30 Questions
What type of vibrations are characterized by high frequency and low amplitude?
High frequency and low amplitude vibrations
In an extra high voltage transmission line, what does the propagation constant 'b = 0.00127 radians per km' represent?
The impedance per unit length of the line
Which item in List-I matches with 'reduce the Ferranti effect' in List-II?
improve power factor
What is the total impedance of a lossless overhead EHV line operating at 50 Hz if the total reactance and suspectance are 0.045 pu and 1.2 pu respectively?
1.2 pu
Which type of capacitor is used to increase the power flow in a line according to List-I and List-II matching?
series capacitor
What is the formula for calculating wavelength given the propagation constant 'b = 0.00127 radians per km'?
$\frac{2\pi}{b}$
What is the efficiency of the transmission line?
80%
For the same voltage boost, where is the reactive power capacity higher?
Shunt capacitor
In which type of transmission lines does Ferranti effect not occur?
Short transmission lines
How can Ferranti effect be compensated?
Both a and b
Which method is typically used to change power factor from leading to lagging?
Shunt reactor
What is the load angle if the transmission line has a reactance of 1 Pu, and the generator is delivering 0.5 Pu of active power?
$30°$
What type of impedance does an overhead transmission line have?
400 Ω – 600 Ω
In a hydroelectric power plant, the amount of electrical energy generated depends significantly on:
Head of water
What is the correct formula to calculate the maximum sag in a conductor with a given span, weight, and working tension?
$s=WL^2/8T$
If the weight of a conductor is 150 kg/m, ice weight is 60 kg/m, and wind force is 200 kg/m, what will be the resultant weight per meter of length using the given formula?
468 kg/m
What factors determine the electrical energy generation capability of a hydroelectric power plant?
Head of water and Specific weight of water
What is the type of impedance for an overhead transmission line ranging between 300 Ω and 900 Ω?
$√(C/L)$
What happens to the inductance per unit length of a transmission line if the distance between the conductors is doubled?
Increases but not double
In a lossless radial transmission line with surge impedance loading, what is the VAR situation at the sending and receiving ends?
Total negative VAR at sending end and zero VAR at receiving end
Why is shunt compensation in an extra high voltage (EHV) system resorted to?
Reduce the fault level
Which of the following circuits is most like the equivalent circuit of a short transmission line?
Series RL circuit
What does the inductance per unit length of an overhead line due to internal flux linkages depend on?
Is independent of the size of conductor and constant
How is the insulation of modern extra high voltage (EHV) lines designed?
The switching voltage
What is one of the advantages of higher transmission voltage?
Increased power transfer capability of the transmission line
How can the maximum power transfer capability of a transmission line be increased?
Parallel transmission lines
What is one of the objectives of a power system?
Supplying rated voltage and frequency to consumers
In an EHV system, why is shunt compensation applied?
To improve the stability
Where does the zero-sequence current exist in a Y-delta transformer with Y-side grounded?
Exists in the lines on the delta side
Which matrix reveals the topology of a power system network?
Bus incidence matrix
Study Notes
Transmission Lines
- High frequency and low amplitude vibrations or high frequency and high amplitude vibrations are not suitable for transmission lines.
- An extra high voltage transmission line can be approximated by a lossless line having a propagation constant b = 0.00127 radians per km.
- The percentage ratio of line length to wavelength can be calculated using the formula LEMDA = 2π/B.
Shunt and Series Capacitors/Reactors
- Shunt capacitors are used to improve power factor, reduce Ferranti effect, and increase power flow in a line.
- Series capacitors are used to reduce the current ripples, increase power flow in a line, and reduce Ferranti effect.
- Shunt reactors are used to reduce the Ferranti effect and improve power factor.
- Series reactors are used to reduce the current ripples.
Efficiency of Transmission Line
- The efficiency of a transmission line can be calculated using the formula: Efficiency = (Output power / Input power) * 100%.
Power Factor Correction
- Shunt capacitors can be used to change power factor from leading to lagging.
- Shunt reactors can be used to change power factor from lagging to leading.
Transmission Line Characteristics
- The characteristics impedance of a loss free transmission line is √(L/C).
- The range of surge impedance for an overhead transmission line is 300 Ω – 900 Ω.
- The inductance per unit length of an overhead line due to internal flux linkages depends on the size of the conductor.
Hydroelectric Power Plant
- The amount of electrical energy that can be generated by a hydroelectric power plant depends on the head of water, quantity of water, and specific weight of water.
Overhead Transmission Line Conductors
- Aeoline vibrations are a type of vibration that occurs in overhead transmission line conductors due to wind.
- The weight of conductor, weight of ice, and wind force can affect the sag of the conductor.
Radial Transmission Line
- A lossless radial transmission line with surge impedance loading has a flat voltage profile and unity power factor at all points along it.
Equivalent Circuit of Short Transmission Line
- The equivalent circuit of a short transmission line is a series RL circuit.
Objectives of Power System
- The objectives of a power system include to minimize the cost of electrical energy per KWh, to supply rated voltage and frequency to the consumers, and to maximize power transfer capability.
ZBUS Matrix
- The ZBUS matrix is a sparse matrix that reveals the topology of the power system network.
- The Bus incidence matrix, Primitive impedance matrix, Primitive admittance matrix, and Bus impedance matrix are all related to the ZBUS matrix.
Test your knowledge on power transmission efficiency, power factor, and Ferranti effect in single-phase transmission lines. Calculate efficiency, compare reactive power capacities, and identify scenarios where Ferranti effect does not occur.
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