Patent GB-201732-A (GB)
Title: Improvements relating to electric motor converter sub-stations
IPC: H02J5/00
Filed: 1922-07-07
Abstract: 201,732. Ross, T. W., Ryder, C., and Metropolitan - Vickers Electrical Co., Ltd. July 7, 1922. Systems for conversion employing rotary converters or rotary transformers.-A control system for starting and synchronizing a motor converter comprises a pilot circuit closed by a time-switch or by a low-voltage direct-current relay connected across the direct-current side of the system, means for short-circuiting the starting resistances when the rotor current has fallen to a, low value for a predetermined time, a relay controlled by an interlock switch associated with a starting resistance short-circuiting device and adapted to introduce a resistance in the field-winding circuit of the converter from the alternating-current mains when the direct-current field fails to excite, and means for disoconnecting the direct-current side of the converter before the disconnection of the alternating-current side. The stator winding 1 of a motor-converter 2 is connected to the alternating-current mains 3 through a switch 4 provided with an operating coil 31 and a no-volt release coil 74. The ends of three of the windings of the rotor 5 are brought out to slip-rings 7 adapted to be connected through starting resistances 8 and to be short-circuited by a device 9 when a solenoid 10 is energized. A solenoid 11 is provided to remove this short-circuit. The device. 9 is adapted in its movement to rock a pivoted contact-member 12. The control system is energized from busbars 18, 18a energized by the closure of a switch 21 operated by a master relay 20 connected to a pilot circuit 19 which is closed by a time switch or by a low-voltage direct-current relay connected across the direct-current side of the system. To Start the converter from rest, with the slip-rings 7 short-circuited by the device 9, the pilot wires 19 are energized to operate the master relay 20, the contact 21 of which energizes the bus-bars 18, 18a. The energization of the bus-bars 18, 18<a> causes the removal of the short-circuit on the following circuit :-lead 34, switch 23, closed when main switch 4 is open, lead 24, solenoid 11, switch 14, closed when device 9 is in short-circuiting position, and lead 25. As the device 9 reaches its " off " position the switch 14 is opened and the switches 15, 16 and 17 are closed. The closure of switch 15 completes the circuit of a relay 29 thus:-lead 34, switch 15, lead 26, switch 27 of a time-relay 28 and coil of relay 29. The contacts 30 of relay 29 completes the circuit of the closing coil 31 of main switch 4. The closure of the switch 4 opens the switch 23 in the circuit of the solenoid 11 of the device 9 and closes the switches 32 and 33. The closure of switch 32 energizes the time-lag relay 28 which opens the circuit of the relay 29 which operates to de-energize the coil 31, the switch 4 being held. in its closed position mechanically and opened when the no-volt coil 74 placed across the bus-bars 18, 18<a> is de-energized. The closure of the switch 33 energizes a coil 36 which operates contactors 37 to close the rotor circuit through startling resistances 8. A coil 38 is also energized to short-circuit a portion of a resistance 42 in the circuit of the field-windings 43 of the converter in order that it may start easily. The coil of a sensitive relay 44 is placed across one of the starting resistances 8. When the machine is approaching synchronism the alternate increases and decreases of current in the starting resistances become very slow and the relay 44 closes for a sufficient interval the circuit of a time-lag relay 46 which controls the circuit of a coil 48 operating to short-circuit the starting resistances at the switches 49, 50 and to close the circuit of the solenoid 10 at the switch 51. The energization of the solenoid 10 operates the device 9 to short-circuit the slip-rings 7, opens the switches 15, 16 and 17 and closes the switch 14. The opening of switches 15, 16 and 17 de-energizes the solenoid 10, and the operating coils 36, 48, 38 and 46 to restore the apparatus to a position for again starting the machine. the directcurrent voltage has reached its normal value a relay 52 operates to close the circuit of an electromagnetic switch 55 the contact 72 of which shunts the contacts 21 of the master relay 20 while a second contact 72<1> connects the direct-current side of the machine to the bus-bars 57 through a limiting resistance 58 as described in Specification 171,796. If the demand on the machine is below a predetermined limit a relay 59 closes the. circuit of a switch 60 which operates to shortcircuit the resistance 58. If an overload occurs the relay 59 opens the circuit of the switch 60 and the resistance 58 is inserted. If the overload persists a thermal relay 61 shortcircuits the operating coil of the master relay 20, thereby de-energizing the bus-bars 18, 18a and the machine is shut down until the resistance, has cooled. Upon the occurrence of a high overload due to a fault on the machine or a " flash-over " on the direct-current commutator a manually reset relay 62 operates to short-circuit the coil of the master relay. The coil of ,the master relay is also adapted to be short-circuited by a reverse current relay 65 on the direct-current side of the machine. If a predetermined interval of time elapses between the closing of the main switch 4 and the switch 72 a time-lag relay 66 operates to short-circuit the coil of the master relay 20. To prevent the converter from increasing in speed to twice its normal synchronous speed due to tho direct-current field failing to excite a relay 69 is provided. The winding of the relay 69 is in the circuit of the field-winding 43 of the machine and its contacts are in series with the contacts of a relay 70 of the induction type. The coil of the relay 70 is connected across a starting resistance 8 and closes its contacts when the torque on its movable element is increased due to the decrease in frequency of the rotor currents below a predetermined value. The relays 69 and 70 preferably control a relay which is manually reset. The relay 70 may be replaced by an additional set of contacts on the relay 46.