📘 What is Skin Effect in Power System?
In electrical engineering, Skin Effect refers to the tendency of alternating current (AC) to concentrate near the surface of a conductor as the frequency increases. This phenomenon reduces the effective cross-sectional area of the conductor, thereby increasing the resistance.
📌 Why Does Skin Effect Occur?
When AC flows through a conductor, it creates a changing magnetic field around it. This varying magnetic field induces eddy currents that oppose the main current flow inside the conductor, forcing the current to move towards the surface.
📐 Skin Depth (δ) Formula:
δ = Skin depth
ρ = Resistivity of the material (Ω·m)
f= Frequency (Hz)
μ = Permeability of the conductor (H/m)
📝 Skin depth decreases with higher frequency and higher permeability.
🔍 Factors Affecting Skin Effect:
| Factor | Effect on Skin Effect |
|---|---|
| Frequency ↑ | Skin effect ↑ |
| Conductor Diameter ↑ | Skin effect ↑ |
| Resistivity ↑ | Skin effect ↓ |
| Permeability ↑ | Skin effect ↑ |
📊 Importance in Power Systems:
- In AC transmission, skin effect increases conductor resistance, causing higher losses.
- Not significant at low frequencies (e.g., 50 Hz) for small diameter conductors.
- Critical in high-frequency applications and thick conductors (like busbars).
✅ Key Points - Skin Effect
- Skin effect occurs in AC only.
- It is negligible in DC circuits.
- It increases effective resistance and power loss.
- It depends on frequency, diameter, resistivity, and permeability.
📝 Previous Year Questions (PYQs)
📌 SSC JE Electrical – 2019
Q. Skin effect in a conductor causes:
A. Increase in resistance
B. Decrease in resistance
C. No change in resistance
D. Increase in capacitance
🟢 Correct Answer: A
📌 RRB JE CBT-2 – 2018
Q. Skin effect is more pronounced in:
A. DC circuits
B. AC circuits at low frequency
C. AC circuits at high frequency
D. None of these
🟢 Correct Answer: C
📌 UPPCL JE – 2021
Q. Skin effect in conductors:
A. Decreases with increase in frequency
B. Increases with increase in frequency
C. Is independent of frequency
D. Occurs only in DC
🟢 Correct Answer: B
📌 UPPSC AE – 2020
Q. Skin effect is caused due to:
A. Heating of conductor
B. Induced eddy currents
C. Capacitive effect
D. Magnetic shielding
🟢 Correct Answer: B
🎯 Exam Tip:
Remember, skin effect is always associated with AC current, and it increases with frequency. In practical systems (50 Hz), skin effect is not significant for small wires but matters for high-voltage cables and busbars.
🔍 FAQs on Skin Effect in Power Systems
Q1. Is skin effect present in DC circuits?
🔹 No, it occurs only in AC circuits due to alternating magnetic fields.
Q2. Why is skin effect important in power systems?
🔹 It affects current distribution and increases power loss at higher frequencies.
Q3. How to reduce skin effect?
🔹 Use stranded conductors (e.g., Litz wire), reduce frequency, or use conductors with lower permeability.
📢 Conclusion
Understanding Skin Effect is crucial for clearing JE and AE level exams. Focus on the concept, influencing factors, and past year questions for scoring well in the Electrical Machines and Power System section.