Question

The steady state stability limit of a synchronous generator can be increased by _______.

• A. an increase in its reactance
• B. an increase in the excitation of the machine
• C. a decrease in the moment of inertia of the machine
• D. an increase in the moment of inertia of the machine

Hint:

Steady-state stability improves with excitation increase, not inertia. Use \(P = \frac{EV}{X} \sin \delta\).

Answer 1

The Correct Option is B

Step 1: Understanding Steady-State Stability
Steady-state stability is the ability of a power system (particularly a generator) to maintain synchronism under small and gradual changes in load. Step 2: Power-Angle Equation
The power transferred is given by: \[ P = \frac{EV}{X} \sin \delta \] where:
- \(E\) = internal voltage of generator,
- \(V\) = terminal voltage,
- \(X\) = reactance between generator and grid,
- \(\delta\) = load angle.
Step 3: How Excitation Affects Stability
Increasing excitation increases the internal EMF \(E\). This directly increases the maximum power transfer capability \(P_{max} = \frac{EV}{X}\), which improves the steady-state stability limit.
Step 4: Why Other Options Are Incorrect?
- Reactance increase → decreases power transfer.
- Inertia impacts transient, not steady-state stability.
Conclusion:
Option (2) is correct. Higher excitation → higher EMF → greater synchronizing power → better steady-state stability.