Patent GB-205109-A (GB)
Title: Improvements in electrical systems for automatic substations
Filed: 1923-10-08
Abstract: 205,109. Metropolitan-Vickers Electrical Co., Ltd., (Assignees of Leonard, S. G.). Oct. 6, 1922, [Convention date]. Systems for conversion, employing rotary converters.-An automatic sub-station comprises means for starting a rotary converter 4 from lowvoltage taps on a transformer, means dependent on the development of a predetermined polarity in the converter for controlling the transfer from the starting voltage to the full running voltage of the transformer, and means for disconnecting the converter from the alternating-current circuit if the development of the predetermined polarity and the subsequent transfer from starting to running conditions are not effected within a predetermined time. The various control devices are energized from an auxiliary transformer 1'7 connected to the alternating-current circuit 1, their operation being initiated bv a voltage relay 8 connected to the direct-current line 5 when the voltage in the latter falls below a predetermined value. When the switch of the relay 8 closes, relays 19, 22 successively operate to energize a master relay 30 controlling three switches 31 - - 33. The switch 31 connects the main control busbar Z to an auxiliary bus-bar X which supplies energy to all the subsequently-operating control devices, so that the latter may be simultaneously de-energized to disconnect the converter from the system by short-circuiting the relay 22 and thereby opening the switch 31. The switch 33 shortcircuits the relay 19 and maintains a hold-on circuit for the relay 22. This relay, in addition to controlling the master relay 30, also energizes a coil 34 which raises all but two of the brushes from the commutator of the converter, and at the same time closes, through a switch 38. the circuit of a relav 39. A switch 43 of this relay controls the closing of the main switch 2 through relays 46, 48 and a closing-coil 49. A low-voltage trip coil 51 is provided for holding the switch 2 closed while the voltage of the circuit 1 remains normal, and the coil 49 is de-energized after a short interval by the operation of a time relay 52. A switch 45 on the relay 39 controls the starting-switch 10 which connects the converter to the low-voltage taps on the transformer. The switch 10, when closing, closes an interlock switch 55 which connects the windings of a polarized relay 12 across the two unraised brushes of the converter. If the polarity of the converter has been developed in the wrong direction, the contact-member 24 of the relay 12 engages contacts 61 in the circuit of a relay 62 controlling a reversing switch 14 for the field winding 13. When correct polarity is established, the contact-member 24 engages contacts 65 and energizes a relay 42 which effects the closing of the running switch 11 and the opening of the starting switch 10. The closing of the switch 11 simultaneously energizes a coil 76 for lowering the brushes on to the commutator. When the field winding is sufficiently energized, a relay 16, co-operating with the switch 32 of the masterrelay 30, causes the direct-current switches 6, 7 to close, and the converter is connected to the direct-current circuit through resistances 87 - - 89, which are subsequently short-circuited, and through an underload relay 90. During the starting operation the switch of the relay 90 is closed, and a relay 100, controlling time switches 105, 110, is energized. The switch 110 is adjusted to close after an interval of from one to one and onehalf minutes, and to energize the circuit of a lock-out relay 111 unless the transfer to running conditions is effected within this interval. When the lock-out relay operates, the relay 22 is shortcircuited and the converter remains disconnected from the system until the relay 111 is re-set by hand. The switch 105 may be set to operate after an interval of from three to thirty minutes, and serves to disconnect the converter from the system by short-circuiting the relay 22 in the event of underload conditions persisting during this interval. The field relay 16 serves to prevent the re-connection of the converter to the system after the switches have been opened until the field current is reduced to a predetermined value- Specification 171,795 is referred to.