Third harmonic current contribution from synchronous generator with filtering during ground fault

Synchronous generator is one of the harmonic sources despite the non-linear load. Zig-zag transformer can be used to filter third harmonic originating from synchronous generator from entering the power system network. During ground fault, the fundamental and third harmonic fault currents share the same path when returning to generator neutral. This will result in higher fault current flowing in neutral cable. The aim of this paper is to study the contribution of third harmonic fault current from synchronous generator with zig-zag transformer filtering method during three-phase to ground (TFG) fault. Laboratory scale experiments were conducted to determine the degree of contribution of the third harmonic current. The presence of neutral earthing resistor (NER) and fault impedance (ZF) are the scenarios in the experiments during normal and filter (using zig-zag transformer) modes. The contribution of third harmonic current to the overall fault level during TFG fault is analyzed for each case. The results show that the NER presence has increased the zero sequence impedance. Thus, NER will lower third harmonic current regardless of with or without ZF and under normal or filter mode. In contrast, the third harmonic contribution to fault current is at the highest when NER and ZF are absent under normal and filter modes. When ZF is present, the third harmonic contribution depends on the effective zero sequence impedance of the network.