GB948130A - Improvements in and relating to frequency convertors - Google Patents

Abstract

948,130. Converting; control of A.C. motors. ASSOCIATED ELECTRICAL INDUSTRIES Ltd. April 21, 1960 [April 24, 1959], No. 14106/59. Headings H2F and H2J. [Also in Division G6] A quasi-sinusoidal waveform is built up from the direct current output of a controllable rectifying magnetic amplifier device which is controlled to give varying output amplitudes and which is connected to an output circuit through a changeover relay to provide positive and negative half cycles, control of both the magnetic amplifier and the changeover relay being effected by a rotatable selector switch. As shown in Fig. 2a, two windings x, y of an electric motor are supplied with 90 degree phase displaced currents which are related to the 25 positions of the selector switch, as shown in Fig. 1, from magnetic amplifiers controlled by windings CLX, CLY respectively through relays controlled by windings RLX, RLY respectively. A step pulse generator PG (Fig. 2), operates the selector switch which is provided with forward and reverse coils FC, RC, respectively. As shown in Fig. 2b, contact segments RSa and Rsb control the relay coils RLX, RLY, and the windings CLX, CLY are fed by a voltage derived from a potentiometer arrangement PQ, which voltage varies as the selector wiper R passes the contacts acb. The pulse generator comprises switch-operating cams displaced round a cam-shaft driven by a motor, each cam operating one switch to index the uniselector through one step. This motor may be speed controlled to vary the output frequency and hence the rotational speed of the driven motor which may control the position of nuclear reactor rods. The direction of movement of these rods is dependent on the rotational direction of the cam-shaft. By providing a cam-shaft with double the number of cams (say 50) two 25-position uniselectors may be operated from the same pulse generator. Each uniselector has two banks of contacts providing the two phase displaced currents x and y. The arrangement is used for slow movement of the nuclear rods and a retroactive feedback arrangement enables a predetermined reactor temperature to be maintained. An auxiliary motor drive provides fast control, and the rods may be lowered quickly under gravity, a resistor being connected across the field winding through a relay for dynamic braking.