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Analysis of misoperation of the differential current relay applied in a Y-Y-Y-{Delta} transformer

Conference ·
OSTI ID:94253
;  [1]
  1. Alfred Univ., NY (United States). Div. of Electrical Engineering
Transformers play an important role in power transmission and distribution systems. For the operation of transformers, the differential current relay is the most important kind of relay in transformer protective relays in present power system.s In principle, a differential current relay may safely and quickly remove the internal fault occurring inside a transformer and in the feeder between the transformer and the busbar within the range of protection. When an external fault happens outside of the transformer, the relay should be reliably locked to ensure that the protected transformer can normally operate. However, because transformers have many different structures and winding connections forms, especially some specially winding-connected transformers, misconnection of the differential current relay may happen in some circumstances. When an external fault occurs, the relay connected in the incorrect way may cause misoperation of the relay, enlarging the range of the system fault. This paper illustrates a misoperation of a set of differential relays applied in a special multi-winding transformer, with triple-Y-connected windings and an additional delta-connected winding, due to the misconnection of the relays in field. An analysis of the difference of the equivalent circuits between the triple-Y-connected winding transformer and the triple-Y-connected winding with an additional delta-connected winding transformer is presented. Some measures to prevent those mistakes are discussed in this paper.
OSTI ID:
94253
Report Number(s):
CONF-950414--
Country of Publication:
United States
Language:
English