A transmission line is protected by a distance relay set with Zone 2 reach at 80% of line length. If the line is 150 km and has impedance of 0.4 Ω/km, what is the Zone 2 reach impedance?
Answer: C
Total line impedance = 150 × 0.4 = 60 Ω. Zone 2 reach = 80% × 60 = 48 Ω
Q.42Medium
The stability of a power system depends on which of the following factors?
Answer: B
Power system stability is determined by the rotor dynamics characterized by inertia (M), damping (D), and synchronizing coefficient (Ks).
Q.43Medium
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.44Medium
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.45Medium
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.
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Q.46Medium
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.47Medium
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.
Q.48Medium
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.49Medium
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.50Medium
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.51Medium
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.
