SE360787B - - Google Patents

Abstract

1278196 Control of AC motors E SCHEUBECK 6 Feb 1970 [27 Feb 1969] 5779/70 Heading H2J The drive motor M of the tap changer mechanism of a transformer is provided with a control system, which ensures that only one tap change is made irrespective of the duration of the control command and which comprises motor contactors Cl, C2, a brake contactor d2, a control relay d1 and two cams driven by the motor, these cams respectively actuating one microswitch b3, Fig. 2 (not shown), and a pair of microswitches b4, b5, Fig. 3 (not shown). In a typical "tap-up" operation, a press button switch b1 is closed to energize contactor Cl and brake contactor d2, so starting the motor M. Switch b3 provides a self-holding circuit until switch b4 is closed to maintain Cl energized. Further motor movement changes over b3 to energize the relay d1 which has self-holding contacts in a circuit including contacts of C1. Further motor movement restores b3 and then opens b4 to de-energize members C1, d1, d2 and so complete the tap change, all the components having returned to their original conditions. Continuous closure of the switch b1 prevents deenergization of d1 at the end of the tap change and thus the initiation of another tap change. Operation of switch b2 to tap down produces a similar sequence of events involving members C2, d2, dl. The control system also provides the following features:-(1) Automatic re-starting after a mains voltage failure during a tap change, all the relays and contactors assuming their conditions prior to failure when the voltage is restored. (2) Automatic travel over one or more dead stages if present in the tap sequence. A contact b9 corresponding to the stage(s) prevents operation of b4 or b5 to terminate the tap change, until the stage(s) is/are traversed. (3) Prevention of a tap change if the motor M is connected to a supply of incorrect phase sequence. Closure of b1 or b2 causes the motor to rotate until b4 or b5 is actuated which, with the connections of the other components, causes the motor to reverse, return to its original position and stop.