Patent GB-407745-A (GB)
Title: Electro-responsive systems, for use particularly for protective purposes
IPC: H02H3/34
Filed: 1932-10-03
Abstract: 407,745. Protective cut-out systems. FITZGERALD, A. S., Box 424, Warwick Road, Wynnewood, Pennsylvania, U.S.A. Oct. 3, 1932, No. 27462. Convention date, Oct. 3, 1931. [Class 38 (v).] Relates to a protective arrangement for a polyphase or other system operable on a predetermined unbalancer between the currents flowing in the conductors of that system, such as would occur on a ground or interphase fault arising, but not with a balanced 3-phase fault. The invention comprises producing unidirectional electrical effects respectively proportional to an electrical quantity in the different phases of the polyphase circuit, and energizing circuit controlling means in accordance with the unbalance between the unidirectional effects. Preferably, the effects are produced proportional to the phase currents. In Fig. 1, the conductors 1 of a 3-phase line are connected by current transformers 5 to transformers 4, the outputs of which are connected to rectifying means 3 of any suitable type, arranged so that their voltages act cumulatively in the closed circuit formed by them. Filtering means 6, 7 may be provided. When balanced currents flow in conductors 1, the points 8 are equipotential and the mesh or star-connected relays 9 connected thereto are not energized. Unbalanced conditions in the conductors 1, however, produce a p.d. between two of the points 8 so that one or other of the relays 9 carries a difference current which trips the breaker 2. If the latter is magnetically retained closed, the difference current may be adapted to impress a voltage on the grid of a thermionic valve in the maintaining circuit, so de-energizing the latter. Other types of relay than that 9 may be employed, the windings being arranged on three cores or on a single core, rectifiers, in the latter case, being so arranged that opposing magnetic effects are prevented. The points 8 may be connected through an arrangement of rectifiers 22 (Fig. 6) so that the unidirectional output of the rectifiers 3 is fed to a single relay coil, or directly to the trip coil of the breaker 2. As actually shown in Fig. 6, however, the output of 22 is fed to the saturating winding of a reactor 33 forming part of a phase-shift net 31 serving to control the grids of a pair of vapour or other electron discharge devices 26 which are energized from a source 28 through a transformer 27. The difference current supplied from 22 reduces or interrupts the output of devices 26. Fig. 7 shows a relay 38 operating on the per-cent out-of-balance principle, one winding 39 carrying the out-of-balance current from the points 8 and rectifiers 22, the other 37 being connected across the parallel-connected groups of rectifiers 3 so as to carry the sum of their outputs. Further contacts, operable by the coil 37, may be provided to adapt to overload protection. In the application of the invention to discriminative protection (Fig. 8) the windings 42 of a device 40, which may be a power-directional or distance relay, or a carrier current system as in Specification 274,070, [Class 38 (v)], responsive to interphase faults, are shunted by the windings 46 of reactors 44, having saturating windings 45 and windings 43 energizable by the outof-balance current. The latter windings oppose the windings 45 and, on predetermined unbalance, raise the impedance of windings 46 to a value such that sufficient current is no longer shunted away from windings 42, which thereupon operate the device 40. A glow tube or the like may be connected across the windings 43 to regulate the current thereto in the event of a heavy short-circuit which might cause 43 to overcome 45 and saturate the reactors again. There is also described and illustrated, Fig. 9 (not shown), a form in which the secondaries of transformers 4 feed thermionic valve circuits that are interconnected so as to circulate equal currents while balance conditions obtain in the line. With unbalance conditions, however, one of the valve sets will carry less current than the others and so offer a large impedance to the current in the circuit. Thus less current is diverted from relay windings in parallel with the primaries of the transformers 4. If desired, relays may be connected to equipotential points of the circulating circuit. The circuit-breaker 2 may be substituted by gridcontrolled valves, so completely eliminating moving parts.