VC = 2.3 m0 g0 r log10 D/r kV/phase
Here, g0 = 21.1 kV (r.m.s.)/cm ; m0 = 0.85 (assumed)
δ = 3.92 × 76/(273 + 40) = 0.952 ; log10 D/r = log10100/1 = 2
∴ Vc = 2.3 × 0.85 × 21.1 × 0.952 × 1 × 2 = 78.54 kV (r.m.s.)/phase
Line value = 78.54 × √3 = 136 kV (r.m.s.)/phase