A single-phase transformer rated 30 kVA, 1200/120 V is connected as an auto-transformer to supply 1320 V from a 1200 V bus. (a) Draw a diagram of the transformer connections showing the polarity marks on the windings and directions chosen as positive for current in each winding so that the currents will be in phase. (6) Mark on the diagram the values of rated current in the windings and at the input and output. (c) Determine the rated kilovolt amperes of the unit as an autotransformer. (d) If the efficiency of the transformer connected for 1200/]20 V operation at rated load unity power factor is 97%, determine its efficiency as an auto trans-former with rated current in the windings and operating at rated voltage to supply a load at unity power factor.
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