Frequency-Selective Grounding for 3ϕ Power Transformers

Abstract

Three phase $(3\phi)$ power transformers can have their windings configured to create local neutral points that can be grounded. The grounding of a $3\phi$ power transformer is designed to limit ground fault currents and maintain low ground potentials. These constraints can be translated into a resistive grounding that is usually designed based on the system ratings and parameters. The resistive grounding, however, can impact the flow of the harmonic components present in the exciting currents. As a result, undesired harmonic components are induced in primary and secondary voltages. This paper presents the design and performance of a frequency-selective grounding that can meet the constraints for grounding a $3\phi$ power transformer. The developed grounding is designed to provide a resistive path for low frequency currents (faults), while providing a low impedance path for high frequency currents (harmonics). The frequency-selective grounding is experimentally tested for a $3\phi$ power transformer with different primary and secondary winding configurations, different fault types, and source grounding. Test results show that the developed grounding can reduce the ground potential, harmonic distortion in primary and secondary voltages, and ground fault currents with a minimum interference with ground fault protective devices.