Thyristors for effecting tap changing on transformers and including current limiting resistors and standby trigger system

Claim 2

Tap-changing means for transformers having thyristors for effecting tap-changes including in combination a. tapped transformer winding means having a pair of taps; b. a load-current-carrying line; c. transfer switch means including two pairs of relatively movable current-carrying contacts for selectively connecting each of said pair of taps to said line, and two pairs relatively movable disconnect contacts; d. two pairs of inverse parallel connected thyristors, each said pairs of thyristors being arranged to shunt one of said pair of current-carrying contacts in the closed position of one of said two pairs of disconnect contacts; e. a pair of current-limiting resistors eaCh shunted by an electric fuse, each of said pair of current-limiting resistors and the shunting fuse thereof being arranged in series with one of said two pairs of thyristors; f. means for sequentially triggering said two pairs of thyristors for performing a tap-changing operation; g. standby trigger means for each of said two pairs of thyristors; h. a pair of relays each responsive to a failure of said means for sequentially triggering and each controlling said standby triggering means of one of said two pairs of thyristors; and i. a pair of auxiliary switch means jointly operated with one of said two pairs of current-carrying contacts and each controlling the energizing circuit of one of said pair of relays.

Claim 3

Tap-changing means as specified in claim 1 wherein each of said pair of auxiliary switch means controls a shunt circuit across one of said two pairs of current-carrying contacts including means for energizing one of said pair of relays in response to a difference of voltage across one of said two pairs of current-carrying contacts.

Claim 4

Tap-changing means as specified in claim 2 including a pair of rectifiers each having two a-c terminals adapted to be connected sequentially by said pair of auxiliary switch means across one of said two pairs of current-carrying contacts and each having d-c terminals connected to one of said pair of relays.

Claim 5

Tap-changing means as specified in claim 1 wherein each of said pair of relays is an electromagnetic relay having a magnetic circuit with such remanence that each of said pairs of relays remains closed upon energization and following deenergization thereof.

Claim 6

Tap-changing means as specified in claim 1 including a. a d-c power source under the control of said pair of auxiliary switch means tending to energize said pair of relays in the closed positions of said pair of auxiliary switch means; b. a pair of trigger pulse transformers each for triggering one pair of said two pairs of thyristors, each of said pair of trigger pulse transformers having a tertiary winding; and c. two electric networks each energized by said tertiary winding of one of said pair of trigger pulse transformers and each bucking the voltage of said d-c power source when said tertiary winding of said pair of trigger pulse transformers is energized and thereby precluding energization of said pair of relays.

Claim 7

Tap-changing means for transformers having thyristors for effecting tap changes including in combination a. tapped transformer winding means having at least one pair of taps; b. a load-current-carrying line; c. transfer switch means including two pairs of relatively movable current-carrying contacts for selectively connecting each of said pair of taps to said line and two pairs of relatively movable disconnect contacts; d. two pairs of inverse parallel connected thyristors, each of said pair of thyristors being arranged to shunt one of said pair of current-carrying contacts in the closed position of one of said two pairs of disconnect contacts; e. principal triggering means for sequentially triggering said two pairs of thyristors when effecting a tap-changing operation; f. standby triggering means for each of said two pairs of thyristors; g. a pair of relays each responsive to a failure of said principal triggering means and each controlling said standby triggering means of one pair of said two pairs of thyristors; h. a pair of auxiliary switch means jointly operated with one of said two pairs of current-carrying contacts each controlling the energizing circuit of one of said pair of relays; and i. means for precluding the flow of excessive currents upon triggering of said pairs of thyristors by said stand-by triggering means, said excessive current precluding means including a pair of current-limiting resistors each arranged in series with one said two pairs of thyristors and each shunted by an electric fuse so that in case of triggering of said pairs of thyrisTors by said standby triggering means said fuse shunting each of said pairs of resistors tends to blow and the current flow subsequent to blowing is limited by at least one of said pair of current-limiting resistors.

Claim 8

Tap-changing means for transformers having thyristors for effecting tap changes including in combination a. tapped transformer winding means having at least one pair of taps; b. a load-current-carrying line; c. transfer switch means including two pairs of relatively movable current-carrying contacts for selectively connecting each of said pair of taps to said line and two pairs of relatively movable disconnect contacts; d. two pairs of inverse parallel connected thyristors, each of said pair of thyristors being arranged to shunt one of said pair of current-carrying contacts in the closed position of one of said two pairs of disconnect contacts; e. principal triggering means for sequentially triggering said two pairs of thyristors when effecting a tap-changing operation; f. standby triggering means for each of said two pairs of thyristors; g. a pair of relays each responsive to a failure of said principal triggering means and each controlling said standby triggering means of one pair of said two pairs of thyristors; h. a pair of auxiliary switch means jointly operated with one of said two pairs of current-carrying contacts each controlling the energizing circuit of one of said pair of relays; and i. means for precluding the flow of excessive currents upon triggering of said pairs of thyristors by said stand-by triggering means, said excessive current precluding means including a pair of current-limiting resistors each arranged in series with one said two pairs of thyristors and each shunted by an electric fuse so that in case of triggering of said pairs of thyrisTors by said standby triggering means said fuse shunting each of said pairs of resistors tends to blow and the current flow subsequent to blowing is limited by at least one of said pair of current-limiting resistors.

Claim 9

Tap-changing means as specified in claim 6 including a d-c power supply tending to energize said pair of relays in the closed positions of said pair of auxiliary switch means, and means responsive to the state of said principal triggering means precluding energization of said pair of relays when said principal triggering means generate trigger pulses.

Claim 10

Tap-changing means as specified in claim 7 including a pair of trigger pulse transformers each having a primary winding energized by said principal triggering means, a pair of secondary windings supplying trigger pulses to one of said pairs of thyristors, and a tertiary winding generating a voltage bucking the voltage of said d-c power supply.

Claim 11

Tap-changing means as specified in claim 6 wherein said standby triggering means include a standby trigger pulse generator, a pair of standby trigger pulse transformers each having a primary winding energized by said standby trigger pulse generator and a pair of secondary windings supplying standby trigger pulses to one of said pairs of thyristors, and wherein the primary circuit of each of said pair of standby trigger pulse transformers is under the control of one of said pair of relays.

Claim 12

Tap-changing means as specified in claim 6 including means tending to energize one said pair of relays in the closed position of one of said pair of auxiliary switch means, and means under the control of said principal triggering means precluding energization of said one of said pair of relays in case that said principal triggering means supply trigger pulses to one of said pairs of thyristors.