Patent GB-409823-A (GB)
Title: Electro-responsive systems, for use particularly for protective purposes
IPC: H02H3/52
Filed: 1932-12-17
Abstract: 409,823. Protective cut-out arrangements. FITZGERALD, A. S., 433, Warwick Road, Wynnewood, Pennsylvania, U.S.A. Dec. 17, 1932, No. 35858. Convention date, Dec. 17, 1931. Addition to 407,745. [Class 38 (v).] The invention described in the parent Specification is modified by providing means for deriving from the polyphase circuit alternating electrical quantities variable in accordance with the electrical conditions prevailing in the individual phases of the circuit and having a frequency different from that of the fundamental of the circuit, for effecting the circuit-controlling action. Preferably the derived quantities comprise multiple frequency currents, such as third harmonics. In Fig. 1, a saturable transformer 4 is connected in each circuit of current transformers 5 supplying the operating coils 6 of an induction disc or (as shown) balanced-beam trip relay 7, the restraining coil 11 of which is energized from the series-connected secondaries of the transformers 4 through a filter 10. With balanced currents in the lines 1, the saturation of the transformers 4 produces third-harmonic currents in the secondaries, which currents are cumulatively applied to winding 11 to counteract the operating currents in 6. The main frequency currents in the secondaries of transformers 4 sum to zero, but are in any case filtered out by 10. With an interphase fault, the currents in the two lines affected will be in opposition, and consequently the third-harmonic currents in the two transformers 4 associated with those lines will be in opposition, so that the restraint is approximately zero and the relay 7 operates. The arrangement can be modified to respond to heavy balanced loads by making the plunger 15 of coil 11 easily saturable, and ground faults can be dealt with by a relay in the neutral wire of the circuit 5, 6. The filter 10 may be a resonant filter, but if the system is to be made operable on more than one frequency, a " highpass " filter may be employed, or the filter can be dispensed with in certain conditions. In another form, Fig. 2 (not shown), the output from the filter 10 may be rectified and applied to the grids of thermionic valves, the anode circuits of which are energized from the transformers 5 and contain the trip coil. The voltages applied to the grids is such as to allow anode current to flow only when unbalance occurs in the line 1. Alternatively, vapour electric devices may replace the circuit-breakers shown, and may be controlled by a device for shifting the phase between the grid and anode voltages, the phase-shift device being fed from the rectifier and serving to interrupt the current in the line 1. In Fig. 4, the output of rectifier 20 is fed to saturating windings 29 of reactors 28, the windings 27 of which are in shunt with windings 26 of a relay 24, which may be of the power-directional or distance type, or a carriercurrent relay system as described in Specification 274,070, [Class 38 (v)]. With balanced conditions in the line, the third-harmonics saturate the reactors 28, thereby reducing their impedance and shunting current away from the windings 26. On unbalance, however, the impedance increases due to absence of the saturating current, so that the relay 24 operates. The windings 26 may alternatively be controlled by electron discharge or vapour devices, or by a holding coil energized by the triple-frequency currents. In another form, Fig. 3 (not shown), the output of 20 is fed to the restraining windings of biassing transformers, of the kind described in Specification 193,434, [Class 38 (v)], having their primaries Y-connected to transformers 5 and their secondaries connected in parallel through full-wave rectifiers to the trip coil.