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An overhead line with surge impedance of 400 ╬й is terminated through a resistance R. A surge traveling over the line will not suffer any deflection at the junction, if the value of R is
100╬й
200╬й
400╬й
800╬й
400╬й
A traveling wave on a transmission line suffers no reflection or deflection when the load impedance connected at the termination is exactly equal to the surge impedance of the line. Under this condition, the line is considered perfectly matched, and the entire incident wave energy is absorbed by the load.
A traveling wave on a transmission line suffers no reflection or deflection when the load impedance connected at the termination is exactly equal to the surge impedance of the line. Under this condition, the line is considered perfectly matched, and the entire incident wave energy is absorbed by the load.
╧Б=R+ZcтАЛRтИТZcтАЛтАЛ тАФ formula for reflection coefficient
ZcтАЛ=CLтАЛтАЛ тАФ expression for surge impedance
The reflection coefficient is defined as ╧Б=R+ZcтАЛRтИТZcтАЛтАЛ, where ZcтАЛ is the surge impedance and R is the load resistance. When R=ZcтАЛ, the numerator becomes zero, resulting in a reflection coefficient of zero, meaning no voltage or current wave is reflected back into the line.
When R=ZcтАЛ, the line is matched and the standing wave ratio (SWR) is 1.
If R>ZcтАЛ, the reflected wave has the same polarity as the incident wave.
If R<ZcтАЛ, the reflected wave has the opposite polarity to the incident wave.
The surge impedance for an overhead line is typically between 400 ╬й and 500 ╬й.
Prevents standing waves which cause heating in conductors
Maximizes power transfer to the terminating load
Practical power systems often have varying loads, making perfect impedance matching difficult
Reflection can be used for fault detection (TDR), which would not work in a perfectly matched system
High-voltage DC (HVDC) transmission termination
Radio frequency (RF) antenna feed lines
Signal integrity in high-speed digital circuits
In power systems, surge impedance is primarily resistive because the resistance and leakage conductance are negligible compared to inductance and capacitance at high frequencies.
Option A (100 ╬й) and Option B (200 ╬й) result in a negative reflection coefficient, causing a dip in the voltage wave.
Option D (800 ╬й) results in a positive reflection coefficient, causing an over-voltage at the junction.
C is correct тАФ A surge traveling over a line will not suffer any reflection at the junction if the terminating resistance R is exactly equal to the surge impedance of the transmission line.
Always verify if the load is pure resistance; if reactive components are present, reflection will occur regardless of the magnitude of R due to phase shifts.