Performance Evaluation of High Voltage Laboratory Grounding

One of the most important parameters to provide safety for personnel and test equipment in high voltage laboratories is a reliable grounding system. The main characteristics of a reliable grounding system include low resistance at low frequency tests (power frequency test) and low potential rise at high frequency tests such as an impulse test. Also, low impedance connections in the test equipment grounding circuits could improve the grounding system's reliability. Therefore, in this paper the reliability of the grounding system is evaluated during routine activities at Mississippi State University's High Voltage Laboratory. For assessment, the ground potential rise was measured at all accessible ground connections for the impulse test system. Also, the effect of moisture variation in the laboratory ground soil layers was studied. In addition, the high frequency response of the laboratory grounding system was measured, and the feasibility of using alternative conductor types for the test equipment grounding circuits was investigated. Results show that several grounding points in the laboratory exhibit high voltage levels (ground potential rise) during impulse testing, which signifies a reduced safety for measuring devices and other equipment in the laboratory. Also, due to the type of grounding soil, its resistivity changes during different seasons throughout the year. Additionally, the harmonic impedance of the grounding system showed resistive behavior for a wide range of frequencies, and using the conductor strips instead of braided wire decreased the test circuit inductance which is a desirable feature from the grounding perspective.