A 10-kVA, 200:400-V, single-phase transformer gave these test results:
• Open-circuit test (LV winding supplied): 200 V, 3.2 A, 450 W
• Short-circuit test (HV winding supplied): 38 V, 25 A, 600 W
Compute the efficiency when the transformer delivers half its rated kVA at 0.85 power factor lagging.