The swing equation in power system stability is given by:
Answer: A
The swing equation relates angular acceleration to net mechanical power (P_m), electrical power (P_e), and damping coefficient (D).
Q.2Hard
The critical clearing time in transient stability refers to:
Answer: A
Critical clearing time is the maximum duration a fault can exist before the system loses synchronism and becomes unstable.
Q.3Hard
The Ferranti effect in long transmission lines is characterized by:
Answer: A
Under light load, capacitive reactance dominates, causing charging current and voltage rise at the receiving end above the sending end voltage.
Q.4Hard
In the Newton-Raphson method for load flow analysis, convergence depends on:
Answer: A
N-R method converges based on good initial guesses (typically 1.0 pu) and the Jacobian matrix representing system sensitivity.
Q.5Hard
The phenomenon of voltage instability leading to voltage collapse occurs primarily due to:
Answer: A
Voltage collapse occurs when reactive power demand exceeds supply, causing progressive voltage reduction that destabilizes the system, as seen in 2012 Indian blackout.
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Q.6Hard
Which among the following is the correct formula for calculating bus voltage magnitude in Gauss-Seidel load flow method?
Answer: C
The Gauss-Seidel iterative formula for bus voltage calculation uses the admittance matrix and network equations: V_i = (1/Y_ii)[P_i + jQ_i - Σ(Y_ij*V_j)]
Q.7Hard
In a 500 kV transmission line, if the receiving end voltage drops to 0.9 pu, what type of compensation is most critical?
Answer: C
For severe voltage drop (10%), both series compensation (to reduce voltage drop) and shunt compensation (to support receiving end voltage) are typically required.
Q.8Hard
In transient stability assessment, what does the 'equal area criterion' determine?
Answer: B
Equal area criterion uses the swing equation graph to compare the accelerating area (energy added to rotor) with decelerating area (energy removed), determining stability.
Q.9Hard
In transient stability studies, which machine variable is most critical for assessing first-swing stability?
Answer: A
Speed deviation determines if the generator can maintain synchronism during the first swing after a disturbance. Excessive Δω leads to loss of synchronism.
Q.10Hard
Which FACTS device provides independent control of both voltage magnitude and phase angle?
Answer: C
UPFC can independently control transmission line voltage magnitude, phase angle, and impedance simultaneously using combined series-shunt compensation.
Q.11Hard
What is the critical clearing angle in transient stability analysis?
Answer: A
Critical clearing angle is the maximum rotor angle at fault clearing beyond which the system loses synchronism. It determines the maximum fault clearing time.
Q.12Hard
What is the primary mechanism of voltage instability in power systems?
Answer: A
Voltage instability occurs when reactive power demand exceeds generation and compensation capabilities, leading to progressive voltage decline and potential collapse.
Q.13Hard
Which formula represents the swing equation for a synchronous machine during a disturbance?
Answer: C
The swing equation 2H(d²δ/dt²) = Pm - Pe - D(dδ/dt) describes rotor angle dynamics, where H is inertia constant, Pm is mechanical power, Pe is electrical power, and D is damping coefficient.
Q.14Hard
As per IEEE 1588-2019 standard, what is the typical accuracy of a Phasor Measurement Unit (PMU) for frequency measurement in power systems?
Answer: B
IEEE 1588-2019 specifies ±0.01 Hz accuracy for steady-state frequency measurement in PMUs used for power system monitoring.
Q.15Hard
A 132 kV transmission line has a shunt capacitance of 0.008 µF/km and length of 200 km. Calculate the total reactive power generated by the line capacitance at steady state (assuming 132 kV operating voltage).
Answer: C
QC = (V²/Xc) where Xc = 1/(ωC), Total C = 0.008 × 200 = 1.6 µF, Qc = (132000)² × 2π × 50 × 1.6×10^-6 = 256.7 MVAR
Q.16Hard
In the context of transient stability, a generator loses synchronism when:
Answer: B
Loss of synchronism occurs when the generator rotor continuously accelerates because decelerating torque never becomes greater than accelerating torque, preventing the rotor from returning to synchronous speed.
Q.17Hard
Which of the following correctly represents the relationship between the steady-state stability limit and transient stability limit?
Answer: B
The transient stability limit is always greater than the steady-state stability limit. A system can maintain transient stability even after a disturbance that would violate steady-state stability.
Q.18Hard
In a power system experiencing voltage instability, the reactive power support margin becomes critical. At what reactive power reserve margin should emergency measures be initiated according to Indian Grid Code?
Answer: C
Indian Grid Code 2023 specifies that when reactive power reserves fall below 15% of the available reactive power limit, emergency corrective measures must be initiated to prevent voltage collapse.
Q.19Hard
The swing equation of a synchronous machine is given by: 2H(d²δ/dt²) = Pm - Pe - D(dδ/dt). What does H represent?
Answer: A
H is the inertia constant (M/2×SB) representing the kinetic energy relative to the system base power.
Q.20Hard
The critical clearing angle (δcr) in transient stability analysis represents:
Answer: A
δcr is the limiting rotor angle; if exceeded during a fault, the machine cannot return to synchronism even after fault clearance.
