# Power Systems Questions and Answers – Effect of Synchronous Machine Excitation – 1

This set of Power Systems Multiple Choice Questions & Answers (MCQs) focuses on “Effect of Synchronous Machine Excitation – 1”.

1. The synchronous machine is operating at a normal condition at the generating system, then the angle between rotor axis and the stator magnetic axis is _____________
b) Power factor angle
c) Impedance angle
d) None of the mentioned

2. The angle shown in the figure depends on which of the following given options? b) Power factor
c) Operating frequency

Explanation: Load angle depends on the loading of the system, as the load in added or decreased, the synchronous machine will accelerate or decelerate with respect to stator field.

3. Swing equation is very famous for describing the relation between the ___________
a) rotor motion and stator field
b) stator and rotor field
c) load angle and rotor field
d) moment of inertia and rotor motion

Explanation: Swing equation describes the relative motion between rotor load angle with respect to stator field as a function of time.

4. Swing equation which describes the relative motion of the rotor of the machine, is a __________
a) linear and second-order differential equation
b) non linear and second-order differential equation
c) non linear and first-order differential equation
d) non linear and hyperbolic equation

5. A variation in the power transfer had been observed at the generating station while power exchange process due to ______ and is known as ______
a) swing of the machine, inertial response
b) sub synchronism, hunting
c) sub synchronism, inertial response
d) swing of the machine, falling out of the rotor

Explanation: The power exchange between the mechanical rotor and the electrical grid due to the swing of the rotor is called inertial response.
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6. Why the angle δ, rotor angle is famously called as the load angle in the equation of rotor dynamics?
a) Due to power exchange is a function of δ
b) Because it dictates the reactive power compensation
d) No dependency on the load dynamics

Explanation: Rotor angle is the emf angle and power is a function of it.

7. The transient stability and the steady state stability of a power transmission system ________
a) maintain synchronism between machine and tie lines at all the circumstances
b) maintains frequency exactly at 50 Hz
c) maintain voltage regulation precisely
d) all of the mentioned

Explanation: Transient stability and steady state stability maintain synchronism between the generating station and tie line.

8. We can say a system is stable at steady state is not affected by ____________
a) line losses
b) line reactance
c) generator reactance
d) excitation of alternators

Explanation: Line losses do not affect the stability limit of the system.

9. The transient instabilities can occur in a system by ___________
b) Switching operation
c) Faults
d) Suddenn load changes, switching operation and faults

Explanation: All the mentioned factors affect the transient stability of a system.

10. Post a three phase fault that occurs in a system, then its transient stability can be examined using ___________
a) solution of swing equation
b) equal area criterion
c) solution of swing equation and equal area criterion
d) solution of swing equation or equal area criterion

Explanation: Swing equation provides the rotor dynamics at the transient conditions.

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