Corona Ring Design of ±800kV DC Composite Insulator Based on Computer Analysis

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Corona Ring Design of 800kV DC Composite Insulator Based on Computer Analysis

Wenxia Sima, Kun Wu, Qing Yang, Caixin Sun

Key Laboratory of High Voltage Engineering and Electrical New Technology, Ministry of Education

College of Electrical Engineering, Chongqing University, Chongqing, China

Abstract: This paper presents a 3D electric-field

calculation model of the 800kV DC transmission line

composite insulators based on finite element method.

With this 3D model, this paper introduces the effect ofthe tower, transmission lines and the parameters of the

corona rings on the potential and e-field distribution

along the composite insulators, and optimizes thecorona ring design in order to control the maximum e-

field along the insulator surface and corona ring surface.

Introduction

The e-field distribution around the ultra high voltage

transmission line insulators, under dry conditions isgoverned by the geometry and the capacitance

distribution along the insulator. In the case of ceramicinsulators formed by a string of discs, which have a

large capacitance, the voltage has a graded distribution

along the insulator string. This phenomenon helps to

avoid high electric field strength at or near the ends of

the string. However, in the case of non-ceramic outdoorinsulators, the permittivity of the material and the shapeof the insulator result in a non-uniform potential

distribution along the insulator, which produces the high

e-field strength in the vicinity of both line and ground

ends[1]-[2].

Corona rings are used to improve the performance ofthe insulator in a multiple of ways. They can reduce

corona and the associated audible noise and radio

interference(RI) and television interference (TVI).

Corona rings can adjust the voltage distribution along

the insulator near the ends of the insulator, thereby

reducing the maximum e-field[3]-[4]. More importantly,

they can eliminate corona degradation of non-ceramic

materials. But there are few standards for corona ring

design up to now. The UHV 800kV transmission line

is to be built in China. The composite insulator is

chosen to be the line insulator of this transmission line.Therefore, it is necessary to optimize the corona designof the UHV composite insulator.

Basis of the 3D E-field Calculation Model

There are many factors that influence the e-field

distribution of the transmission line composite

insulators. The most important factors include:

1. Geometry of composite insulator, both weather-shed systems, fiberglass rod and electrodes.

2. Electrical properties of the silicon-rubber and

fiberglass rod material.3. The dimension and position of the corona rings as

well as the attachment method.

4. The geometry and relative positions of theattachment hardware, for example, conductor

bundles, tower and shielding lines.

Each of these factors needs to be taken into accountwhen determining the e-field distribution of composite

insulators. These factors may have more or less effecton the e-field distribution of composite insulators. Fig.1

gives the section planes of the model used in the

simulation. The factors mentioned above are all taken

into consideration.

Fig. 1 The section planes of the model used in the simulations

With a commercial finite element software, COMSOL

Multiphysics, the calculation of the potential and e-fielddistribution along the composite insulator is to solve the

Possions equations in the whole domain as

= Vr0 (1)

The boundary condition between two dielectrics is

1-4244-0547-5/06/$20.00 2006 IEEE

2006 Annual Report Conference on Electrical Insulation and Dielectric Phenomena

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corona ring are considered, which are the R, r and hshown in Fig.5

Fig.5Corona ring parameters in the model

Fig.6 and Fig.7 present the potential and e-fielddistribution along the composite insulator with and

without corona rings. It can be seen from Fig.6 andFig.7 that the potential and e-field distribution along thecomposite insulator is uniform with the corona rings,

and the maximum fields near both ends are reduced

rapidly.

0 2 4 6 8 100

200

400

600

800

Distance from the energized end fitting [m]

Potential[kV]

With corona rings

Without corona rings

Fig.6 Potential distribution along the composite insulator with and

without corona rings

0 2 4 6 8 100

5

10

15

20

25

Distance from the energized end fitting [m]

Electric

field[kV/cm]

Without corona rings

With corona rings

Fig.7 E-field distribution along the composite insulator with and

without corona rings

The purpose of the corona ring optimization is to reduce

the corona ring size when the maximum e-field on the

insulator surface and the maximum e-field on the corona

ring surface are controlled below 4.5kV/cm (the coronainception e-field strength of the insulator) and 22kV/cm

sepearately (the corona inception e-field strength of the

corona ring).

Fig.7 shows that there are four peak e-field strengths

along the insulator surface. The e-field strength nearenergized end is always larger than that of the ground

end. Therefore, only 3 e-field strengths are considered

in this paper, which are the e-field strength at the joint

of the insulator and the energized electrode, the peak e-field strength along the sheds near the energized end andthe maximum e-field strength on the corona ring of the

energized end.

In order to explore the effect of the three different

parameters, the e-field was computed at different values

of R, r, and h, as shown in Figures 6, 7 and 8. Twoparameters were fixed while the other vary in a practical

range. (O stands for the e-field strength at the

connection of the insulator and the energized electrode, stands for the e-field strength along the sheds near the

energized end and stands for the maximum e-fieldstrength on the corona ring of the energized end)

0.7 0.8 0.9 1 1.1 1.2 1.3 1.40

1

2

3

4

5

6

The corona ring diameter(R) [m]

Electricfie

ld[kV/cm]

Fig.8 The three e-field strengths with variation of R (r=0.4m and

h=0.2m.)

0.2 0.3 0.4 0.50

1

2

3

4

5

6

The semidiameter of the ring tube(r) [m]

Electricfield[kV/cm]

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Fig.9 The three e-field values with variation of r. (R=1m and h=0.2m)

Fig.10 The three e-field strengths with variation of h ( r=0.3m and

R=1m)It can be concluded from Fig.8 to Fig.10 that :

1. the e-field strength at the joint of the insulator andthe energized electrode increases with the increaseof R, decreases with the increase of r, increases at

the beginning and then decreases with the increaseof h.

2. the peak e-field strength along the sheds near the

energized end increases with the increase of R. Ithas nothing to do with the other two parameters, r

and h. When R 0.3m, this e-field strength can be

controlled below 4kV/cm.

3. the maximum e-field strength on the corona ring of

the energized end is mainly associated with r. It

increases with the increase of r, and keep at the

same value with the varition of Rand h. When r

0.05m, this e-field strength can be controlled below

20kV/cm.To be uniform with the practical situation, the

parameters R, r and h, utilizing the results above, the

optimal parameters of the corona ring of the 800kVDC transmission line composite insulators are R=0.3m,

r=0.1m, and h=0.08m. From Fig. 11, it can be found

that the maximum electric field on insulator surface is

4.16kV/cm(Fig.3.7) and that on the surface of the

corona ring is 18.4kV/cm .

Fig.11 E-field distribution along the insulator when R=0.4m

r=0.14m and h=0.2m.

Conclusions

1. A 3D potential and e-field calculation model of

800kV DC transmission line composite insulatorsis established in this paper. The calculation results

of the 3D model is more accurcate than that of the

traditional 2D axial symmetry model because there

are many fators affecting the e-field distribtion.2. The e-field distribtion of the 800kV DC

transmission line composite insulators is non-uniform. In the energized side, 20% of the arc

distance sustains about 50% of the applied voltage.

The corona rings can help the e-field distribution

of the composite insulator to be uniform,especially near the ends of the insulator.

3. The parameters of the corana rings play an

important role in the e-field distribution along theinsulator. With the help of the optimizationcalculation in this paper, the optimized corona ring

could ensure the safety requirement of the

electrical performance.

References:

[1] Chen Shuting, Li Rilong. The application of composite

insulators[J]. Insulators and surge arresters, 2004,199(3):8-10.

[2] W. Sima, F. P. Espino-Cortes, Edward A. Chemey et al.

Optimization of corona ring design for long-rod insulators using

FEM based computational analysis[C]. Conference Record of

the 2004 IEEE International Symposium on Electrical

Insulation. Indianapolis, IN USA, 2004,9:19-22

[3] Weiguo Q, Stephen A.S.Electric field and potential distributions

along dry and clean non- ceramic insulators[J]. IEEE CNF,

2001, 10: 437-440

[4] Mao Fenglin, Wang Xuesong. E-field distribution influence of

corona ring on composite insulator[J]. High voltage technique,

2000, 26(4):29-42

Author address: Wenxia Sima, Key Laboratory ofHigh Voltage Engineering and Electrical New

Technology, Ministry of Education College of Electrical

Engineering, Chongqing University, Chongqing, China.

Email: [email protected]

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Corona Ring Design of ±800kV DC Composite Insulator Based on Computer Analysis

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