Abstract A step-switching arrangement for changing the taps on a transformer winding without interrupting the flow of current from the winding to a loadline includes a first switch and a resistance connected in series therewith extending from the transformer tap-changing contacts to the loadline which is paralleled by a changeover switch and vacuum switch connected in series therewith also extending from the transformer tap changing contacts to the loadline. A circulating current through the switches and resistance and part of the transformer winding occurs during a change in taps and this circulating current is normally interrupted by opening the contacts of the vacuum switch. Should the vacuum switch fail to open and interrupt the circulating current, then as the changeover switch is actuated from one main contact to the other, the circulating current will be caused to flow from an auxiliary contact on this switch through an auxiliary circuit which includes a fuse. Blowing of the fuse interrupts the circulating current and thus takes over the function of the failing vacuum switch.
In a step-switching device for changing the taps on a transformer winding connected to a loadline, the combination comprising a tap selector mechanism including at least two contact members movable sequentially along different taps of the transformer winding, a first switch including two stationary contacts connected respectively with said movable contact members of said tap selector mechanism and a movable contact member selectively connectible with said stationary switch contacts, a resistance element connected in series with said first switch to a loadline a changeover switch including two stationary main switching contacts connected respectively with said movable contact members of said tap selector mechanism and a movable contact member selectably connectible with said main switching contacts, a vacuum switch connected in series with said changeover switch to said loadline, said changeover switch further including a pair of stationary auxiliary switching contacts located intermediate said main switching contacts in the path of travel of said movable contact member, and an auxiliary circuit extending between each of said auxiliary switching contacts and a respective one of said movable contact members of said tap selector mechanism, each said auxiliary circuit including a fuse element adapted to blow whenever said movable contact member of said changeover switch engages its corresponding auxiliary switching contact and current flows through the auxiliary circuit as a result of failure of said vacuum switch to open its contacts.
Claim 2
Dependent Claim
228 words
In a step-switching device for changing the taps on a transformer winding connected to a loadline, the combination comprising a tap selector mechanism including at least two contact members movable sequentially along different taps of the transformer winding, a first switch including two stationary contacts connected respectively with said movable contact members of said tap selector mechanism and a movable contact member selectively connectible with said stationary switch contacts, a resistance element connected in series with said first switch to a loadline a changeover switch including two stationary main switching contacts connected respectively with said movable contact members of said tap selector mechanism and a movable contact member selectably connectible with said main switching contacts, a vacuum switch connected in series with said changeover switch to said loadline, said changeover switch further including a pair of stationary auxiliary switching contacts located intermediate said main switching contacts in the path of travel of said movable contact member, and an auxiliary circuit extending between each of said auxiliary switching contacts and a respective one of said movable contact members of said tap selector mechanism, each said auxiliary circuit including a fuse element adapted to blow whenever said movable contact member of said changeover switch engages its corresponding auxiliary switching contact and current flows through the auxiliary circuit as a result of failure of said vacuum switch to open its contacts.