Power System Dynamics, Excitation System Models & Stability Enhancement Methods (GATE/AE level)

 Q101. Power system dynamics primarily deals with:

A) Rotor motion and system oscillations
B) Transformer magnetics
C) Transmission losses
D) Frequency measurement
Ans: A

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Q102. The small-signal stability of a system depends on:
A) Damping torque and synchronizing torque
B) Only damping torque
C) Only synchronizing torque
D) None
Ans: A

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Q103. The dynamic equation of a synchronous machine neglecting damping is:
A) $M \frac{d^2δ}{dt^2} = P_m - P_e$
B) $D\frac{dδ}{dt} = P_m - P_e$
C) $M \frac{dδ}{dt} = P_m - P_e$
D) None
Ans: A

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Q104. Damping torque is proportional to:
A) Rate of change of rotor speed
B) Rotor angle
C) Field current
D) None
Ans: A

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Q105. Negative damping causes:
A) Oscillations to increase
B) Oscillations to decrease
C) Constant response
D) None
Ans: A

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Q106. A typical oscillation frequency of electromechanical modes is:
A) 0.2–2 Hz
B) 5–10 Hz
C) 20–50 Hz
D) 100 Hz
Ans: A

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Q107. The excitation system affects mainly:
A) Voltage and reactive power
B) Frequency
C) Active power
D) None
Ans: A

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Q108. The transfer function of an excitation system is expressed in terms of:
A) Gain and time constants
B) Impedance
C) Reactance
D) None
Ans: A

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Q109. A DC excitation system uses:
A) DC generator
B) AC generator
C) Thyristor rectifier
D) None
Ans: A

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Q110. Static excitation systems use:
A) Thyristor-based rectifiers
B) DC generators
C) Induction motor drives
D) None
Ans: A

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Q111. The ceiling voltage in an excitation system is the:
A) Maximum obtainable field voltage
B) Rated voltage
C) Minimum voltage
D) None
Ans: A

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Q112. The response ratio of an excitation system is defined as:
A) Ratio of ceiling voltage to rated voltage
B) Ratio of field current to armature current
C) Ratio of terminal to field voltage
D) None
Ans: A

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Q113. High gain in AVR results in:
A) Better voltage regulation but possible instability
B) Poor regulation
C) Reduced damping
D) None
Ans: A

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Q114. Power System Stabilizer (PSS) generates a signal proportional to:
A) Speed deviation
B) Voltage
C) Current
D) None
Ans: A

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Q115. The output of a PSS is applied to:
A) Excitation system input
B) Governor
C) Turbine
D) None
Ans: A

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Q116. The primary purpose of PSS is to:
A) Provide damping torque
B) Increase synchronizing torque
C) Control power
D) None
Ans: A

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Q117. The washout circuit in a PSS acts as:
A) High-pass filter
B) Low-pass filter
C) Band-stop filter
D) None
Ans: A

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Q118. The gain of a PSS is tuned to:
A) Provide optimal damping
B) Reduce voltage
C) Maintain current
D) None
Ans: A

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Q119. The transfer function of a simple PSS includes:
A) Lead-lag and washout blocks
B) Integrator
C) Differentiator only
D) None
Ans: A

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Q120. Excitation control directly affects:
A) Reactive power and voltage
B) Active power
C) Frequency
D) None
Ans: A

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Q121. The governor system primarily controls:
A) Frequency
B) Voltage
C) Reactive power
D) None
Ans: A

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Q122. Turbine-governor dynamics are represented by:
A) First-order system
B) Second-order system
C) Nonlinear
D) None
Ans: A

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Q123. Droop control characteristic defines:
A) Frequency vs power output
B) Voltage vs current
C) Torque vs angle
D) None
Ans: A

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Q124. A smaller droop constant implies:
A) Stiffer frequency control
B) Poor control
C) Unstable system
D) None
Ans: A

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Q125. The frequency deviation after disturbance is reduced by:
A) Secondary control
B) Primary control
C) Both
D) None
Ans: A

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Q126. The tie-line power flow in a two-area system depends on:
A) Frequency difference
B) Voltage difference
C) Phase difference
D) None
Ans: A

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Q127. Automatic Generation Control (AGC) maintains:
A) Frequency and tie-line power
B) Voltage
C) Power factor
D) None
Ans: A

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Q128. The area control error (ACE) is:
A) $ACE = ΔP_{tie} + BΔf$
B) $ACE = ΔP + ΔQ$
C) $ACE = ΔV + ΔI$
D) None
Ans: A

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Q129. Load frequency control (LFC) operates in the time frame of:
A) Seconds to minutes
B) Milliseconds
C) Hours
D) None
Ans: A

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Q130. Voltage control operates in:
A) Faster time frame than frequency control
B) Slower
C) Equal
D) None
Ans: A

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Q131. Governor dead band refers to:
A) Small frequency deviation without control action
B) Overshoot limit
C) Damping region
D) None
Ans: A

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Q132. Speed droop of 5% means:
A) 5% frequency change gives 100% power change
B) 5% voltage drop
C) 5% damping
D) None
Ans: A

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Q133. Secondary control is implemented using:
A) Integral controller
B) Proportional controller
C) Derivative controller
D) None
Ans: A

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Q134. Tertiary control in power systems deals with:
A) Economic load dispatch
B) Governor control
C) AVR
D) None
Ans: A

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Q135. Frequency bias constant (B) is expressed in:
A) MW/Hz
B) Hz/MW
C) VAR/V
D) None
Ans: A

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Q136. In multi-area systems, frequency stability is maintained by:
A) Tie-line bias control
B) Independent area control
C) Reactive compensation
D) None
Ans: A

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Q137. Synchronous condensers provide:
A) Reactive power
B) Active power
C) Both
D) None
Ans: A

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Q138. The inertia constant reduces when:
A) More renewables replace synchronous machines
B) More thermal units added
C) System load decreases
D) None
Ans: A

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Q139. Low-inertia systems are:
A) More prone to frequency excursions
B) More stable
C) Slower
D) None
Ans: A

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Q140. Fast-acting FACTS devices help in:
A) Dynamic voltage support
B) Frequency control
C) Protection
D) None
Ans: A

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Q141. TCSC (Thyristor Controlled Series Capacitor) primarily controls:
A) Line reactance
B) Voltage
C) Frequency
D) None
Ans: A

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Q142. SSSC (Static Synchronous Series Compensator) injects:
A) Series voltage
B) Series current
C) Shunt current
D) None
Ans: A

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Q143. The phase angle regulator is used to control:
A) Real power flow
B) Reactive power
C) Voltage
D) None
Ans: A

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Q144. The Unified Power Flow Controller (UPFC) combines:
A) SSSC and STATCOM
B) SVC and TCSC
C) SSSC and SVC
D) None
Ans: A

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Q145. Dynamic reactive power control improves:
A) Transient stability
B) Frequency
C) Load shedding
D) None
Ans: A

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Q146. The transient stability improvement by series capacitors is due to:
A) Reduction of line reactance
B) Increase in resistance
C) Voltage drop
D) None
Ans: A

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Q147. Line reactance compensation ratio is:
A) $X_c / X_L$
B) $X_L / X_c$
C) $V/I$
D) None
Ans: A

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Q148. The optimal compensation ratio for series capacitor is about:
A) 0.5
B) 0.1
C) 1.0
D) None
Ans: A

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Q149. The major limitation of series capacitor compensation is:
A) Sub-synchronous resonance
B) High cost
C) Losses
D) None
Ans: A

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Q150. SSR occurs due to:
A) Interaction between turbine shaft and capacitor-reactance
B) Voltage fluctuations
C) Excitation instability
D) None
Ans: A

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Q151. Damping controllers are added to mitigate:
A) SSR oscillations
B) Voltage drop
C) Overvoltage
D) None
Ans: A

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Q152. Modern excitation systems are mostly:
A) Static
B) Rotating
C) Manual
D) None
Ans: A

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Q153. The “lead-lag” compensation in PSS is used to:
A) Provide phase compensation
B) Reduce amplitude
C) Increase gain
D) None
Ans: A

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Q154. Increasing excitation reduces:
A) Armature current for lagging load
B) Terminal voltage
C) Power factor
D) None
Ans: A

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Q155. Load frequency control loop mainly uses:
A) Integral control
B) Derivative control
C) Open loop
D) None
Ans: A

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Q156. For an under-frequency condition, generators:
A) Increase mechanical power input
B) Reduce excitation
C) Trip immediately
D) None
Ans: A

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Q157. Excitation limiters prevent:
A) Field overheating
B) Rotor overspeed
C) Frequency deviation
D) None
Ans: A

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Q158. Supplementary control in excitation systems aims at:
A) Damping low-frequency oscillations
B) Reducing high-frequency noise
C) Current limiting
D) None
Ans: A

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Q159. Inter-area oscillations usually occur in range:
A) 0.1–1 Hz
B) 5–10 Hz
C) 20–50 Hz
D) None
Ans: A

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Q160. The Heffron–Phillips model represents:
A) Linearized small-signal model of synchronous machine
B) AVR circuit
C) Transmission line
D) None
Ans: A

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Q161. In the Heffron–Phillips model, constant K5 represents:
A) Excitation gain effect
B) Damping
C) Speed governor
D) None
Ans: A

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Q162. The AVR loop introduces:
A) Negative damping
B) Positive damping
C) No effect
D) None
Ans: A

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Q163. Properly tuned PSS compensates the:
A) Negative damping introduced by AVR
B) Positive damping
C) Field current
D) None
Ans: A

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Q164. Eigenvalue analysis is used to determine:
A) System modes and stability
B) Voltage magnitude
C) Frequency deviation
D) None
Ans: A

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Q165. The dominant eigenvalue with positive real part indicates:
A) Instability
B) Stability
C) Neutral response
D) None
Ans: A

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Q166. Time constant of mechanical system is in:
A) Seconds
B) Milliseconds
C) Microseconds
D) None
Ans: A

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Q167. Time constant of excitation system is typically in:
A) 0.1–1 second
B) 5–10 seconds
C) 0.001 second
D) None
Ans: A

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Q168. Voltage stability can be improved using:
A) Shunt capacitor
B) FACTS
C) Both
D) None
Ans: C

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Q169. Dynamic reactive support is faster using:
A) STATCOM
B) SVC
C) Synchronous condenser
D) None
Ans: A

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Q170. The mechanical input power of a generator is controlled by:
A) Governor
B) Exciter
C) AVR
D) None
Ans: A

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Q171. A two-area system oscillates around:
A) Center of inertia
B) Mid-point voltage
C) Reference bus
D) None
Ans: A

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Q172. Frequency deviation in an area is corrected by:
A) Secondary control
B) AVR
C) Tap changer
D) None
Ans: A

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Q173. Automatic Voltage Regulators improve:
A) Transient and steady-state stability
B) Frequency
C) Speed
D) None
Ans: A

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Q174. Governor droop prevents:
A) Hunting among units
B) Voltage dip
C) Rotor heating
D) None
Ans: A

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Q175. Multi-machine transient stability analysis uses:
A) Swing equation for each rotor
B) One for all
C) Static equation
D) None
Ans: A

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Q176. Numerical integration for swing curve uses:
A) Euler or Runge-Kutta
B) Trapezoidal
C) Both
D) None
Ans: C

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Q177. The critical clearing angle is determined by:
A) Equal area criterion
B) Damping coefficient
C) Excitation voltage
D) None
Ans: A

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Q178. The smaller the inertia, the:
A) Faster the rotor acceleration
B) Slower the acceleration
C) No effect
D) None
Ans: A

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Q179. The transient energy function method uses:
A) Kinetic + Potential energy equality
B) Power flow equation
C) Current equation
D) None
Ans: A

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Q180. The area under $P_m - P_e$ curve during fault acceleration equals:
A) Kinetic energy gain
B) Electrical energy
C) Mechanical energy loss
D) None
Ans: A

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Q181. The system is stable if:
A) Decelerating area ≥ accelerating area
B) Opposite
C) Equal to zero
D) None
Ans: A

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Q182. Increasing damping torque reduces:
A) Oscillation amplitude
B) Voltage
C) Frequency
D) None
Ans: A

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Q183. AVR acts through:
A) Field voltage
B) Armature voltage
C) Rotor speed
D) None
Ans: A

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Q184. A negative synchronizing torque results in:
A) Instability
B) Steady operation
C) High damping
D) None
Ans: A

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Q185. The steady-state stability can be improved by:
A) Increasing excitation
B) Reducing X
C) Both
D) None
Ans: C

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Q186. Damping factor is defined as:
A) Ratio of actual damping to critical damping
B) Torque ratio
C) Time constant
D) None
Ans: A

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Q187. The system is critically damped when:
A) ζ = 1
B) ζ < 1
C) ζ > 1
D) None
Ans: A

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Q188. Overdamped response results in:
A) Slow settling
B) Oscillations
C) Overshoot
D) None
Ans: A

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Q189. Underdamped response has:
A) Oscillations
B) No oscillations
C) Infinite delay
D) None
Ans: A

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Q190. The stability margin is measured in:
A) Degrees of δ
B) Voltage
C) VAR
D) None
Ans: A

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Q191. The first swing stability depends mainly on:
A) System inertia and clearing time
B) Damping
C) Excitation
D) None
Ans: A

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Q192. Long-term stability involves:
A) Thermodynamic and load controls
B) AVR
C) PSS
D) None
Ans: A

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Q193. Load modeling affects:
A) Voltage stability
B) Frequency response
C) Both
D) None
Ans: C

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Q194. Static load model assumes:
A) Constant P and Q
B) Constant impedance
C) Both
D) None
Ans: C

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Q195. Dynamic load model includes:
A) Motor dynamics
B) Heater resistance
C) Transmission line
D) None
Ans: A

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Q196. Reactive power deficiency causes:
A) Voltage collapse
B) Frequency drop
C) Speed rise
D) None
Ans: A

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Q197. Voltage collapse is a form of:
A) Static instability
B) Dynamic instability
C) Rotor instability
D) None
Ans: A

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Q198. The PV curve shows:
A) Voltage vs reactive power
B) Power vs voltage
C) Both
D) None
Ans: B

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Q199. The nose point of PV curve corresponds to:
A) Voltage stability limit
B) Frequency limit
C) Damping limit
D) None
Ans: A

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Q200. Reactive power support beyond the nose point:
A) Restores voltage stability
B) Cannot stabilize system
C) Increases frequency
D) None
Ans: B