215,189. Peebles & Co., Ltd., B., and Menderson, G. May 2, 1923. Systems for conversion, employing rotary converters.-In an automatic control system for starting a motor converter, the following operations are carried out successively at correct time intervals; the machine is caused to rotate; a choking coil is inserted across certain of the rotor windings; a non-inductive resistance in series with some of the rotor windings is shortcircuited; and finally all the rotor windings are short-circuited. In the arrangement shown in Fig. 1, on closing the main switch B, by hand or electrically, the motor-converter starts to rotate, three of the rotor windings being con nected to starting resistances D, D<1>, D<2> through slip rings C'. The direct-current voltage begins to build up, and, as soon as it reaches a predetermined value, if its polarity is correct, a relay P connected across the direct-current mains G, G<1> closes a switch E' and connects a choking-coil E across the resistances D, D'. A polarized relay F' in the circuit of the relay F keeps this circuit open until the direct current has the correct polarity. In an automatic substation the relay F<4> may be arranged to correct the polarity, if necessary, by energizing a field-reversing switch on the direct-current side. When synchronism is attained, a relav H in the form of a light contactmaking volt-meter across one of the starting resistances D closes its contacts H<1> and connects the coil J of a heavier current relay to the control bus-bars K, K<1>, which mav be energized with direct or alternating current The closing of the contacts J<1> of the relay J energizes another relay I. which closes the switch D<3> short-circuiting the starting resistances, and at the same time closes contacts L' in the circuit of another relay M which connects a motor N to the bus-bars K, K<1>. This motor drives a continuous cam which operates a ring N<1> short-circuiting all the rotor phases, in the manner described in Specification 219,430. The motor afterwards opens a switch 0 and closes switches P and R. The opening of the switch O de-energizes the relay F, whereupon the circuits of the choking coil E, relay L, and relay M are all opened and the motor N is disconnected from the bus-bars. The switch P, when closed, short-circuits a portion of the regulating resistance S<1> of the shunt field S<2> on the direct-current side of the converter, so that the resistance has the correct value for the no-load direct-current voltage. When the switch is open, the resistance has the correct value for synchronizing. The switch R is included in the circuit of a relay T, but this circuit also includes a switch B<1> which remains open as long as the main switch B is closed. When the latter is opened, the relay T breaks the field circuit through a resistance T<4>. The relay M is again energized through the closing of the switch B<1>, and the motor N again rotates, thereby opening the short-circuiting ring N, and bringing the switches O, P, R back to the starting positions. The opening of the switch R breaks the circuit of the relays M and T, and the motor N again shuts down, the whole of the circuits being in a condition for a re-start when required. A speed-limiting device U may be provided on the end of the motor-converter shaft to open the main switch B through a tripping circuit U<2> if the speed of the machine exceeds a predetermined limit. The switches E<1>, D<3> and the short-circuiting ring N<1> may be provided with handles, so that the motor-converter mav be started manually if any of the relays break down. A two-phase or three-phase choking coil may be employed instead of the single-phase coil E shown in Fig. 1. A modified arrangement for use on a three-wire direct-current system is shown in Fig. 4. In this arrangement, the third or neutral wire G<2> is connected to the short-circuiting switch D<3> which must therefore remain closed during the running of the motor-converter. In order to effect this, the switch O is arranged to remain closed unti. the motor N starts to re-open the short-circuiting ring, and an additional switch V is provided to open the circuit of the motor N at the close of the starting operations.