Ee6711 Pss Lab Pre Assesment
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Questions and Answers
- 1.
Inductance of transmission line will decrease when
- A.
Both GMD and GMR increases
- B.
both GMD and GMR decreases
- C.
GMD increases and GMR decreases
- D.
GMD decreases and GMR increases
Correct Answer
D. GMD decreases and GMR increasesExplanation
When the geometric mean distance (GMD) decreases and the geometric mean radius (GMR) increases, the inductance of a transmission line will decrease. This is because the GMD represents the average distance between the conductors, and when it decreases, the conductors are closer together, resulting in a decrease in the inductance. On the other hand, when the GMR increases, it means that the conductors have a larger radius, which reduces the magnetic field strength and therefore decreases the inductance.Rate this question:
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- 2.
If we increase the spacing between the phase conductors, the line capacitance
- A.
Increases
- B.
Decreases
- C.
remains unaffected
- D.
Cannot be predicted
Correct Answer
B. DecreasesExplanation
When the spacing between phase conductors is increased, the line capacitance decreases. This is because capacitance is directly proportional to the area of overlap between the conductors. When the spacing is increased, the area of overlap decreases, resulting in a decrease in capacitance. Therefore, increasing the spacing between phase conductors reduces the line capacitance.Rate this question:
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- 3.
In ACSR conductors, due to steel the resistance of conductor __________. (increases/decreases)
Correct Answer
increasesExplanation
The resistance of a conductor in ACSR (Aluminum Conductor Steel Reinforced) conductors increases due to the presence of steel. Steel is a material that has a higher resistivity compared to aluminum, which is the primary conductor material in ACSR conductors. When steel is added to the conductor, it increases the overall resistance of the conductor, making it less efficient for the transmission of electricity. This is why the resistance increases in ACSR conductors due to steel.Rate this question:
- 4.
Which of the following is the significance of transposing line conductors?
- A.
To make the voltage drop equal for all the phases
- B.
To neutralize the effect of unbalanced currents
- C.
to reduce the disturbances to the nearby communication circuits
- D.
all of the above
Correct Answer
D. all of the aboveExplanation
The significance of transposing line conductors is that it helps to make the voltage drop equal for all the phases, neutralize the effect of unbalanced currents, and reduce disturbances to nearby communication circuits. Transposing the conductors ensures that each phase experiences the same level of voltage drop, which helps maintain a balanced electrical system. It also helps to minimize the negative effects of unbalanced currents, which can cause overheating and other issues. Additionally, transposing the conductors can reduce electromagnetic interference and disturbances to nearby communication circuits, improving overall system performance.Rate this question:
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- 5.
If the height of transmission towers is increased, which of the following parameters is likely to change ?
- A.
Resistance
- B.
Inductance
- C.
Capacitance
- D.
None of the above
Correct Answer
C. CapacitanceExplanation
When the height of transmission towers is increased, the parameter that is likely to change is capacitance. Increasing the height of the transmission towers increases the distance between the conductors, which in turn increases the capacitance between them. Capacitance is a measure of the ability of a system of conductors to store electrical energy in the form of an electric field, and increasing the distance between the conductors increases the capacitance. Therefore, increasing the height of transmission towers is likely to result in a change in capacitance.Rate this question:
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- 6.
In short transmission lines the shunt capacitance is totally neglected and the series impedance is a __________ parameter. (lumped/distributed)
Correct Answer
lumpedExplanation
In short transmission lines, the shunt capacitance is usually very small compared to other parameters and can be neglected. Therefore, the series impedance becomes the dominant parameter in the transmission line. This implies that the series impedance is considered a lumped parameter, meaning that it can be represented as a single value for the entire length of the transmission line.Rate this question:
- 7.
For some given transmission line the expression for voltage regulation is given by (Vs - Vr)/Vr =100%. Hence,
- A.
This must be a short line
- B.
This may either be a medium line or short line
- C.
This expression is true for any line
- D.
None of the above
Correct Answer
A. This must be a short lineExplanation
The given expression for voltage regulation, (Vs - Vr)/Vr = 100%, indicates that the percentage change in voltage from the sending end (Vs) to the receiving end (Vr) is 100%. This suggests that the line is short because in short transmission lines, there is minimal voltage drop due to the shorter distance and lower resistance. In medium or long transmission lines, the voltage drop would be higher, resulting in a lower percentage change in voltage. Therefore, the correct answer is "this must be a short line".Rate this question:
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- 8.
For transmission line which one of the following relation is true?
- A.
AD - BC = 0
- B.
AD + BC = 0
- C.
AD - BC = 1
- D.
AD - BC = -1
Correct Answer
C. AD - BC = 1Explanation
The relation AD - BC = 1 is true for a transmission line. This equation represents the characteristic impedance of the transmission line, where A and D are the capacitance and inductance per unit length, and B and C are the conductance and resistance per unit length. The equation indicates that the difference between the product of the capacitance and inductance and the product of the conductance and resistance is equal to 1. This relationship is important in understanding the behavior and performance of transmission lines.Rate this question:
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- 9.
In short lines A = 1. B = Z, C = 0 and D = A.
- A.
True
- B.
False
Correct Answer
A. TrueExplanation
The given statement is true because it states that in a certain system, the letter A is equal to 1, the letter B is equal to Z, the letter C is equal to 0, and the letter D is equal to A.Rate this question:
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- 10.
The Ybus matrix can be used for
- A.
Load Flow Studies
- B.
Fault Studies
- C.
Stability Studies
- D.
Both a and c
Correct Answer
D. Both a and cExplanation
The Ybus matrix is a mathematical representation of a power system network, which includes information about the admittance (reciprocal of impedance) of each element in the network. Load Flow Studies involve analyzing the steady-state behavior of the power system, while Stability Studies focus on analyzing the dynamic behavior of the system during disturbances. Both of these studies require the use of the Ybus matrix to accurately model and analyze the power system. Hence, the correct answer is "Both a and c" as the Ybus matrix can be used for both Load Flow Studies and Stability Studies.Rate this question:
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- 11.
Which among the following matrix is sparse?
- A.
Jacobian matrix only
- B.
Y bus matrix only
- C.
Z bus matrix only
- D.
Both (a) and (b)
Correct Answer
D. Both (a) and (b)Explanation
A sparse matrix is a matrix in which most of the elements are zero. In the given options, both the Jacobian matrix and the Y bus matrix are likely to be sparse matrices. The Jacobian matrix represents the partial derivatives of a set of equations and is often sparse because many of these derivatives may be zero. Similarly, the Y bus matrix represents the admittance values of a power system network, and since many branches may not be connected, it is also likely to be sparse. Therefore, both (a) and (b) options can be considered as sparse matrices.Rate this question:
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- 12.
Suppose you have to design a new power system. The following studies are essential to design any power system.1. Short Circuit studies2. Load Flow studies3. Transient stability studyWhat should be order of these studies?
- A.
1,2 then 3
- B.
2,1 then 3
- C.
2, 3 then 1
- D.
No order is necessary, we can perform analysis/study in any order to design a power system.
Correct Answer
B. 2,1 then 3Explanation
The order of the studies should be 2,1 then 3. Load flow studies should be conducted first to determine the steady-state operating conditions of the power system. This information is then used in the short circuit studies, which analyze the system's response to faults. Finally, the transient stability study is performed to assess the system's ability to maintain stable operation following a disturbance.Rate this question:
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- 13.
Why are load flow studies carried out?
- A.
To study of stability of the system
- B.
For fault calculations
- C.
For planning the power system
- D.
All of these
Correct Answer
C. For planning the power systemExplanation
Load flow studies are carried out to plan the power system. These studies help in determining the steady-state operating conditions of the system, including voltage levels, power flows, and losses. By analyzing the load flow, engineers can identify potential issues such as overloading, voltage drops, and inadequate system capacity. This information is crucial for designing and optimizing the power system, ensuring its reliability, and meeting the demand requirements efficiently. Additionally, load flow studies also aid in evaluating the impact of system changes, such as adding new generation sources or modifying the network configuration.Rate this question:
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- 14.
Which among theses quantities are to be determined in slack bus?
- A.
P and Q
- B.
Q and |V|
- C.
|V| and δ
- D.
Q and δ
Correct Answer
A. P and QExplanation
In a power system, the slack bus is the reference bus that maintains the system's voltage magnitude and angle. The quantities that need to be determined at the slack bus are P (active power) and Q (reactive power). This is because the slack bus is responsible for supplying or absorbing any mismatch between the generated and consumed power in the system. By controlling the values of P and Q at the slack bus, the voltage magnitude and angle can be adjusted to maintain system stability and meet the load demand. Therefore, the correct answer is P and Q.Rate this question:
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- 15.
Which types of equations are solved using Newton Raphson method?
- A.
Non-linear differential equations
- B.
Linear differential equations
- C.
Non-linear algebraic equations
- D.
Both (a) and (c)
Correct Answer
C. Non-linear algebraic equationsExplanation
The Newton Raphson method is a numerical method used to find the roots of a function. It is particularly effective for solving non-linear algebraic equations, where the equation cannot be expressed as a linear combination of variables. Non-linear differential equations, on the other hand, involve derivatives and are typically solved using other methods such as separation of variables or numerical methods like Euler's method. Therefore, the correct answer is non-linear algebraic equations.Rate this question:
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- 16.
Which among the following methods are highly accurate?
- A.
Gauss Seidel method
- B.
Newton Raphson method
- C.
Fast decoupled load flow method
- D.
All of the above methods
Correct Answer
B. Newton Raphson methodExplanation
The Newton Raphson method is highly accurate because it is an iterative numerical method used to find the roots of a function. It uses an initial guess and then iteratively improves the guess until it converges to the correct root. This method is known for its fast convergence and high accuracy, making it a popular choice for solving complex equations and systems of equations in various fields of science and engineering.Rate this question:
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- 17.
Initially, ___________ p.u. will be the voltage assumed at all the PQ buses for solving the load flow problem
Correct Answer
1Explanation
Initially, the voltage assumed at all the PQ buses for solving the load flow problem will be 1 p.u. This means that the voltage at all the PQ buses is assumed to be equal to the base voltage of the system. This assumption is made to simplify the load flow calculations and is based on the fact that the load flow problem is a steady-state analysis where the system is assumed to be operating under normal conditions.Rate this question:
- 18.
__________ (linear / quadratic) type of convergence takes place in NR method
Correct Answer
quadraticExplanation
The NR method, also known as the Newton-Raphson method, is an iterative numerical method used to find the roots of a function. It converges quadratically, which means that with each iteration, the number of correct digits approximately doubles. This rapid convergence is a result of the method's use of the derivative of the function, allowing it to approach the root with increasing accuracy. Therefore, the correct answer is quadratic.Rate this question:
- 19.
Which of the following transmission line is most practically used in load flow analysis?
- A.
Nominal T
- B.
Nominal ∏
- C.
Either 1 or 2
- D.
Neither 1 nor 2
Correct Answer
B. Nominal ∏Explanation
In load flow analysis, the most practically used transmission line is the Nominal ∏ configuration. This configuration is commonly used because it provides a balanced and symmetrical structure, making it easier to analyze and calculate power flow. The Nominal ∏ configuration also allows for easy control of voltage and current, making it a suitable choice for load flow analysis.Rate this question:
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- 20.
What is / are the cause(s) for transient disturbance?
- A.
Sudden load changes
- B.
Faults in the power system
- C.
Switching operations
- D.
All of these
Correct Answer
D. All of theseExplanation
Transient disturbances in a power system can be caused by sudden load changes, faults in the power system, and switching operations. Sudden load changes can lead to voltage fluctuations and current surges, affecting the stability of the system. Faults in the power system, such as short circuits or equipment failures, can cause sudden changes in voltage and current levels. Switching operations, such as opening or closing circuit breakers, can create transient disturbances due to the rapid change in the electrical circuit. Therefore, all of these factors can contribute to transient disturbances in a power system.Rate this question:
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- 21.
Which among these is the most commonly occurring fault?
- A.
Single line to ground fault
- B.
line to line fault
- C.
Three-phase to ground fault
- D.
Double line to ground fault
Correct Answer
A. Single line to ground faultExplanation
A single line to ground fault is the most commonly occurring fault in electrical systems. This fault occurs when one phase conductor comes into contact with the ground or a grounded object. It can be caused by factors such as insulation breakdown, equipment failure, or accidental contact. This fault is more common compared to other types of faults because of the high probability of a single conductor coming into contact with the ground.Rate this question:
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- 22.
Which among the following are unsymmetrical faults?
- A.
Single line to ground fault
- B.
Double line to ground fault
- C.
Line to line fault
- D.
All of the above
Correct Answer
D. All of the aboveExplanation
All of the mentioned faults - single line to ground fault, double line to ground fault, and line to line fault - are unsymmetrical faults. Unsymmetrical faults occur when there is an imbalance in the three phases of a power system. In single line to ground fault, one phase is shorted to the ground, causing an imbalance. In double line to ground fault, two phases are shorted to the ground. In line to line fault, two phases are shorted together without any connection to the ground. These faults can cause significant damage to the power system and need to be quickly detected and cleared.Rate this question:
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- 23.
What percentage of fault occurring in the power system is line to line fault?
- A.
5%
- B.
30%
- C.
75%
- D.
15%
Correct Answer
D. 15%Explanation
The correct answer is 15%. This suggests that out of all the faults occurring in the power system, 15% of them are line to line faults.Rate this question:
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- 24.
The zero sequence and negative sequence networks are connected in _______ (series/parallel) in the case of double line to ground fault
Correct Answer
parallelExplanation
In the case of a double line to ground fault, the zero sequence and negative sequence networks are connected in parallel. This means that the currents flowing through these networks are additive and contribute to the fault current. By connecting the networks in parallel, the fault current can be accurately calculated and protective devices can be coordinated to quickly isolate the fault and minimize damage to the system.Rate this question:
- 25.
What is the value of zero sequence impedance in line to line faults?
- A.
Z0 = 1
- B.
Z0 = infinity
- C.
Z0 = 0
- D.
Z0 = 3Zn
Correct Answer
C. Z0 = 0Explanation
The value of zero sequence impedance in line to line faults is zero. This means that in a fault where two phases of a power system are short-circuited, the zero sequence current will not flow. This is because the zero sequence current requires a return path through the neutral conductor, which is not present in a line to line fault. Therefore, the zero sequence impedance is effectively zero in this case.Rate this question:
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- 26.
Stability of a system is not affected by
- A.
Reactance of line
- B.
Reactance of generator
- C.
Losses
- D.
Machine internal voltage
Correct Answer
C. LossesExplanation
The stability of a system is not affected by losses. Stability refers to the ability of a system to return to its original state after being disturbed. Losses, such as resistive losses in transmission lines or generator losses, do not directly impact the ability of the system to maintain stability. Losses only result in a decrease in efficiency and an increase in heat dissipation, but they do not affect the overall stability of the system.Rate this question:
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- 27.
Which among these is related to the critical clearing time of a fault in a power system?
- A.
Transient stability limit
- B.
Steady state stability limit
- C.
Frequency limit
- D.
All of these
Correct Answer
A. Transient stability limitExplanation
The transient stability limit is related to the critical clearing time of a fault in a power system. Transient stability refers to the ability of a power system to maintain synchronism after a disturbance or fault occurs. The critical clearing time is the maximum time allowed for the fault to be cleared before the system loses stability. Therefore, the transient stability limit is directly linked to the critical clearing time as it determines the maximum time the system can withstand a fault without losing stability.Rate this question:
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- 28.
At what value of ‘δ’ the maximum power transfer takes place?
- A.
45 degrees
- B.
90 degrees
- C.
180 degrees
- D.
120 degrees
Correct Answer
B. 90 degreesExplanation
At 90 degrees, the maximum power transfer takes place in an AC circuit. This is because at this phase angle, the impedance of the load is purely resistive, resulting in maximum power transfer according to the maximum power transfer theorem. At other phase angles, the load impedance will have a reactive component, leading to less power transfer.Rate this question:
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- 29.
ALFC stands for ___________________________________________
Correct Answer
Automatic Load Frequency ControlExplanation
ALFC stands for Automatic Load Frequency Control. This system is used in power generation to maintain a balance between the load demand and the power generated by adjusting the frequency of the power supply. It ensures that the power generated matches the load demand, preventing frequency deviations that can lead to power system instability. ALFC continuously monitors the system frequency and adjusts the power output accordingly to maintain a stable and reliable power supply.Rate this question:
- 30.
The ratio of change of fuel cost with active power generation is called as incremental fuel cost
- A.
True
- B.
False
Correct Answer
A. TrueExplanation
The ratio of change of fuel cost with active power generation is called incremental fuel cost. This means that as the active power generation increases, the fuel cost also increases in a certain ratio. Therefore, the statement is true.Rate this question:
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