Patent GB-423544-A (GB)
Title: Improvements in and relating to protective systems for electric distribution net-works
IPC: H02H3/44
Filed: 1934-03-02
Abstract: 423,544. Protective cut-out systems. BRITISH THOMSON - HOUSTON CO., Ltd., Crown House, Aldwych, London.- (Assignees of McNairy, J. W. ; 1019, Washington Place, Erie, Pennsylvania, U.S.A.) March 2, 1934, No. 6736. Convention date, March 2, 1933. [Class 38 (v)] A system of distribution, particularly for railways, comprising a high-voltage feeder forming one leg of a high-voltage circuit, a low-voltage conductor forming the other leg of the high-voltage circuit carrying both high and low-voltage current, a grounded circuit, and auto-transforming means interconnecting the circuits, is protected by means responsive only to a predetermined rate of increase in the low-voltage component of the current in the conductor for operating the tripping means of a breaker connected in circuit with the conductor. In Fig. 2, a feeder 50 supplies over auto-transformers 33, 34, at substations E, F, a trolley conductor 51, which serves as a return for the feeder current and, with the grounded rails 40, to supply the locomotives on the section between E, F. The breaker 60 at one end only of the conductor 51 is shown and is of the type disclosed in Specification 187,993, [Class 38 (v)], having a holding winding 65 and a flux-shifting release winding 66 in series with interlock contacts 103 and normally-open contacts of a high-speed relay 70, which is released to close its contacts. The release circuit comprises an arrangement as described in Specification 266,359, [Class 38 (v)], for producing in the release coil 75 a unidirectional impulse of correct polarity. Secondaries 97, 98 of transformers 90, 91 are normally saturated by direct current from the supply 67, 68, whereas the primaries 92, 93 are reversely connected in series with mutually-opposing current transformers 95, 96 in the conductor 51 and feeder 50. Thus the voltage applied to 90, 91 is a function of the vector difference between the currents flowing in 50, 51, and the tripping impulse is a function of the rate of increase of this difference, and when a predetermined current of fault dimensions suddenly flows between 51 and ground, transformer 95 causes an impulse to flow through 75 which closes the contacts of relay 70 and trips the breaker 60. The arrangement is rendered trip-free by timing the motor-driven cams 82, 87 and contacts 103 so that the contact of 70 closes first, then contacts 103, then the contact of 60. Fig. 3 shows a form in which the auto-transformer 33 is interconnected with another 32 at a substation D by means of parallel feeders 48, 49 and parallel trolley conductors 52, 53 having manuallyclosed breakers 110, 111. Transformers 123, 124 in the feeders are in opposition to transformers 125, 126 in the conductors 52, 53 so as to be unaffected by normal circulating current therebetween. The trip devices 114, 115 are connected to the release coils 116, 117 in a similar manner to that disclosed in Specification 314,085, [Class 38 (v)], so as to provide discriminative operation of the two breakers. If a fault occurs on 52, an impulse from 114 will flow through both 116, 117, in the former in the tripping direction but in the latter in the non-tripping direction. With simultaneous faults on both 52, 53, both breakers are tripped by impulses from 114, 115 provided the resistances 145, 159 of the return paths are low enough. In this case a greater current increase in each feeder is usually necessary than with a fault on one alone. The invention is also described in connection with a two feeder-four trolley conductor arrangement, Fig. 4 (not shown).