Patent GB-267217-A (GB)
Title: Improvements in or relating to the control of rotary converters
IPC: H02K47/04
Filed: 1925-12-10
Abstract: 267,217. Reyrolle & Co., Ltd., A., Mather & Platt, Ltd.,Grime, R. E., and Leeson, B. H. Dec. 10, 1925. Systems depending on two or more machines; synchronizing dynamo-electric machines; running generators in parallel.-Relates to an automatic synchronizing arrangement for a rotary converter started by a motor controlled, for example accord. ing to one of the four methods described in Specification 137,144* and 140,554* and in which a synchronizing switch is automatically operated to change the starting connections near synchronous speed. A voltage relay energized from the d.c. side of the converter cuts out the starting motor at a critical voltage. The field of the converter is controlled so as to prevent the building up of the voltage to the critical value unless its polarity is correct. The correction of polarity is preferably attained according to Specification 256,335. The synchronizing switch may be operated by a voltage relay across the d.c. brushes of the converter or across an auxiliary generator driven by the converter which may excite the converter field and be utilized in ensuring correct polarity, The Specification describes a complete automatic substation supplying a three-wire d.c. circuit from three-phase mains, capable of three successive attempts to go on load and then to lock out, and susceptible of distant control. In the system illustrated three-phase current is supplied from mains 10, Fig. 1, through transformers 13 a synchronizing switch 19 and the stator 20 of a three phase starting motor to the brushes 17 of a sixphase rotary converter 15. Near synchronous speed a voltage relay 55, connected across the converter d.c. bus-bars. 22, 23 energizes from the same source the synchronizing switch coil 45 and the switch 19 then cuts out part of the starting motor windings. When the converter has pulled into synchronism and built up its voltage to a critical value at the correct polarity a relay 69 energized from the d.c. bus-bars switches on the closing coil 56 of a running switch 16 which short-circuits the starting motor windings. According to the invention in one form a polarized relay 85 is energized from the d.c. bus-bars to control the circuit of a relay 83 which is completed by auxiliary contacts on the synchronizing switch 19. The relay 83 energizes a field contactor 72 from a transformer 13 to reverse the field and prevent the converter voltage building up. Each time the polarity is correct the relay 85 lifts its contacts and the field contactor sets the field connections right. After one or two such operations the machine pulls into synchronism at correct polarity and the voltage builds up until the running switch coil 56 is energized by the closure of voltage relay 69. In a modification, Fig. 2, the polarized relay 85 has normally open contacts and the field circuit is opened by a contact 152 when the synchronizing switch 19 is operated. The occurrence of correct polarity them causes the relay 85 to operate the field contactor 72 so that the field circuit is closed and simultaneously a contact 150 closes an open phase of the starting windings 20, the combined operation increasing the synchronizing forces. The relay 85 and contactor 72 are de-energized through a contact 153 when the receiving switch 16 closes, but the field is maintained by the contact 152 since the synchronizing switch is restored to its original position at this stage. In a further alternative, Fig. 3, an auxiliary generator 160 is driven by the converter. The field of the converter is normally connected to its terminals by a transfer relay 161. A contact 34 in the main oil switch 11 connects the synchronizing switch contactor 55 to this generator. An additional polarized relay 162 is connected across the converter brushes. This operates at a relatively low voltage and an incorrect polarity energizes the transfer relay which connects the field to the converter brushes, and closes at contact 164 a holding circuit independent of the relay 162 the relay itself being de-energized at contact 169. The remaining operations proceed as described in the arrangement of Fig. 1 under the control of the polarized relay 85. The operation of the substation system shown in Fig. 1 is as follows :- Starting. Starting up relays 117, 118 set so that the machine will pick up an. economical load when switched in drop their parallel-connected contacts upon low volts on either side of the three-wire system 21, 24, 25. The motor 133 of a time delay mechanism and a starting-up clutch coil 134 are thus energized from control bus-bars 28, 30 fed from a transformer 31 across the mains 10. The relays 117, 118 are robust and are made sensitive by lifting coils 119, 120 which are switched in by contacts 136, 137 of the time delay mechanism and they will open and stop operations, allowing the starting-up time delay mechanism to reset itself if the load circuit conditions do not persist for a time determined by the setting of the next switch 138 of the mechanism. When this closes the starting-up relay contacts are short-circuited and the contact 139 closes. This energizes the master control relay 39 from the control bus-bars through interlocks on the main oil switch 11, synchronizing switch 19, running switch 16, field reversing contactor 72 and positive d.c. circuit breaker 26 ensuring that these are in correct starting positions, and through a contact 145 on the underload time delay mechanism. The master control relay closes the main oil switch 11 through the motor 32, and prepares a circuit for the parallelling relay 104, 105. Auxiliary switches on the oil switch 11 close circuits to the contactor 55 controlling the synchronizing switch (energized from the d.c. bus-bars 22, 23, now dead), to the master control relay 39 and to an auxiliary parallelling relay 98 which is next operated. This makes a maintaining circuit, and energizes a raise volt relay 87 to cause a motor 86 to drive the field rheostat arm 78 in the raise volts direction. Limit switch 79 is first moved to prepare the lower volts relay circuit and on reaching limit switch 80 opens it thus deenergizing the relay 98 and the raise volts relay. The field rheostat is thus moved to starting-up position. The oil switch 11 in closing supplies current to the converter through the transformer 13 and full windings of the starting motor 18. Synchronizing. The d.c. volts build up and at a predetermined value cause contactor 55 to energize the coil 45 which operates the synchronizing switch 19 which cuts out half the starting motor windings. Auxiliary contacts on the synchronizing switch close circuits to a holding coil 46, field contactor relay 83, running switch contactor 69 (which operates only at the critical d.c. voltage) and, after a short delay, the polarized relay 85. The relay 83 energizes the field reversing contactor 72 from the transformer secondary 13 and prevents the building up of the voltage to the critical value until the relay 85 opens its contacts on correct polarity. This operation is repeated until synchronism is attained. Parallelling. The contactor 69 closes at the critical voltage and operates the running switch 16 through the coil 56. This short-circuits the starting motor. The switch remains closed independently of the coil 56 until tripped by a coil 57. Auxiliary contacts in the running switch close circuits to the master control relay 39 independent of the time delay mechanism, to the motor 133 and underload clutch coil 135 of the time delay mechanism through underload relay contacts 129 - - 132 (the clutch coil 134 is deenergized and the time delay mechanism for starting up reset) to the lower volts relay 92 and after a short delay to the trip coil 47 of the synchronizing switch which returns to starting position. The field rheostat is now driven in the lower volts direction until the limit switch 79 is operated to de-energize the lower volts relay and energize the auxiliary parallelling relay 98. This energizes the raise volts relay 87 and places the machine coil 104 of the parallelling relay across the converter bus-bars the other coil 105 being connected across the mains 24, 25. The field rheostat now begins to raise the d.c. voltage of the converter and when this is slightly above the mains voltage the parallelling relay closes its contacts. A contactor 107 then energizes the coils 108, 109 of d.c. circuit breakers 26, 27 and the machine goes on load. Load discriminating arrangements of the usual kind may be used to control the closing of these circuit breakers. Auxiliary switches on the circuit breakers close holding circuits therefor, prepare the circuit for their trip coil 111 and de-energize the auxiliary parallelling relay 98 (which causes the field rheostat to stop in its correct running position) and the machine coil 104 of the parallelling relay which opens and de-energizes contactor 107. Taking up load. Up to this stage underload conditions have existed upon the converter busbars and the underload relay contacts 129 - - 132 being closed the underload time delay mechanism has been running and the contacts 141, 142 and 143 have closed to energize the lifting coils 127, 128 of the underload relays and an independent circuit for the motor 133. When the converter takes up its load the underload relays will open de-energizing the clutch coil 135 and causing the time delay mechanism to reverse. On reaching its original position contacts 141--143 cpen and the motor 183 stops. Faulty operation. During the starting and synchronizing periods the starting-up time delay mechanism is being run by the motor 133. Should anything prevent the running switch 16 closing within a period depending upon the adjustment of the time limit contact 139 this contact will open and break the circuit of the master control relay 39. The contact 42 on this relay then operates the trip coil 33 of the mai