When the potential difference between two conductors of a transmission line is raised beyond a certain limit, a point is reached when a violet glow appears around the conductor surface with a hissing noise and ozone gas smell this phenomenon is called Corona.
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Power loss due to the corona effect is called corona power loss in the transmission line. Here we will see an equation and formula to calculate corona loss.
Corona Power Loss
When a corona occurs it causes power loss in the transmission line. Which reduced the efficiency of the transmission line.
Can be calculated using an equation known as Peek’s Formula.
Vph= Phase voltage in Kv
Vd0= Critical Disruptive Voltage in Kv
f= Supply Frequency in Hz
d= Distance between conductors
𝛿= air density correction factor.
r =radius of the conductor
Peek’s formula is applicable to calculate visual corona. This formula gives inaccurate results when power losses are low and Vph/Vdo is less than 1.8 hence Peterson’s formula holds good in some condition.
The Corona power loss is small and varies from 1 to 2 kW/Km for a 500kv line and power losses increase with the bad weather conditions.
Corona loss has several high-frequency harmonics that cause radio interference with neighboring communication lines.
Factor Affecting
Different factors affecting corona power loss in the transmission line as:
- Effect of Frequency:- From corona power loss equation Pc∝(f+25), We can see that corona loss increase with the increase in supply frequency because it is directly proportional to supply frequency. Thus corona loss for the HVDC line is less than the EHV ac line. It is less for the monopolar line.
- Effect of System Voltage: Corona power loss happens due to the high electric field around the conductor surface. Therefore higher the potential difference between the conductor, the higher the electric field, and the higher power loss due to corona. The line voltage greatly affects the corona. If it is low, there is no charge in the air surrounding the conductors and hence no corona is formed. However, if the line voltage has such a value that electrostatic stress developed at the conductor surface make the air around the conductor conducting then corona is formed
- Effect of conductivity of Air: Higher the conductivity of airs means more numbers of the ions around the conductor surface. Hence higher power losses due to corona. Due to this reason in the rainy season atmosphere become more conducting and the result of this corona loss increases.
- Effect of Density of Air: From the equation we can see that δ(air density correction factor) is in the denominator of the formula, hence a decrease in density of air increases corona power losses. Losses are more in the hilly area than the plane area.
- Effect of conductor radius: with an increase in conductor radius field intensity decrease near-surface area thus power loss decreases.
