A harmonic-based approach for open-neutral fault detection in low voltage systems

In three-phase four-wire low voltage systems supplying unbalanced loads, open neutral fault may lead to serious overvoltage at the feeder terminal because of neutral potential shift, in turn damage appliances and even cause fire. Nowadays, all open-neutral fault detection devices have to be installed close to the loads or at feeder terminal, which results in higher cost and maintenance issues. A new detection approach is proposed in the paper. By using it, the detection device can be simply installed at the feeder head, even the feeder supplies for multiple loads. Main idea of the proposed approach is that the fault can be identified according to the 3^rd harmonic variation measured at the feeder head since the 3^rd harmonic current shall vary significantly when open neutral fault occurs. Analysis on harmonic characteristics of open neutral fault, factors impacting validity of proposed approach and simulation results are presented in this paper.