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Inductance of overhead line in comparison to that of a cable of same capacity is
Larger
Smaller
Of the same order
None of above
Larger
The inductance of an overhead transmission line is significantly larger than that of an underground cable for the same capacity ┬╖ This is primarily because overhead lines have a much larger spacing between conductors compared to the tightly packed configuration of cables.
The inductance of an overhead transmission line is significantly larger than that of an underground cable for the same capacity ┬╖ This is primarily because overhead lines have a much larger spacing between conductors compared to the tightly packed configuration of cables.
L=2├Ч10тИТ7ln(rтА▓DтАЛ)┬аH/m тАФ Inductance of a single phase transmission line
C=ln(D/r)2╧А╧╡тАЛ┬аF/m тАФ Capacitance (notably higher in cables due to small D)
Inductance per unit length is determined by the spacing between conductors and the radius of the conductor ┬╖ In cables, conductors are placed very close to each other with insulation in between, which significantly reduces the magnetic flux linkage and thus the inductance ┬╖ Overhead lines have large inter-conductor distances, which increases the flux linkage path, resulting in higher inductance per unit length.
Overhead lines have larger conductor spacing (D) compared to cables.
Higher spacing leads to higher inductance (L) according to the natural log function in the inductance formula.
Underground cables have high capacitance (C) due to their physical construction and closeness of conductors to the sheath/ground.
Overhead: Lower capacitance, reducing charging current requirements.
Cable: No interference with communication lines, aesthetically superior.
Overhead: Prone to lightning strikes and atmospheric interference.
Cable: Higher manufacturing and installation costs, restricted current capacity due to heat dissipation.
Overhead: Long-distance bulk power transmission.
Cable: Urban distribution, high-voltage subsea or subterranean connections.
| Feature | Overhead Line | Underground Cable |
|---|---|---|
Conductor Spacing (D) | Large | Small |
Inductance (L) | High | Low |
Capacitance (C) | Low | High |
Cables utilize screen/sheath layers, which keep the electrostatic field confined, leading to much higher capacitance compared to overhead lines.
Because L is proportional to ln(D/r), the larger physical dimensions of overhead line configurations directly dictate a larger inductance value.
A is correct тАФ The inductance of an overhead line is larger than that of a cable because the conductors in an overhead line are separated by a much larger distance compared to the closely packed conductors in a cable.
Remember that inductance and capacitance follow opposite trends in transmission lines versus cables: cables have high capacitance and low inductance, whereas overhead lines have high inductance and low capacitance.