12 Questions
What is the classification of an overhead transmission line with a length of up to 50 km and line voltage less than 20 kV?
Short Transmission Line
In a short transmission line, which of the following effects are neglected due to the smaller length and lower voltage?
Capacitance effects
What is the range of length for a medium transmission line?
50 km to 150 km
Which model is used for short transmission lines with low voltage according to the text?
Short Line Model
In a balanced three-phase line, what assumption is made regarding the given voltages and currents?
All voltages are line-to-line values, all currents are line currents
What are the major parameters considered for short transmission lines?
Resistance and inductance
What is the purpose of calculating the performance of transmission lines?
All of the above
How is voltage regulation defined in transmission lines?
The change in voltage magnitude between sending and receiving ends
What is the definition of efficiency for transmission lines?
The ratio of input power to output power
For what length and voltage are the capacitive effects in transmission lines considered?
Lines longer than 150 km and voltage higher than 100 kV
What is the classification of a transmission line that is 200 km long and operating at 66 kV?
Long transmission line
What is the purpose of calculating the line-to-neutral capacitance in a transmission line?
To calculate the charging current due to line capacitance
Study Notes
Classification of Overhead Transmission Lines
- A short transmission line has a length of up to 50 km and a voltage less than 20 kV, with capacitance effects neglected.
- A medium transmission line has a length of 50 km to 150 km and a voltage range of 20 kV to 100 kV, with capacitance effects considered.
- A long transmission line has a length of more than 150 km and a voltage higher than 100 kV, with capacitance effects significant.
Performance of Transmission Lines
- The performance of a transmission line includes the calculation of sending-end voltage, current, power factor, power loss, and efficiency of transmission.
- Performance calculations are helpful in system planning.
- Voltage regulation is the change in voltage magnitude between the sending and receiving ends of the transmission line.
Transmission Line Constants
- Line constants (line to neutral) include R (resistance), XL (inductive reactance), and BC (shunt capacitance).
- The line constants are used to calculate the performance of a transmission line.
Line Models and Generalized Circuit Constants
- The short line model is used for short transmission lines, with A = 1, B = Z, C = 0, and D = 1.
- The three-phase line model is an extension of the single-phase model, with per phase basis adopted.
Capacitance and Charging Current
- Line-to-neutral capacitance is an important parameter in transmission line performance.
- Charging current per phase can be calculated if the line is maintained at a specific voltage and frequency.
Efficiency and Power Flow
- The efficiency of transmission lines is defined as the ratio of input power to output power.
- Surge impedance load (SIL) is the ideal load, where the current and voltage are uniform along the line.
- The wave of current and voltage is in phase when the reactive power consumed is equal to the reactive power generated by the transmission line.
Explore the classifications of overhead transmission lines and how they impact the efficiency and voltage regulation calculations. Learn about short transmission lines, where length is up to 50 km and voltage is less than 20 kV, resulting in negligible capacitance effects.
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