Patent GB-744340-A (GB)
Title: Improvements in or relating to power feeding arrangements for telecommunication systems
Inventor: LAWTON JOHN
IPC: H04B3/44
Filed: 1953-10-09
Abstract: 744,340. Telephone transmission systems. BRITISH TELECOMMUNICATIONS RESEARCH, Ltd. Sept. 30, 1954 [Oct. 9, 1953; Feb. 26, 1954], Nos. 27874/53 and 5782/54. Class 40 (4). In an arrangement for feeding power to intermediate repeater stations on a transmission line, a fault affecting power feeding operates test equipment, provided at each station, to cut-off and re-apply the power a predetermined number of times in order to ensure that the station has not been disconnected unnecessarily, and the absence of power from stations beyond the fault causes power to be supplied in the reverse direction from the remote end. Power is connected to the station equipment shown, at terminals 10, 11, Fig. 1, and supplied to succeeding equipment from terminals 12, 13. Power unit APU is energized over winding T1C of transformer T1 and relays AA, MC and MB operate. Relay AB is energized over lead 14 but test relays TA, TTA, TB, TTB in a counting chain are prevented from operating by a thermal relay TG in its normal condition. The thermal relay has several seconds delay and on closing it operates a relay MA to disconnect a dummy load DL1 which takes a load equivalent to that of the succeeding stations, and switch through to the succeeding station. The supervisory and alarm relay VV may operate momentarily at this stage but it is restored when power is connected to the bus-bars 16, 17. Relays SAA, SBB, SCC, SDD appropriate to different racks are also operated over lead 14 to disconnect dummy load DL4, connect heater power and complete a circuit for a thermal relay TSA. After a delay of the order of 45 seconds TSA operates a self-locking relay SA to disconnect dummy load DL3 and apply anode power. Relay TSA is then released. Self-locking relays RSA-RSD are operated by relays CA-CD in response to equipment faults on the respective racks to release relays SA and SAA, to give an alarm over leads 36, 37 and to light supervisory lamp L5. An open circuit on the outgoing cable causes relay CE to make its low contacts and relay V to make its high and in consequence bi-stable relay TA is changed over to prepare a circuit including the left-hand winding of bistable relay TTA, to energize slow-to-operate relay SO, to energize thermal relay TH and to release relays MA and ME. Relay SO changes over relay TTA. which transfers the initial operating circuit from TA to TB, opens its own energizing circuit, releases SO, prepares a circuit for relay ME and re-operates relay MA. If the fault persists the re-operation of MA changes over relay TB and relay SO is again energized to change over relay TTB. Relay MA is again released and a new circuit is prepared by TTB and so on according to the number of relays in the counting chain until relay TC is reached and operated. TC releases MA, ME and TH, gives an alarm over leads 34, 35 and lights supervisory lamp L7. Since each station is arranged so that it re-connects the power to the following section of line once more than the adjacent station more remote from the feeding station all the stations are restored to normal by thermal relay TH when the station adjacent the fault has made its final disconnection. A short circuit on the outgoing cable closes the high contacts of relay CE and if in spite of the short there is sufficient voltage operates relay TA as before if not relay AB releases and releases relay MA. The release of all stations beyond the fault connects the emergency supply to the distant end and power is supplied to the power units BPU. The counting chains of the stations thus fed are now controlled by relay CF. Relay MB is changed over and relays MD, ME and bus bars 16, 17 are energized. Relays MD, ME extend emergency power to the station connected to terminals 10, 11 in all stations up to the station preceding the fault where after the predetermined number of connections TC is made to operate. The emergency power supply may be connected in the position of the dummy load DL1 at the emergency power feeding station so that the emergency power is connected when the relay MA thereat releases. A suitable time delay is incorporated in order to allow the relays TG at the stations devoid of power to be released. Restoration can be effected after the emergency supply has been withdrawn by the manual operation of key KE at the last station fed with normal power or by withdrawing normal power and restoring it in 5-40 seconds. Testing arrangements to ascertain the current distribution over a number of parallel feeder cables are provided and are caused to short-circuit the normal or reverse relays NP or RP if a conductor is not carrying its due proportion. Relays MA or ME respectively are in consequence released. An auto-transformer AT provides for adjustment of the voltage in cases where the load is likely to change with system development. The use of a single transformer instead of transformers T1, T2 is described with reference to Fig. 4 (not shown). Specification 515,529, [Group XXXVII], is referred to.