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# A 100 MVA, 66 kV/230 kV, Delta- Wye three phase transformer is protected by a differential...

A 100 MVA, 66 kV/230 kV, Delta- Wye three phase transformer is protected by a differential relay. Current transformer ratio at the LV side is 1000 :5 A.
a) Sketch connection of differential relays to the transformer
b) Current transformers available for use at the HV side are 800:5, 600:5, 400:5 and 200:5. Select the suitable CT ratio.
c) Sketch the phasor diagram to show currents in current transformers windings and power transformers windings
d) Calculate the percentage of the current through the operating coil under full load condition of the transformer

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