If If is the full load current/phase and %X_s is the percentage synchronous reactance, maximum power output of an alternator is:

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SSC JE Electrical 16 Nov 2022 Shift 3 Official Paper

Answer 1

The maximum power output per phase:

\(P_{max}=VI_{max}cos\phi\)

\(P_{max}=VI_{max}\frac{E}{\sqrt{E^2 + V^2}}\)

Where I_max = Current per phase in case of maximum power output.

E = Excitation voltage

V = Terminal voltage

I_f = Full load current

% X_s = Percentage synchronous reactance

Then \(\%X_s=\frac{I_fX_s}{V}\times 100\)

\(\frac{V}{X_s}=\frac{I_f\times100}{\%X_s}\)

∴ \(P_{max}=VI_{max}\frac{E}{\sqrt{E^2 + V^2}} = \frac{EV}{X_s} \)

\(P_{max}=\frac{EI_f\times 100}{\%X_s}\)