Electricalfield Distribution 380 Kv

8/17/2019 Electricalfield Distribution 380 Kv

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Study on Potential and Electrical Field

Distribution

along

380

kV

V‐

Insulator

String

Using Boundary Element Method

Abstract

Computation of potential and electrical field strength along the insulatorstrings is an important aspect for their designs. This study is concerned withthe voltage and the electric field distribution along 380 kV V-type suspensionstrings composed of cap and pin type porcelain and glass insulators. It’s one

of the main structure utilized in 380 kV Turkish National Power Transmission

Systems. Boundary Element Method based software, COULOMB 3D,was used three dimensional modeling and simulations. The effects of coronaring, transmission tower, insulator type and angle between V-strings onpotential and electric field distribution were analyzed. Experimental studieswere conducted at Fuat Kulunk High Voltage Laboratory of IstanbulTechnical University.

Index Terms

Boundary Element Method, Corona Ring Electric Field, Insulator String,

Potential Distribution.

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Study on Potential and Electrical FieldDistribution along 380 kV V-Insulator String

Using Boundary Element MethodS. Ilhan, A. Ozdemir

Abstract—Computation of potential and electrical field

strength along the insulator strings is an important aspect for

their designs. This study is concerned with the voltage and the

electric field distribution along 380 kV V-type suspension

strings composed of cap and pin type porcelain and glass

insulators. It’s one of the main structure utilized in 380 kV

Turkish National Power Transmission Systems. Boundary

Element Method based software, Coulomb 3D, was used threedimensional modeling and simulations. The effects of corona

ring, transmission tower, insulator type and angle between V-

strings on potential and electric field distribution were

analyzed. Experimental studies were conducted at Fuat

Kulunk High Voltage Laboratory of Istanbul Technical

University.

Index Terms— Boundary Element Method, Corona Ring

Electric Field, Insulator String, Potential Distribution.

I. I NTRODUCTION

ONTROL of electrical field distribution within and

around high voltage equipment is one of the basicaspects of the design of such equipment. Audible noise,radio noise, partial discharges and corona discharges aresome of the possible results of high level electrical fields[1]. Several studies assign a value of 2.20 kVrms/mm - 2.28kVrms/mm as the corona inception electric field under drycondition [2, 3].

Cap-and pin type porcelain and toughened glassinsulators (U210 BL and U160 BL) are the most commonones used in 380 kV Turkish National Power TransmissionSystems. According to past experience, one of the mostfrequent failures related with V-suspension sets of cap-and

pin type insulators are the transient outages due to the

flashovers from the corona ring (grading device) of the setto the transmission tower.

It is known that the potential distribution along theinsulator strings is not linear. The voltage is shared inrelationship to the self capacitance of each insulator unit andthe stray capacitances of each insulator to earth [5, 6].Corona ring, transmission tower, insulator type and angle ofV-strings affect the potential and electrical fielddistributions.

This work was supported in part by the Turkish National PowerTransmission Syatems

Aydogan Ozdemir is with Department of Electrical Engineering,Istanbul Technical University, 34469 Maslak, Istanbul/Turkey

(e-mail: [email protected]).Suat Ilhan is with the Department of Electrical Engineering, Istanbul

Technical University, 34469 Maslak, Istanbul/ Turkey(e-mail: [email protected]).

This paper presents the potential and electrical fielddistributions under the effects of corona ring, transmissiontower, insulator type and different angle between V-insulator strings. Since the laboratory model is differentfrom the actual tower, several simulations for ACexcitations are conducted to validate the laboratory tests.Later, power frequency flashover voltages and visiblecorona inception voltages on the corona ring areexperimentally determined from the number of laboratorytests. Corona inception voltages are also determined fromcomputer simulations. Experimental and simulation resultsare seen to be in good concordance which can provide theextension of the simulations for several different cases.Coulomb 3D electrostatic simulation program was used forthe simulations.

II. INSULATOR, CONDUCTORS, AND CORONA RING TO BE MODELLED

Fig. 1 shows the 380 kV V-suspension string composed of20 cap and pin type porcelain insulator units. In the

simulations, porcelain and glass insulators are used. Three bundle 3*1272 MCM transmission line hanged by porcelainand glass insulators is considered and Ø 35 mm aluminumtubes are used to simulate the actual power lines.

Fig. 1 Basic dimensions of cap and pin type insulator, insulator numberingand angle of V-Insulator string

Fig.2 illustrates the full model of an odd shape gradingdevice and a yoke plate for three bundle 3*1272 MCMconductors. Grading device is composed of corona tubewith diameter of 48 mm.

C

12

34

56 7

8910

1112

13

19

17

1514

16

18

20

280 mm

1 7 0 m m

20*170+60 = 3460 mmα0


3/7


4/7

3

(a)

(b)

Fig.4 Simulation results (a) Equipotential contours for 90o V glass insulatorstrins (b) Solid view of equipotential surfaces

0

10

20

30

40

50

60

70

80

90

100

0 500 1000 1500 2000 2500 3000 3500

Insulation Distance (mm)

P o t e n t i a l ( % )

w ith corona ring

w ithout corona ring

(a)

2

4

6

8

10

12

14

16

1 3 5 7 9 11 13 15 17 19

Insulator No

P o t e n t i a l ( % )

w ith corona ring


(b)

Fig.5 (a) Potential distribution along the center line of glass insulators fromthe voltage side to the earth side (b) Voltage sharing across each cap and pin type glass insulator unit.

Voltage sharing is improved by approximately 1 % percent by the voltage grading device. Flat sections in Fig.5.(a) show the floating potential values of metal parts (cap and

pin).

2

4

6

8

10

12

14

1 3 5 7 9 11 13 15 17 19

Insulator No

P o t e n t i a l ( % )


w ith corona ring

Fig.6 Voltage sharing across each cap and pin type porcelain insulator unit

Fig.6 shows the voltage sharing across each porcelaininsulator unit. Nearly, 14 % of the voltage is developed onthe live end insulator. The usage of corona ring brings more

uniform distribution along the string. It’s more effective onthe % potential distribution of the first two-three insulatorsnear the power line. On the other hand, the usage of coronaring results in slight increases on the shares of the insulatorsnear the ground side. Potential shares under porcelain andglass insulators show 2 % differences due to the dielectricconstant of the mediums. Maximum electrical field strengthson the corona ring are 6.108 kV rms/cm and 6.01 kVrms/cm(points A and B in Fig.2 (a)) for glass and porcelaininsulators, respectively

Fig.7 illustrates % voltage shares of glass insulators for900 and 1100-V insulator strings. From the simulation

results, voltage shares are very similar for the insulatorunits. There is slightly a difference for potentialdistributions. Maximum electrical field on the corona ring,on the other hand, increases up to to 6.50 kV rms/mm for 110

0 V-strings.


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4

1

3

5

7

9

11

13

15

17

1 4 7 10 13 16 19Insulator No

P o t e n t i a l ( % )

90-V string

110-V string

Fig.7 Voltage sharing across each cap and pin type glass insulator units for900 and 1100 V-sets

Fig.8 shows the maximum electrical field magnitudealong the centre line of glass insulators from the voltage

side to the earth side. Maximum electrical field near thevoltage side is reduced by means of corona ring.

In the computer simulations, approximately 40000triangular and quadrangle 2D boundary elements were usedand computation times are roughly 3 hours.

Without Corona Ring

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

0 500 1000 1500 2000 2500 3000 3500


M a x i m u m E

l e c t r i c a l F i e l d

( k V / m m )

(a)

With Corona Ring

0

0.1

0.2

0.3

0.4

0.5

0.60.7

0.8

0.9

0 500 1000 1500 2000 2500 3000 3500


M a x i m u m E

l e c t r i c a l F

i e l d

( k V / m m )

(b)

Fig.8 Maximum electrical field strength (kVrms/mm) for 900 V glass

insulators (a) withou corona ring (b) with corona ring

B. Practical (Real) Model

It’s very important to know the potential and theelectrical field distribution under full-scale real model of thesystem to compare with the laboratory results. In this study,380 kV suspension tower with three bundle conductors areused. The conductors are modeled as smooth conductorsand positioned parallel to the earth surface. The length ofeach conductor is 30 m and 40 x 40 m plane with zero

potential is positioned under the leg of the tower. The toweris assumed as a single volume at ground potential becauseof the modeling difficulties of the tower cage structure.

11.2

9.49

7.5 7.5

8 . 0

4 . 9

8

2 7 . 0

4 4 . 5

3.9units: m

αo

(a)

(b)

Fig.9 (a) Major dimensions of 380 kV 3B1 type suspension tower (b) Solidview of the simplified tower model

Fig.9 shows the 380 kV suspension tower and simplified

tower model. Simulations were only conducted for V-stringlocated centre of the tower.

Fig.10 illustrates equipotential contours for 900 V-glassinsulator strings in the case of the real tower model.


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Fig.10 Equipotential contours for 90o V glass insulator strings in the caseof real model

Simulation results show that (Fig.11) laboratory modelresults are in good concordance with the exact tower case.

This concordance brings the possibility of extending realcases with laboratory models. Maximum electrical fieldintensity on the corona ring for the laboratory model of 900 glass insulators is 6.37 kVrms/cm on the points of Fig.2 (a) Aand B points.

0

2

46

8

10

12

14

16

18

1 3 5 7 9 11 13 15 17 19

Insulator No

P o t e n t i a l ( % )

w ith corona ring


(a)

0

2

4

6

8

1012

14

16

18

1 3 5 7 9 11 13 15 17 19

Insulator No

P o t e n t i a l ( %

)

Laboratory model

practical (real) model

(b)

Fig.11 (a) Voltage sharing across each cap and pin type 900 V-glassinsulator units for real model (b) Comparison of laboratory model and realtower model

IV. LABORATORY TESTS

Power frequency flashover voltages and visible coronainception voltages of the corona ring for porcelain and glass900 V-suspension insulator strings are experimentallydetermined at Fuat Kulunk High Voltage Laboratory ofIstanbul Technical University. The main laboratory hall hasa floor area of 25 x 35 m and a ceiling height of 21 m. All

the outer surfaces of the laboratory are shielded againstelectromagnetic filed. In the laboratory tests, 1000 kVA, 50Hz, 1200 kVrms three stages cascade high voltage testtransformer is used power frequency tests. Fig. 12 shows thelaboratory model of 900 –V porcelain insulators. A pictureof flashover path between corona ring and the simulatedtower is also given in the Fig.12.

Fig.12 Laboratory model of 380 kV 900 V-porcelain insulator string

TABLE IITEST RESULTS FOR 900 GLASS INSULATORS

1st run 2st run 3st run Average

CoronaInceptionVoltage

380 kVrms 390 kVrms 380 kVrms 383 kVrms

FlashoverVoltage


FlashoverVoltageWithoutThe Ring


Table II and Table III illustrates visible corona inceptionvoltages on the corona ring, flashover voltages with and

without corona ring for porcelain and glass insulators. In thecase of no corona ring, flashovers occurred between yoke plate and simulated tower. All the visible corona inceptionvoltages were observed on the points of A and B in Fig.2 (a)like the simulation results.


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TABLE IIITEST RESULTS FOR 900 PORCELAIN INSULATORS

1st run 2st run 3st run Average

CoronaInceptionVoltage


FlashoverVoltage 720 kVrms 710 kVrms 700 kVrms 700 kVrms

FlashoverVoltageWithout theRing


250

300

350

400

450

500

0 1 2

P o t e n t i a l ( k V r m s )

3

Observed Values

Estimated Values

Fig. 13 Observed and estimated visible corona inception voltages for glassand porcelain insulators

Test results showed that the usage of corona ring caused 7% -8 % percent reductions in the flashover voltages. Fig.13

shows observed and estimated corona inception voltages onthe corona ring. If corona inception electric field strength isassumed to be 2.2 kVrms/mm, the voltage initiating coronadischarges can be calculated as 360.18 kV rms and 366.05kVrms for 6.108 kVrms/mm and 6.01 kVrms/mm maximumelectric field strengths, respectively.

V. CONCLUSIONS

1) 14 %- 17 % of the transmission line voltage isdeveloped across the nearest insulator to the line-end. Thevoltage sharing on the other insulators considerabledegreases toward the earth end. The potential is distributed

in relations to the self and stray capacitances.2) With the usage of grading device, 12 % - 14 % ofthe line voltage is shared by the line-end insulators. Increasein the line stray capacitances results in slightly potentialrises on the insulators near the ground end.

3) Potential distribution under porcelain and toughenedglass insulators has nearly 2 % differences because of thedielectric constant of the mediums.

4) Laboratory model and practical model are in a goodaccordance. Observed and estimated voltage values relatedto visible corona inception voltage are also in a goodcohesion.

5)

Increasing the angle of V-suspension sets has nosignificant effect on the potential distribution but hasimportant effect on the maximum electrical field on thecorona ring.

6) Although corona ring improves the potentialdistribution for the line-end insulators, it degreases theflashover voltage at about 7 % - 8 % because of the wrongcorona ring settings. The voltage sharing and flashovervoltage can however be significantly improved by speciallydesigning the voltage grading devices.

VI. REFERENCES[1] Zhao T. and Comber M.G. “Calculation of Electric Field and

Potential Distribution Along Nonceramic Insulators Considering theEffects of Conductors and Transmission Towers”, IEEE TransactionsOn Power Delivery, Vol. 15, No. 1, pp 313–318, January 2000

[2] Sima W., Espino-Cortes F.P., Edward A.C. and Jayaram H.S.,“Optimization of Corona Ring Design for Long-Rod Insulators UsingFEM Based Computational Analysis” IEEE Int. Symposium on Electrical Insulation, Indianapolis, in USA, pp 480 – 483, 19-22September 2004

[3] Que W., Sebo S. A. , Hill R. J., “Practical Cases of Electric FieldDistribution Along Dry and Clean Nonceramic Insulators of High-Voltage Power Lines”, IEEE Transactions On Power Delivery, Vol.22, No. 2, pp 1070–1078, April 2007

[4] IEC Overhead lines – Requirements and test for fittings, IEC

International Standard 61284, 1997-09[5] Dhalaan, S.M.A.; Elhirbawy, M.A.; “Investigation on the

Characteristics of a String o Insulator due to the Effect of Dirt”,Transmission and Distribution Conference and Exposition, 2003

IEEE PES Volume 3, 7-12 Page(s):915 - 920 vol.3, Sept. 2003[6] Dhalaan,S.M.A.; Elhirbawy, M.A.; “Simulation of Voltage

Distribution Calculation Methods over a String of SuspensionInsulators” Transmission and Distribution Conference and Exposition, 2003 IEEE PES Volume 3, 7-12 Page(s):909 - 914 vol.3,Sept. 2003

GlassInsulator

PorcelainInsulator

[7] Integrated Engineering Software— Users and Technical Manual forCoulomb 3D, Version 6.4, Winnipeg: Enginia Research Inc., 2008.

[8] G. Gorur, Raju, Dielectrics in Electric Field, New York: Marcel Dekker , c2003.

VII. BIOGRAPHIES

Suat İlhan was born in Malatya, Turkey, onFebruary 1979. He received the B.Sc. andM.Sc. degrees in Electrical EngineeringDepartment from Istanbul TechnicalUniversity, Istanbul, Turkey in 2001 and2004, respectively. He is currently a researchassistant at the same university. His researchinterest is in the area of high voltageengineering.

Aydoğan Özdemir was born in Artvin,Turkey on January 1957. He received theB.Sc., M.Sc. and Ph.D. degrees in ElectricalEngineering from Istanbul Technicaluniversity, Istanbul, Turkey in 1980, 1982and 1990, respectively. He is currently a full professor at the same university. His currentresearch interests are in the area of electric power system with emphasis on reliabilityanalysis, modern tools (neural networks,

fuzzy logic, genetic algorithms etc.) for power system modeling, analysis and controland high-voltage engineering.
http://ieeexplore.ieee.org/xpl/RecentCon.jsp?punumber=9275http://ieeexplore.ieee.org/xpl/RecentCon.jsp?punumber=9275http://ieeexplore.ieee.org/xpl/RecentCon.jsp?punumber=9275http://ieeexplore.ieee.org/xpl/RecentCon.jsp?punumber=9275http://ieeexplore.ieee.org/xpl/RecentCon.jsp?punumber=9275http://ieeexplore.ieee.org/xpl/RecentCon.jsp?punumber=9275http://ieeexplore.ieee.org/xpl/RecentCon.jsp?punumber=9275http://ieeexplore.ieee.org/xpl/RecentCon.jsp?punumber=9275

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