A 6.6 kV, 3-phase, star-connected turbo-alternator of synchronous reactance 0.5 ohm/phase is applying 40 MVA at 0.8 lagging p.f. to a large system. If the steam supply is suddenly cut off, explain what takes place and determine the current the machine will then carry. Neglect losses.

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Solution:Given that steam input (Supply) is suddenly cut offKy point: Effect of steamsuprey cut off:Now since steam supply of synchronous geverator is cut off, the synctronous Generator will draw power from the Grid and will behave as a synchronous motor.synchronous motor takes current from the grid. That means current reversal will takes Rlace.wiven: complex power (S)=40 \mathrm{MVA}\begin{array}{l}\text { Valtage }(V)=6.6 \mathrm{KV} \\\text { Now } S=\sqrt{3} V I\end{array}\begin{array}{c}I=\frac{S}{\sqrt{3} \mathrm{~V}}=\frac{40 \times 10^{6}}{\sqrt{3} \times 6.6 \times 10^{3}} \\\operatorname{current}(I)=3499 \mathrm{~A}\end{array} ...