GB542287A - Improvements in or relating to electric protective arrangements - Google Patents

Abstract

542,287. Protective cut-out systems. REYROLLE & CO., Ltd., A., and COATES, R. H. July 1, 1940, No. 11072. [Class 38 (v)] A section or unit comprising a feeder A<SP>1</SP> ... A' directly connected to a star-constructed transformer (or other power) winding, is protected by balancing the output of current transformers C' ... C<SP>3</SP> in the three phases at the end remote from the winding, against that of current transformers D<SP>1</SP>, D<SP>2</SP> in two of the phases adjacent the winding and of a transformer E in the earthconnection of the winding, the former transformers being star-connected in the usual way to the primary G of a saturable summation transformer, whereas the star point of transformers D<SP>1</SP>, D<SP>2</SP> is connected to the tapping H<SP>2</SP> of the primary H and transformer E between that tapping and the end H' of the transformer at that end. The secondaries G<SP>5</SP>, H<SP>5</SP> are inter-connected by a pilot circuit J including tuned relay transformers K supplying the operating coils of relays L, the restraining coils L<SP>1</SP> of which are energized by further secondaries G<SP>6</SP>, H'. The arrangement provides full protection for the feeder and earth-fault protection for the winding, but is stable against external earth or phase faults. For example, with an earth fault on A<SP>3</SP> equal parts of the transformers G. H are energized by C<SP>3</SP> and E, respectively, and balance is obtained, whereas with an external fault on A<SP>1</SP>, the whole of both primaries are energized by C<SP>1</SP> at one end and D', E at the other end and adequate balance is obtained in spite of the unequal burdens on the current transformers at the respective ends.