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Characteristic impedance of an overhead transmission line is usually in the range of
100 to 200 ╬й
200 to 300 ╬й
0 to 100 ╬й
400 to 500 ╬й
400 to 500 ╬й
The characteristic impedance (ZcтАЛ) of an overhead transmission line is primarily determined by its physical configuration, specifically the ratio of inductance per unit length to capacitance per unit length. For standard overhead lines, this value typically falls within the range of 400 to 500 ╬й.
The characteristic impedance (ZcтАЛ) of an overhead transmission line is primarily determined by its physical configuration, specifically the ratio of inductance per unit length to capacitance per unit length. For standard overhead lines, this value typically falls within the range of 400 to 500 ╬й.
ZcтАЛ=CLтАЛтАЛ тАФ Definition of characteristic impedance in terms of per-unit parameters
ZcтАЛтЙИ60ln(rDтАЛ) тАФ Approximate formula for overhead line impedance where D is spacing and r is radius
The characteristic impedance is defined as ZcтАЛ=CLтАЛтАЛ, where L is the series inductance and C is the shunt capacitance per unit length of the conductor. Since the spacing between overhead lines is large compared to the conductor diameter, the inductance is relatively high while the capacitance is relatively low, resulting in a high characteristic impedance value compared to underground cables.
Characteristic impedance is independent of line length.
Higher conductor spacing increases L and decreases C, thus increasing ZcтАЛ.
Underground cables have much lower ZcтАЛ (typically 30-50 ╬й) due to high shunt capacitance from insulation.
It is a purely resistive value for a lossless line.
Useful for calculating traveling wave reflections.
Essential for surge protection coordination.
Cannot be measured with a simple DC ohmmeter.
Varies slightly with frequency due to skin effect.
Designing surge arresters.
Fault analysis in power systems.
Determining reflection coefficients at junctions.
Surge impedance loading (SIL) is inversely proportional to ZcтАЛ.
Option A, B, and C provide values significantly lower than the standard industry average for aerial lines.
D is correct тАФ The characteristic impedance of overhead transmission lines is consistently in the 400 to 500 ╬й range due to the geometry-dependent values of L and C.
Remember that ZcтАЛ for cables is significantly lower (approx. 50 ╬й) compared to overhead lines due to the high permittivity of the cable dielectric.