Patent GB-526831-A (GB)
Title: Improvements in arrangements for detecting irregularities in or failure of one or more of a plurality of parallel fed current consuming devices
IPC: H04J1/16
Filed: 1939-03-24
Abstract: 526,831. Detecting faults. STANDARD TELEPHONES & CABLES, Ltd., and KIDNER, H. G. March 24, 1939, No. 9322. [Class 37] [Also in Group XL] An arrangement for detecting irregularities in or failure of current consumption of one or more of a number of parallel fed devices comprises a pair of windings on a magnetic core through at least one of which current determined by the total current is passed, and the other winding is fed with current so that the effective flux in the magnetic core has a definite value under normal conditions. A tertiary winding is wound on the same core and means responsive to any change in the current induced therein is adapted to operate and to cause the initiation of a desired operation. The filaments or heaters of six similar valves V1 ... V6, Fig. 1, are supplied from a transformer T through a current transformer CT having a centre-tapped primary winding a, b. Equal and opposite currents normally flow through the windings a, b and no resulting flux is produced in the core. If one of the filaments V1 ... V6 breaks the currents become unequal and a voltage is induced in a secondary winding c which operates a D.C. relay P through a rectifier W. The relay closes at p<1>, a circuit through pilot wires AL1, AL2 or operates a local alarm or performs any other function. Relays P1, P2 Fig. 2, at two stations S1, S2 have their contacts connected through oppositely polarized rectifiers W1, W x to a single pair of pilot wires K1, K2 which are connected at a terminal station S to two polarized relays Q1, Q2, in series with an A.C. source and oppositely polarized rectifiers W3, W4. The relays Q1, Q2 are operated by opposite, half-waves depending on which of the relays P1, P2 has operated, and operate alarms to indicate at which of the stations S1, S2 a fault has occurred. In a modification, Fig. 3, the primary coils of the current transformer CT are split to preserve balance of the voltage gradient on the filaments. A compensating resistance R1 may be connected in parallel with the valve filaments V4, V5, V6 if the currents taken by the two groups V1, V2, V3 and V4, V5, V6 are not equal. If an amplifier is provided with valves taking different filament currents, separate windings on the transformer CT are employed for the different groups of valves and are so arranged that the out-of-balance ampere turns due to a filament failure in any group are approximately equal. Fig. 5 shows an arrangement for a coaxial repeater comprising two A to B and two B to A amplifiers, a common relay being used to indicate failure of any filament. Separate current transformers CT1 ... CT4 are used for the separate amplifiers and are provided with indicator lamps L1 ... L, to indicate the faulty amplifier. Each amplifier may have its own filament transformer. In order to indicate failure of an incoming power fuse, two balanced potential windings a, b, Fig. 6, on a transformer PT are connected one on each side of the main fuses F1, F2 in series with resistances R1, ... R4. A separate potential transformer may be employed, in which case the relay P may switch in a spare amplifier into the cable or a dummy load across the line to maintain the received voltage at a constant value. Where a separate current transformer is provided for each amplifier stage the relay, P. Fig. 3, may alter the anode feed and biasing resistances. Failure of anode current may be indicated by means similar to those described for indicating filament failure. If a separate transformer is used for each amplifier the ampere turns due to the rectifier input current may be balanced by a potential coil b, Fig. 9, energized from the supply. A similar arrangement may be employed for detection of filament failure. Overloading of the rectifier W may be avoided by designing the current transformer so that its core is nearly saturated .under minimum out-ofbalance conditions, or bv means of a neon tube in shunt with the winding C. The balancing windings may alternatively be wound directly on an A.C. relay. Similar apparatus may be used for D.C. circuits, change in flux due to a difference in ampere turns of the two windings of a pair causing a current impulse in the secondary winding which may operate a relay which is locked in its operated position.