A Case Study of Transformer Neutral Common Grounding Effects

Abstract

The paper presents practical issue experienced with nuisance tripping of incomer earth fault protection relay due to insufficient considerations of possible ground current paths in case of common grounding connection for multiple transformers. The design scenarios considered here represent the common industrial practice in Medium voltage [MV] & Low Voltage [LV] distribution network. The effect of different grounding & power distribution designs on the ground fault currents are analysed. The exemplary cases that can be referred to perform fault current calculations necessary for each fault protection co-ordination are presented. The paper also provide guideline to avoid inappropriate grounding design in case of common grounding for multiple transformers.

The examples given in this paper can be used as a reference by power engineers to study the fault current distribution and therefore avoiding inappropriate designs in grounding studies, earth fault protection co-ordinations and associated safety practices.