Seminar

Cyprus International University 1

CORONA PHENOMENON AND CORONA LOSS CALCULATION IN TRANSMISSION LINES

ALIYU ALIYU

Outline

Introduction

How corona discharge effect occur

Factors affectıng corona discharge effect

Advantages and disadvantages of corona

Methods of reducing corona discharge

Calculation on power loss due to corona discharge

Conclusion


Introduction What is corona?

Where do we find corona ?

At what voltage level do corona occur ?


Corona discharge effect

Ionization of air

Produces sound

Produces bluish glow on the conductor

Produces ozone gas

Reduces efficiency


How corona discharge occur


Factors affecting corona discharge effect

Conductor

Line Voltage

Atmosphere

Spacing between the Conductors


Advatages of corona

Corona reduces the effects of transientsproduced by surges.

Due to corona formation, the airsurrounding the conductor becomesconducting and hence virtual diameter ofthe conductor is increased. The increaseddiameter reduces the electro-static stressesbetween the conductors.

Removal of unwanted volatile organics,such as chemical pesticides, solvents, orchemical weapons agents, from theatmosphere.


Disadvanges of corona

Ozone is produced by corona and may cause corrosion of the conductor due to chemical action.

Corona is accompanied by a loss of energy. This affects the transmission efficiency of the line.

The current drawn by the line due to corona is non-sinusoidal and hence non-sinusoidal Voltage drop occurs in the line. This may cause inductive interference with neighboring Communication lines.


Methods of reducing corona

By increasing the spacing between the conductors

By increasing the diameter of the conductor

By using Bundled Conductors


Power loss due to corona

P = 𝟐𝟒𝟐.𝟐

𝜹𝑭 + 𝟐𝟓

𝒓

𝒅𝑽 − 𝑽𝒄

𝟐 × 𝟏𝟎−𝟓 KW/Km/Phase

Where

P = corona loss

𝛿= air density factor

𝐹= frequency

r= conductor radius in cm

d= conductor spacing in cm

V= supply voltage per phase

𝑉𝑐= disruptive critical voltage


Power loss due to corona

Disruptive critical voltage is given as

𝑽𝒄= 𝒎𝟎×𝒈𝟎𝛿r𝐥𝐧𝒅

𝒓KV

Where

𝑚0= irregularity factor

𝑔0=dielectric strength of air

𝛿=air density

t= temperature

Where

𝛿=3.92×𝑏

273+𝑡


Question

A three phase 220KV transmission line consist of 1.5cm radius conductor spaced 2m apart in equilateral triangle formation. If the temperature is 40 degree Celsius and the atmospheric pressure is 76cm. Calculate the corona loss per KM of the line. Take 𝑚0= 0.85 and 𝑔0=21.2KV per cm.


Summary

In summary, to reduce corona loss in transmission lines the critical breakdown voltage should be increased by adding the diameter of the conductors, increasing the spacing between the conductors and using bundled conductors instead of the normal conductor.

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References

Y. Nie, Y. Wen, C. Liu, X. Yin, M. Mao, Z. Tian, C. Peng, and J. Yin,“Thestudy of the corona current characteristics of transmission lineinsulators,” inProc. Int. Elect. Insulating Materials Conf., 2001.

Y. Cheng, C. Li & X. Huang, Study of corona discharge pattern on high voltage transmission line for inspecting faulty proceleın insuator.

Power System Analysis, By VK Mehata, AK Mehta.

Li Chengrong, S. Qian, C. Yangchun, H. Xingquan, and S. Wei, “Thesensitivity of identifying faulty insulator strings by detecting insulatorcorona current,” in Proc. Int. Electrical Insulating Materials Conf.,1998.


Thank You


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