Question 4.17: A 3 MVA, 6600 V, three-phase, star connected synchronous gen...
A 3 MVA, 6600 V, three-phase, star connected synchronous generator has a resistance of 0.2 Ω and synchronous reactance of 3.5 Ω per phase. Calculate the regulation at rated output at 0.8 power factor lagging. The speed and excitation remain constant.
Given line voltage = 6600 V
phase voltage V_{Ph} = \frac{6600}{\sqrt{3}}
= 3810 V
R_{a} = 0.2 Ω
X_{s} = 3.5 Ω, \cos Φ = 0.8 lagging, \sin Φ = 0.6
Total MVA = 3
Total VA = 3 × 10^{6}
This VA is for the three phases. VA per phase will be one-third of the total VA
VA per phase = 1 × 10^{6}
Current per phase I_{a} = \frac{1 × 10^{6}}{V_{Ph}} = \frac{10,00,000}{3,810} = 262.5 A
Induced EMF, E = \sqrt{( V \cos Φ + I_{a} R_{a})² + ( V \sin Φ + I_{a} X_{S} )² }
= 4049.4 V
Percentage regulation = \frac{(E – V)}{V} × 100 = \frac{(4049.4 – 3810)}{3810} × 100 = 6.28 per cent
