GB1088754A - Transformer control arrangement - Google Patents

Abstract

1,088,754. Tap change arrangements for parallel - connected transformers. BRUCE PEEBLES INDUSTRIES Ltd., and A. N. SCOTT. July 9, 1964 [July 12, 1963; March 6, 1964], Nos. 27822/63 and 9693/64. Heading H2H. A tap change control system for three transformers in parallel is arranged so that a tap change on the master transformer initiates a sequential tap change on the remaining two. The Figure shows the control circuit of one transformer which circuit is identical with the other two and comprises a voltage regulating relay 22, a line drop compensator 21 and a directional current relay 16, the relay 22 having a contact 26 controlling tap raising and lowering relays 23, 24, and the relay 16 having a contact 32 controlling raising and lowering stepping relays 29, 31, which in turn control contacts 33 ... 38. A multi-contact switch 27 provides for independent, master or follower operation or will switch the control circuit off. Another switch 41 provides manual tap change through switches 42, 43 or automatic tap change through the relay 22. Each control circuit includes a current transformer 12 coupled through a current transformer 13 to a circulating current circuit 28 which normally carries load current. A tap change on the master transformer (e.g. operation of raise relay 23) produces a circulating current due to terminal voltage difference and current flows in one direction through the master relay 16 and in the other direction through the relays 16 of the other two transformers, each relay being responsive to the component of circulating current provided by its respective current transformer 13. As a result master relays 23, 24 are disconnected to prevent a further tap change and the follower relays 29 are connected by contacts 32, although the position of the switch contacts 27 ensures that only the first follower is tap changed. When this is completed the reversal of current through the first follower relay 16 prevents a further tap change and initiates the tap change on the second follower, after which the circulating current due to terminal voltage difference disappears and relays 16 restore to normal. Relay 16 is protected by the contact 19 of an overcurrent relay 18 and has a biasing resistor 17 for use if the transformers have dissimilar tapping ranges or impedances. In a modification, use is made of the circulating current due to terminal voltage difference and its effect on the directional current relays to ensure that two parallel-connected transformers operating independently do not get more than one tap or a predetermined number out of step with each other, Figure (not shown) filed with Provisional Specification cognate 9693/64.