Electronics and Communication Engineering - Power Electronics - Discussion

9. 

For a 12 pulse operation, the two 6 pulse units are fed by

[A]. Y - Y and Y - Y transformers
[B]. Δ - Δ and Δ - Δ transformers
[C]. Y - Y and Y - Δ transformers
[D]. Y - Δ and Y - Δ transformers

Answer: Option C

Explanation:

30° phase difference is necessary.


Suman said: (Jan 29, 2015)  
Please explain.

Bips said: (Aug 19, 2015)  
I am not getting it, please elaborate it.

Pvkrishna said: (May 12, 2017)  
The phase displacement between the two AC supplies is usually 30° and is realised by using converter transformers with two different secondary windings (or valve windings). Usually one of the valve windings is a star (Y)-connected and the other is delta-connected. With twelve valves connecting each of the two sets of three phases to the two DC rails, there is a phase change every 30°, and harmonics are considerably reduced. For this reason, the twelve-pulse system has become standard on almost all line-commutated converter HVDC systems.

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