Patent GB-299318-A (GB)
Title: Improvements in systems for automatically paralleling alternating current circuits
IPC: H02J3/42
Filed: 1928-10-22
Abstract: 299,318. Associated Electrical Industries, Ltd., (formerly Metropolitan- Vickers Electrical Co., Ltd.), (Assignees of Thomas, P.). Oct. 20, 1927, [Convention date]. Synchronizing dynamoelectric machines. - A paralleling switch is controlled by a relay energized by a transformer with a flux-controlling winding energized through a rectifier either by the resultant of the voltages of the circuits to be paralleled or by a voltage obtained by a phase splitter from one of the circuits. The arrangement is such as to effect closure of the switch at the instant of synchronizing. The relay preferably has a time lag preventing operation at inadmissible frequencydifference, and is of the thermionic type. To permit paralleling when one of the voltages is low, even at a considerable phase difference, the controlling winding may be additionally energized, in accordance with the voltage of one of the circuits and by an opposite e.m.f. equivalent to the normal voltage of that circuit. Two relays may be used, one preventing closure of the paralleling switch when the incoming machine is either fast or slow, as required. As shown in Fig. 1 the voltage on the cathode of the thermal relay 25 is controlled by a transformer 18 responsive to the resultant of opposed line and machine volts. A d.c. winding 21 on a transformer 20, which is energized through an impedance 23<1> from the machine and supplies the cathode current, is fed by the transformer 18 through a rectifier 19, e.g. of copper oxide-disc type. The phase angle between the line and machine circuits when synchronism is initiated is automatically permitted to increase where line volts are low by inserting in the circuit of winding 21 a d.c. e.m.f. opposed to the rectified e.m.f. of a compensating transformer connected across the line and equal to it at normal line volts. The d.c. e.m.f. may be a battery or a rectified voltage derived from the machine. The arrangement of Fig. 6 comprises a transformer 43 subject to the combined voltages of line and machine, a compensating transformer 42 subject to line volts and a transformer 44 to provide the opposing e.m.f. The transformer 41 receives current from a phasesplitter 40 and its dephased component is made effective to control the instant of initiation of paralleling by introducing it through a rectifier into the circuit of the controlling winding of a transformer 50. The transformer 51 is controlled by the transformer 43 and energizes a thermal relay 60 at exact synchronism. If this occurs before the coincidence of phase of machine and dephased line volts it effects a short circuit of the coil 65 and prevents paralleling a slow machine since the relay 59 is ineffective. By connecting the phase-splitter to the machine (or substituting a condenser for the inductance shown) the arrangement will prevent parallelling a fast machine. A system combining both arrangements is described, the locking out relay 60. being included and preventing paralleling at excessive frequency differences. The Specification as it became open to public inspection under Sect. 91 (3) (a) described an. adjustable phase-splitter 16, 17, Fig. 1, (cancelled), for dephasing the machine component, the line and machine components being combined so that a thermionic relay 11 and a switch 13 might initiate the operation of the paralleling switch 5 at an adjustable instant prior to synchronism. This subject-matter does not appear in the Specification as accepted.