Patent GB-304324-A (GB)
Title: Improvements in and relating to systems of electric distribution
IPC: H02J3/38
Filed: 1929-01-18
Abstract: 304,324. British Thomson-Houston Co., Ltd., (Assignees of Bany, H.). Jan. 19, 1928, [Convention date]. Running generators in parallel; regulation, automatic.-In a system in which a number of current sources are connected and disconnected in sequence the output of the most recently connected is automatically controlled in accordance with the load circuit voltage and the outputs of the others maintained constant. As the output of each attains a given value it is maintained constant and a further source is connected when this load has persisted for a given time. A reversal of current in any source may cause a resumption of voltage control and the excitation of the reversed source may be increased if the load circuit voltage is below normal. Current regulating relays associated with each source may have a calibration changing winding operative when a succeeding source is connected, and when the output of the latter is below a certain value, to reduce the constant load level of the former source. The Figure shows d.c. generators A, B, C each with a reversible motor 15 actuating a field rheostat and a paralleling switch 2. The control devices may effect the operation of known starting devices in addition to the switches 2. The operating circuit of each switch 2 includes protective contacts 8 such that no machine can be parallelled if in an inoperative condition. Upon rising load a time-delay voltage relay 6 effects the paralleling of machine A whilst timedelay over-current relays 10 start the succeeding machines. The relays 6, 10 each energize a closing coil and a time relay 9 which causes the next machine to be parallelled if the first fails thereof within the time delay. Contacts 31 on each switch 2 place in operation a current regulating relay 19 and a voltage regulating relay 18 which control the rheostat motor 15; so long as a machine is the last connected its relay 18 is operative until the load limit is reached whereupon its relay 19 supersedes to maintain this load. After a certain time the over-current relay 10 closes and a second machine is parallelled. Contacts 42, 36 bridge contacts 33 and open the circuit of contacts 35 of the voltage regulating relay 18 of the last machine leaving the current regulating relay 19 alone operative. Contacts 40 energize a winding 23 on the relay 19 which reduces the load limit until the second machine has sufficient load to open its load responsive relay 24 which interrupts the current in winding 23 and restores the original calibration. The second machine is now regulated by the load circuit voltage until it reaches its load limit, whereupon the process is repeated. Upon falling load the load-responsive relay 24 of the last machine connected re-energizes the coil 23 of the preceding machine and reduces its load; the relays 24 are designed to close their contacts at a load lower than that at which they open. An under current relay 11 de-energizes switch 2 of the last connected machine when its load has remained below a limit for a given time. Contacts on the switch 2 then restore the voltage control of the next machine in the sequence and disconnect coil 23. Upon reversal of any source current directional relays 20 and relays 21 restore the voltage control of the previously connected source whereby its load is reduced if the load circuit voltage is above normal; the relay 21 also prevents the field of the reversed machine from being reduced and ensures its being increased when the load circuit voltage is below normal. A single voltage-responsive relay may control all the voltage responsive contacts to ensure simultaneous operation.