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Reply To: Protection riddle No.2 – Stability of transformer differential protection

#1887
Hamid

    Yes I agree you, according to IEEE C37.91-1985 PAGE 38, the modern differential relays are of even low burden than the usual auxiliary current transformers. Thus, the common point of the relay connections should not be connected to the common point of the Y-connected transformers ( a connection which is necessary without the zero-sequence filter). Only the filter neutral should be connected to the current transformer common point. Unfortunately some of reference documents ,such as ABB special publications, have not considered this technical point. Please note to diagarm below: