Protection Engineering Basics and Schemes Protection Engineering | Page 221

6.3.4 Case 2:

I am now tasked to designed differential protection scheme for 45 MVA, 11 / 66KV star delta transformer.

Step 1: I will find full load current on transformer

I full = MVA ∗

1000 1.732 ∗ V primary

I Primary = 45 ∗

1000 1.732 ∗ 11

I primary = 2361.957A

I secondary = 45 ∗

1000 1.732 ∗ 66

I secondary = 393.6595A

CT Ratios are At primary I will suggest 3000 / 1 At secondary I will suggest 500 / 1 At 3000 / 1 CT, Secondary side of 2361.957A will be

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