Patent GB-245876-A (GB)
Title: Improvements relating to starting equipment for electric current converters
IPC: H02K47/08
Filed: 1924-10-30
Abstract: 245,876. Ross, T. W., Townend, R., and Metropolitan-Vickers Electrical Co., Ltd. Oct. 30, 1924. Synchronizing dynamo-electric machines. - Starting equipment for rotary converters comprises an auxiliary source of continuous current adapted to be connected to the field winding of the converter for polarizing at starting, the field winding being connected in parallel with a circuit comprising the armature winding of the converter and a resistance, and means for automatically disconnecting the continuous current source and' cutting out a part of the resistance when the voltage of the converter at the continuous current terminals reaches a predetermined value.. Means are also provided for disconnecting the converter from the alternating current supply if it comes up to synchronous speed with wrong polarity, and for locking out the converter if it fails to attain correct polarity within a predetermined period. In the arrangement shown, energization of the supply transformer 3 energizes a coil 5 actuating the switch 4 of the starting motor 2 of a rotary converter 1. Closure of the switch 4 completes also the circuit of a coil 12 closing a switch 11 which starts a motor-generator set 8 supplying direct current for polarizing the field winding 13 of the converter, through the coil 17 of a relay 16, thereby opening the contacts 31. Flow of current through the armature of the converter is limited by the resistance 33, 34 until the converter begins to build up, whereupon the consequent reduction of current in the coil 17 allows the contacts 31 to close, thereby energizing the coil 15 of a relay 14 which short-circuits the part 34 of the resistance through the contacts 35. At the same time the coil 12 of the switch 11 is de-energized by opening of the contacts 29, and the motor-generator set 8 is shut down, the generator being simultaneously disconnected by opening of the, contacts 30. Meanwhile the contacts 37 of a relay 18, the coil 19 of which is connected across one phase of the starting motor, have been held open due to the voltage drop in the latter, but the reduction in current as the converter approaches synchronous speed allows these contacts to close, thus connecting the armature of a polarized time lag relay 20 across the continuous current terminals of the converter, whereupon after the predetermined time interval and if the converter is of correct polarity, the contacts 38 are closed, thus energizing a coil 7 which closes the running switch 6 of the converter and breaks the circuit of the coil 5 at the contact 27. If the converter comes up to speed with incorrect polarity, on closing of the contacts 37. the relay 20 operates in the reverse direction, closing the contacts 39, thereby omitting to close the running switch 6 and energizing the coil 22 of a relay 21, thus interrupting at the contacts 28 the circuit of the coil 5 which shuts down the starting motor. The fall in voltage at the continuous current terminals of the converter as it slows down permits the contacts 28 to close again, thus causing a repetition of the starting operation. Limitation of the number of starting operations in case of repeated wrong polarity is effected by a time lag relay 23 adapted to complete the circuit of the coil 26 of a hand reset lock-out relay 25 adapted to trip the switch on the primary side of the supply transformer. The lock-out relay is also adapted to be actuated in the event of failure of the relay 18 to respond to the voltage drop across the starting motor when the contacts 32 of the relay 16 are closed, the circuit of the coil 26 being closed at the contacts 36 of the relay 18. The invention is stated to be applicable also to motor-generators and motor-converters, and may also be applied to " tap starting and " reactance " starting systems. Further, the motorgenerator employed as the source of auxiliary current may be replaced by a battery.