Experimental Assessment of Grounding System Impacts on Ground Currents and Transient Overvoltage

In this article, experimental performance assessment and comparison are presented for solid, low impedance, high impedance, frequency-selective, and isolated grounding (IG) systems. The typical design of a grounding system (for low and medium voltage generation, transmission, and distribution systems) is based on selecting an impedance (ZG), which is used to connect the neutral point and the ground. The impedance ZG 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 ZG on ground currents and potentials during ground faults. In this article, solid, low impedance, high impedance, frequency-selective, and IG 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 overvoltage, and service continuity.