Patent GB-342700-A (GB)
Title: Improvements in alternating current electric distribution systems
IPC: H02H3/06
Filed: 1929-11-04
Abstract: 342,700. Protective cut-out arrangements. WESTINGHOUSE ELECTRIC & MANUFACTURING CO., East Pittsburg, U.S.A.-(Assignees of Parsons, J. S. ; 94, Ellington Street, East Orange, and Milne, G. R. ; 18, Baldwin Place, Bloomfield, both in New Jersey, U.S.A.) Nov. 4, 1929, No. 33523. Convention date, Nov. 3, 1928. [Class 38 (v).] Induction-relays.-Relates to A.C. distribution systems of the type described in Specification 254,300, [Class 38 (v), Electric switches &c.], wherein parallel feeders 12 .. 15 supply a low-tension network 27 through circuit-breakers 18, each of which has a relay for automatically opening same on reversal of energy flow, and for closing same on dependence on magnitude and phase relations on both sides of same, and further having antipumping means for ensuring stable operation. According to the invention, the anti-pumping means is connected across the terminals of the circuit-breaker 18 and prevents the latter from closing until the voltage across its terminals has the proper phase position for stable closure. The supply bus-bars 1 .. 3 are connected through breakers 16 and step-down transformers 17 to the network switches 18 shown in detail in Figs. 2a and 2b. The relay 41 has three elements 42, 43, 44 associated with the phases A, B, C respectively, each element comprising a current coil 52, a phasing coil 53, an a voltage coil 54. The current coil 52 is connected to a current transformer 34 arranged to saturate at about 150-200 per cent overload and having relatively few turns so as to be sensitive to small reverse currents. The phasing coil 53 is connected in series with a lamp 55 across the terminals of the breaker 18 so as to be energized in dependence on the magnitude and phase of the voltage thereacross. The voltage coil 54 is connected between ground and one phase on the network side of the breaker 18 and co-operates with (i) the phasing coil 53 to close the switch 18 in dependence on voltage condition, and (ii) the current coil 52 when the coil 53 is shorted by the closed switch 18, to open or hold closed the latter depending on the direction and magnitude of the current. The closing coil 38 of the switch 18 is in series with contacts 48 of relay 41 across the phases A, C, whereas the shunt trip coil 39 is in series with relay contacts 49 across those phases. A holding coil 61 is arranged, when the contacts 48 are open, to cooperate with an iron vane riveted to the disc, the coil being connected across the terminals of the switch 18 to prevent closure of the latter until conditions are such that it will remain closed under normal conditions. A resistance 67 in series with each voltage coil 54 ensures the necessary phase of the voltage component in that coil. When the whole system is de-energized and the contacts 48 of the relays 41 are held closed by a spring, closure of the switch 16 of feeder 14 will energize the closing coil 38 and close the switch 18, thereby energizing the current and voltage coils 52, 54. If it is desired to close the switches 18 of feeder 14 when the network 27 is already being supplied by, say, the feeder 12, then, when switch 16 of feeder 14 is closed, two voltages are applied one on either side of switches 18, the resultant of which energizes the phasing coils 53 to close, in co-operation with the voltage coils 54, the contacts 48 and thereby the switches 18. A fault in the network 27 is allowed to burn clear because no changes of current direction past the switches 18 occur, but a fault at 73 or 74 causes such a change and the switches 18 open accordingly and disconnect the feeder 4 from the network. Further, if the system is working normally and the switch 16 of feeder 14 is opened by an operator, the magnetizing current for transformers 17 is fed from the network and opens all the switches 18. In Fig. 2b, the relay 41 is divided into two relays, according to the functions, the opening relay 111 having current and voltage windings and the tripping contacts 49, whereas the closing relay 112 has phasing, holding, and voltage windings, and closing contacts 48. The Specification as open to inspection under Sect. 91 (3) (a) describes a further modification (Fig. 4 Cancelled, not shown) in which the holding magnet is replaced by a phasing-relay having a single voltage coil and a single phasing coil connected to one phase of the conductor only. The contacts of this relay are connected in series with those of the main relay so that the latter cannot close the switch except in favourable conditions. This subject-matter does not appear in the Specification as accepted.