Power System Analysis PYQs

 Q1 >> A 3-phase, 50 Hz overhead transmission line has inductance per phase 

$L$ and capacitance per phase $C$. The surge impedance $Z_0$ of the line is:
A) $\sqrt{\dfrac{L}{C}}$
B) $\sqrt{\dfrac{C}{L}}$
C) $L/C$
D) $C/L$
ANS: A

Q2 >> In per-unit system, if you change base MVA from $S_{base1}$ to $S_{base2}$ (same base kV), the p.u. reactance $X_{pu2}$ relates to $X_{pu1}$ as:
A) $X_{pu2} = X_{pu1}$
B) $X_{pu2} = X_{pu1}\dfrac{S_{base1}}{S_{base2}}$
C) $X_{pu2} = X_{pu1}\dfrac{S_{base2}}{S_{base1}}$
D) $X_{pu2} = X_{pu1}^2$
ANS: B

Q3 >> For balanced three-phase short-circuit fault at a bus, sequence networks required are:
A) Positive only
B) Positive and negative in series
C) Positive, negative and zero in parallel
D) Positive, negative and zero all separate (not connected)
ANS: A

Q4 >> The Y-bus matrix of a power network is:
A) Symmetric and sparse for passive networks
B) Always diagonal
C) Skew-symmetric
D) Dense and non-symmetric
ANS: A

Q5 >> In Newton-Raphson load flow using polar form, the Jacobian size (number of rows) for an n-bus system with 1 slack bus is:
A) (n−1) × (n−1)
B) 2(n−1) × 2(n−1)
C) (2n) × (2n)
D) n × n
ANS: B

Q6 >> A single line-to-ground (L-G) fault at the receiving end of a line (solid fault) is best modeled using sequence networks connected as:
A) Positive, negative and zero in series
B) Positive and negative parallel, zero separate
C) Positive only
D) All three in parallel to source
ANS: A

Q7 >> The equal-area criterion is applicable to:
A) Small-signal (linear) stability only
B) First-swing transient stability for a single machine infinite bus model
C) Frequency control steady state
D) Load flow convergence
ANS: B

Q8 >> A transmission line is classified as a medium line when its length is approximately:
A) < 80 km (short line)
B) 80–250 km (medium line)
C) > 250 km (long line)
D) Any length (classification irrelevant)
ANS: B

Q9 >> In economic dispatch without losses, the necessary condition for optimality is:
A) All units produce equal real power
B) Incremental cost ($dC/dP$) are equal for all committed units
C) Largest unit loaded to maximum
D) Minimum spinning reserve used
ANS: B

Q10 >> Ferranti effect (voltage rise at receiving end) is most significant for:
A) Short heavily loaded line
B) Long lightly loaded or open-circuited line
C) Transformer with tap changer
D) Underground cable at low voltage
ANS: B

Q11 >> The zero-sequence impedance of a buried neutral overhead line depends mainly on:
A) Line inductance only
B) Earth return path and earth resistivity
C) Positive-sequence impedance only
D) Transformer neutral grounding only
ANS: B

Q12 >> For a synchronous generator connected to infinite bus, steady synchronous operation requires:
A) Mechanical torque = electrical torque (on average)
B) Rotor angle = 0 always
C) Field current = mechanical torque
D) No damping torque required
ANS: A

Q13 >> The per-unit impedance of a transformer referred to secondary side when primary base voltage is different is changed using:
A) Turns ratio (or voltage ratio) only
B) Current ratio only
C) Impedance is invariant under reference change
D) Temperature correction factor
ANS: A

Q14 >> The short-circuit MVA at a bus is inversely proportional to:
A) The per-unit reactance at that bus
B) Base voltage at that bus
C) Base MVA only
D) None of these
ANS: A

Q15 >> In Z-bus building algorithm, adding a new shunt element at bus k updates Z-bus by:
A) A rank-one update (Sherman-Morrison type)
B) Complete re-inversion of Y-bus required every time
C) No change to Z-bus
D) Changing only diagonal element by subtraction
ANS: A

Q16 >> A single generator connected to an infinite bus with small disturbance — the small-signal stability is determined by:
A) Eigenvalues of linearized swing and control equations
B) Equal-area criterion only
C) Load flow Jacobian only
D) Y-bus sparsity
ANS: A

Q17 >> The X/R ratio of a transmission network influences:
A) The magnitude and DC offset of fault currents (symmetrical)
B) Only steady-state load flow results
C) Transformer tap settings exclusively
D) Conductor sag
ANS: A

Q18 >> In sequence network analysis, negative sequence components arise due to:
A) Unbalanced loads or asymmetrical faults
B) Balanced three-phase operation only
C) Zero-impedance paths to earth
D) High power factor loads only
ANS: A

Q19 >> A STATCOM (voltage-source converter based) connected at a bus primarily provides:
A) Steady active power injection only
B) Rapid, controllable reactive power support to regulate bus voltage
C) Permanent frequency control for grid
D) Steady state harmonic elimination only
ANS: B

Q20 >> The maximum power transferable (Pmax) between two equal voltage magnitude nodes through reactance X occurs at δ = 90°, and equals:
A) $\dfrac{V_1 V_2}{X}$
B) $\dfrac{V_1 V_2}{2X}$
C) $\dfrac{V_1^2}{X}$
D) $\dfrac{V_1+V_2}{X}$
ANS: A

Q21 >> In load flow, a PV bus is one where:
A) Active power (P) and voltage magnitude (V) are specified
B) Reactive power (Q) and voltage magnitude (V) are specified
C) P and Q are specified
D) None of these
ANS: A

Q22 >> The Newton-Raphson method converges faster than Gauss-Seidel because:
A) It uses second-order derivatives
B) It uses linear approximation (Jacobian) leading to quadratic convergence near solution
C) It avoids solving linear equations
D) It uses fewer buses
ANS: B

Q23 >> The effect of series compensation (capacitor) on a transmission line is to:
A) Increase the effective series reactance
B) Reduce the effective series reactance and increase power transfer capability
C) Increase corona loss
D) Reduce thermal rating of line
ANS: B

Q24 >> For a three-phase balanced system, symmetrical components consist of:
A) Positive, negative and zero sequences; only positive exists for balanced system
B) Positive and negative only always present
C) Zero sequence only for balanced system
D) None of the above
ANS: A

Q25 >> The breaker fault interrupting rating selection primarily requires knowledge of:
A) Symmetrical and asymmetrical (peak) fault current at point of fault
B) System load factor only
C) Line capacitance only
D) Average daily load
ANS: A

Q26 >> A two-area AGC (automatic generation control) scheme is primarily designed to:
A) Maintain scheduled tie-line power exchange and system frequency after load changes
B) Control reactive power at buses only
C) Reduce harmonic distortion in HVDC links
D) Protect transformers from overload
ANS: A

Q27 >> HVDC back-to-back links between two AC systems are used mainly to:
A) Transfer active power while allowing asynchronous operation and control of power flow
B) Supply only reactive power between systems
C) Replace single phase AC transmission lines
D) Reduce the need for circuit breakers in AC system
ANS: A

Q28 >> In a long transmission line, distributed-parameter model is required because:
A) Shunt capacitance is negligible and can be ignored
B) Line parameters (R, L, C) are distributed continuously along length and wave effects matter
C) Computation is simpler than lumped models
D) Line is always lightly loaded
ANS: B

Q29 >> The participation factor and eigenvalue analysis in small-signal stability help to:
A) Identify modal frequencies, damping and which states (machines/controllers) participate in an oscillatory mode
B) Replace load flow studies entirely
C) Compute switching transients only
D) Determine insulation coordination
ANS: A

Q30 >> Transmission line corona onset voltage reduces if:
A) Conductor radius increases
B) Surface roughness or irregularities increase or air pressure decreases
C) Bundle spacing increases always
D) Frequency decreases only
ANS: B

Q31 >> The Kron reduction technique is mainly used to:
A) Eliminate load buses from network equations
B) Compute symmetrical components
C) Reduce line length in short line models
D) Estimate transmission losses
ANS: A

Q32 >> For a synchronous generator connected to an infinite bus, the rotor angle δ increases suddenly due to a disturbance. For stability, the accelerating area (Pa > Pm) must be followed by:
A) Decelerating area (Pm > Pe) of smaller size
B) Decelerating area of equal size
C) Increasing angle without deceleration
D) Constant power transfer
ANS: B

Q33 >> In per-unit system, transformer impedance remains almost:
A) Invariant with change of base values
B) Dependent on turns ratio
C) Different for primary and secondary
D) Zero if referred to low-voltage side
ANS: A

Q34 >> Which of the following is true for Gauss-Seidel load flow?
A) Requires Jacobian matrix at each iteration
B) Slow convergence but simple implementation
C) Quadratic convergence
D) Best suited for large, sparse systems
ANS: B

Q35 >> Newton-Raphson load flow in polar form is widely used because:
A) Jacobian matrix elements are simple derivatives of P and Q wrt |V| and δ
B) No need of matrix inversion
C) It always converges in one iteration
D) It does not require initial guess
ANS: A

Q36 >> In a short transmission line, which component is neglected?
A) Resistance
B) Inductance
C) Shunt capacitance
D) None
ANS: C

Q37 >> The swing equation is:
A) Nonlinear second-order differential equation
B) Linear first-order equation
C) Algebraic equation
D) Static equation
ANS: A

Q38 >> The inertia constant (H) of a machine is defined as:
A) Kinetic energy stored at synchronous speed per MVA rating
B) Maximum accelerating torque per MVA
C) Electrical energy generated per hour
D) Ratio of rotor mass to torque angle
ANS: A

Q39 >> Which of the following FACTS device is series connected?
A) SVC
B) STATCOM
C) TCSC
D) UPFC (only shunt)
ANS: C

Q40 >> A PV bus in load flow may switch to PQ bus when:
A) Generator reactive power limit is violated
B) Bus voltage becomes zero
C) Active power limit is violated
D) Slack bus fails
ANS: A

Q41 >> Symmetrical components were introduced by:
A) Fortescue
B) Kron
C) Kirchhoff
D) Gauss
ANS: A

Q42 >> Zero sequence current does not flow in:
A) Star-connected system with isolated neutral
B) Delta-connected system
C) Balanced three-phase system
D) All of these
ANS: D

Q43 >> Critical clearing time is:
A) Maximum time allowed to clear a fault without losing synchronism
B) Time to restore steady state
C) Time of oscillation cycle
D) None
ANS: A

Q44 >> The surge impedance loading of a line is equal to:
A) $V^2/Z_c$
B) $V/Z_c$
C) $V^2 \times Z_c$
D) None
ANS: A

Q45 >> In steady-state stability, maximum power transfer occurs when:
A) δ = 90°
B) δ = 180°
C) δ = 0°
D) δ = 45°
ANS: A

Q46 >> Equal area criterion is valid only for:
A) Single machine infinite bus system
B) Multi-machine systems
C) Short transmission line
D) Underground cables
ANS: A

Q47 >> Fault current in a power system is limited by:
A) System reactance
B) System resistance
C) Circuit breakers
D) Relays
ANS: A

Q48 >> Which fault is least severe in terms of fault current magnitude?
A) L-G
B) L-L
C) L-L-G
D) 3-phase fault
ANS: A

Q49 >> In Y-bus matrix, off-diagonal elements are:
A) Negative of line admittance between buses
B) Positive of line impedance
C) Always unity
D) Zero
ANS: A

Q50 >> The diagonal dominance of Y-bus ensures:
A) Stability of load flow solution
B) Symmetry
C) Sparsity
D) None
ANS: A

Q51 >> The iterative methods for load flow are preferred because:
A) Networks are sparse and nonlinear
B) Y-bus is always diagonal
C) Computation cost is higher otherwise
D) None
ANS: A

Q52 >> In Newton-Raphson method, convergence is:
A) Linear
B) Quadratic
C) Cubic
D) Logarithmic
ANS: B

Q53 >> Which of the following affects steady-state stability limit?
A) Line reactance
B) Generator excitation
C) Infinite bus voltage
D) All of these
ANS: D

Q54 >> In economic dispatch, penalty factor > 1 indicates:
A) Transmission loss present
B) No transmission loss
C) Generation at unity power factor
D) None
ANS: A

Q55 >> The DC offset in fault current is due to:
A) X/R ratio of the system
B) Reactive power
C) Fault resistance
D) Corona
ANS: A

Q56 >> For a 3-phase balanced system, negative sequence current produces:
A) Double frequency torque pulsations in rotating machines
B) Constant torque only
C) Zero torque
D) None
ANS: A

Q57 >> The main objective of AGC (Automatic Generation Control) is:
A) Maintain frequency and tie-line power within limits
B) Improve load factor
C) Increase plant efficiency
D) Reduce transformer loss
ANS: A

Q58 >> Which HVDC control mode is generally used?
A) Constant current control at rectifier and constant extinction angle at inverter
B) Constant voltage at both ends
C) Constant power at inverter
D) Constant reactive power
ANS: A

Q59 >> Bundled conductors are used in EHV lines to:
A) Reduce corona and inductance, increase surge impedance loading
B) Reduce resistance
C) Reduce skin effect only
D) Increase losses
ANS: A

Q60 >> Load factor is defined as:
A) Average load / Maximum demand
B) Maximum demand / Connected load
C) Average load / Plant capacity
D) None
ANS: A

Q61 >> Ferranti effect is prominent in:
A) Short transmission lines under heavy load
B) Long lightly loaded transmission lines
C) Medium lines with compensation
D) Cable networks only
ANS: B

Q62 >> Surge impedance of a line is:
A) √(L/C)
B) √(C/L)
C) L/C
D) C/L
ANS: A

Q63 >> The per-unit reactance of large synchronous machines lies typically between:
A) 0.1 to 0.3 pu
B) 0.5 to 1.0 pu
C) 1.0 to 2.0 pu
D) 2.0 to 3.0 pu
ANS: A

Q64 >> The main advantage of per-unit system is:
A) Values are independent of voltage level
B) Easy to compare different machines
C) Reduces calculation complexity
D) All of the above
ANS: D

Q65 >> Infinite bus concept means:
A) Constant voltage and frequency source
B) Large generator with varying frequency
C) Small isolated system
D) System with infinite reactance
ANS: A

Q66 >> For stability studies, the system is represented by:
A) One machine equivalent model
B) Detailed winding model
C) Per-phase equivalent
D) Kron reduction always
ANS: A

Q67 >> In symmetrical fault analysis, sequence networks are connected:
A) In series for 3-phase fault
B) In parallel for L-L fault
C) Positive, negative, zero in series for L-G
D) Positive and negative in parallel for L-L
ANS: A

Q68 >> For an unloaded transmission line, receiving end voltage is:
A) Greater than sending end (Ferranti effect)
B) Less than sending end
C) Equal
D) Zero
ANS: A

Q69 >> The transient stability limit is always:
A) Greater than steady state limit
B) Equal to steady state limit
C) Less than steady state limit
D) Independent of steady state limit
ANS: C

Q70 >> Fast decoupled load flow neglects:
A) Coupling between P–V and Q–δ
B) Coupling between P–δ and Q–V
C) All active power
D) All reactive power
ANS: A

Q71 >> If the fault level at a bus is 2000 MVA, the Thevenin equivalent reactance at that bus (base 100 MVA) is:
A) 0.05 pu
B) 0.1 pu
C) 0.2 pu
D) 0.5 pu
ANS: A

Q72 >> Equal area criterion neglects:
A) Damping
B) Mechanical power
C) Inertia constant
D) Fault clearing
ANS: A

Q73 >> The governor’s primary role in power system is to control:
A) Frequency
B) Voltage
C) Power factor
D) Load factor
ANS: A

Q74 >> The phase shift produced by a 400 kV, 100 km line under load is proportional to:
A) Line reactance
B) Line resistance
C) Line capacitance
D) Surge impedance
ANS: A

Q75 >> Maximum power transfer capability of a line increases with:
A) Higher X
B) Lower X
C) Higher R
D) Lower R
ANS: B

Q76 >> Zero sequence network of a transformer depends on:
A) Winding connections and grounding
B) Core type
C) Voltage ratio
D) Load type
ANS: A

Q77 >> In power flow studies, slack bus is also called:
A) Swing bus
B) Generator bus
C) Load bus
D) Reference bus
ANS: A

Q78 >> In an overhead line, resistance and reactance per unit length:
A) R decreases with conductor size, X depends on spacing
B) Both decrease with conductor size
C) Both depend only on length
D) None
ANS: A

Q79 >> A synchronous condenser is used for:
A) Power factor improvement
B) Active power generation
C) Harmonic filtering
D) Frequency control
ANS: A

Q80 >> If the bus admittance matrix is singular, the system is:
A) Islanded
B) Stable
C) Balanced
D) Overloaded
ANS: A

Q81 >> In transient stability analysis, critical clearing angle is:
A) The maximum rotor angle permissible after fault clearance
B) Angle of voltage drop
C) Zero
D) Infinity
ANS: A

Q82 >> Short-circuit capacity of a bus is equal to:
A) Reciprocal of Thevenin reactance at the bus
B) Inverse of Thevenin resistance
C) Y-bus diagonal term
D) None
ANS: A

Q83 >> In Gauss-Seidel method, acceleration factor is used to:
A) Improve convergence rate
B) Reduce memory
C) Change Jacobian size
D) Eliminate mismatch
ANS: A

Q84 >> Line charging susceptance is due to:
A) Shunt capacitance
B) Series inductance
C) Resistance
D) Skin effect
ANS: A

Q85 >> The base MVA selected in per-unit system affects:
A) Numerical value of impedance but not % impedance
B) Actual current
C) Real power only
D) Frequency
ANS: A

Q86 >> In power system stability studies, damping torque helps in:
A) Reducing oscillations
B) Increasing synchronizing power
C) Reducing load angle
D) Increasing fault level
ANS: A

Q87 >> Load frequency control loop mainly consists of:
A) Speed governor, turbine, generator
B) AVR
C) Synchronous condenser
D) Transmission line
ANS: A

Q88 >> A 3-phase line has self GMR = r and mutual GMR = d. Inductance per conductor depends on:
A) log(d/r)
B) log(r/d)
C) d/r²
D) None
ANS: A

Q89 >> Kron reduction reduces:
A) Size of Y-bus by eliminating load buses
B) Impedance of lines
C) Fault level
D) Swing equation order
ANS: A

Q90 >> HVDC transmission is preferred for:
A) Long distance bulk power transfer
B) Short distance rural feeders
C) Low power only
D) Substation auxiliary supply
ANS: A

Q91 >> The main disadvantage of overhead lines compared to cables is:
A) More corona and line losses
B) Higher cost
C) Difficult maintenance
D) All of the above
ANS: A

Q92 >> The reactance of transmission line is proportional to:
A) log(D/r)
B) log(r/D)
C) D/r²
D) 1/D
ANS: A

Q93 >> Which type of bus does NOT have specified P and Q?
A) Slack bus
B) PV bus
C) PQ bus
D) None
ANS: A

Q94 >> In economic load dispatch without considering transmission losses, λ (incremental cost) is:
A) Same for all units
B) Different for each unit
C) Zero
D) Maximum for largest unit
ANS: A

Q95 >> The surge impedance loading of a 400 kV line is approximately:
A) 600 MW
B) 1000 MW
C) 2000 MW
D) 4000 MW
ANS: B

Q96 >> Corona loss decreases with:
A) Smooth conductors and higher spacing
B) Rough conductors
C) Increased frequency
D) Higher humidity
ANS: A

Q97 >> A line has resistance R and reactance X. For maximum power transfer, load power factor angle should be:
A) Equal to line impedance angle
B) Zero
C) Unity
D) 90° lagging
ANS: A

Q98 >> Under transient conditions, rotor angle stability is mainly affected by:
A) Acceleration power (Pm–Pe)
B) Reactive power only
C) Damping
D) Excitation alone
ANS: A

Q99 >> The iterative load flow solution terminates when:
A) Power mismatch is below tolerance
B) Y-bus becomes singular
C) All bus voltages are unity
D) Slack bus is eliminated
ANS: A

Q100 >> For a given system, if the inertia constant doubles, the frequency of rotor oscillations will:
A) Decrease
B) Increase
C) Remain unchanged
D) Become infinite
ANS: A

Power System Analysis MCQs

 

Power System Analysis MCQs (51–100)

Q51. The impedance diagram of a power system is usually drawn on:
A) kV base only
B) MVA base only
C) Common MVA and kV base
D) None
Ans: C

Q52. If base MVA is changed, per unit reactance will:
A) Remain same
B) Change
C) Be zero
D) Be infinite
Ans: B

Q53. Load flow solution gives:
A) Only real power flow
B) Only reactive power flow
C) Both bus voltages and line flows
D) Only losses
Ans: C

Q54. The main drawback of Gauss-Seidel method is:
A) Slow convergence
B) Large memory requirement
C) Complex programming
D) None
Ans: A

Q55. Newton-Raphson method requires:
A) Less memory
B) Faster convergence
C) Both faster convergence and more memory
D) None
Ans: C

Q56. In load flow studies, flat start means:
A) Voltage magnitude = 1.0 p.u., angle = 0°
B) Voltage magnitude = 0 p.u.
C) Angle = 90°
D) Random initialization
Ans: A

Q57. The slack bus provides:
A) Active power only
B) Reactive power only
C) Both P and Q balance
D) None
Ans: C

Q58. In economic dispatch, the cost function is usually:
A) Linear
B) Quadratic
C) Exponential
D) Cubic
Ans: B

Q59. Transmission loss formula involves:
A) B-coefficients
B) Z-bus
C) Y-bus
D) Jacobian
Ans: A

Q60. Voltage stability problem is related to:
A) Reactive power support
B) Real power flow
C) Frequency control
D) Economic dispatch
Ans: A

Q61. A bus with specified P and V is:
A) PQ bus
B) PV bus
C) Slack bus
D) None
Ans: B

Q62. Short circuit MVA is used to:
A) Design transformers
B) Design generators
C) Rate circuit breakers
D) Improve stability
Ans: C

Q63. The most common fault in power systems is:
A) Single line-to-ground fault
B) Three-phase fault
C) Line-to-line fault
D) Double line-to-ground fault
Ans: A

Q64. Sequence networks are connected in series for:
A) L-G fault
B) L-L fault
C) L-L-G fault
D) 3-phase fault
Ans: A

Q65. Sequence networks are connected in parallel for:
A) L-L fault
B) L-L-G fault
C) L-G fault
D) None
Ans: A

Q66. The Z-bus matrix is:
A) Inverse of Y-bus
B) Equal to Y-bus
C) Square of Y-bus
D) None
Ans: A

Q67. In symmetrical components, zero sequence current has:
A) Equal magnitude, 0° phase displacement
B) Equal magnitude, 120° displacement
C) Different magnitudes
D) None
Ans: A

Q68. Negative sequence current causes:
A) Rotor heating in synchronous machines
B) Overvoltage
C) Corona
D) Stability improvement
Ans: A

Q69. The inertia constant (H) is expressed in:
A) kWh
B) MJ/MVA
C) kVA
D) Hz
Ans: B

Q70. The swing equation is a:
A) First order differential equation
B) Second order differential equation
C) Algebraic equation
D) None
Ans: B

Q71. The equal area criterion is valid for:
A) First swing stability
B) Multi-swing stability
C) Steady state stability
D) None
Ans: A

Q72. Critical clearing angle depends on:
A) System inertia
B) System reactance
C) System voltage
D) All of these
Ans: D

Q73. Real power transfer capability of a line increases with:
A) Decrease in line reactance
B) Increase in reactance
C) Increase in resistance
D) None
Ans: A

Q74. Reactive power flow in a line depends on:
A) Voltage magnitude difference
B) Phase angle difference
C) Line resistance
D) None
Ans: A

Q75. In steady state, synchronous generator rotor speed is:
A) Equal to synchronous speed
B) Greater than synchronous speed
C) Less than synchronous speed
D) Random
Ans: A

Q76. Infinite bus has:
A) Constant voltage and frequency
B) Constant load
C) Constant current
D) None
Ans: A

Q77. In transmission line modeling, shunt capacitance is neglected in:
A) Short line
B) Medium line
C) Long line
D) None
Ans: A

Q78. Surge impedance loading (SIL) is proportional to:
A) (V²/Zc)
B) (V/Zc²)
C) (V²/2Zc)
D) (V/Zc)
Ans: A

Q79. Bundled conductors are used to:
A) Increase corona inception voltage
B) Reduce reactance
C) Increase current capacity
D) All of these
Ans: D

Q80. Stability of power system can be improved by:
A) Fast excitation system
B) High speed breakers
C) Series compensation
D) All of these
Ans: D

Q81. FACTS controllers include:
A) STATCOM
B) TCSC
C) SSSC
D) All of these
Ans: D

Q82. SVC (Static Var Compensator) provides:
A) Active power support
B) Reactive power support
C) Frequency control
D) None
Ans: B

Q83. In HVDC, rectifier end operates at:
A) Lagging power factor
B) Leading power factor
C) Unity power factor
D) None
Ans: A

Q84. In HVDC, inverter end operates at:
A) Lagging power factor
B) Leading power factor
C) Unity power factor
D) None
Ans: B

Q85. HVDC link control is achieved by:
A) Controlling firing angle of converters
B) Changing transmission line parameters
C) Changing frequency
D) None
Ans: A

Q86. Corona discharge is reduced by:
A) Increasing conductor size
B) Increasing spacing
C) Bundling conductors
D) All of these
Ans: D

Q87. Power factor of a transmission line is improved by:
A) Series capacitor
B) Shunt capacitor
C) Reactor
D) Resistor
Ans: B

Q88. Series capacitor in a line reduces:
A) Effective reactance
B) Effective resistance
C) Line charging
D) Surge impedance
Ans: A

Q89. The primary purpose of load frequency control is to:
A) Maintain scheduled frequency
B) Control reactive power
C) Minimize fuel cost
D) Improve transient stability
Ans: A

Q90. Automatic Generation Control (AGC) maintains:
A) Tie-line power and frequency
B) Voltage profile
C) Reactive power
D) Transmission loss
Ans: A

Q91. In two-area load frequency control, the tie-line power depends on:
A) Frequency difference
B) Voltage difference
C) Impedance
D) None
Ans: A

Q92. Reactive power compensation using shunt capacitors results in:
A) Increased voltage
B) Decreased losses
C) Improved stability
D) All of these
Ans: D

Q93. In per unit system, base kV on each side of a transformer is chosen in proportion to:
A) Turns ratio
B) Current ratio
C) Impedance
D) Resistance
Ans: A

Q94. Load curve gives information about:
A) Maximum demand
B) Energy consumed
C) Load factor
D) All of these
Ans: D

Q95. Diversity factor is:
A) Sum of individual maximum demands ÷ Maximum demand of system
B) Maximum demand ÷ Connected load
C) Average load ÷ Maximum demand
D) None
Ans: A

Q96. Load factor is:
A) Average load ÷ Maximum demand
B) Maximum load ÷ Average load
C) Load ÷ Connected load
D) None
Ans: A

Q97. Plant capacity factor is:
A) Average demand ÷ Plant capacity
B) Maximum demand ÷ Plant capacity
C) Connected load ÷ Plant capacity
D) None
Ans: A

Q98. Power system frequency is controlled by:
A) Active power balance
B) Reactive power balance
C) Voltage
D) None
Ans: A

Q99. Power system voltage profile is mainly controlled by:
A) Reactive power
B) Real power
C) Frequency
D) Load factor
Ans: A

Q100. The overall objective of power system analysis and operation is:
A) Reliability and economy
B) Voltage reduction
C) Minimum load
D) Frequency rise
Ans: A

Power System Analysis MCQs

 

Power System Analysis MCQs

Q1. The main objective of power system analysis is:
A) To reduce cost of generation
B) To minimize transmission loss
C) To analyze performance under various operating conditions
D) To increase voltage levels
Ans: C

Q2. In a power system, per unit (p.u.) values are mainly used because:
A) They simplify analysis
B) They increase accuracy
C) They reduce cost
D) They improve protection
Ans: A

Q3. The per-unit value of any quantity is defined as:
A) Actual value × Base value
B) Base value ÷ Actual value
C) Actual value ÷ Base value
D) Actual value + Base value
Ans: C

Q4. Kron’s reduction method is used for:
A) Reducing buses in a power system network
B) Load flow analysis
C) Short-circuit analysis
D) Transient stability
Ans: A

Q5. Y-bus matrix is:
A) Symmetric
B) Skew symmetric
C) Diagonal
D) Non-symmetric
Ans: A

Q6. The diagonal elements of Y-bus are known as:
A) Self-admittance
B) Mutual-admittance
C) Transfer-admittance
D) None of these
Ans: A

Q7. In Gauss-Seidel method, acceleration factor is used to:
A) Improve convergence
B) Slow down iteration
C) Reduce error
D) None
Ans: A

Q8. Which method is best suited for large power system load flow?
A) Gauss-Seidel
B) Newton-Raphson
C) Z-bus method
D) Gauss elimination
Ans: B

Q9. The Jacobian matrix in Newton-Raphson load flow consists of:
A) Partial derivatives of active and reactive power with respect to bus angles and voltages
B) Power loss terms only
C) Voltage magnitudes only
D) Admittance matrix terms only
Ans: A

Q10. The swing equation of a synchronous machine is used for:
A) Steady state stability
B) Transient stability
C) Load flow analysis
D) Short circuit analysis
Ans: B

Q11. Steady state stability limit is:
A) Maximum power transfer limit without losing synchronism
B) Minimum power transfer limit
C) Equal to surge impedance loading
D) None
Ans: A

Q12. Surge impedance loading (SIL) of a transmission line depends on:
A) Line length only
B) Line resistance only
C) L and C of the line
D) G and R of the line
Ans: C

Q13. Equal area criterion is used for:
A) Small signal stability
B) Steady state stability
C) Transient stability
D) Voltage stability
Ans: C

Q14. The maximum power transfer occurs when:
A) Load impedance = Line resistance
B) Load impedance = Source impedance
C) Load reactance = Source reactance
D) Source impedance = Zero
Ans: B

Q15. Short circuit MVA is equal to:
A) Base MVA ÷ p.u. reactance
B) Base MVA × p.u. reactance
C) Base kV ÷ Base MVA
D) None
Ans: A

Q16. A PV bus in load flow study is known as:
A) Slack bus
B) Generator bus
C) Load bus
D) None
Ans: B

Q17. In load flow, slack bus is used to:
A) Balance active and reactive power
B) Supply only reactive power
C) Maintain constant load
D) Maintain zero losses
Ans: A

Q18. The Newton-Raphson method in polar form is preferred over rectangular because:
A) It requires less memory
B) It gives faster convergence
C) Jacobian is simpler
D) More accurate
Ans: B

Q19. Symmetrical fault analysis assumes:
A) Equal fault current in all phases
B) Unequal fault current in phases
C) Open circuit fault
D) None
Ans: A

Q20. Unsymmetrical faults are analyzed using:
A) Z-bus method
B) Sequence components
C) Kron reduction
D) Load flow
Ans: B

Q21. The most severe fault in a power system is:
A) Single line-to-ground
B) Double line-to-ground
C) Line-to-line
D) Three-phase
Ans: D

Q22. The positive sequence network represents:
A) Balanced system operation
B) Negative sequence faults
C) Zero sequence components
D) None
Ans: A

Q23. The zero-sequence impedance of a transmission line depends on:
A) Earth return path
B) Positive sequence impedance
C) Transformer tap settings
D) Surge impedance
Ans: A

Q24. The value of X/R ratio in short circuit studies is important because:
A) It affects circuit breaker rating
B) It affects line charging
C) It reduces voltage drop
D) None
Ans: A

Q25. A line is said to be short if its length is less than:
A) 50 km
B) 80 km
C) 100 km
D) 150 km
Ans: B

Q26. A long transmission line is modeled using:
A) π-model
B) T-model
C) Distributed parameter model
D) None
Ans: C

Q27. In economic load dispatch, the objective is:
A) To minimize cost of generation
B) To minimize system loss
C) To minimize voltage drop
D) To improve stability
Ans: A

Q28. Penalty factor in economic dispatch accounts for:
A) Transmission losses
B) Generator fuel cost
C) Reactive power losses
D) Transformer losses
Ans: A

Q29. Optimal load dispatch is obtained when:
A) Incremental fuel cost of all units is equal
B) Minimum fuel cost is used
C) Maximum power transfer occurs
D) Load is minimum
Ans: A

Q30. Power angle δ is the angle between:
A) Rotor axis and stator axis
B) Voltage and current
C) Infinite bus voltage and generator voltage
D) None
Ans: C

Q31. If the load angle δ increases beyond 90°, the machine:
A) Remains stable
B) Becomes unstable
C) Transfers more power
D) Operates at unity power factor
Ans: B

Q32. Ferranti effect is observed in:
A) Long unloaded transmission line
B) Short loaded line
C) Transformers
D) Short circuit
Ans: A

Q33. The main cause of Ferranti effect is:
A) Line capacitance
B) Line inductance
C) Line resistance
D) Corona
Ans: A

Q34. Corona loss increases with:
A) Decrease in frequency
B) Decrease in voltage
C) Increase in supply frequency and voltage
D) Decrease in conductor diameter
Ans: C

Q35. The surge impedance of a line is:
A) √(L/C)
B) √(C/L)
C) L/C
D) C/L
Ans: A

Q36. For maximum power transfer in a line:
A) Pmax = EV/X
B) Pmax = EV/X × sinδ
C) Pmax = EV/2X
D) None
Ans: A

Q37. Real power transfer depends on:
A) Line resistance
B) Line capacitance
C) Angle δ
D) Reactive power only
Ans: C

Q38. Reactive power transfer depends mainly on:
A) Voltage magnitude difference
B) Phase angle difference
C) Resistance
D) Power factor
Ans: A

Q39. In power system stability studies, small-signal stability is due to:
A) Eigenvalue analysis
B) Equal area criterion
C) Load flow
D) Fault analysis
Ans: A

Q40. Reactive power compensation improves:
A) Stability
B) Voltage profile
C) Transmission efficiency
D) All of these
Ans: D

Q41. FACTS devices are mainly used for:
A) Real power compensation
B) Reactive power control and stability improvement
C) Voltage reduction
D) Frequency control
Ans: B

Q42. HVDC transmission is preferred for:
A) Short distance, high power
B) Long distance, bulk power
C) Low voltage networks
D) Small loads only
Ans: B

Q43. The main advantage of HVDC is:
A) No skin effect
B) Reduced corona
C) Reduced transmission losses and stability improvement
D) All of these
Ans: D

Q44. In load flow, PQ bus is:
A) Load bus
B) Generator bus
C) Slack bus
D) None
Ans: A

Q45. Bus admittance matrix is mainly used in:
A) Load flow analysis
B) Economic dispatch
C) Stability study
D) Fault analysis
Ans: A

Q46. Z-bus building algorithm is used for:
A) Short circuit analysis
B) Load flow
C) Economic dispatch
D) Ferranti effect
Ans: A

Q47. A three-phase balanced system has:
A) Only positive sequence components
B) Only negative sequence
C) Only zero sequence
D) All three sequences
Ans: A

Q48. Negative sequence components cause:
A) Heating in rotor of synchronous machine
B) Overvoltage
C) Reduced corona
D) Increased SIL
Ans: A

Q49. In transient stability analysis, critical clearing time means:
A) Maximum time fault can persist without loss of synchronism
B) Minimum fault clearing time
C) Time for steady state to re-establish
D) None
Ans: A

Q50. Power system oscillations after disturbance are mainly:
A) Damped
B) Undamped
C) Growing oscillations
D) None
Ans: A