What is the primary function of a transformer in a power system?
Answer: A
Transformers step up voltage for transmission (reducing current and losses) and step down voltage for distribution to consumers.
Q.2Easy
The per unit system in power system analysis is based on:
Answer: B
Per unit system uses selected base values for voltage, power, and impedance to normalize calculations across different system parts.
Q.3Easy
Which of the following represents the power factor in a three-phase AC circuit?
Answer: A
Power factor is defined as cos(φ), the cosine of the phase angle between voltage and current waveforms.
Q.4Medium
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.5Medium
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.
Advertisement
Q.6Medium
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.7Medium
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.8Medium
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.9Easy
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.10Medium
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.11Hard
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.12Medium
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.13Hard
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.14Medium
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.15Medium
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.16Hard
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.17Easy
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.18Hard
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.19Medium
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.20Hard
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.
