Patent GB-254300-A (GB)
Title: Improvements in or relating to alternating-current distribution systems
IPC: H01H75/04
Filed: 1926-06-17
Abstract: 254,300. Metropolitan-Vickers Electrical Co., Ltd., (Assignees of Parsons, J. S.). June 27, 1925, [Convention date]. Feeder arrangements; switching systems; systems depending on the use of static transformers.-An alternating current distribution system comprises a high voltage supply 1, Fig. 1, supplying through circuit-interrupters 4, feeders 6. Step-down transformers 3 at the ends of the feeders are connected through automatic circuit interrupters 5 to the low voltage network 2. The interrupter 5 open automatically upon voltage failure or reverse energy flow such as would result from opening the interrupter 4 or a fault occurring in the transformer or feeder. A relay 7, Fig. 5, is associated with each phase of each interrupter 5 and governs the action of that interrupter. Assuming the interrupters are open, the feeders 6 are de-energized and the interrupters 5 are open. If one interrupter 4 is closed, the corresponding transformer 3 is energized, whereupon electromagnetic switches 23 associated with each relay are closed, their energizing circuit being from the right-hand contact of interrupter 5, resistor 27, resistor 26 and relay winding 11 in parallel, normally closed contacts 21 of the relay 7, switch 23 to earth. Closure of the three switches 23 completes a circuit through a low-voltage device 9 which in turn energizes coil 8 to close the interrupter 5, and thereby connects the transformer 3 to the network 2. A phasing winding 12 on each relay connected across the contacts of the interrupter 5 co-operates with a network voltage winding 14 to open the contacts 21 against a spring if the phase and voltage relations on opposite sides of the interrupter 5 are such that energy will not be fed to the network 2. However, before the energization of the first feeder 6 the winding 14 was dead and therefore the winding 12 was inoperative to open the contacts 21. When additional feeders 6 are energized, the phasing winding is operative because the voltage winding 14 is already energized and therefore the contacts 21 are opened if phase and voltage relations are not correct for the corresponding interrupter 5 to be closed. Upon closure of the interrupter 5, the phasing winding is short-circuited, but a current winding 13 tapped across an inductive shunt 25 becomes operative. Should there be a reverse How of energy such as due to a fault on the feeder 6, or due to the opening of an interrupter 4 whereupon the magnetizing current for the associated transformer 3 is drawn from the network 2, the windings 11 and 13 cause the contacts 21 to open, whereupon switches 23 are de-energized and the device 9 opens and moves a trip lever 10 to open the interrupter 5. Failure of voltage on the entire system similarly causes the device 9 to open and therefore the interrupter 5 also to open. The possibility of " pumping " due to conditions being suitable for the interrupter to close when open, but the load characteristics being such that immediately the interrupter is closed the relay contacts 21 open, is obviated by providing a holding magnet 15 in series with the current winding 13, the magnet providing a large torque upon the armature of the relay only when the contacts 21 are closed. The reactive shunts 25 comprise copper bars on which are disposed a number of iron discs, and become saturated at low current values, thus the winding 13 can be made sensitive for small currents as the current therethrough does not increase proportinnally with the main current through the shunt 25.