Reflection coefficient of the voltage wave in overhead line is | Electrical MCQ | Examoogle

Back to Practice Questions

ElectricalPower System

Prev Next

Reflection coefficient of the voltage wave in overhead line is

$R_{0} R_{0} - R_{L}$

$R_{L} R_{0} - R_{L}$

$R_{L} - R_{0} R_{0} + R_{L}$

$R_{0} + R_{L} R_{0} - R_{L}$

Correct Answer

⚙️ TE • Technical Concept & PrincipleElectricalPower System

Option C

$R_{L} - R_{0} R_{0} + R_{L}$

Quick Summary:

The reflection coefficient ( $\rho$ ) of a voltage wave on a transmission line is defined as the ratio of the reflected voltage wave to the incident voltage wave. When a traveling wave encounters a junction with a load impedance ( $R_L$ ) different from the surge impedance ( $R_0$ ) of the line, part of the wave is reflected to satisfy boundary conditions.

⚙️TETechnical SolutionConcept & Principle

💡 Explanation

🔢 Key Formulas

$\rho = \frac{R_L - R_0}{R_L + R_0}$ — Voltage reflection coefficient formula

$\tau = \frac{2R_L}{R_L + R_0}$ — Refraction (transmission) coefficient formula

⚙️ Working Principle

When a voltage wave traveling on a line with surge impedance $R_0$ reaches a load $R_L$ , continuity of voltage and current at the junction must be maintained. By applying Kirchhoff's laws at the interface, the reflected voltage $V_r$ is determined by the mismatch between $R_0$ and $R_L$ . If $R_L > R_0$ , the reflection is positive; if $R_L < R_0$ , it is negative; and if $R_L = R_0$ , no reflection occurs.

📌 Key Points

▸
If $R_L = \infty$ (Open Circuit), $\rho = +1$ (Full reflection in phase).
▸
If $R_L = 0$ (Short Circuit), $\rho = -1$ (Full reflection with phase reversal).
▸
If $R_L = R_0$ (Matched condition), $\rho = 0$ (No reflection).
▸
Reflection coefficient is dimensionless.

✅ Advantages

▸
Allows prediction of transient overvoltages at busbars.
▸
Used in designing protection schemes for power system transients.

❌ Disadvantages / Limitations

▸
Assumes lossless line model for simplicity; actual lines have frequency-dependent losses.
▸
Requires accurate knowledge of surge impedance values.

🛠️ Applications / Uses

▸
Surge protection of power transformers.
▸
Analysis of switching surges in overhead lines.
▸
Communication signal integrity analysis.

📄 Additional Information

▸
The surge impedance $R_0$ for an overhead line is typically between 400 $\Omega$ and 500 $\Omega$ .
▸
Option A and B are incorrect as they represent non-standard ratios of impedances which do not satisfy boundary conditions.

📊 Diagram / Illustration

✅

C is correct — The reflection coefficient is the normalized difference between the load impedance and the surge impedance.

Core Concepts Used

Click any tag to open in AI Tutor

Traveling Wave Theory Surge Impedance Boundary Conditions in Transmission Lines

💡 EXAM TIP

Remember: A short-circuited line always results in a reflected wave with inverted polarity ( $\rho = -1$ ), which is a critical concept for understanding ground faults.

Discussion (0)

Loading discussion...

Prev Next

Correct Answer

Related Questions

Discussion (0)