(b) A 50 MVA, 132 / 66 kV, delta/star, three-phase power transformer is protected by biased differential relay. If the current transformers located on delta and wye sides are 300/5 A and 1200/5 A, respectively, determine (i) the output current at full load, (ii) the relay current at full load, (iii) the minimum relay current setting to permit 25% overload.
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4 A Since the transformer is delta/star connected, the current in the delta side (HV side) is √3 times the line current. Therefore, the current in the HV winding, I_HV = 218.4 * √3 = 378.3 A The current transformer (CT) on the HV side has a ratio of 300/5. Show more…
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