Q.1 What is the primary objective of load flow analysis in power systems?
Determine short‑circuit currents
Estimate relay coordination
Calculate bus voltages and line flows
Compute generator torque
Explanation - Load flow analysis aims to find the steady‑state voltage magnitude and angle at each bus and the resulting power flows on lines.
Correct answer is: Calculate bus voltages and line flows
Q.2 Which iteration method is most commonly used for solving the Newton‑Raphson load flow problem?
Gauss‑Seidel
Fast Decoupled Load Flow
Newton‑Raphson
Bi‑section method
Explanation - The NR method constructs the Jacobian matrix and converges quadratically, making it the most popular for large systems.
Correct answer is: Newton‑Raphson
Q.3 What does a PQ bus represent in load flow analysis?
A bus with fixed voltage magnitude and angle
A generator bus with fixed voltage
A load bus with specified active and reactive power
A slack bus with reference voltage
Explanation - A PQ bus has its active and reactive power set, and its voltage magnitude and angle are unknowns to be solved.
Correct answer is: A load bus with specified active and reactive power
Q.4 What does a PV bus represent in load flow analysis?
A load bus with fixed active and reactive power
A generator bus with fixed active power and voltage magnitude
A slack bus with reference voltage and angle
A bus with only voltage magnitude fixed
Explanation - A PV bus is a generator bus where active power and voltage magnitude are fixed; reactive power is solved.
Correct answer is: A generator bus with fixed active power and voltage magnitude
Q.5 Which matrix is used to represent the admittance of a power network?
Z‑bus
Y‑bus
A‑bus
T‑bus
Explanation - The Y‑bus (admittance matrix) contains all branch admittances and shunt admittances of the network.
Correct answer is: Y‑bus
Q.6 In the Newton‑Raphson load flow method, what does the Jacobian matrix contain?
Second derivatives of power equations
First derivatives of power equations with respect to voltage magnitude and angle
Voltage magnitudes only
Line impedances only
Explanation - The Jacobian matrix consists of partial derivatives of active and reactive power equations with respect to voltage magnitude and angle.
Correct answer is: First derivatives of power equations with respect to voltage magnitude and angle
Q.7 Which iterative method has the slowest convergence for large systems?
Gauss‑Seidel
Fast Decoupled
Newton‑Raphson
Direct solution
Explanation - Gauss‑Seidel can converge slowly, especially for poorly conditioned systems, compared to NR or FD methods.
Correct answer is: Gauss‑Seidel
Q.8 What is the main advantage of the Fast Decoupled Load Flow method?
Simplified Jacobian leading to faster solution
Accurate solutions for heavily loaded systems
No need for initial guess
Direct analytical solution
Explanation - FD assumes decoupling and uses a simpler Jacobian, reducing computation time significantly.
Correct answer is: Simplified Jacobian leading to faster solution
Q.9 Which of the following must be satisfied at each bus during load flow?
Kirchhoff’s Voltage Law (KVL)
Kirchhoff’s Current Law (KCL)
Ohm’s Law
Power factor = 1
Explanation - Load flow solves the nodal power balance equations derived from KCL at every bus.
Correct answer is: Kirchhoff’s Current Law (KCL)
Q.10 What is the voltage at the slack bus in a load flow study?
Unknown, solved by iteration
Fixed reference voltage and angle
Only the magnitude is fixed
Only the angle is fixed
Explanation - The slack bus provides both a fixed voltage magnitude and a reference angle, absorbing system mismatch.
Correct answer is: Fixed reference voltage and angle
Q.11 What is a common initial guess for the Newton‑Raphson method?
Flat start: all V=1.0 p.u., angles 0
Random values
All voltages 1.05 p.u., angles 30°
Slack bus voltage only
Explanation - A flat start sets all voltage magnitudes to 1.0 p.u. and angles to 0°, providing a neutral starting point.
Correct answer is: Flat start: all V=1.0 p.u., angles 0
Q.12 In load flow, what criterion indicates convergence?
Change in voltage < 0.001 p.u.
All angles zero
All currents equal
Number of iterations > 100
Explanation - Convergence is typically declared when the maximum change in any voltage magnitude or angle falls below a specified tolerance.
Correct answer is: Change in voltage < 0.001 p.u.
Q.13 What is the main disadvantage of the Gauss‑Seidel method?
Requires large Jacobian
Slow convergence for large systems
Cannot handle PV buses
Uses complex arithmetic
Explanation - GS can be very slow for large, ill‑conditioned systems because it updates one bus at a time.
Correct answer is: Slow convergence for large systems
Q.14 Which buses are typically assumed in the Fast Decoupled Load Flow method?
Only slack buses
PQ and PV buses
All PQ buses
All PV buses
Explanation - FD uses the decoupled equations for PQ and PV buses; the slack bus provides reference values.
Correct answer is: PQ and PV buses
Q.15 What is the purpose of line charging in load flow studies?
Represent series transformer tap ratio
Model shunt admittance of lines
Increase voltage magnitude
Reduce line impedance
Explanation - Line charging accounts for the shunt admittance at each end of a transmission line, affecting reactive power flow.
Correct answer is: Model shunt admittance of lines
Q.16 Which term refers to maintaining the reactive power at each bus during load flow?
Reactive power balance
Active power balance
Voltage balance
Power factor control
Explanation - Reactive power balance ensures that reactive power injected equals reactive power consumed plus losses at each bus.
Correct answer is: Reactive power balance
Q.17 What is the role of the slack bus in the load flow solution?
Absorb the system mismatch
Provide generator reactive power
Set the system voltage magnitude
Set the system frequency
Explanation - The slack bus supplies the difference between total load and generation to maintain system balance.
Correct answer is: Absorb the system mismatch
Q.18 In a balanced three‑phase system, how many equations per bus are solved in the Newton‑Raphson method?
One
Two
Three
Four
Explanation - For each bus we solve one active power equation and one reactive power equation, giving two equations.
Correct answer is: Two
Q.19 What is the typical convergence speed of the Newton‑Raphson method for large systems?
Linear
Quadratic
Exponential
Logarithmic
Explanation - NR converges quadratically near the solution, often requiring only a few iterations for large systems.
Correct answer is: Quadratic
Q.20 What is the size of the Jacobian matrix for a 100‑bus system (ignoring the slack bus) using the Newton‑Raphson method?
100 × 100
200 × 200
150 × 150
50 × 50
Explanation - For a system with 100 buses we have 99 PQ buses and 1 slack, leading to 99 × 2 = 198 equations, approximately a 200 × 200 Jacobian.
Correct answer is: 200 × 200
Q.21 What is the expression for active power at bus _m_ in load flow?
P_m = V_m Σ V_n (G_mn cosθ_mn + B_mn sinθ_mn)
P_m = V_m Σ V_n (G_mn sinθ_mn - B_mn cosθ_mn)
P_m = V_m Σ V_n (B_mn cosθ_mn + G_mn sinθ_mn)
P_m = Σ V_n (G_mn cosθ_mn + B_mn sinθ_mn)
Explanation - The active power equation uses the real part of the product of bus voltages and branch admittances.
Correct answer is: P_m = V_m Σ V_n (G_mn cosθ_mn + B_mn sinθ_mn)
Q.22 What is the expression for reactive power at bus _m_ in load flow?
Q_m = V_m Σ V_n (G_mn sinθ_mn - B_mn cosθ_mn)
Q_m = V_m Σ V_n (B_mn cosθ_mn + G_mn sinθ_mn)
Q_m = V_m Σ V_n (G_mn cosθ_mn + B_mn sinθ_mn)
Q_m = Σ V_n (G_mn sinθ_mn - B_mn cosθ_mn)
Explanation - The reactive power equation uses the imaginary part of the product of bus voltages and branch admittances.
Correct answer is: Q_m = V_m Σ V_n (G_mn sinθ_mn - B_mn cosθ_mn)
Q.23 Which element of the Y‑bus matrix represents shunt admittance at bus _i_?
Diagonal element Y_ii
Off‑diagonal element Y_ij
Imaginary part of Y_ii
Zero
Explanation - Shunt admittances appear on the diagonal of the Y‑bus matrix.
Correct answer is: Diagonal element Y_ii
Q.24 How is the per‑unit line admittance calculated?
Y = Z per unit
Y = 1/Z per unit
Y = Z × base impedance
Y = 1/Z × base impedance
Explanation - Admittance is the reciprocal of impedance, both expressed in per‑unit values.
Correct answer is: Y = 1/Z per unit
Q.25 What effect does a series transformer have on the Y‑bus matrix?
Adds a tap ratio in the off‑diagonal elements
Adds a shunt admittance on the diagonal
Reduces all line admittances to zero
Does not affect the matrix
Explanation - Transformers introduce tap ratios that modify the off‑diagonal admittances in the Y‑bus.
Correct answer is: Adds a tap ratio in the off‑diagonal elements
Q.26 What does the voltage angle difference between two buses determine?
Power flow direction
Reactive power consumption
Line impedance
Transformer tap ratio
Explanation - The sign of the angle difference indicates the direction of active power flow on the line.
Correct answer is: Power flow direction
Q.27 In a PV bus, how is reactive power treated during load flow?
It is fixed
It is zero
It is an unknown solved for
It is always negative
Explanation - Reactive power at a PV bus is solved to maintain the specified voltage magnitude.
Correct answer is: It is an unknown solved for
Q.28 What is a common maximum number of iterations allowed for load flow?
5–10
10–15
20–30
50–100
Explanation - Practitioners often limit iterations to 20–30 to avoid endless loops when convergence fails.
Correct answer is: 20–30
Q.29 What is the effect of a high impedance line on voltage drops in load flow?
Causes larger voltage drops
Reduces voltage drops
Has no effect
Increases line current
Explanation - Higher line impedance leads to greater voltage drops for a given power flow.
Correct answer is: Causes larger voltage drops
Q.30 In load flow, what does a "dead" or isolated bus mean?
No connection to the rest of the network
Always at zero voltage
Has no load or generation
Is a slack bus
Explanation - A dead bus is disconnected and thus has no power flow into or out of it.
Correct answer is: No connection to the rest of the network
Q.31 In Fast Decoupled Load Flow, which two sub‑matrices are used?
B' (imag part) and B'' (real part)
B'' (real part) and B''' (imag part)
B (real part) and C (imag part)
A and D
Explanation - FD approximates the Jacobian by separating it into an imaginary part B' and a real part B''.
Correct answer is: B' (imag part) and B'' (real part)
Q.32 Which assumption allows decoupling in Fast Decoupled Load Flow?
Neglecting B'' in P‑angle equations and B' in Q‑voltage equations
Assuming all lines are purely reactive
Assuming zero line charging
Assuming all buses are PQ
Explanation - The FD method assumes the cross‑coupling terms are small, decoupling P–θ from Q–V equations.
Correct answer is: Neglecting B'' in P‑angle equations and B' in Q‑voltage equations
Q.33 What is the typical speed advantage of Fast Decoupled over Newton‑Raphson?
About 2× faster
About 5× faster
About 10× slower
Same speed
Explanation - FD reduces computational effort by simplifying the Jacobian, often giving roughly five times the speed of NR.
Correct answer is: About 5× faster
Q.34 In Fast Decoupled Load Flow, what variable represents the voltage magnitude change at PQ buses?
ΔV
Δθ
ΔP
ΔQ
Explanation - ΔV denotes the incremental change in voltage magnitude for PQ buses.
Correct answer is: ΔV
Q.35 Which load flow method is suitable for distribution networks with unbalanced loads?
Symmetrical components load flow
Fast Decoupled
Gauss‑Seidel
Newton‑Raphson only
Explanation - Unbalanced distribution studies use symmetrical component or full unbalanced models.
Correct answer is: Symmetrical components load flow
Q.36 In unbalanced load flow, how many sets of equations are solved?
One for all phases
Three (A, B, C)
Two (positive, negative)
Four
Explanation - Unbalanced analysis requires separate equations for each of the three phases.
Correct answer is: Three (A, B, C)
Q.37 What is the purpose of shunt capacitors in load flow?
Increase line impedance
Provide local reactive power compensation
Reduce active power losses
Increase fault currents
Explanation - Shunt capacitors supply reactive power to maintain voltage levels and improve power factor.
Correct answer is: Provide local reactive power compensation
Q.38 In load flow, what is the effect of load growth on voltage stability?
Reduces voltage stability margin
Increases voltage stability margin
Has no effect
Always improves voltage profiles
Explanation - Higher loads increase reactive power demands, reducing the system’s ability to maintain voltage.
Correct answer is: Reduces voltage stability margin
Q.39 What does "voltage stability margin" refer to?
Difference between operating point and point of collapse
Maximum voltage swing allowed
Maximum power transfer limit
Minimum reactive power needed
Explanation - It measures how close the system is to voltage instability under current loading.
Correct answer is: Difference between operating point and point of collapse
Q.40 Which of the following is NOT a typical cause of non‑convergence in load flow?
Poor initial guess
Ill‑conditioned Y‑bus matrix
High line losses
High load demand
Explanation - High line losses do not inherently prevent convergence; poor initial guess, ill‑conditioned matrix, or extreme loads can.
Correct answer is: High line losses
Q.41 What technique is used to improve convergence of the Newton‑Raphson method?
Line‑loading (damping) factors
Zero initial guess
Increase iteration count arbitrarily
Use only real parts of admittance
Explanation - Applying a damping factor (also called line‑loading) can help stabilize NR when the Jacobian is poorly conditioned.
Correct answer is: Line‑loading (damping) factors
Q.42 In load flow, what does a "stuck" generator refer to?
A generator unable to adjust Q to maintain voltage
A generator with zero active power
A generator that fails to start
A generator that operates at maximum capacity
Explanation - If a generator cannot supply the necessary reactive power, its voltage may become unstable.
Correct answer is: A generator unable to adjust Q to maintain voltage
Q.43 What is the purpose of a "break‑even" point in load flow?
The point where power injection equals consumption
The point where voltage equals nominal
The point where generator cost is minimized
The point where line losses are maximum
Explanation - At break‑even, the sum of generation equals load plus losses, ensuring balance.
Correct answer is: The point where power injection equals consumption
Q.44 What does a "soft‑start" refer to in load flow?
Gradual ramping of voltage set‑points
Gradual ramping of generator output
Rapid increase of line capacity
Sudden start of load
Explanation - Soft‑start mitigates voltage swings by slowly changing set‑points during transient events.
Correct answer is: Gradual ramping of voltage set‑points
Q.45 Which parameter is most critical for accurate load flow results?
System frequency
Y‑bus matrix values
Load type
Generator type
Explanation - Accurate admittance values are essential; any error propagates through the entire solution.
Correct answer is: Y‑bus matrix values
Q.46 What is a typical tolerance for power mismatch in a load flow study?
0.5% of system MVA
0.1% of system MVA
1% of system MVA
5% of system MVA
Explanation - A small tolerance ensures that the solution is close to the exact power balance.
Correct answer is: 0.1% of system MVA
Q.47 In a multi‑area load flow, what is the role of tie‑lines?
Transfer power between areas
Provide fault current
Set voltage magnitude
Set generator reactive limits
Explanation - Tie‑lines connect different control areas and allow power exchange.
Correct answer is: Transfer power between areas
Q.48 In load flow, how are transformer tap settings represented in the Y‑bus matrix?
As complex tap ratios
As additional shunt admittances
As modifications to line impedance
As additional buses
Explanation - Tap ratios appear as complex numbers in the off‑diagonal terms of the Y‑bus.
Correct answer is: As complex tap ratios
Q.49 What does "voltage collapse" refer to?
System voltage falling below acceptable limits under load increase
Line over‑current due to high load
All generators tripping
An increase in fault currents
Explanation - Voltage collapse is a failure of the system to maintain acceptable voltage levels when overloaded.
Correct answer is: System voltage falling below acceptable limits under load increase
Q.50 A PV bus is also known as what?
Slack bus
Generator bus
PQ bus
Load bus
Explanation - PV stands for “Power‑Voltage” and refers to generator buses with fixed active power and voltage magnitude.
Correct answer is: Generator bus
Q.51 In load flow, what is the difference between a PQ bus and a PV bus?
PQ bus has fixed P and Q; PV has fixed P and V
PQ bus has fixed P and V; PV has fixed Q and V
PQ bus is a slack bus; PV is a load bus
Both are identical
Explanation - PQ buses specify both power injections; PV buses specify voltage magnitude and active power.
Correct answer is: PQ bus has fixed P and Q; PV has fixed P and V
Q.52 What is a "dead‑bus" in load flow?
A bus with no load, no generation, no connections
A bus with only generation
A bus with only load
A bus that is isolated by a fuse
Explanation - A dead‑bus is completely disconnected and has no power flow to or from it.
Correct answer is: A bus with no load, no generation, no connections
Q.53 What is the main function of a capacitor bank in load flow?
Supply reactive power locally
Reduce active power losses
Increase fault currents
Lower line impedance
Explanation - Capacitor banks provide reactive power to support voltage levels in the network.
Correct answer is: Supply reactive power locally
Q.54 What does a "line flow limit" refer to?
Maximum permissible power transfer
Maximum voltage drop
Maximum fault current
Maximum generator output
Explanation - Line flow limits constrain how much power can safely pass through a transmission line.
Correct answer is: Maximum permissible power transfer
Q.55 Which load flow method uses successive over‑relaxation?
Gauss‑Seidel
Fast Decoupled
Newton‑Raphson
Direct solution
Explanation - Gauss‑Seidel can be accelerated by applying an over‑relaxation factor.
Correct answer is: Gauss‑Seidel
Q.56 In load flow, how is a fault typically represented?
As a zero‑impedance branch
As a large shunt admittance
As a high‑resistance line
As a series transformer
Explanation - Faults are often modeled as short circuits with negligible impedance.
Correct answer is: As a zero‑impedance branch
Q.57 Which software is commonly used for load flow analysis?
PSS‑E
PowerWorld
DIgSILENT PowerFactory
All of the above
Explanation - All listed packages are standard tools for performing load flow studies.
Correct answer is: All of the above
Q.58 What is the purpose of the "DC Load Flow" algorithm?
Provide a quick estimate of active power flows
Include reactive power in the solution
Calculate fault currents
Compute dynamic stability margins
Explanation - DC load flow ignores reactive power and line charging, giving fast active‑power results.
Correct answer is: Provide a quick estimate of active power flows
Q.59 Which programming language is often used to implement custom load flow?
MATLAB
Python
C++
All of the above
Explanation - Custom load flow tools are built in many languages including MATLAB, Python, and C++.
Correct answer is: All of the above
Q.60 In DIgSILENT PowerFactory, how is a transformer tap set?
Through the "Tap Settings" window
By editing the Y‑bus manually
Through a command line script
It cannot be changed
Explanation - The user interface provides a dedicated window to adjust transformer taps.
Correct answer is: Through the "Tap Settings" window
Q.61 What is a "unit system" in load flow studies?
Per‑unit scaling for consistency
Absolute voltage values
Time‑based scaling
Frequency scaling
Explanation - Per‑unit (p.u.) normalizes quantities to a common base for easier calculation.
Correct answer is: Per‑unit scaling for consistency
Q.62 Which optimization method is used in Optimal Power Flow (OPF)?
Gradient methods
Interior‑point methods
Genetic algorithms
All of the above
Explanation - OPF can use various algorithms depending on problem size and requirements.
Correct answer is: All of the above
Q.63 In OPF, what is the typical objective function?
Minimizing generation cost
Maximizing voltage margin
Minimizing losses
All of the above
Explanation - The standard OPF seeks to reduce the cost of generation while satisfying constraints.
Correct answer is: Minimizing generation cost
Q.64 What additional constraints are added in OPF compared to load flow?
Generator limits
Voltage limits
Line limits
All of the above
Explanation - OPF includes operational limits that are not part of a basic load flow.
Correct answer is: All of the above
Q.65 What does "security‑constrained OPF" consider?
Potential contingencies
Only active power limits
Only generator costs
None of the above
Explanation - Security‑constrained OPF ensures the system remains secure under possible contingency scenarios.
Correct answer is: Potential contingencies
Q.66 What is a "dynamic load flow" study?
Time‑dependent loads
Static voltage profile
Fault current calculation
Reactive power balancing
Explanation - Dynamic load flow tracks how loads change over time and their impact on voltages.
Correct answer is: Time‑dependent loads
Q.67 Which method is used for large‑scale load flow in power grids?
Distributed load flow
Centralized load flow
Single‑bus load flow
None
Explanation - Distributed load flow partitions the network into zones for parallel computation.
Correct answer is: Distributed load flow
Q.68 What is a "bus shunt" in load flow?
Shunt admittance at a bus
Line impedance
Transformer tap ratio
Load model
Explanation - A bus shunt is a conductance or susceptance connected in parallel with the bus.
Correct answer is: Shunt admittance at a bus
Q.69 What is the effect of a large shunt capacitor on bus voltage?
Raises bus voltage
Lowers bus voltage
Has no effect
Increases line losses
Explanation - Large shunt capacitors inject reactive power, pushing up local voltage levels.
Correct answer is: Raises bus voltage
Q.70 In load flow, what does the term "reliability index" refer to?
Probability of failure
Voltage swing magnitude
Maximum loadability
Minimum reactive power
Explanation - Reliability indices estimate the chance that the system will fail to meet service standards.
Correct answer is: Probability of failure
Q.71 What is "distribution load flow" primarily concerned with?
Voltage regulation in feeders
Transmission line losses
Generator cost
System frequency
Explanation - Distribution studies focus on maintaining voltage within limits across feeder lines.
Correct answer is: Voltage regulation in feeders
Q.72 In distribution systems, what is "unbalanced load flow"?
Different phase loads
All phases equal
Zero load
Only reactive loads
Explanation - Unbalanced load flow handles scenarios where each phase carries a different load.
Correct answer is: Different phase loads
Q.73 What is a "cable" in distribution load flow?
Low‑voltage cable with high impedance
High‑voltage transmission line
Transformer
Capacitor bank
Explanation - Distribution cables typically have higher impedance compared to overhead lines.
Correct answer is: Low‑voltage cable with high impedance
Q.74 How is a "load" represented in distribution load flow?
Equivalent PQ or VQ representation
Only active power
Only reactive power
None of the above
Explanation - Loads are modeled as either fixed PQ or voltage‑dependent VQ models.
Correct answer is: Equivalent PQ or VQ representation
Q.75 What is the typical voltage level for distribution systems?
11 kV, 33 kV, 132 kV
110 kV, 220 kV, 500 kV
10 kV, 20 kV, 30 kV
500 kV, 700 kV, 900 kV
Explanation - Distribution networks operate at lower voltages compared to transmission.
Correct answer is: 11 kV, 33 kV, 132 kV
Q.76 In distribution load flow, what does a "transformer" do?
Step voltage up or down
Provide fault current
Create a new bus
Regulate frequency
Explanation - Distribution transformers adjust voltage levels between feeders and the main network.
Correct answer is: Step voltage up or down
Q.77 What is a "feeder" in distribution systems?
Branch of lines supplying load
Transformer tap
Load bank
Switching station
Explanation - A feeder is a distribution line that delivers power from the substation to end users.
Correct answer is: Branch of lines supplying load
Q.78 In distribution load flow, what is the impact of "capacitor banks"?
Provide local reactive support
Increase line losses
Reduce fault currents
All of the above
Explanation - Capacitor banks supply reactive power locally to improve voltage profiles.
Correct answer is: Provide local reactive support
Q.79 What is a "recloser" in distribution?
Automatic circuit breaker that recloses after fault
Permanent switch
Load tap changer
Transformer
Explanation - Reclosers isolate faults temporarily and then automatically re‑connect the circuit.
Correct answer is: Automatic circuit breaker that recloses after fault
Q.80 What is the impact of a "smart grid" on load flow?
Adaptive load management
Dynamic voltage control
Both of the above
None
Explanation - Smart grids use real‑time data to adjust loads and voltages for optimal operation.
Correct answer is: Both of the above
Q.81 What does a "dead‑end" line mean in load flow?
One‑ended line with no connection at the other end
Line with zero impedance
Line with high losses
Line that can’t carry current
Explanation - A dead‑end line terminates in an isolated point, affecting voltage drops.
Correct answer is: One‑ended line with no connection at the other end
Q.82 What is a "swing‑bus" in a two‑bus system?
The bus that supplies the difference between load and generation
The slack bus only
The generator bus
The load bus only
Explanation - In a two‑bus system, the swing bus balances the power difference in the network.
Correct answer is: The bus that supplies the difference between load and generation
Q.83 Which load flow method is commonly used for post‑fault analysis?
Newton‑Raphson
Fast Decoupled
DC load flow
Gauss‑Seidel
Explanation - NR can handle the changed network after a fault and provide accurate results.
Correct answer is: Newton‑Raphson
Q.84 What is the purpose of a "short‑circuit" study in load flow?
Determine fault currents
Find optimal dispatch
Calculate voltage drops
Estimate line losses
Explanation - Short‑circuit studies compute the currents during faults, informing protection settings.
Correct answer is: Determine fault currents
Q.85 What does a "blackout" scenario mean in load flow?
Loss of multiple buses due to cascading failures
Complete loss of all generators
Increase in all voltages
Only line outages
Explanation - A blackout occurs when system disturbances propagate and lead to widespread outages.
Correct answer is: Loss of multiple buses due to cascading failures
Q.86 What is the role of relays in load flow?
Detect over‑current and disconnect lines
Compute voltage profiles
Set generator angles
Control transformer taps
Explanation - Relays monitor currents and voltages and can isolate lines when limits are exceeded.
Correct answer is: Detect over‑current and disconnect lines
Q.87 In load flow, how is a fault represented?
Zero‑impedance branch
Large shunt admittance
High‑resistance line
Series transformer
Explanation - Faults are often modeled as short circuits with negligible impedance.
Correct answer is: Zero‑impedance branch
Q.88 What is the typical recovery time after a fault for load flow calculations?
Depends on system size
Always 1 second
Always 1 minute
Always 1 hour
Explanation - Recovery time varies with system complexity and computational resources.
Correct answer is: Depends on system size
Q.89 What is a "voltage sags" scenario in load flow?
Temporary voltage drop below nominal
Permanent voltage drop
Voltage rise above nominal
No voltage change
Explanation - Voltage sags are brief voltage reductions that can affect sensitive equipment.
Correct answer is: Temporary voltage drop below nominal
Q.90 What is a "voltage swell" scenario in load flow?
Temporary voltage rise above nominal
Permanent voltage rise
Voltage drop below nominal
No voltage change
Explanation - Voltage swells are brief over‑voltages that can harm equipment.
Correct answer is: Temporary voltage rise above nominal