📘 Corona in Transmission Lines
Corona is the ionization of air surrounding conductors in high voltage transmission lines. It causes power loss and noise.
🔹 1️⃣ What is Corona?
When electric field around conductor exceeds critical value: ✔ Air ionizes ✔ Violet glow appears ✔ Hissing noise ✔ Power loss occurs🔹 2️⃣ Critical Disruptive Voltage
Vd = 21.1 m0 δ r ln(D/r) (kV per phase)
Where: m0 = surface irregularity factor δ = air density factor r = conductor radius (cm) D = spacing between conductors (cm) Very important formula for GATE.🔹 3️⃣ Factors Affecting Corona
- Line voltage (Higher voltage → more corona)
- Conductor spacing
- Conductor radius
- Weather conditions
- Surface roughness
🔹 4️⃣ Corona Loss (Peek's Formula)
Pc = 242.4 (f + 25) / δ × √(r/D) (V − Vd)² × 10⁻⁵ kW/km/phase
(Important conceptual formula)🔹 5️⃣ Advantages of Corona
- Reduces surge effects
- Limits overvoltage
🔹 6️⃣ Disadvantages
- Power loss
- Radio interference
- Audible noise
- Ozone formation
🔹 7️⃣ Example Problem
Given: r = 1 cm D = 100 cm m0 = 0.85 δ = 1 Vd = 21.1 × 0.85 × 1 × 1 × ln(100/1) ln(100) ≈ 4.6 Vd ≈ 21.1 × 0.85 × 4.6 ≈ 82.5 kV per phaseCritical Disruptive Voltage ≈ 82.5 kV
🎯 GATE Focus
- Remember Vd formula
- Effect of conductor radius
- Corona more in bad weather
- Mostly theory-based questions
Corona = Ionization Loss in High Voltage Lines
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