Wow...tricky. Thanks!The square root of three comes from the fact that T1 is composed of three individual single-phase transformers. They give the turns ratio of the individual units rather than that of the resulting three-phase transformer.
Since the low side (10 kV) is connected delta, VLine=VPhase = 10 kV
The high side (80kV) is connected wye, VLine=sqrt3*VPhase = sqrt(3)*80 kV = 138.56 kV
In terms of line voltage, the T1 turns ration is 10:138.56.
Setting the high side voltage to 138 kV:
The voltage at G1 is 138 kv (10/138.56) = 9.959 kV
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