Importance

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Abstract

A tap changer voltage regulator permits a tap changer selector contact to engage an open circuited new tap without arcing and has a half-tap voltage auxiliary winding which permits halving the inter-tap voltage to thus double the number of steps, and an auxiliary switch with a pair of movable contacts. A first auxiliary contact initially connects a selector contact which has moved to a new tap through a circulating current limiting resistor to a load, preventing load current interruption. A second auxiliary contact is in series with a normally-closed switch through which load current and circulating current flow. A first set of inverse parallel SCR's is in series with the resistor, while the normally-closed switch is shunted by a second pair of inverse parallel thyristors. The first pair of thyristors is not gated until the first auxiliary contact has attained its new position, precluding initial arcing. The normally-closed switch is then opened to transfer the current to the thyristors, and gating current is subsequently removed from the second pair of thyristors so that load and circulating current are statically interrupted by the thyristors at current zero, thus completing the tap change by permitting the second auxiliary contact to arclessly interrupt the circuit to the selector contact on the previous tap.

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First Claim