Importance Of Negative Phase Sequence Overcurrent Protection For Solidly Grounded Delta-Wye Transformer

The objective of this paper is to discuss about the requirement of Negative Phase Sequence (NPS) overcurrent protection for solidly grounded Delta-Wye transformer and to provide guidelines to select the setting for NPS overcurrent protection. Currently NPS overcurrent protection is not used to protect the static device like transformers in any industrial projects. However for certain risk related to failure of protection equipment, only NPS overcurrent protection can provide backup protection to solidly grounded Delta-Wye transformers. Hence NPS overcurrent protection function can't be avoided in transformer protection relay at delta side of transformer. The comparison between all the transformer protections based on failure of certain protection equipment under fault condition is also discussed in this paper.