GB745895A - Improvements in and relating to protection means for voltage control devices - Google Patents

Abstract

745,895. Automatic control systems for alternators. BRITISH THOMSON-HOUSTON CO., Ltd. May 29, 1952 [July 26, 1951], No. 17761/51. Class 38 (4). A protective system for the automatic voltage regulator of a polyphase alternator in which the detector of the voltage regulator is supplied from a polyphase voltage transformer, consists of a no-volt relay which disconnects the regulator should a severe local fault reduce the voltage detected below a predetermined value; this no volt relay being over-ridden by a relay responsive to system conditions so that the regulator will remain in service during a system fault; plus either one of two alternative arrangements to eliminate the possibility of the regulator responding to a false voltage due to a minor local fault, the false voltage not being low enough to have tripped the no-volt relay. The regulator 4 is energized over the no-volt relay 5 from one phase of the voltage transformer 1. The relay 5 is over-ridden by the relay 10 responsive to system faults and which may be any one of the following-current transformers 12, current transformers plus a phase sequence component detector 11; residual current current transformer 13; or residual voltage voltage transformer 14. A further relay 15 may be provided, operated by current transformer 16 to additionally over-ride relay 5. In order to discriminate against a fault on one or two phases of the voltage transformer 1, a phase sequence component detector 7 and relay 8 is provided to disconnect the regulator under such conditions. In a modification, Fig. 4 (not shown) a time delay relay is used between the relays 8, 5 and the protective circuit to introduce a time lag to prevent false operation should relays 8 or 5 operate faster than relays 10 or 15. In a further modification, Fig. 6 (not shown), further protection against faults on one phase of star-connected apparatus is obtained by including the no-volt relay in the circuit arrangement disclosed in Specification 617,279, [Group XXXVII]. In an alternative embodiment, Fig. 8 (not shown), the possibility of a single phase fault on the voltage transformer and hence the need for the phase sequence component detector, is eliminated by connecting the windings of the voltage transformer in an opendelta arrangement with separately fused primary windings.