GB857687A - Improvements in or relating to generator control and protective system - Google Patents

Abstract

857,687. Protective cut-out arrangements. WESTINGHOUSE ELECTRIC CORPORATION. Aug. 26, 1958, No. 27322/58. Class 38 (5). [Also in Group XXXV] A differential fault protection circuit for a generator 1, Fig. 4, and feeders 8 supplying a set of bus-bars 4 comprises current transformers 125a, 125b, 125c, 126a, 126b, 126c connected together in voltage opposition. On the occurrence of a fault, a voltage will appear across two or more of lines 128a, 128b, 128c connected to rectifiers 127a, 127b, 127c which are connected to earth through a resistor 129. A part of the voltage across this resistor is applied through a rectifier 132 and a Zener diode 134 to transistors 76, 77, 80, 81 effecting energization of the field excitation trip coil 57, which also closes a contact 60, tripping a circuit-breaker 3. Resistors 131a, 131b 131c may provide a fixed load on the current transformers and a smoothing capacitor 130 may be provided. Overvoltage protection is provided by a 3-phase transformer 135, 137 connected to the generator terminals, which supplies a rectifier 138 feeding an inverse time delay circuit comprising a capacitor 140 connected to the rectifier 138 through a Zener diode 141 and a resistor 142, a discharging circuit being provided by a resistor 143 and a rectifier 144. Under over-voltage conditions, the diode 141 breaks down charging capacitor 140, the voltage from which is applied through a diode 146 and a rectifier 148 to the transistor 76 effecting the energization of the trip coil 57 and hence tripping the circuitbreaker 3. An anti-reclosing circuit is provided by a bi-stable circuit 61 (Fig. 3B, not shown), which changes its state and prevents cycling of the system when a signal is passed to it from the transistor 77 through a Zener diode 82 and resistor 83.