The per-unit (p.u.) system in power systems is used primarily to:
Answer: A
Per-unit system normalizes all quantities relative to chosen base values, simplifying analysis and comparison across different voltage levels and equipment ratings.
Q.282Medium
Which protective relay is used for phase-to-phase fault detection in transmission lines?
Answer: B
Differential relays compare currents at both ends of a line and trip if there is a mismatch indicating an internal fault.
Q.283Medium
A synchronous motor operating at no-load consumes:
Answer: B
At no-load, a synchronous motor supplies only magnetizing current (reactive power) to maintain the magnetic field.
Q.284Medium
The reactive power generated by an over-excited synchronous generator is:
Answer: B
Over-excitation increases the magnetic field, causing the generator to supply lagging reactive power to support system voltage.
Q.285Medium
What is the primary cause of voltage instability in a power system?
Answer: A
Voltage instability occurs when reactive power demand cannot be met, causing voltage collapse, particularly at weak points in the grid.
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Q.286Hard
The swing equation of a synchronous machine is given by: 2H(d²δ/dt²) = Pm - Pe - D(dδ/dt). What does H represent?
Answer: A
H is the inertia constant (M/2×SB) representing the kinetic energy relative to the system base power.
Q.287Easy
In India's 2024-25 grid, which state has the highest installed renewable energy capacity?
Answer: A
Gujarat leads in combined renewable capacity including solar parks and wind farms as per latest 2024-25 CEA reports.
Q.288Hard
The critical clearing angle (δcr) in transient stability analysis represents:
Answer: A
δcr is the limiting rotor angle; if exceeded during a fault, the machine cannot return to synchronism even after fault clearance.
Q.289Medium
Power system harmonics in Indian grids are primarily caused by:
Answer: A
Modern non-linear loads like switch-mode power supplies, VFDs, and renewable energy inverters are major sources of harmonics in contemporary Indian grids.
Q.290Hard
The fault level (short-circuit capacity) at a bus is determined by:
Answer: A
Fault level = MVA base / (Zth in p.u.), where Zth is the equivalent impedance of the entire network.
Q.291Medium
In load flow analysis, which bus type is used to specify active power and voltage magnitude?
Answer: A
PV buses represent generators where active power injection and voltage magnitude are specified; reactive power is calculated.
Q.292Hard
The maximum power transfer in an AC transmission system occurs when the sending and receiving end voltages are:
Answer: C
Maximum power transfer (Pmax = V²/X) occurs when power angle δ = 90°, regardless of absolute voltage magnitudes.
Q.293Medium
Which of the following is a measure of power quality as per Indian Standards (IS 16001:2017)?
Answer: A
IS 16001:2017 defines power quality parameters including THD (Total Harmonic Distortion) and voltage flicker limits.
Q.294Medium
In a three-phase power system with balanced conditions, the zero-sequence current flows through:
Answer: A
Zero-sequence currents (equal in all three phases and same direction) require a return path through neutral or ground.
Q.295Easy
In a 400 kV transmission line in India's western grid, if the series reactance is 0.35 Ω/km and the line length is 250 km, what is the total series reactance of the transmission line?
Answer: A
Total series reactance = 0.35 Ω/km × 250 km = 87.5 Ω. This is a fundamental calculation for transmission line parameters commonly tested in GATE and ESE.
Q.296Easy
What is the primary function of a feedback control system?
Answer: A
Feedback control systems work by comparing the desired output with actual output and reducing the error between them through corrective action.
Q.297Easy
The transfer function of a system is defined as the ratio of:
Answer: B
Transfer function G(s) = Y(s)/U(s) is the ratio of Laplace transforms of output to input assuming zero initial conditions.
Q.298Easy
Which of the following represents a first-order system?
Answer: B
A first-order system has only s¹ as the highest power in the denominator. G(s) = K/(τs + 1) is the standard first-order form.
Q.299Medium
What is the steady-state error for a unit step input to a Type 0 system?
Answer: C
For Type 0 system with unit step input, e_ss = 1/(1 + Kp) where Kp is the position error constant.
Q.300Easy
The characteristic equation of a system is s² + 4s + 3 = 0. The system is:
Answer: C
Roots are s = -1 and s = -3 (both negative). All poles are in the left half-plane, making the system stable.
