230,867. Metropolitan-Vickers Electrical Co., Ltd., (Assignees of White, T. U.). March 17,1924, [Convention date]. Selective distant control systems; tell-tale apparatus.-In a supervisory control system for apparatus units at a substation of the kind having chains of counting relays at the control station and substation which are operated synchronously upon the change of condition of an apparatus unit at the substation, or the operation of a manually operated key at the control office, to select corresponding supervisory signals or prepare the operating circuit of a unit respectively, groups of selecting relays, such as N, N<1>, at each station which are associated with the keys and apparatus units respectively are connected successively by switching relays 310, 311, 312 and 514, 515, 516 individual to each group to single counting chains M, M<1>. A complete cycle of operation of the counting chains operates successively the relays of the first selecting groups at each station and then the chains are re-operated to .actuate the next selecting relay groups and so on. Figs. 1 to 4 show the control office apparatus and Figs. 5 to 8 the apparatus at the substation. When it is desired to operate any particular unit, such as the circuit breaker C, Fig. 8, the corresponding key K<1> at the control office is operated to prepare the operating circuit of the unit and a common key K<2> is depressed to initiate the operation of the groups of selecting relays which are energized under the control of the counting chains until the selecting relays corresponding to the unit and key are operated. An alternating current from one or other of the generators G', G<2> of a frequency dependent upon the nature of the operation to be effected is then sent over a control line 393 to operate the unit. When the unit is operated, a direct current impulse is transmitted over a signalling line 394 to actuate the appropriate supervisory signalling lamp, such as 280 or 281 and restart the selecting equipment. If the unit is selected by a relay in the first group, the remaining relays of the first group and the relays in the second .and third groups are then operated until finally the. equipment is restored to normal. Each selecting relay has a key which when operated holds up the selecting operation to enable the operator to remain in connection with a selected unit. A key K<13>, Fig. 2, initiates the operation of the relav chains and enables a check on the proper working of the selecting equipment to be obtained. A key K, Fig. 2, may be actuated to release the equipment during operation. The apparatus at the substation is released by a relay 726 which is responsive to the alternating current of a generator G and that at the control office, by relays 125, 402. A circuit for treating . the continuity of the, control and signalling lines is completed upon the operation of the first selecting relays. The supervisory signals are controlled by relays having mechanical interlocks which hold their contacts closed after energization so as to prevent a change of signals due to a failure of the source of supply for said relays. The counting relay chains are operated synchronously bv pairs of control relays 411, 616 and 414, 619 which are alternately connected to a line 272 and are controlled by the alternate application of current from batteries B, B<1> at the control office and substation respectively. Normal condition of system. Normally the relays 218, Fig. 2, and 912, Fig. 8, are energized in series of the line 272. Selection of circuit breaker C, Fig. 8. If it is desited to close the circuit breaker, the key K<1> is operated to close the contacts 267, 269 and the common key K<2> is then operated and released to energize a relay 212 which opens the circuit of the relays 218, 912 at the armature 250. When the relay 218 is de-energized a relay 213 energizes a switching relay 210 and associated the selecting relays 300 - - 309 with the counting chain 101 - - 124. Simultaneously, a relay 219 prepares the circuit of the control relay 414. Similarlv, when at the substation the relay 912 is de- . energized, the relays 911, 917 complete the control circuit over the line 272 and the relays 414, 619 and operate a switching relay 516 to associate the selecting relays 500 - - 509 with the counting chain 700 - - 723. The control relays 414, 619 are thus energized in series by the battery B, Fig. 4. The relay 414 operates a relay 401 to energize the first counting relay 112 and a relay 417, which operates a relay 208 to open the. control circuit at the armature 241. The counting relay 112 completes the circuit of the next relav 111. This relay, however, is shortcircuited by the energizing circuit of the relay 112, but when the control circuit is opened the short circuit is removed and the relay 11 operates the first selecting relay 309, and prepares the circuit of the next counting relay 124. Simultaneously, the relay 619 at the substation, operates the relays 700, 701 to energize the selecting relay 500 and prepare the circuit of the next counting relay 712. When the selecting relays 309, 500 are. operated the lines 393, 394 are earthed and circuits are completed through the key K for relays 315, 316 which operate to illuminate lamps 318, 319 and give an indication of the electrical continuity of the lines. The selecting relays 309, 500 also operate relays 206, 900 which transfer the control circuit over the line 272 to the relays 411, 616 which energize in series with a battery B', Fig. 6. The relays 411, 616 operate the counting relays 124, 712, which open the circuits of the selecting relays 309, 500 and prepare the circuits of the next counting relays 123, 713. The relays 124, 712 also open the control circuit over the line 272 and thereby allow the relays 123, 713 to operate the selecting relays 308, 501 and prepare the circuit of the next counting relays 110, 702. The selecting relays 308, 501 cause the transfer of the control circuit to relays 414, 619 and the control circuit again functions to de-energize the relays 308, 501 and operate the selecting relays 307, 502. The operation of the selecting equipment is stopped after the operation of the relays 307, 502 which are associated with the key K<1> and unit C, since the circuit of the relay 206 over the contacts of the relay 307 and wire 14 is open at the contacts of the key. Operating the circuit breaker. After the initiation of the cycle of operations by the key K<2>, the key is again depressed so that when the selecting relays 307, 502 are operated, a circuit is established from the generator G<1> through the keys K<2>, K<1>, K to the line 393 and relay 731 at the substation which is mechanically tuned to currents from the generator G<1>. The relay 731 operates a relay 724 which energizes a relay 925, Fig. 8, over contacts of the selecting relay 502 to complete the circuit of the closing coil 926 and operate the circuit breaker C. Signalling condition of circuit breaker. On closing, the circuit breaker operates relays 905, 908 which complete a signalling circuit through the relay 907, contacts of selecting relay 502, line 394, contacts of relay 307 to relay 221. The relay 221 illuminates the supervisory lamp 280, and energizes a relay 220 which opens the circuit of the generator G<1> and de-energizes the relay 724.. The relay 220 completes a circuit for the relay 206 over the lead 14 and the de-energization of the relay 724 earths the lead 800 and energizes the relay 900. The relays 206, 900 are operated to complete the control circuit over the relays 411, 616. Completing the cycle of operations. The system then continues to function under the control of the relays 411, 414, 616, 619 and the counting relays are operated successively to actuate the remaining relays in the first selecting group until the relays 102, 710 are operated and the relays 300, 509 are de-energized. The counting relays 101, 111 then operate the relays 313, 513 and thereby energize, the, relay 409, 609. These relays prepare circuits for the " start " relays 212, 918. In addition the relays 313, 513 complete the line circuit over the relays 411, 616 and the next counting relays 114, 722 are operated to energize the switching relays 311, 515 associated with the second groups of selecting relays. The counting relays 113, 723 are then operated to open the circuits of all the counting relays and complete a circuit over the line 272 for the relays 218, 912. When these relays are energized, the circuits of the " start " relays 212, 918 are completed and the operation of the counting chains is restarted. When the second cycle of operations is completed, the switching relays 312, 514 are operated and the counting chains are again operated to control the selecting relays in the third group. These relays are operated successively until the last counting relays restore the line circuit over the relays 218, 912 and the selecting equipment to normal. Signalling position of circuit breaker when automatically operated by load conditions. Assuming the circuit breaker C is tripped automatically, the relay 922 is momentarily energized to initiate the operation of the control circuit and the selecting relays are operated in succession until the relays 307, 502 are operated to energize a relay 202 which controls the supervisory signal lamps 280, 281. If the circuit breaker is tripped automatically immediately after the breaker is operated from the control office, and whilst the selecting relays associated with the circuit breaker still remain connected to the line wires, the operation of the control circuit is held up until the new condition is signalled. If, however, the automatic operation takes place after the selecting relays are disconnected from the lines, the equipment is operated a second time to signal the new condition. Checking operation of system. The proper working of th