Which statements about the maximum power output of a cylindrical rotor synchronous generator are correct?

I. Maximum power output occurs when the load angle (δ) is 90°.

II. Maximum power is proportional to the square of the terminal voltage (V).

III. Over-excitation increases the generator’s maximum power capability.

IV. Maximum power is independent of the synchronous reactance (Xs).

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  1. Statements I and III only are correct. 
  2. Statements II and IV only are correct.
  3. Statements II and III only are correct.
  4. Statements I and IV only are correct. 

Answer (Detailed Solution Below)

Option 1 : Statements I and III only are correct. 
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Detailed Solution

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Concept

The power in a cylindrical rotor synchronous generator is given by:

\(P={EV\over X}sinδ\)

where, E = Induced EMF

V = Terminal voltage

X = Rotor reactance

δ = Load angle

Calculation

In the above expression, if δ = 90°, then sinδ = 1 and the power will be maximum.

\(P_{max}={EV\over X}\)

Hence, statement I is correct.

If the excitation of the generator is increased to an overexcited state, then the value of induced emf (E) will also increase, hence the power capability of the generator also increases.

Hence, statement III is correct.

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