In load flow analysis, which bus is used to represent the reference point for voltage angle?
Answer: C
The slack bus serves as the reference point with fixed voltage magnitude and phase angle (typically 0°) in load flow studies.
Q.2Medium
What is the effect of increasing system frequency above nominal value in a power system?
Answer: C
Since inductive reactance X_L = 2πfL and capacitive reactance X_C = 1/(2πfC), increasing frequency increases X_L and decreases X_C.
Q.3Medium
The stability of a power system is primarily concerned with:
Answer: A
Power system stability requires maintaining frequency near 50 Hz and voltage within ±5-10% of nominal to ensure safe and reliable operation.
Q.4Medium
Which protection device is used to protect transformers from overcurrent conditions?
Answer: B
Circuit breakers with overcurrent relays (IDMT or instantaneous) provide selective protection and can be reclosed, unlike fuses.
Q.5Medium
The corona effect in transmission lines occurs when:
Answer: A
Corona is a luminous discharge that occurs when the electric field strength at the conductor surface exceeds the breakdown strength of air (~30 kV/cm).
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Q.6Medium
What does HVDC transmission primarily advantage over HVAC transmission for long distances?
Answer: B
HVDC transmission has lower I²R losses (lower current for same power) and no skin effect, making it economical for distances >500 km like India's inter-state links.
Q.7Medium
Which of the following is NOT a component of FACTS devices?
Answer: C
Transformer tap changers are conventional mechanical devices, whereas SVC, STATCOM, and UPFC are electronic FACTS devices for dynamic power system control.
Q.8Medium
What is the relationship between real power (P) and reactive power (Q) in terms of apparent power (S)?
Answer: D
Apparent power S is the vector sum of P and Q, so S² = P² + Q², and S = P/cos(φ), Q = S × sin(φ).
Q.9Medium
In a transmission line, which parameter is primarily responsible for reactive power generation?
Answer: B
Series inductance creates inductive reactance that consumes reactive power, while shunt capacitance generates reactive power.
Q.10Medium
Which standard defines the grid code for Indian power system operation?
Answer: A
CERC Grid Code 2023 specifies operational standards, frequency bands (±2%), and voltage tolerance (±5-10%) for Indian power system.
Q.11Medium
In the 2024 Indian grid code, what is the minimum frequency threshold below which load shedding is mandatorily initiated?
Answer: B
As per latest POSOCO guidelines and Indian Grid Code 2024, automatic load shedding initiates at 48.5 Hz frequency threshold to maintain grid stability.
Q.12Medium
Under what condition does maximum power transfer occur in a transmission line?
Answer: B
Maximum power transfer theorem states that maximum power is delivered when load impedance is the complex conjugate of source impedance.
Q.13Medium
In the context of Indian Power System, what does 'UI' (Unscheduled Interchange) in real-time market signify?
Answer: B
UI is the real-time balancing mechanism in Indian power market where deviations from scheduled power are settled at dynamic prices determined by frequency deviations.
Q.14Medium
Which factor does NOT directly affect the surge impedance loading (SIL) of a transmission line?
Answer: C
SIL = V²/Z_c, where Z_c is surge impedance = √(L/C). It depends on L and C per unit length and frequency, but NOT on total line length.
Q.15Medium
What is the significance of 'P-Q capability curve' in generator operation?
Answer: A
The P-Q capability curve defines the operating region of a generator considering thermal limits, stability limits, and excitation limits for both active and reactive power.
Q.16Medium
What is the relationship between voltage stability limit and transmission line loading?
Answer: B
As reactive power demand increases with line loading, voltage stability margin decreases. The maximum power that can be transferred is limited by voltage stability.
Q.17Medium
Which FACTS device can simultaneously control both voltage and power flow independently?
Answer: C
UPFC has both series and shunt components, allowing independent control of voltage and power flow. It can inject voltage in both magnitude and phase.
Q.18Medium
What does the 'rotor angle' or 'power angle' represent in power system stability analysis?
Answer: A
The rotor angle (δ) is the angle between the generator's rotor magnetic field axis and the reference axis of the network voltage, critical for stability analysis.
Q.19Medium
What is the primary function of a Static Synchronous Compensator (STATCOM) in modern power systems?
Answer: B
STATCOM uses power electronics to inject/absorb reactive power independently from active power, providing fast voltage support and damping of oscillations.
Q.20Medium
Which parameter is most affected by temperature variation in overhead transmission lines?
Answer: B
Temperature causes resistance to change (R = R₀[1 + α(T-T₀)]) and significantly affects sag due to thermal expansion of conductor, impacting clearances and voltage drop.
