GB516265A - Improvements in and relating to emergency power generating plant - Google Patents

Abstract

516,265. Electricity supply. ENGLISH ELECTRIC CO., Ltd., and WELSH R. J. July 22, 1938, No. 21771. [Class 38 (iv)] [Also in Group XXVII] Substituting sources in service.-An emergency electricity generating system comprises a main switch, biassed - to the open position, latching means for holding the switch closed to connect a load to an external supply, means responsive to the failure of the external supply or a predetermined fall of its voltage to unlatch said switch, means responsive to the opening of the switch to start an internal combustion engine driving a generator and to connect the latter to the load, and means temporarily responsive to the restoration of. the external supply, and disconnection of the load from the generator to reclose said switch. In Fig 1 three-phase mains L<1> supply a load through a gravitybiassed switch 4 which is normally held closed by a latch 2 under the influence of a high impedance magnet coil 1 energized from the mains. Should the mains voltage fail or fall below a predetermined value spring 3 unlatches switch 4 thus connecting the load from the mains. On opening, part of switch 4 strikes the actuating member 5 of a valve device 6 which thereupon supplies compressed air to start an emergency internal combustion engine driving an alternator and a direct current exciter therefor. This starting air is cut off when the engine is up to speed either by an electromagnet energized by the exciter voltage or mechanically from the speed governor. When the engine has reached a predetermined speed the energization of operating coil 8, through lines E from the exciter, closes switch 9 to connect the emergency supply, through lines L<2> to the load.. Auxiliary contacts 4a on switch 4 ensure that switch 9 cannot be closed unless switch 4 is open. Auxiliary contacts 9a on switch 9 insert an economy resistance 10 in series with coil 8 while the latter holds switch 9 closed. The operating coil of relay 11 is also energized by the exciter to connect the operating coil of relay 12 across one phase of the mains L' so that, as soon as this supply is restored relay 12 closes to connect a further relay 13 across another phase of L<1> thereby opening the circuit of coil 8 to open switch 9, and closing contacts in series with operating coil 7 so' that when switch 9 opens and closes auxiliary contacts 9b coil 7 is energized and closes switch 4 to reconnect the load and the main supply. Valve 6 closes to stop the engine when switch 4 closes, and the resulting disappearance of the exciter voltage opens relays 11, 12, 13 so that coil 7 is only energized during transition. Trip coil 1 may also be arranged to respond to any singlephase failure of the supply. Fig. 2 (not shown) is a modification for a direct current system. In a modification of the three-phase arrangement, Fig. 3 (not shown), switch 9 is also latched-in and is opened by a tripping coil operating on the latch. With this arrangement failure of the emergency supply does not prevent the restoration of the normal supply to the load, as in Fig. 1. If single phase only of the supply is restored the connection of the relays may be arranged to connect this supply to the load. Alternatively it may be necessary that all phases are restored before connection is made, as in Fig. 1. The compressed-air supply for starting the internal combustion engine is from a reservoir the pressure in which is maintained by a compressor driven by an electric motor. In Fig. 4 the actuating member 5 is struck by a part of the main switch, as it opens, to upset toggle gear 17, 18 and allow spring, 19 to open valve 14 thereby supplying compressed air from the reservoir to the operating cylinder of a main air-valve controlling the supply of air to the cylinders of the engine or to an auxiliary starting motor. When the main switch recloses, the toggle gear may be reset by a spring or by an electromagnet energized simultaneously with the reclosing coil of the main switch. When open, valve 15 at the other end of a pivoted lever 16 connects the cylinder of the air-valve to atmosphere. In a modification Fig. 6 (not shown) the toggle gear is replaced by a weighted lever held in the normal position by a latch which is tripped by the main switch as it opens. The lever is reset electromagnetically. The Provisional Specification states that the emergency set 'may be used to supply a network from the normal network.