Which of the following statements regarding corona are true? 1. It causes radio interference 2. It attenuates lightning surges 3. It amplifies switching surges 4. It causes power loss 5. It is more prevalent in the middle conductor of a transmission line employing a flat conductor configuration.

Option C: 1, 2, 4 and 5 Explanation & Concepts: Corona is the partial discharge phenomenon occurring when the voltage gradient at the conductor surface exceeds the dielectric strength of the surrounding air. It leads to energy dissipation, electromagnetic interference, and chemical ozone formation, while simultaneously acting as a dampening mechanism for high-frequency transients. Working Principle: When the electric field strength at the conductor surface exceeds the breakdown strength of air (approx. 30 kV/cm peak), air molecules ionize. This ionization creates a luminous glow and conductive path near the conductor, which increases the effective diameter of the conductor. Because this phenomenon is non-linear and consumes energy, it effectively attenuates the peak of incoming surge waves (lightning surges) while producing unwanted radio frequency noise and power losses ($P_c \propto (f+25) \sqrt{\frac{r}{d}}(V-V_c)^2$). Key Formulas: $V_c = g_0 \delta m_0 r \ln(\frac{D}{r})$ — Disruptive critical voltage (rms); $P_c \propto (f+25) \sqrt{\frac{r}{D}}(V-V_c)^2$ — Empirical power loss formula Key Points: Corona produces ozone which is corrosive to conductor materials.; The middle conductor in a flat configuration has higher potential stress due to lack of symmetry, making it more prone to corona.; Corona provides an attenuation effect on traveling waves by absorbing surge energy.; Corona does NOT amplify switching surges; rather, it typically dissipates/limits their amplitude. Advantages: Reduces the steepness of incoming lightning surge wavefronts.; Acts as a natural surge protection mechanism by absorbing high-frequency components. Disadvantages: Causes significant I^2R equivalent power loss.; Induces radio and television interference due to high-frequency harmonic generation.; Produces ozone, causing corrosion of overhead line conductors. Applications: Used in the design of Bundle Conductors to increase effective radius and reduce corona.; Considered during the selection of ACSR conductor sizes to maintain surface gradients below critical limits. Additional Info: Statement 3 is incorrect because corona acts as a damping element that limits, not amplifies, the peak magnitude of switching surges.. In a flat configuration, the middle conductor experiences a different electrostatic field compared to the outer conductors, leading to higher stress. Answer: C is correct — Corona causes power loss, radio interference, and lightning surge attenuation, and it is most pronounced on the middle conductor of a flat transmission configuration. Exam Tip: Always remember that corona is a self-limiting phenomenon; it dissipates energy, which is why it attenuates rather than amplifies voltage surges.

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Which of the following statements regarding corona are true?

It causes radio interference
It attenuates lightning surges
It amplifies switching surges
It causes power loss
It is more prevalent in the middle conductor of a transmission line employing a flat conductor configuration.

1, 3 and 5

2, 3 and 4

1, 2, 4 and 5

2, 3, 4 and 5

Correct Answer

⚙️ TE • Technical Concept & PrincipleElectricalPower System

Option C

1, 2, 4 and 5

Quick Summary:

Corona is the partial discharge phenomenon occurring when the voltage gradient at the conductor surface exceeds the dielectric strength of the surrounding air. It leads to energy dissipation, electromagnetic interference, and chemical ozone formation, while simultaneously acting as a dampening mechanism for high-frequency transients.

⚙️TETechnical SolutionConcept & Principle

💡 Explanation

🔢 Key Formulas

$V_c = g_0 \delta m_0 r \ln(\frac{D}{r})$ — Disruptive critical voltage (rms)

$P_c \propto (f+25) \sqrt{\frac{r}{D}}(V-V_c)^2$ — Empirical power loss formula

⚙️ Working Principle

When the electric field strength at the conductor surface exceeds the breakdown strength of air (approx. 30 kV/cm peak), air molecules ionize. This ionization creates a luminous glow and conductive path near the conductor, which increases the effective diameter of the conductor. Because this phenomenon is non-linear and consumes energy, it effectively attenuates the peak of incoming surge waves (lightning surges) while producing unwanted radio frequency noise and power losses ( $P_c \propto (f+25) \sqrt{\frac{r}{d}}(V-V_c)^2$ ).

📌 Key Points

▸
Corona produces ozone which is corrosive to conductor materials.
▸
The middle conductor in a flat configuration has higher potential stress due to lack of symmetry, making it more prone to corona.
▸
Corona provides an attenuation effect on traveling waves by absorbing surge energy.
▸
Corona does NOT amplify switching surges; rather, it typically dissipates/limits their amplitude.

✅ Advantages

▸
Reduces the steepness of incoming lightning surge wavefronts.
▸
Acts as a natural surge protection mechanism by absorbing high-frequency components.

❌ Disadvantages / Limitations

▸
Causes significant $I^2R$ equivalent power loss.
▸
Induces radio and television interference due to high-frequency harmonic generation.
▸
Produces ozone, causing corrosion of overhead line conductors.

🛠️ Applications / Uses

▸
Used in the design of Bundle Conductors to increase effective radius and reduce corona.
▸
Considered during the selection of ACSR conductor sizes to maintain surface gradients below critical limits.

📄 Additional Information

▸
Statement 3 is incorrect because corona acts as a damping element that limits, not amplifies, the peak magnitude of switching surges.
▸
In a flat configuration, the middle conductor experiences a different electrostatic field compared to the outer conductors, leading to higher stress.

📊 Diagram / Illustration

✅

C is correct — Corona causes power loss, radio interference, and lightning surge attenuation, and it is most pronounced on the middle conductor of a flat transmission configuration.

Core Concepts Used

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Ionization of Air Disruptive Critical Voltage Transient Attenuation Electromagnetic Interference

💡 EXAM TIP

Always remember that corona is a self-limiting phenomenon; it dissipates energy, which is why it attenuates rather than amplifies voltage surges.

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