GB1166911A - A System for Controlling the Motors of at least two On-load Transformer Voltage Changers - Google Patents

Abstract

1,166,911. Control of motors. G. RINALDO. 5 Jan., 1967, No. 621/67. Heading H2J. Two or more motors for operating on load tap changers of a like number of parallel connected transformers are energized at least initially via a series circuit which includes contacts in each of the contactors associated with each motor, so that the motors must be energized simultaneously. As shown, two three-phase motors 3a, 3b, 3c and 3d, 3e, 3f are initially connected in series with each other and with contacts 41 or 42 of one contactor, and 51 or 52 of another, according to required direction of rotation and in delta across supply RST. The appropriate contactors are energized by a single automatic voltage regulator connected to the transformer secondaries. A relay 60 across motor windings 3f and 3c then closes 61, 62 to establish independent star connection for each motor, which enables the slower motor to complete its tap change after the faster one has had its contactor opened by a cam-operated limit switch. A timer B 1 starts when one contactor closes and sounds an alarm and disconnects the regulator if the second contactor does not close within the preset time; a second timer B 2 with a longer period similarly sounds an alarm and also opens the star point relay 60 if one motor runs unduly longer than the other. A third timer has contacts in parallel with those of B1 and operates if the motors are energized 1À5 times longer than normal. In Figs. 4 and 5 (not shown) the two motors are permanently connected in parallel with each other, but in series with both contactors and in Figs. 6 and 7 (not shown), this is expanded to a three-motor arrangement. In Figs. 8 and 9 (not shown), the two motor, parallel connection arrangement, is modified to include timer-operated contacts which allow independent operation after starting. In Figs. 10 and 14 (not shown), the motors are D.C. or single phase A.C. machines (500, 501); they are in parallel with each other but initially in series with both main contactors, but after starting a relay (511) establishes independent operation. A timer (504) sounds an alarm and opens the relay (511) if one contactor only is closed for more than the preset time.