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A sample of copper wire has a resistance of 50 Ω at 100C. The maximum operating temperature of the wire if its resistance is to increase by at most 10 percent will be:
(Given, the Temperature coefficient at 100C is a = 0.004090C-1).
A single-phase, two wire transmission line, 15 km long, is made up of round conductors, each 0.8 cm radius, separated from each other by 40 cm. The equivalent diameter of a fictitious hollow, thin-walled conductor having the same inductance as the original line is given by
The fictitious conductor is one whose radius is r' and whose diameter is therefore,
If the conductor radius increases, inductance of the line,
Here, GMR radius of conductor.
Hence, if radius increases, GMR also increases. As a result of which inductance will decrease.
For an underground cable, the surge impedance is generally taken as
For underground cable, Zs = 40 Ω
For overhead line, Zs = 400 Ω
Consider the following phenomenon occuring in a power system:
1. Corona loss
2. Charging current
3. Ferranti effect
4. Dielectric loss
5. Skin effect
Which of the above are associated with transmission lines?
Dielectric loss occurs in underground cables not in a transmission line.
The corona loss or the critical disruptive voltage in a transmission line at a temperature (f) and pressure (b) can be foundout by Using “air density correction factor (δ)” given by
A three-phase, 50 Hz, 400 kV, transmission line is 300 km long. The line inductance is 0.97 mH/km per phase and capacitance is 0.0115 μF/km per phase. Assuming a lossless line, the surge impedance of the line will be
Surge impedance of the line is given by
The resistance and reactance of a short line are equal. At zero regulation the load will be
Zero regulation of a transmission line occurs at a leading power factor when φ = θ.
Since R = X
Shunt reactors are needed
Shunt reactors are used to bring down receiving end voltage during light load or no-load condition to overcome Ferranti effect.
Operating transmission lines close to their maximum power transfer capability will impair