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Charging current in transmission line increases due to corona effect because corona increases
Line current
Line voltage
Power loss in line
Conductor diameter
Conductor diameter
The corona effect creates a virtual increase in the conductor diameter because the ionized air surrounding the conductor becomes conductive ┬╖ This effective increase in the radius reduces the capacitance per unit length between conductors, but the ionization discharge path essentially acts as an extension of the conductor, modifying the electrostatic field distribution.
The corona effect creates a virtual increase in the conductor diameter because the ionized air surrounding the conductor becomes conductive ┬╖ This effective increase in the radius reduces the capacitance per unit length between conductors, but the ionization discharge path essentially acts as an extension of the conductor, modifying the electrostatic field distribution.
IcтАЛ=VтЛЕ╧ЙтЛЕC тАФ Charging current relation
C=ln(D/r)2╧А╧╡0тАЛтАЛ тАФ Capacitance per unit length
When the surface potential gradient exceeds the dielectric strength of air (~30 kV/cm peak), air ionizes ┬╖ This plasma sheath acts as a conducting surface, effectively increasing the physical radius of the conductor to a larger 'corona diameter'. Since the capacitance of a transmission line C=ln(D/r)2╧А╧╡тАЛ, an increase in the effective radius r changes the geometric parameters, which influences the charging current IcтАЛ=V╧ЙC.
Corona discharge is the partial breakdown of air near high-voltage conductors.
Ionization of air creates a luminous discharge and produces an effective virtual diameter larger than the metallic diameter.
The charging current IcтАЛ is directly proportional to line capacitance C.
Increasing conductor diameter (e.g., using bundled conductors) is the primary method to reduce corona loss.
Reduces the surface voltage gradient
Decreases corona power loss
Increases the charging current which may impact reactive power compensation
Introduces radio interference and audible noise
High Voltage (HV) and Extra High Voltage (EHV) transmission line design
ACSR (Aluminum Conductor Steel Reinforced) conductor sizing
The virtual radius depends on the voltage magnitude and atmospheric conditions.
Option B is incorrect because voltage increases corona, but corona itself does not increase the system voltage.
Option C is incorrect because power loss is a result of corona, not the cause of charging current increase.
D is correct тАФ The corona effect creates a virtual enlargement of the conductor radius, which modifies the line capacitance and subsequently the charging current.
In transmission line problems, remember that bundling conductors is the most effective engineering solution to increase the 'effective diameter' and reduce both corona loss and inductive reactance.