Consider the following statements 1. By using bundle conductors in overhead line, corona loss is reduced 2. By using bundle conductors, inductance of transmission line increases and capacitance reduces 3. Corona loss causes interference in adjoining communication lines Which of the statements are correct?

Option C: 1 and 3 Explanation & Concepts: Bundle conductors effectively increase the GMR (Geometric Mean Radius) of the conductor bundle, which reduces the surface voltage gradient and consequently minimizes corona loss. Statement 2 is incorrect because increasing the bundle radius decreases inductance ($L$) and increases capacitance ($C$), whereas the statement claims the opposite. Working Principle: Corona is a discharge caused by the ionization of air when the surface potential gradient exceeds the breakdown strength of air (approx 30 kV/cm). By using multiple conductors per phase (bundling), the effective conductor diameter increases, which lowers the maximum electric field stress at the conductor surface, thus suppressing corona formation. This increase in effective radius results in lower $L = 2 \times 10^{-7} \ln(\frac{GMD}{GMR})$ and higher $C = \frac{2\pi \epsilon}{\ln(\frac{GMD}{r_{eq}})}$. Key Formulas: $L = 2 \times 10^{-7} \ln(\frac{GMD}{GMR})$ — Inductance per unit length; $C = \frac{2\pi \epsilon}{\ln(\frac{GMD}{r_{eq}})}$ — Capacitance per unit length Key Points: Bundling increases the effective radius of the conductor.; Corona loss occurs when surface stress exceeds air breakdown strength.; Corona generates high-frequency components causing EMI (Electromagnetic Interference).; Bundle conductors are standard for EHV/UHV lines (400kV and above). Advantages: Reduced corona loss and radio interference; Reduced line inductance, increasing power transfer capability; Increased line capacitance, improving voltage profile Disadvantages: Increased wind loading due to larger surface area; Complex hardware/tower design; Higher initial capital cost Applications: Extra High Voltage (EHV) transmission lines; Ultra High Voltage (UHV) transmission lines Additional Info: Statement 2 is false because $L$ is inversely proportional to the logarithm of the radius; increasing the bundle spacing/GMR decreases $L$.. Corona loss leads to power dissipation and generation of ozone and nitrogen oxides. Answer: C is correct — Statement 1 and 3 are technically accurate, while statement 2 is false as bundling decreases inductance and increases capacitance. Exam Tip: Always remember the relationship: increasing conductor radius reduces $L$ and increases $C$. This is a classic concept tested in both Power Systems and Electromagnetic Field Theory.

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Consider the following statements

By using bundle conductors in overhead line, corona loss is reduced
By using bundle conductors, inductance of transmission line increases and capacitance reduces

3. Corona loss causes interference in adjoining communication lines

Which of the statements are correct?

1 and 2

2 and 3

1 and 3

1, 2 and 3

Correct Answer

⚙️ TE • Technical Concept & PrincipleElectricalPower System

Option C

1 and 3

Quick Summary:

Bundle conductors effectively increase the GMR (Geometric Mean Radius) of the conductor bundle, which reduces the surface voltage gradient and consequently minimizes corona loss. Statement 2 is incorrect because increasing the bundle radius decreases inductance ( $L$ ) and increases capacitance ( $C$ ), whereas the statement claims the opposite.

⚙️TETechnical SolutionConcept & Principle

💡 Explanation

🔢 Key Formulas

$L = 2 \times 10^{-7} \ln(\frac{GMD}{GMR})$ — Inductance per unit length

$C = \frac{2\pi \epsilon}{\ln(\frac{GMD}{r_{eq}})}$ — Capacitance per unit length

⚙️ Working Principle

Corona is a discharge caused by the ionization of air when the surface potential gradient exceeds the breakdown strength of air (approx 30 kV/cm). By using multiple conductors per phase (bundling), the effective conductor diameter increases, which lowers the maximum electric field stress at the conductor surface, thus suppressing corona formation. This increase in effective radius results in lower $L = 2 \times 10^{-7} \ln(\frac{GMD}{GMR})$ and higher $C = \frac{2\pi \epsilon}{\ln(\frac{GMD}{r_{eq}})}$ .

📌 Key Points

▸
Bundling increases the effective radius of the conductor.
▸
Corona loss occurs when surface stress exceeds air breakdown strength.
▸
Corona generates high-frequency components causing EMI (Electromagnetic Interference).
▸
Bundle conductors are standard for EHV/UHV lines (400kV and above).

✅ Advantages

▸
Reduced corona loss and radio interference
▸
Reduced line inductance, increasing power transfer capability
▸
Increased line capacitance, improving voltage profile

❌ Disadvantages / Limitations

▸
Increased wind loading due to larger surface area
▸
Complex hardware/tower design
▸
Higher initial capital cost

🛠️ Applications / Uses

▸
Extra High Voltage (EHV) transmission lines
▸
Ultra High Voltage (UHV) transmission lines

📄 Additional Information

▸
Statement 2 is false because $L$ is inversely proportional to the logarithm of the radius; increasing the bundle spacing/GMR decreases $L$ .
▸
Corona loss leads to power dissipation and generation of ozone and nitrogen oxides.

📊 Diagram / Illustration

✅

C is correct — Statement 1 and 3 are technically accurate, while statement 2 is false as bundling decreases inductance and increases capacitance.

Core Concepts Used

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Corona Discharge GMR (Geometric Mean Radius) Transmission Line Parameters

💡 EXAM TIP

Always remember the relationship: increasing conductor radius reduces $L$ and increases $C$ . This is a classic concept tested in both Power Systems and Electromagnetic Field Theory.

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