Experimental Performance of Grounding Systems

Abstract

In this paper, experimental performance assessment and comparison are presented for the solid, low impedance, high impedance, frequency-selective, and isolated grounding systems. The typical design of a grounding system (for low and medium voltage generation, transmission, and distribution systems) is based on selecting an impedance ( Z̄G), which is used to connect the neutral point and ground. The impedance Z̄G is typically composed from a combination of R, L, and C elements. The combination type (series or parallel), along with the values of R, L, C elements, allow estimating the possible effects of Z̄G on ground currents and potentials during ground faults. In this paper, the solid, low impedance, high impedance, frequency-selective, and isolated grounding systems are designed for a 35 kVA 3φ transformer and a 5 kVA 3φ synchronous generator, for purposes of assessing and comparing their effects on ground currents and potentials during ground faults. The laboratory transformer and generator are tested for line-to-ground and double line-to-ground faults with all designed grounding systems under different loading levels. Experimental results show that some grounding systems can effectively reduce ground currents, and other grounding systems can effectively reduce ground potentials. These capabilities and features can be used to achieve certain system and operation mandates, including ground capacity, maximum allowed over-voltage, and service continuity.