A 1500 kVA, 6600 V, three phase, star connected alternator with R, = 0.5 /ph and Xs=50/ph delivers a full load current at 0.8 lagging

A 1500 kVA, 6600 V, three phase, star connected alternator with R, = 0.5 Ω/ph and Xs=50/ph delivers a full load current at 0.8 lagging pf load. Find ad the induced e.m.f. per phase. If this induced emf per phase is maintained constant but lo is changed to full load unity p.f. estimate terminal voltage per phase