Editing Rectifier (section)

==== Twelve-pulse bridge ====
[[File:12 pulse bridge.png|thumb|left|350px|Twelve pulse bridge rectifier using [[thyristor]]s as the switching elements. One six-pulse bridge consists of the even-numbered thyristors, the other is the odd-numbered set.]]
Although better than single-phase rectifiers or three-phase half-wave rectifiers, six-pulse rectifier circuits still produce considerable harmonic distortion on both the AC and DC connections. For very high-power rectifiers the twelve-pulse bridge connection is usually used. A twelve-pulse bridge consists of two six-pulse bridge circuits connected in series, with their AC connections fed from a supply transformer that produces a 30° phase shift between the two bridges. This cancels many of the characteristic harmonics the six-pulse bridges produce.

The 30-degree phase shift is usually achieved by using a transformer with two sets of secondary windings, one in star (wye) connection and one in delta connection.
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