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The Surge impedance of 400 km long overhead transmission line is 400 ╬й.┬аFor 200 km length of the same line the Surge impedance will be
200╬й
800╬й
400╬й
100╬й
400╬й
The Surge Impedance (also known as Characteristic Impedance) of a transmission line is an inherent property determined solely by the line's geometry and physical parameters, specifically the distributed inductance (L) and capacitance (C). Since these parameters are defined per unit length, the ratio remains constant regardless of the total line length.
The Surge Impedance (also known as Characteristic Impedance) of a transmission line is an inherent property determined solely by the line's geometry and physical parameters, specifically the distributed inductance (L) and capacitance (C). Since these parameters are defined per unit length, the ratio remains constant regardless of the total line length.
ZcтАЛ=CLтАЛтАЛ тАФ Surge impedance defined by distributed parameters
ZcтАЛ=yzтАЛтАЛ=G+j╧ЙCR+j╧ЙLтАЛтАЛтЙИCLтАЛтАЛ тАФ General expression for lossless line
The Surge Impedance ZcтАЛ is calculated as the square root of the ratio of the series impedance per unit length (z) to the shunt admittance per unit length (y). Because both inductance and capacitance scale linearly with length, the length cancels out in the ratio C/lL/lтАЛтАЛ=CLтАЛтАЛ. Consequently, doubling or halving the line length does not change the characteristic impedance.
Surge impedance is independent of the line length.
For typical overhead lines, ZcтАЛ ranges between 350╬й to 450╬й.
It is a purely resistive value for a lossless transmission line.
Simplifies transient analysis in power systems.
Allows for consistent termination design regardless of line distance.
Does not account for frequency-dependent losses (resistance and leakage conductance).
Calculation of traveling wave behavior during switching surges.
Determination of Natural Load (SIL) of a transmission line.
The Surge Impedance Loading (SIL) is defined as P=ZcтАЛV2тАЛ. While SIL is independent of length, the actual power transfer capability of a long line is limited by stability, not just SIL.
Option B (800 ╬й) and A (200 ╬й) are common distractors assuming a linear dependency on length, which is incorrect.
C is correct тАФ The surge impedance is an intrinsic property of the line material and geometry, making it independent of the transmission line length.
Remember that while surge impedance is independent of length, Surge Impedance Loading (SIL) is a power level, and total line voltage drop is highly dependent on length.