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.102Medium
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.103Medium
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).
Q.104Easy
In the Indian power system (2024-25), what is the nominal frequency?
Answer: C
Indian power system operates at 50 Hz nominal frequency with allowed frequency variation of ±2% (49-51 Hz) as per grid code standards.
Q.105Medium
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.
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Q.106Hard
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.107Medium
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.108Hard
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.109Medium
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.110Medium
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.111Hard
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.112Easy
What is the primary role of a circuit breaker in a power system?
Answer: A
Circuit breakers carry normal load current and automatically open when fault current exceeds preset relay settings, isolating the faulty section.
Q.113Hard
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.114Medium
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.115Hard
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.
Q.116Medium
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.117Hard
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.118Easy
What is the primary purpose of shunt capacitors in power systems?
Answer: B
Shunt capacitors supply reactive power locally, improving voltage profile and reducing the burden on generators and transmission lines to supply reactive power.
Q.119Medium
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.120Medium
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.
