Patent GB-346960-A (GB)
Title: Improvements in or relating to electric power transmission systems employing rotary converters
IPC: H02P9/00
Filed: 1930-03-24
Abstract: 346,960. Rotary converter control systems. SEEGER, E. W. and MORTENSEN, N. L., 12th Street, Milwaukee, Wisconsin, U.S.A. March 24, 1930, No. 9348. Convention date, March 25, 1929. [Class 38 (iv).] Synchronizing dynamo - electric machines. - A rotary converter has a separately excited field, a direct coupled exciter and a starting motor. A relay subject to the voltage of the exciter controls a time delay relay which applies alternating current to the converter through an impedance at about synchronous speed, cuts out the impedance and then fully excites the field and connects the direct current main circuit. Interlocks and safety devices ensure correct sequence and provide for stopping the starting process or shutting down the machine on overheating of a part of the converter, failure of field current or of the alternating current supply, overload on the starting motor, prolonged operation of the starting motor or overdraft of alternating current. The machine will be restarted and re-connected automatically after a failure or overdraft of alternating current but is braked out on inadequate field current. If the starting process should be prolonged a thermally operated latch has to be reset by hand before a further attempt at starting can take place. The converter RC is started by closure of a pilot switch PB, the disconnecting switch 1 being closed and the transformer T energized. A switch 13 is thus operated by way of thermostatic switches Tm on various parts of the converter and the contacts of a lock-out relay 20, of an overload relay 2, and of a switch 21. The last switch is retained closed, though biased to open, by a thermostatic element heated by a coil in parallel with the starting motor control coil and can only be reclosed by hand if opened by prolonged operation of the starting motor. The switch 13 operates a switch 9 to connect up the starting motor M through an overload relay 22, one circuit of the switch 9 comprising the contacts of this relay. The exciter E is shunt wound. It is connected in circuit with a voltage relay 18 through a contact on switch 13 ; it is permanently in circuit with the field of the converter through a rheostat and a resistance FR. The voltage relay 18, when energized by a voltage corresponding approximately to synchronous speed of the converter, closes its contact and energizes a relay 17 which at 17b energizes a switch 14. This action short circuits contact 17b, prepares a circuit to energize a switch 10 and de-energizes the relay 17. The armature of the relay falls at a rate controlled by a dash-pot 17 and contacts 17c, 17d, 17e and 17f close in turn. The first contact energizes the switch 10, which applies A.C. to the converter through impedances; the next, a switch 15, which operates a switch 11 to short-circuit the impedance, and a switch 16, which short-circuits the resistance FR in the field circuit. Contact 17f closes a circuit causing the D.C. switch 12 to close, but before this can occur contact 17e prepares a circuit for lock-out relay 20 by way of a closed contact on switch 14, a closed contact on switch 11 and the contact of a field current relay 19. If before the D.C. circuit is closed or at any time during operation the field should fail the lock-out relay is energized and latched open. This de-energizes the switch 13 and the converter is shut down. The starting motor is disconnected by a contact on switch 11 and a resistance AB is inserted in the circuit of the voltage relay 18 by a contact on switch 16 rendering it sensitive to voltage changes during operation of the converter. All switches will open on failure of the A.C. supply but automatic restarting will occur when supply is resumed if the circuit of switch 13 be complete. A field-disconnecting or splitting switch may replace the resistance controlling switch 16.