We Claim:
1. A transformer system (1) for a direct current converter system (20),
5 comprising a plurality of windings (4a, 4b, 4c, 5a, 5b, 5c) for three electrical phases (3a, 3b, 3c),
the windings (4a, 4b, 4c, 5a, 5b, 5c) being electrically connected to provide a 15° phase shift, and comprising at least three separate tanks (6a, 6b, 6c,
10 18a, 18b, 18c), wherein the windings (4a, 4b, 4c, 5a, 5b, 5c) associated to different electrical phases (3a, 3b, 3c) are located in different ones of the separate tanks (6a, 6b, 6c, 18a, 18b, 18c), comprising for each electrical phase (3a, 3b, 3c) at least
15 one first winding (4a, 4b, 4c) and at least one second
winding (5a, 5b, 5c) electrically connected to each other, wherein the first winding (4a, 4b, 4c) and the second winding (5a, 5b, 5c) for the same electrical phase (3a, 3b, 3c) are located in the same tank (6a, 6b, 6c, 18a, 18b, 18c),
20 wherein the first winding (4a, 4b, 4c) and the second winding (5a, 5b, 5c) for the same electrical phase (3a, 3b, 3c) are located on a common core (10),
wherein the windings (4a, 4b, 4c, 5a, 5b, 5c) are connected in an extended-side delta connection, where the first
25 windings (4a, 4b, 4c) are connected to each other in a delta configuration and the second windings (5a, 5b, 5c) are the extended windings and are connected between the associated first windings (4a, 4b, 4c) and the electrical phases (3a, 3b, 3c).
30
2. The transformer system (1) according to claim 1,
18
wherein the first winding (4a, 4b, 4c) and the second winding (5a, 5b, 5c) are located on separate limbs (11, 12) of the common core (10).
5 3. The transformer system (1) according to any of the
preceding claims, wherein the first winding (4a, 4b, 4c) and the second winding (5a, 5b, 5c) for the same electrical phase (3a, 3b, 3c) are electrically connected to each other within the same tank (6a, 6b, 6c, 18a, 18b, 18c) . 10
4. The transformer system (1) according to any of the preceding claims, wherein a ratio of a number of turns in the first winding (4a, 4b, 4c) and in the second winding (5a, 5b, 5c) and/or a ratio of a voltage during operation at the first
15 winding (4a, 4b, 4c) and at the second winding (5a, 5b, 5c) is a square root of three.
5. The transformer system (1) according to any of the preceding claims, comprising at least three lead-through
20 connections (7a, 7b, 7c, 8a, 8b, 8c, 9a, 9b, 9c) for one of the transformer sides for each electrical phase.
6. The transformer system (1) according to claim 5, comprising exactly three and not more lead-through
25 connections (7a, 7b, 7c, 8a, 8b, 8c, 9a, 9b, 9c) for one of the transformer sides for each electrical phase.
7. A direct current converter system (20) comprising a transformer system (1) according to any of the preceding
30 claims and comprising a line commutated converter (25, 26) connected to the windings (4a, 4b, 4c, 5a, 5b, 5c) of the transformer system (1).
8. The direct current converter system (20) of claim 7, comprising two of the transformer systems (1) and comprising two line commutated converters (25, 26), each line commutated converter (25, 26) being connected to the windings (4a, 4b, 5 4c, 5a, 5b, 5c) of one of the transformer systems (1).