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In context of corona with smooth and polished conductors
There will be no current glow
Glow will be uniform along the length of the conductor
There will be minimum power loss
Hissing sound will be more intense
Glow will be uniform along the length of the conductor
Corona discharge is a phenomenon of ionization of air surrounding a conductor when the surface electric field intensity exceeds the dielectric strength of air. When a conductor is smooth and polished, the electric field intensity distribution is uniform along its entire surface, leading to a consistent and uniform glow.
Corona discharge is a phenomenon of ionization of air surrounding a conductor when the surface electric field intensity exceeds the dielectric strength of air. When a conductor is smooth and polished, the electric field intensity distribution is uniform along its entire surface, leading to a consistent and uniform glow.
EmaxтАЛ=rln(rDтАЛ)VтАЛ тАФ Electric field intensity at the surface of a cylindrical conductor
PlossтАЛтИЭ(f+25)DrтАЛтАЛ(VтИТVcтАЛ)2 тАФ Peek's formula for corona power loss
The surface electric field intensity E is inversely proportional to the radius of curvature r. For a smooth, uniform cylindrical conductor, E=rln(D/r)VтАЛ is constant along the longitudinal axis. In contrast, surface irregularities (scratches or dust) create local regions of high field intensity, resulting in non-uniform or 'point-source' corona discharge.
Corona occurs when surface potential gradient exceeds the breakdown strength of air (approx 30 kV/cm peak).
Surface smoothness directly dictates the uniformity of the ionization layer.
Polished conductors minimize the formation of local 'streamers' which cause audible noise and interference.
Reduced electromagnetic interference (EMI) with communication lines
Lower power loss compared to weathered or rough conductors
Higher initial cost due to manufacturing requirements
Surface can be damaged by environmental exposure over time
EHV (Extra High Voltage) transmission line design
High-precision laboratory high-voltage equipment
For rough conductors, the irregularity factor m (where 0<m<1) is introduced, reducing the critical disruptive voltage VcтАЛ.
Option A is incorrect because corona occurs if voltage exceeds the critical value. Option C is incorrect as smooth conductors minimize, but do not eliminate, loss. Option D is incorrect as rough surfaces produce more intense/erratic hissing.
B is correct тАФ A smooth and polished conductor ensures a uniform electric field distribution along its surface, resulting in an even, uniform corona glow.
Always remember that Peek's formula for corona loss incorporates a surface irregularity factor m; for smooth polished wires, m=1 (the theoretical maximum), while for weathered wires, m drops significantly.