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Corona loss is less when the shape of the conductor is
Circular
Flat
Oval
Independent of shape
Circular
Corona loss is minimized when the electric field intensity at the surface of the conductor is uniform. A circular conductor provides a perfectly uniform distribution of the electric field around its perimeter, which prevents localized regions of high field intensity that trigger air ionization.
Corona loss is minimized when the electric field intensity at the surface of the conductor is uniform. A circular conductor provides a perfectly uniform distribution of the electric field around its perimeter, which prevents localized regions of high field intensity that trigger air ionization.
PcтАЛ=242.2тЛЕ╬┤f+25тАЛтЛЕDrтАЛтАЛтЛЕ(VтИТVcтАЛ)2├Ч10тИТ5 тАФ Empirical formula for Corona Loss in kW/km/phase
gmaxтАЛ=rтЛЕln(D/r)VтАЛ тАФ Maximum electric field intensity at the surface
Corona discharge occurs when the voltage gradient at the conductor surface exceeds the breakdown strength of air (dielectric strength). The gradient is given by g=rln(D/r)VтАЛ. By using a smooth circular conductor, we ensure that the radius r is constant at every point, maintaining a uniform g and minimizing localized ionization concentrations.
Corona loss is directly proportional to the frequency and the square of the overvoltage above the critical disruptive voltage.
Non-circular shapes like flat or oval conductors create sharp edges or regions with smaller radii of curvature, leading to higher local electric field stress.
Higher field stress leads to easier air ionization and increased power loss.
Smoothness of the conductor surface is crucial; surface irregularities (nicks, scratches) act as local points of increased stress.
Lower power loss in transmission lines
Reduced electromagnetic interference (EMI)
Less audible noise and ozone production
High-voltage AC transmission line design
ACSR (Aluminum Conductor Steel Reinforced) conductor selection
Surface condition is as important as the shape; stranded conductors are preferred over flat ribbons to approximate circular geometry.
Option B (Flat) and C (Oval) are poor choices because sharp edges concentrate electric flux lines (Gauss's Law applications), significantly increasing local field intensity (E=╧Г/╧╡0тАЛ).
A is correct тАФ A circular conductor ensures a uniform electric field distribution, which keeps the surface voltage gradient constant and minimizes the likelihood of reaching the ionization threshold.
Always remember that field intensity is inversely proportional to the radius of curvature; sharp corners increase the local gradient and drastically increase corona discharge.