A synchronous generator has the following ratings: 100 MVA 21kV 60 Hz and 8 pole

Question

A synchronous generator has the following ratings: 100 MVA 21kV 60 Hz and 8 poles; and
the following parameters: Rs=0.3?, Xs=4.8 ? the stator windings are connected as ?. The rotational and
excitation losses together are 2.5 MW. The generator is part of a thermal power plant and it is driven by
a steam turbine. The stator line terminals are connected to the electric power grid and the stator
voltage and frequency are maintained at 21 kV and 60 Hz respectively.
a. Calculate the internally generated voltage, the torque angle and the torque as well as the power
efficiency, if the generator supplies 100 MW to the grid at 1 pf.
b. Calculate the previous values if the generator supplies 100 MW to the grid at a 0.8 lagging
power factor.
c. What is the magnitude of the voltage loss due to the armature reaction in a and b? What is the
voltage regulation of the generator in a and b?
d. How much torque must be supplied to the rotor by the steam turbine in a and b?
(For parts a to e you may ignore the effects of Rs in order to calculate the stator currents and voltages;
but you may not ignore Rs for calculating the power efficiency.)

Explanation / Answer

Gnerated voltage = 21 + (100/21) x (0.3 + 4.8 j) = 22.428 + 22.857 j = 32.02 kv at an angle of 45.54

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