In a 400 kV transmission line, if the sending end voltage is 400 kV and receiving end voltage drops to 380 kV, what is the percentage voltage regulation?
Which of the following is NOT a component of the Indian National Load Despatch Centre (NLDC)?
Answer: C
NLDC coordinates scheduling and operation but does not directly maintain transmission lines. That responsibility lies with POWERGRID.
Q.63Medium
A synchronous generator has a subtransient reactance (X''d) of 0.15 pu and transient reactance (X'd) of 0.25 pu. During a three-phase fault, which reactance is used for the initial fault current calculation?
Answer: C
Subtransient reactance X''d represents the initial response of the generator to a sudden disturbance and is used for calculating the first few cycles of fault current.
Q.64Hard
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.65Easy
In load flow analysis, if a bus is specified with PV (constant voltage and active power), what variable is calculated?
Answer: B
In PV buses, active power (P) and voltage magnitude (V) are specified, and the load flow solution calculates the reactive power (Q) and voltage angle (δ).
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Q.66Hard
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.67Medium
Which protection scheme is mandated for inter-state transmission lines in India according to Grid Code 2023?
Answer: C
Indian Grid Code 2023 requires differential protection as primary with distance protection as backup for critical transmission lines to ensure faster fault clearance.
Q.68Hard
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.69Medium
A capacitor bank rated 50 MVAR at 400 kV is to be switched in a power system. Which device is most suitable for controlled switching to avoid transient overvoltages?
Answer: C
Pre-insertion resistors and reactors limit the inrush current and transient overvoltages when capacitor banks are switched, ensuring smooth energization.
Q.70Medium
In the Indian power system, the frequency regulation bandwidth for Load Frequency Control (LFC) is typically maintained within:
Answer: A
As per CEA guidelines and recent Grid Code specifications, LFC keeps the system frequency within ±0.2 Hz of 50 Hz nominal frequency to ensure quality power supply.
Q.71Hard
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.72Medium
A 50 MW, 11 kV, 50 Hz synchronous generator has an inertia constant H = 6 seconds. Calculate the kinetic energy stored in the rotor at rated speed.
Answer: B
KE = H × S where S = rated MVA. KE = 6 × 50 = 300 MJ. (H is defined as H = KE/MVA)
Q.73Medium
In a multi-machine power system stability study, which parameter is used to measure relative rotor angle instability between two generators?
Answer: B
The stability of a multi-machine system depends on relative rotor angles between machines. Loss of synchronism occurs when relative rotor angle exceeds critical limits.
Q.74Medium
A STATCOM (Static Synchronous Compensator) is installed in a 220 kV network. In what mode should it operate to provide reactive power support during a voltage sag?
Answer: D
During voltage sag, STATCOM operates as a voltage source injecting capacitive reactive power (leading current) to support and restore the system voltage.
Q.75Medium
In selective coordination of protective devices, what is the minimum time interval required between the operation of primary and backup fuses as per Indian standards?
Answer: C
IS 1885 and IEEE standards recommend a minimum coordination time interval of 0.5 seconds between protective device operations to ensure selectivity.
Q.76Easy
Which type of power system stability is primarily concerned with the system's ability to maintain synchronism after a small disturbance?
Answer: B
Steady-state stability examines the system's response to small, gradual disturbances, while transient stability deals with large, sudden disturbances.
Q.77Easy
In the Indian grid, renewable energy penetration targets for 2024-2025 (non-hydro) approximately target what percentage of total generation capacity?
Answer: C
As per India's national renewable energy targets and Ministry of Power guidelines, approximately 45% non-fossil capacity addition is targeted for 2024-2025.
Q.78Medium
A transmission line is protected by a distance relay set with Zone 2 reach at 80% of line length. If the line is 150 km and has impedance of 0.4 Ω/km, what is the Zone 2 reach impedance?
Answer: C
Total line impedance = 150 × 0.4 = 60 Ω. Zone 2 reach = 80% × 60 = 48 Ω
Q.79Easy
Which of the following voltage levels is NOT part of the Indian transmission network classification?
Answer: D
The standard Indian transmission voltage levels are 765 kV, 400 kV, 275 kV, and 220 kV. 150 kV is typically sub-transmission voltage level.
Q.80Hard
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.
