Development of Modern Phase Earthing System for Improving Quality of Supply in MV Network

This paper introduces the methods development of the modern phase earthing system. The target is reducing the harmful short interruptions experienced by the customers and electricity producers with temporary phase-to-earth faults of an MV system. Especially in neutral isolated MV networks the earth fault arc does not usually become extinct without an automatic reclosing function. It can be extinguished using shunt circuitbreaker to earth the faulty phase temporarily at the feeding primary substation. The functioning of the shunt-circuit breaker does not cause any voltage break to customers or DG units connected to the MV or LV system. An essential requirement enabling the applying of the phase earthing is that the residual current at the fault location must be determined reliably in order to evaluate fulfilling of the touch voltage regulations. The inexact information on the magnitude of the residual current has restricted the utilization of phase earthing. The main attention was paid to the modeling of the phase earthing system for developing the method for determining the residual phase-toearth current. The developed novel algorithm was tested applying PSCAD simulation environment. The results show that the residual fault current can be calculated with the actual fault case (e.g. IED or Centralized Protection System, CPS). The prototype of shunt circuit-breaker has also been installed and tested with artificial earth faults.