes in time domain. The portable instrument and test object for experimental tests are simply described. Field tests were carried out to the grounding grid in a 35 kV substation for 3 consecutive times with different impulse currents, while the corresponding IGI calculated with processing of the impulse current and voltage waveshapes are also given. All of that provides a reference for basic research of lightning protection for the small substation and a better understanding of transient characteristics of grounding grid under the lightning stroke.