Determine the perunit resistance and perunit synchronous rea

Determine the per-unit resistance and per-unit synchronous reactance of a 37.5-kVA, 480-V, 60-Hz, wye-connected alternator whose synchronous impedance is 1.47 + j7.68 ohm/phase.

Solution

impedance=(1.47+j7.68) ohms/phase.

KVA BASE=37.5

KV BASE=0.48

BASE CURRENT=KVA BASE/KV BASE=(37.5/0.48)=78.125

BASE CURENT=0.078125 KAMPS.

BASE IMPEDANCE=(BASE VOLTAGE/BASE CURRENT)=0.48/0.078125=6.144 OHMS.

P.U. IMPEDANCE= (ACTUAL IMPEDAANCE/BASE IMPEDANCE)=(1.47+j7.68)/6.144=(0.239+j1.25) pu.

P.U. RESISTANCE=0.239

P.U. REACTANCE=1.25