Patent GB-171796-A (GB)
Title: Improvements in automatic electrical substation systems
IPC: H02P11/00
Filed: 1920-08-26
Abstract: 171,796. Metropolitan-Vickers Electrical Co., Ltd., (Westinghouse Electric & Manufacturing Co.). Aug. 26, 1920. Systems for conversion, employing rotary converters or rotary transformers.-In an automatic rotary converter substation, the converter is started by relay-controlled devices energized by the alternating-current circuit and controlled by a voltage relay on the direct-current circuit, and a direct-current generator driven by a rotary converter ensures the correct polarity of the converter when starting. The converter may be selfexcited after synchronism is attained, and a resistance is inserted between the converter and the direct-current circuit during connection and when the current in the directcurrent circuit changes rapidly. Overfeed, reverse-current, and low-current devices are arranged to disconnect the converter. Thermostats are placed in the control circuit and near the protective resistance or the bearings of the converter, or in the oil-containing receptacles of the transformer. The relay devices controlling the connection and disconnection of a rotary-converter 3 to an alternating-current supply circuit 1 and to a direct-current load circuit 2 are energized from a transformer 30, Fig. 1, and controlled by a voltage relay 13 connected across the direct-current circuit 2. When the potential of the circuit 2 falls below a predetermined value the relay 13 operates to complete the circuit of a relay 15 which in turn completes the circuit of a quick-closing and slow-opening relay 19. The closing of the relay 19 completes the circuit of a relay 24 over thermostats 22 and when the relay 24 is closed the low-voltage release coil 33 of a switch 5 and a relay 37 are energized. Relay 37 operates to complete the circuit of the closing winding 38 of the switch 5 which is mechanically connected to signalling switches 9. The closure of the relay 24 completes a circuit comprising a switch 11, interconnected with a switch 8, the operating-winding 39 of a switch 7, the contacts 40, 41 of a relay 42, and the signal switches 9. The switch 7 is operated to connect the low-voltage taps cf a transformer 6 to the converter 3 and the field winding 43 of the converter is connected to the terminals of a generator 44, driven by the converter, so that the polarity of the converter 3 is determined and may be connected directly to the circuit 2 when the converter reaches a state of synchronism. When the converter 3 is in synchronism, a polarized relay 46 closes the circuit of a relay 42 which operates to open the circuit of the winding 39 of a switch 7 and completes the circuit of the operating- winding 49 of a switch 8 through a switch 10 interconnected with switch 7 and the contacts 27 of the relay 24. The closure of the switch 8 connects the high-potential taps of the transformer 6 to the converter 3. and a switch 12 completes the circuit of a relay 51 to energize the latter by the generator 44. The operation of the relay 51 opens a short-circuit upon a resistance 55 in the circuit of the relay 46 and energizes a relay 57, which operates to connect the converter 3 to the circuit 2 through a resistance, 25. The closure of switch 58 associated with the relay 57 completes the circuit of the operating-coil 59 of a quick-acting switch 60 over a switch 61 associated with a switch 62. A switch 63 associated with the switch 60 controls the circuit of the operating coil 64 of the switch 62 over the contacts of a timerelay 70 and the switch 62 is closed to shortcircuit the resistance 25. The switch 61 associated with the switch 62 is opened to break the circuit of the operating winding 59 of the switch 60. When a short-circuit or ground occurs a condenser 67, connected in parallel with an inductance 69, discharges through a trip coil 68 to open the switch 60 and finally the switch 62. For ordinary overload conditions a relay 66 operates to open the circuit of the operating coil 64 of the switch 62 and if the overload is not sufficiently reduced by the insertion of the resistance 25, overload relays 71 energized by the alternating current operate to short-circuit the low-voltage trip coil 33 and thus open the switch 5. The trip coil 33 is also adapted to be short-circuited by an overspeed device 72 and by a reverse-current device 74. A relay 75 is adapted to open the circuit of the relay 15 when the current on the directcurrent side falls to ten per cent of the normal and after an interval of three or five minutes the relay 19 opens the circuit of the relay 24 to disconnect the converter. In a modification the excitation of the converter is transferred from the generator 44 to the converter 3 when the latter attains seventy-five per cent of its normal speed.