GB597302A - Improvements in or relating to relay apparatus for controlling electric power networks - Google Patents

Abstract

597,302. Protective cut-out arrangements; induction relays. NALDER BROS. & THOMPSON, Ltd., RUSSELL, L. W. G., and WEBB, C. R. Aug. 13, 1945, No. 20780. [Class 38(v)] Relay apparatus for connecting a network to supply mains when the voltage of the former is lower by a predetermined amount than that of the latter, comprises an induction relay having a plurality of electromagnets, one of said magnets having a winding connected across the supply mains or the network and another of said magnets having a winding supplied with current proportional to the difference in voltage between the network and the supply mains to cause the relay to operate a circuit-breaker connected between the mains and the network. The relay comprises a conducting cylinder 6 mounted on a toothed spindle 7 co-operating with a toothed segment 13. Contacts 16, 17, operated by members 15 carried by the segment 13, are in series with two holding coils 22, 23, respectively, which act on a soft-iron armature 20 also carried by the segment 13. Four of the magnets 10 have windings 24 connected in pairs in series across the phases of the mains or the network. The other four magnets carry current windings 25, 26, responsive to the current in the phases, and windings 27, in series, responsive to the voltage difference between the supply and the network. The windings 27 are energised from the opposed secondaries of the two matched transformers 28, 29, and are de-energised by contacts 34 when the circuit-breaker is closed. If the voltage of the network is too low, the cylinder 6 moves counter-clockwise to close contacts 16, thereby energising a relay 32 and a closing motor 30 for the breaker. The current windings 25, 26 are then energised and hold the cylinder 6 in position against the bias of a spring 9, Fig. 1. This position is maintained until the breaker is manually tripped by switch 33 to energise relay 31 or the network voltage exceeds that of the mains, whereupon the flux due to coils 25, 23, reverses and the cylinder 6 moves clockwise to close trip contacts 17. In a modification, Figs. 4-6 (not shown), the differential windings are each wound in two parts which are connected in series with the primary and secondary respectively of separate transformers for each phase in series with phase-shifting chokes. The primaries of all the transformers are connected to the respective phases on the supply side, and the secondaries to corresponding phases on the network side, of the breaker, the corresponding windings of two of the sets being connected in series and to one phase, as in the case of windings 26 of Fig. 3. In this arrangement, if a phase difference only exists between the mains and network voltages, other than one dependent upon the phase-shift due to the chokes, the contacts 17 will be closed, thereby preventing closure of the breaker.