Patent GB-207788-A (GB)
Title: Improvements in and relating to automatic control equipments for electric rotary converters
IPC: H02K47/08
Filed: 1923-09-17
Abstract: 207,788. British Thomson-Houston Co., Ltd., (Assignees of McDonald, G. R.). Nov. 20, 1922, [Convention date]. Systems for conversion, employing rotary converters.-In an automatic control system for a rotary converter, means are provided for connecting the field winding 14 of the converter to a source of direct current during the starting process, and the field winding is subsequently connected across the direct-current brushes 11 through tl operation of a relay 49 having two windings 50, 51, the winding 51 being connected in series with the source of direct-current and the field winding, while the winding 50 is connected across the direct-current brushes. The converter is started by closing a switch 20 which connects the coil 21 of a master relay 22 across the control circuit 23, which may be energized from two of the phases of the three-phase supply 3. The closing of the contacts 31 of the relay 22 completes the circuit of the coil 33 of the starting contactor 8, which connects the slip rings 2 of the converter to low-voltage taps of a transformer 4, and at the same time connects the motor 40 of a motor generator set across two of the phases of the transformer. As soon as the converter has reached a predetermined speed a voltage relay 41, which has been connected across the direct-current brushes 11 of the converter through contacts 38 on the master relay 22, operates to complete the circuit of the coil 46 of a contactor 17, which connects the field winding 14 of the converter to the direct-current generator 15 driven by the motor 40. When the converter has correct polarity and the field current has built up to a predetermined steady value, the relay 49 operates and opens the circuit of the coil 46 of the contactor 17 and closes the circuit of the coil 54 of a contactor 18 which connects the field winding across the direct-current brushes. As soon as the shunt field current builds up to a predetermined value, a relay 25 operates to energize a relay 32 which opens the circuit of the coil 33 of the contactor 8 and closes the circuit of the coil 36 of a contactor 10. The slip rings 2 are thereby disconnected from the low-voltage taps and connected to the full voltage of the transformer, while the opening of the contactor 8 also shuts down the motor generator set. The energization of the coil 36 also opens the circuits of the coils 42, 50 of the relays 41, 49 so that these relays resume their normal position. The coil 51 of the relay 49 has already been deenergized on the opening of the contactor 17, but the relay, which was closed under the joint effect of the two coils, has been maintained closed by the action of the coil 50 alone. The relay 41 is of the "hesitating control" type, i.e. it is inductively damped, so that an appreciable interval elapses after the de-energization of the coil before the relay resumes its normal position. The relay 25 is also of this type, so that the system is not upset by any transient disturbance in the field current which may result from the connection of the converter to the full voltage of the transformer. When the relay 41 has resumed its normal position, if the polarity of the converter is correct and its direct-current is above a predetermined voltage, the circuit of the coil 59 of a contactor 13 is completed through a polarized relay 62, and the converter is connected to the direct-current circuit 12. The converter is disconnected by opening the circuit of the coil 21, either at the switch 20 or through the operation of the usual protective devices indicated at 28.