Question

A 110 km long three-phase transmission line, rated at 275 kV (line-line) / 50 Hz, is fed by a 180 MVA generator. The transmission line has the following characteristics: R=0.05

Ω/km , km.X- 0.47 Ωkm, y = 4.2 x 106 S/km, The transmission line supplies a city with 194.4 MW, at 271 kV anda power factor of 0.88 lagging. The generator has an automaticover-voltage relay that will trip if the voltage gets above 280 kV.Determine: if the relay will trip. (ii)if the generator is over-loaded, and if so, by how much in %. (b) Consider that the generator in 3(a) above has sub-transient reactance of 0.18 p.u. Calculate the fault current and the rating of a suitable circuit breaker, if a fault occurs at the receiving end of the line in 3(a) above. Use a base of 200 MVA for your calculations and ignore the line parallel admittance. (c)Briefly describe a distinct difference of zero-sequence components against positive or negative sequence components.

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