Ozone effect can be detected by

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Option D: All of above

Explanation & Concepts:
The phenomenon of corona discharge in overhead transmission lines produces specific sensory effects including a distinct ozone odor, a hissing sound, and a faint bluish luminous glow. These effects are characteristic indicators of the electrical ionization occurring in the air surrounding high-voltage conductors.

Working Principle: When the potential gradient at the surface of a conductor exceeds the dielectric strength of air (approximately 30 kV/cm peak), the air surrounding the conductor becomes ionized. This breakdown process creates ozone ($O_3$) via chemical reaction, causes vibration of air particles resulting in audible noise (hissing), and generates photons leading to visible luminosity.

Key Formulas: $E_{critical} \approx 30 	ext{ kV/cm}$ — Breakdown strength of air at NTP; $P \propto (f+25) \sqrt{\frac{r}{d}} (V-V_c)^2$ — Empirical power loss formula due to corona

Key Points: Corona is accompanied by power loss, radio interference, and chemical ozone formation.; The bluish glow is a result of excitation and de-excitation of air molecules.; Presence of ozone can also be detected by its chemical reactivity on metal surfaces.; Higher atmospheric humidity can influence the intensity of the audible noise.

Advantages: Acts as a natural lightning discharge mechanism to some extent; Serves as a visual warning of high-voltage proximity

Disadvantages: Causes significant power loss on transmission lines; Induces electromagnetic interference (EMI) with radio and communication signals; Ozone production can lead to the corrosion of nearby metallic components

Applications: Ozone generators for water purification; Electrostatic precipitators; Photocopying machines

Additional Info: Corona discharge occurs when the voltage gradient at the conductor surface exceeds the air's disruptive critical voltage.. Option D is correct because all listed phenomena (sound, smell, light) are standard sensory observations of corona discharge.

Answer: D is correct — The phenomena of hissing sound, ozone odor, and faint bluish glow are the three primary detectable signatures of corona discharge occurring on transmission lines.

Exam Tip: Always remember that corona effect increases with the increase in supply frequency and line voltage; bundle conductors are used to reduce the effective gradient and mitigate these effects.

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Option A: Presence of ozone odour

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Option B: Hissing sound

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Option C: Faint Luminous glow of bluish color

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