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Negative polarity on the line in HVDC scheme helps to reduce
Power Factor
Reactive Power
Line Reactance
Corona loss
Corona loss
Negative polarity in HVDC transmission lines significantly reduces corona discharge and radio interference compared to positive polarity. This is because the critical disruptive voltage for corona inception is higher for a negative conductor than a positive one.
Negative polarity in HVDC transmission lines significantly reduces corona discharge and radio interference compared to positive polarity. This is because the critical disruptive voltage for corona inception is higher for a negative conductor than a positive one.
PcтАЛ=kтЛЕfтЛЕ(VтИТVcтАЛ)2 тАФ Empirical relation for corona power loss
EcтАЛ=E0тАЛ╬┤(1+╬┤rтАЛ0.3тАЛ) тАФ Peek's law for critical disruptive field intensity
Corona discharge is a non-linear phenomenon where ionization of air occurs due to high electric field intensity. Negative polarity conductors produce fewer positive ions that can travel towards the conductor surface. Since positive space charge accumulates more rapidly near the positive conductor (enhancing the local field), negative polarity results in a more stable and less intense corona discharge at the same operating voltage.
Corona loss depends heavily on the conductor surface gradient and air density.
Positive conductors have lower critical inception voltage, leading to higher losses.
Negative polarity allows for smaller conductor spacing in some HVDC designs due to lower corona interference.
Atmospheric conditions like rain or dust significantly increase corona losses.
Reduced radio interference
Lower power loss due to corona discharge
Improved dielectric stability in high voltage environments
Requires careful consideration of ion cloud behavior near converters
May impact vegetation and local electric field profiles
Long distance HVDC transmission lines
Submarine HVDC cables
In DC systems, corona loss is less than in AC systems for the same RMS voltage because the space charge cloud around the conductor reduces the effective potential gradient.
Option A (Power Factor) is irrelevant as HVDC lines do not have reactive power issues like AC lines; Option B (Reactive Power) is controlled by converters; Option C (Line Reactance) is irrelevant for DC steady state.
D is correct тАФ Negative polarity on an HVDC line results in a higher corona inception voltage compared to positive polarity, thereby reducing the associated energy loss.
Always remember that in HVDC systems, the polarity refers to the conductor relative to ground; negative polarity is chosen as the default for transmission to leverage the natural asymmetry in air breakdown characteristics.