GB906049A - Improvements in and relating to protective relay systems for three-phase power circuits - Google Patents

Abstract

906,049. Protective cut-out arrangements. ENGLISH ELECTRIC CO. Ltd. April 7, 1959 [Jan. 7, 1958], No. 590/58. Class 38 (5). A three-phase distance relay arrangement has means for deriving a D.C. operating signal proportional to the amplitude of a vector quantity IZ-V for each phase, means for deriving a D.C. restraining signal proportional to the amplitude of the phase-to-neutral voltage V for each phase, and means which respond when the sum of the three D.C. operating signals exceeds the sum of the three D.C. restraining signals. In Fig. 1, transactors 9a ... 9c each have a primary winding supplied from a current transformer 8a ... 8c and a secondary winding connected to a phase-shift circuit 13a ... 13c. Voltage signals from voltage transformers 14a ... 14c are also applied to the phase-shift circuits and the resulting combined A.C. signals are supplied to auxiliary voltage transformers 15a ... 15c before being rectified by rectifiers 16a. . . 16c. Voltage signals from the transformers 14a ... 14c are also supplied to auxiliary voltage transformers 17a. . . 17c and rectified by rectifiers 18a. . . 18c. The output terminals of the rectifiers are connected in parallel so that the sum of the outputs from the rectifiers 16a ... 16c is opposed by that of the rectifiers 18a ... 18c. The resulting signal is applied to the bases of transistors 19, 20 controlling a polarized relay 5 having its contacts 6 in the tripping circuit of a circuit-breaker 4. To improve the response of the arrangement to earth faults, the transactors 9a. . . 9c may have additional primary windings which are energized by a zero sequence current component derived from an autotransformer 10. The power supply for the transistors may be derived from transformers 11, 12 and rectifiers 21, 22 as shown or from a battery.