Which of the following is/are the phenomenon associate with overhead transmission line?

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The correct answer is Option D: All of These. Overhead transmission lines exhibit several electromagnetic and electro-static phenomena due to the interaction between conductors, the surrounding air medium, and the supply frequency. The Skin Effect, Proximity Effect, Ferranti Effect, and Corona Effect are all fundamental behaviors that influence line parameters, efficiency, and voltage regulation in high-voltage power transmission systems.

Step-by-Step Solution & Concepts:
Overhead transmission lines exhibit several electromagnetic and electro-static phenomena due to the interaction between conductors, the surrounding air medium, and the supply frequency. The Skin Effect, Proximity Effect, Ferranti Effect, and Corona Effect are all fundamental behaviors that influence line parameters, efficiency, and voltage regulation in high-voltage power transmission systems.

Working Principle: 1. Skin Effect: Non-uniform distribution of AC current towards the surface of the conductor due to internal magnetic flux. 2. Proximity Effect: Distortion of current distribution due to magnetic fields of adjacent conductors. 3. Ferranti Effect: Rise in receiving-end voltage at light loads in long lines due to line capacitance. 4. Corona Effect: Ionization of air around conductors under high electric stress, leading to a visible glow and power loss.

Key Formulas: $R_{ac} = R_{dc} 	imes (1 + \alpha f^2)$ — Skin Effect resistance increase; $V_{r} = V_{s} \sqrt{\frac{Z_{oc}}{Z_{sc}}}$ — Ferranti effect voltage calculation; $P \propto (f + 25) \sqrt{\frac{r}{d}} (V - V_c)^2$ — Corona loss (Peek's formula)

Key Points: Skin effect increases with the square of frequency.; Ferranti effect is most pronounced in long, lightly loaded lines.; Corona loss increases significantly during rainy/humid weather.; Proximity effect becomes significant in high-frequency or bundled conductor arrangements.

Advantages: Understanding these helps in selecting optimal conductor spacing and diameter.; Mitigation techniques improve power transfer efficiency and voltage stability.

Disadvantages: Corona leads to radio interference and audible noise.; Ferranti effect requires shunt reactors for voltage control.

Applications: HVAC Transmission System Design; Power Grid Load Management; Insulation Coordination

Additional Info: The Ferranti effect is primarily observed in long transmission lines exceeding 250km.. Skin effect is independent of the conductor material but depends on frequency and geometric cross-section.

Answer: D is correct — All listed phenomena are inherent electrical and electromagnetic behaviors of high-voltage AC overhead transmission systems.

Exam Tip: Always remember that the Ferranti effect is a capacitive phenomenon (long lines), whereas Corona is a dielectric breakdown phenomenon.

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Option A: Skin Effect & Proximity Effect

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Option B: Ferranti Effect

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Option C: Corona Effect

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