Corona loss increases with

Question

Examoogle · Accepted Answer

Option B: Increase in supply frequency but reduction in conductor size

Explanation & Concepts:
Corona loss is directly proportional to the supply frequency and inversely related to the conductor radius. An increase in frequency increases the number of times the ionization process occurs per second, while a reduction in conductor size increases the surface electric stress, leading to higher ionization rates.

Working Principle: Corona occurs when the electric field intensity at the surface of a conductor exceeds the dielectric strength of air (approx. 30 kV/cm peak). The Peek's formula shows that the loss ($P_c$) is given by $P_c \propto (f + 25) \sqrt{\frac{r}{d}} (V - V_c)^2$. Because the frequency ($f$) term is additive and the radius ($r$) appears in the square root of the denominator, increasing $f$ or decreasing $r$ results in higher power dissipation due to corona discharge.

Key Formulas: $P_c \propto (f + 25) \sqrt{\frac{r}{d}} (V - V_c)^2$ — Peek's formula for corona loss calculation; $E_g = \frac{V}{r \ln(D/r)}$ — Electric field intensity at conductor surface

Key Points: Corona loss increases linearly with $(f+25)$.; Smaller conductor radius increases the surface electric field intensity.; Higher frequency results in more frequent ionization cycles per second.; Corona discharge is more prominent in extra high voltage (EHV) lines.

Advantages: Reduces potential gradient by using bundled conductors.; Helps in identifying faulty insulation locations.

Disadvantages: Causes significant power loss.; Generates ozone gas leading to corrosion.; Interferes with telecommunication lines (radio interference).

Applications: Transmission line design optimization.; Selection of conductor diameter for EHV lines.

Additional Info: Corona loss is also significantly affected by atmospheric conditions such as rain, fog, and dust, which reduce the disruptive critical voltage.. Option A is incorrect because increasing conductor size (radius) actually decreases the electric stress at the surface, thereby reducing corona loss.

Answer: B is correct — Corona loss increases with frequency due to higher ionization frequency and with smaller conductor sizes due to increased surface electric stress.

Exam Tip: Always remember that bundling conductors is a standard technique to increase the effective radius, thereby reducing surface stress and corona loss.

Examoogle · Answer

Option A: Increase in supply frequency and conductor size

Examoogle · Answer

Option C: Decrease in supply frequency and conductor size

Examoogle · Answer

Option D: Decrease in supply frequency but increase in conductor size

Correct Answer

Discussion (0)

Correct Answer

Related Questions

Discussion (0)