GB566805A - Improvements in electric impedance relay means and in protective equipment for electrical power systems utilising same - Google Patents

Abstract

566,805. Protective cut-out systems. KAUFMANN, M., HODGKISS, J. W., and METROPOLITAN-VICKERS ELECTRICAL CO., Ltd. July 2, 1943, No. 10795. [Class 38 (v)] An impedance-responsive relay device, suitable for protecting feeders against fault, comprises a network in which rectified voltages representative of, respectively, the voltage impressed across the impedance and the resulting current therethrough, are balanced against one another, the out-of-balance voltage being applied to an attracted-armature or other electromagnet relay. The current effect is applied across terminals 2 to a full-wave rectifier 3 which is in series with the relay 4 across a diverter resistance 5, the voltage effect being applied either directly across resistance 5 in opposition to the current effect, or, as shown, across a load resistance 7 which is shunted by 5 and a further, less-sensitive, relay 6. The voltage effect may be rectified by an arrange: ment such as 3, but preferably, in order to make the arrangement as independent as possible of phase-angle between current and voltage waves, the terminals 1 are connected to a resistance-capacity arrangement 8 ... 11 to yield a balanced-voltage, three-phase system which is fully rectified at 12 before passing to resistor 5 or 7. A preferably-saturable choke 13 and adjustable resistor 14 are series-connected across terminals 2, and to prevent excess voltages being developed, the latter may be shunted by a non-linear resistance 18 such as " Metrosil " (Registered Trade Mark). The primary of transformer 15 may be connected across the impedance either directly or through an auxiliary transformer. The terminals 2 may be connected by a current transformer 16. In a three-phase application, line-to-line faults can be detected by employing a further current transformer 17 and connecting it to 2 in opposition to 16. Complete three-phase systems involving this arrangement at both the supply and load end of a feeder are described, Figs. 6, 7 (not shown), the impedance relays being used as starting relays for controlling directional relays for transmitting locking signals to the far circuit-breaker in the known way. A further line-to-line fault protective system has the current side of the network energized by mesh-connected auxiliary transformers, the star-connected primaries of which are energized by star-connected line current transformers, Fig. 7 (not shown).