Impact of parallel high voltage transformers with and without earthing transformer

Abstract

The research focuses on the impact of parallel two power transformers with and without earthing transformer based on potential earth fault events. Paralleling two power transformers is recommended in medium voltage substation topology to adopt N-1 criteria and minimize interruption time. However, the paralleling transformers may cause other issues such as increasing the level of fault current and oblige additional protection coordination to isolate the exact transformer during the fault. This research will examine and analyze the benefit and consequence after parallel both transformers with and without earthing transformer. The study focuses on 132/22 kV transformers with star-delta vector group that connected to the diverse topology involving earthing transformer before connected to neutral earth resistor. Based on the investigation, it found that the star-delta transformer without earthing transformer at one side of transformers has a higher potential to cause poor isolation during any event of an earth fault due to insulation design. Moreover, the transformer that connected to earthing transformer has a higher possibility to experience higher fault current which indirectly reduces the life span of that earthing transformer as well as power transformer due to unavailability of the earthing transformer at the other transformer.