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  1. ∆-Y and ∆-Y
  2. Y-Y and ∆-Y
  3. ∆-∆ and ∆-Y
  4.  Y-∆ and ∆-∆
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1 Answers

Option 1 : ∆-Y and ∆-Y

Concept: Conditions to be satisfied for parallel operation of transformers:

1. Voltage ratings must be same.

2. Must be connected with correct polarity.

3. The phase sequence must be same.

4. Apart from phase sequence matching, the phase displacement between the seconderies of both transformers must be zero. This condition can be fulfilled if the two transformers belong to same phasor group.

Phasor displacement Transformer connections
Phasor group 1

0° Δ/Δ, Y/Y, Δ/Zig Zag Y

180° Δ/Δ, Y/Y, Δ/Zig Zag Y
Phasor group 2

±30° Δ/Y, Y/Δ, Y/Zig Zag Y

±150° Δ/Y, Y/Δ, Y/Zig Zag Y

 

Therefore, option 1 satisfies the above criteria.

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