Which protection scheme is typically used for protecting transmission lines in Indian grid?
Answer: B
Distance relays provide selective protection for transmission lines by measuring impedance from relay location to fault point, standard in Indian POWERGRID.
Q.142Medium
In a 3-phase balanced fault at a bus, what is the fault current expression for a synchronous generator?
Answer: A
Subtransient reactance (Xd'') is used immediately after fault occurrence. Fault current = V/Xd'' for a 3-phase symmetrical fault at the generator terminals.
Q.143Medium
What is the economic dispatch problem in power systems?
Answer: A
Economic dispatch optimally allocates power generation among committed units to minimize fuel costs while satisfying load demand and operational constraints.
Q.144Easy
Which Indian renewable energy initiative aims at 500 GW by 2030?
Answer: C
India's target to achieve 500 GW renewable energy capacity by 2030 is part of the Renewable Energy Capacity Addition Plan as per 2024-25 policy.
Q.145Medium
What is the relationship between power factor and reactive power in a 3-phase system?
Answer: A
Reactive power Q = P × tan(φ), where φ is the phase angle between voltage and current. This fundamental relationship determines VAR compensation requirements.
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Q.146Medium
In voltage stability analysis, what does the P-V curve represent?
Answer: A
P-V curves show how voltage varies with increasing active power at a bus. The nose point indicates the maximum power that can be transmitted before voltage collapse.
Q.147Medium
What is the primary purpose of a phasor measurement unit (PMU) in modern Indian grids?
Answer: B
PMUs measure voltage and current phasors synchronized via GPS, enabling real-time monitoring and control. India has deployed PMUs across POWERGRID network for situational awareness.
Q.148Hard
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.149Hard
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.150Hard
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.151Easy
In the Indian grid code, what is the specified frequency band for normal operation?
Answer: C
As per Indian Grid Code 2023, the normal frequency band is 49.7-50.3 Hz. Operation outside this range triggers corrective actions.
Q.152Hard
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.153Medium
In selective fuse coordination, which fuse should operate first during a downstream fault?
Answer: B
Selective coordination requires the fuse nearest to the fault to operate first, isolating only the faulted section while maintaining service to other areas.
Q.154Hard
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.155Medium
What is the primary function of phase-shifting transformers in Indian grid operation?
Answer: A
Phase-shifting transformers control power flow by introducing a phase shift between primary and secondary voltages, enabling effective power flow management on parallel transmission corridors in Indian grid.
Q.156Medium
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.158Medium
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.159Hard
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.160Easy
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).
