Patent GB-314098-A (GB)
Title: Improvements relating to automatic electric control systems
IPC: H02H1/00
Filed: 1929-06-19
Abstract: 314,098. Associated Electrical Industries, Ltd., (Assignees of Moss, C. M., and Peterson, A. J. A.). June 23, 1928, [Convention date]. Void [Published under Sect. 91 of the Acts]. Running generators in parallel; systems depending on static transformers.- Translating devices such as rotary converters, motor generators, transformers, mercury arc rectifiers and the like operating in parallel between a supply system and a common load are switched in and out of service automatically in a given sequence by a control system comprising a balance relay 15 with two coils, one 19 energized in accordance with the total load and the other 20 in accordance with the number of translating devices 1 in series. The movable contact 16 is biassed by a spring 21 towards the position in which it effects the switching in, which may include the starting up, of translating devices and a spring 22 prevents its movement into the position for switching out on small decreases in load and permits this only when the total load has decreased to the capacity of the translating devices to remain in service. In the switching-in position (shown) a relay 31 is energized from a control bus-bar 25. This prepares the forward running circuit of a motor 37 and energizes a timing relay 38 which completes the motor circuit if the load condition persists. The motor 37 drives a switching drum 41 which brings into operation the first translating device by energizing from a source 55 closing coil 56 at contact 43. The circuit of coil 20 includes resistances 27, 28, 29 one for each translating device and one of these, 27 is short circuited when the coil 56 is energized. The contact member 16 thus leaves contact 18 and the motor 37 is stopped. This occurs at each stage as soon as the load demand on the translating devices connected reaches their capacity but a spring 22 prevents the member 16 engaging contact 17. Should the load exceed the total capacity of the station plant the drum 41 will be driven till a contact 48 is engaged and a lock-out relay 86 is energized and an alarm given. This lock-out relay stops the motor 37 but the translating devices continue in operation though it may be adapted to cut them out of service. When the load has fallen to an extent, determined by the spring 22, equal to that which can be carried by one translating device fewer, contact is made at 17 and relay 75 energized; a sticking magnet 23 is also energized to hold the arm 16 in the switching-out position. After a delay produced by a dash pot 75<1> relay 75 energizes timing relay 38 simultaneously with prepairing a reverse driving circuit for the motor 37 and the sending of a tripping current from source 55 over contact 43, for example, to trip coil 60. A translating device is thus removed and a resistance 27 thrown into circuit with the coil 20 whereupon the member 16 leaves the contact 17. The invention is applicable to stations having water driven turbines and to pneumatic and hydraulic switching: The system operates by virtue of lock-out relays 82 to pass over any translating device out of commission and to switch in the next; similarly any device cut-out by a protective device will be replaced automatically by another.