GB863231A - Improvements in or relating to electric protective systems - Google Patents

Abstract

863,231. Protective cut-out arrangements. GENERAL ELECTRIC CO. Ltd. Sept. 10, 1959 [Sept. 10, 1958], No. 29031/58. Class 38 (5). In a circulating-current protective arrangement for a polyphase transformer 1, a closed loop circuit is inductively coupled to pilot wires interconnecting the current transformers 4 . . . 9 on both sides of the transformer 1, the loop circuit including rectifiers connected in series and each rectifier rectifying current induced from the inductive coupling with a different one of the pilot wires. In the Figure, the pilot wire circuit includes differential current transformers 26 . . . 28 having their primary windings connected between a star point 16 and centre-tappings on the primary windings of load bias transformers 11, 14 and 15. The first secondary windings 29 . . . 31 of the differential current transformers 26 . . . 28 are connected through circuits 32 . . . 34, tuned to the fundamental frequency, to rectifiers 35 . . . 37 having their output terminals connected in series in a closed loop circuit to supply operating current to a polarized relay 38. The second secondary windings 39 . . . 41 of the differential current transformers 26. . . 28 are connected to rectifiers 42 . . . 44 which have their output terminals connected in series in a closed loop circuit which supplies harmonic biasing current to the relay 38. Similarly, the secondary windings of the load-bias transformers are connected to rectifiers 48 . . . 50 which supply load bias current to the relay 38. Specification 767,188 is referred to.