Performance of 20 kV Epoxy Resin Outdoor InsulatorUnder Various Environment Conditions

Melda Latif', Suwarno2IDepartment of Electrical Engineering, Andalas University

Ji. Kampus Limau Manis Padang 25163, Indonesia2Department of Electrical Engineering, Bandung Institute ofTechnology

Ji. Ganesha 10 Bandung 40132, Indonesia*email: i oo.co.uk

Abstract: This paper explains the research results ofleakage current and flashover measurement on EpoxyResin 20 kV Outdoor Insulators in a chamber at variousartificial polluted conditions. The waveform of theleakage current(LC) was measured using a digitalstorage oscilloscope. The digital data was transferred toa personal computer using a RS-232 cable. Furtheranalysis of the waveform was done using Fast FourierTransform. The result showed that LC was affected byvarious environment conditions like pollution, humidityand temperature. The flashover of insulators occurredat 64 kV for 2600 [[S and 53 kV for 4300 [[S in cleanfog and high humidity condition.

Keywords: outdoor insulator, epoxy resin, leakagecurrent, flashover voltage

INTRODUCTION

In some tropical countries, such as Indonesia, insulatorflashover frequently happens and greatly affects theelectric power system. Insulator flashover mechanismusually relates with leakage current (LC) on insulatorsurface, and influenced by environment condition, suchas pollution, humidity and temperature [1-8].

Several methods for measuring the performance ofinsulator conditions are reported. Amarh [9] uses LCenvelope as parameter of performance, Piah [10] usesdimensional technique for modeling LC, and Yong Zhu[11] reports 3D dynamic model for studying LCwaveform. This paper describes the measurement ofperformance of insulator surface using LC and flashoverunder various environment conditions.

[[/cm 4300 [[/cm. IEC-507 standard was used in thisartificial pollution arrangement[12].

r. .................Fig. 1 20 kV Epoxy Resin Polimer Insulator

The LC was measured using a digital oscilloscopeTextronik TDS 220 with digitizer of 8 bit, 100 MHzbandwidth, and the maximum sampling rate of 1 GS/s.Digital camcorder was used for flashover monitoring.

LC waveform was analyzed using Fast FourierTransform (FFT) for getting Total Harmonic Distortion(THD) . The THD can be expressed as:

2lLn

THD 2I1

where In = nth harmonic for n= 2,3,4,...Ii = fundamental harmonic (n= 1).

RESULTS AND DISCUSSION

Leakage Current as Function of Test Voltage

Fig. 2 shows LC as function of test voltage for clean andEXPERIMENTAL polluted insulators under low and high humidity.

Tested insulator used in this experiment is Epoxy Resin20 kV pin type, and 1.8 kg weight. Insulator Filler isATH (Alumina Tri-Hydrate) with composition 50% ofthe weight. The Chamber dimensions are 90x90x120cm3 with 80x80 cm2 transparent acrylic door, chamberhumidity varied in low (50-60%) and high humidity(85-95%). Artificial pollutant used in this experimentwas kaolin-salt with conductivity varied from 300

From the figure it is seen that LC increased withhumidity. LC magnitude flows at polluted insulatorsurface is more greater than clean insulator. Thisindicated that at higher humidity, vapor willcondensate on the insulator surface resulting in higherconductive layer will occur on insulator surface. Thispromotes a higher leakage current.

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120

100

80 -

60 -

40

20

10 12 15 20 25 30 35 40 45 50

Tegangan (kV)

- * Clean, lowRH -Clean, high RH - 300uS/cm,low RH- 300uS/cm polluted, high RH - - 600 uS/cm polluted, low RH 600 uS/cm polluted, high RH

Fig. 2 LC as Function of Test Voltage

Leakage Current as Function of Temperature

Table 1 shows the LC waveforms, maximum andfundamental of leakage current for clean and pollutedinsulators at low humidity and at different temperatures.

temperature increased slightly for clean insulators. Forhighly polluted insulators, LC magnitude increasedrapidly with temperature up to about 420C. Above thistemperature, LC magnitude decreased drastically. Thisis due to dry band formation caused by heating by theflowing LC assisted by high temperature of thesurrounding.

350

300

250

200

V 150

100

50-

28 30 32 34 36 38 40 42 44 46 48

Temperature

Table 1 LC as function of temperature, RH: 85-95%

300CTHD = 27%I1ax=46pAI1=25,81 iA

300CTHD= 15%I, =60tpAI1=56,28 iA

300CTHD = 23%I 4A=37,05,tA11=42,uA

70 io 35 msPnd 0rs eid 0

3100

44°C 44°C 44°CTHD=18%o THD=12% THD=9%oImax=64pA Ima,=3O4,uA II11X=496,uA

I3 56,75iA b276,465 I1=467,O4jA

100

P-35 d 20 ms

p~~~id20Nn.d 20 ~~~~~~~~~~~~~~Period 20 n

440C 446C 442C

THD=180o THD=12% THD=91I, 8=4tA 1~,,,304~tA THD bo46ot11=567,54~A 11=277,46p 11=34604~A___________________________________ Ii~~~~~~~~4033- 94

Fig. 3 shows that in general LC magnitude increasedwith temperature for clean and medium pollutedinsulators. For insulators with high pollution and highhumidity, the characteristics of LC as function oftemperature changed drastically at around 420C. This isshown in figure 3. LC magnitude as function of

-+Clean 300uS/cmPolluted --600 uS/cmPolluted

Fig. 3 LC as function oftemperature at 12 kV

Flashover

Flashover experiment was conducted using test voltagefrom 50 - 85 kV with 2 kV increment at roomtemperature. For clean insulator at various humidity itwas found that flashover did not occur even the testvoltage was increased up to 85 kV.

For 2600 [S/cm polluted insulator, in low humidity (drycondition) flashover did not occur with the voltageincreased from 50 kV to 85 kV. On the other hand, inhigh humidity (wet condition) spark occurred first at 54kV and finally flashover occurred at 64 kV. Thiscondition was recorded and shown in Fig. 4. For 4300[[/cm polluted insulator at low humidity spark did notoccur. Flashover occurred at 82 kV.

a. spark b. FlashoverFig. 4 Spark and flashover in polluted insulator at

2600 [[/cm, RH:85-95%

Fig. 5 shows the LC waveform and harmonic spectrumof spark at 75 kV. The peak magnitude of LC was 672[A and THD 40%. In high humidity this heavy pollutedinsulator had LC magnitude approach to 500 pA for 12

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4 lo1-1 -lo

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-50

70-,

35

0 -/ `..-35

-70

354

60

40

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kV applied voltage. Spark occurred starting at 20 kVand flashover took place at 53 kV.

magnitude was observed. The THD of the LC reducedsignificantly from those at low humidity.

High humidity gave vapor contents in chambercontributing the wetting process of the insulatorsurface. Heating effect by LC flow at the surface driedwater droplets that absorbed by polluted surface. Theflashover process is shown in table 2. This phenomenonrelates to dryband forming at insulator surface. Then,this continued until sparkover occurred [13-16].

Flashover observation showed that the environmentconditions greatly influenced the performance ofinsulator surface. Humidity, especially for highhumidity, gives strong effect to flashover. Asillustration, in high humidity for clean insulator noflashover occurred, for 2600 [[/cm flashover occurredon 64 kV, and for 4300 [[/cm flashover occurred on 53kV.

700 -

600 -

500 -

400 -

300 -

200-

V 100-

0-

-100o

-200 -

-300 -

-400 -

u

500 -

400 -

300 -

200 -

100 -

0-0:

-100 -

-200-

-300-

-400-

-500-

0. 1 02 0.3 004 0.05second

(a)

500

400

300

200

100

01 2 3 4 5 6 7 8 9 10 1112 13

n-th Harmonic

(b)0 002 0 00.( 10.2 0. 0.04 0.05

second Fig 6. Typical LC waveform (a) and harmonic content(b) for 4300 [[/cm polluted insulator at high

humidity, and 12 kV

5a. LC Waveform

250 -"6.

2100 -

364272

114 1021277.6 8.6 G 18 49 59666 5.7 S.S 4446 1664846 4.7,nuElm M lnm lll -Mllnnl lM lnlU lM ll Ul

3 5 7 9 1 1 13 15 17 19 21 23 25

n-th Harmonic

5b. Spectrum Harmonics

Fig. 5 Typical LC waveform (a) and harmonic content(b) of insulator with spark at 4300 [[/cm pollution and

low humidity, at 75 kV

Fig. 6 Shows typical LC waveform and harmoniccontent for highly polluted insulator at 12 kV. High LC

Table 2 Flashover Process for 4300 [[/cm pollutedinsulator, at high humidity

1 second 13 second 22 second

31 second 40 second 53 second

59 second 61 second 70 second

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Table 3 shows the correlation between arch length andapplied voltage. The table clearly indicates that the archlength is strongly affected by the applied voltage. Thisis more clearly seen from Fig. 7.

Table 4 Correlation between arch length and appliedvoltage

21

25

30

35

37

48

50

51

53

26.38

28.59

60.34

77.52

80.54

86.44

96.91

103.3

400

400 400

350 -

, 300-

250-. 200- /o 150 -

50-

21 25 30 35 37 48 50 51

Arching voltage (kV)

53

Fig. 7 Arching distance as function of applied voltage

CONCLUSION

The performance of 20 kV Epoxy Resin OutdoorInsulator under various environment conditions hasbeen analyzed in this paper. The result showed thatpollution, humidity and temperature give influence tothe performance. LC magnitude, THD, and flashover asindicators showed that they strongly correlated toinsulator performance.

REFERENCES

[1] Gorur, R.S, et al, "Electrical Performance ofCycloaliphatic Epoxy Materials and Insulators forOutdoor Use", IEEE Trans. On Power Delivery,Vol.15, No. 4, pp.1274-1278, Oct.2000

[2] Fernando M.A.R.M., et al, "Leakage Current onNon-ceramic Insulators and Materials", IEEETrans. Dielect. Elect. Insul., vol. 6 No.5, pp. 660-664, Oct. 1999.

[3] Schwardt W.H., et al, "A Comparison BetweenMeasured Leakage Current And SurfaceConductivity During Salt Fog Tests, preprint

[4] Gustavsson Tomas G., Silicone Rubber Insulators-Impacts of material formulation in coastalenvironment, Thesis For The Degree Of Doctor OfPhilosophy, Goteborg, Sweden, April 2002

[5] Gorur, R.S, E.A. Cherney, et al, "The ElectricalPerformance Of Polymeric Insulating MaterialsUnder Accelerated Aging In A fog Chamber",IEEE Trans. On Power Delivery, Vol. 3, No. 3,pp.1157-1164, July 1988

[6] Besztercey G. G., et al, "An ArtificialContamination Method for Composite Insulators",IEEE Trans. On Power Delivery, Vol.15, No. 2,pp.732-736, April 2000

[7] Sillars. R.W, et al, Electrical Insulating Materialsand Their Application, Peter Peregrinus Ltd., 1973

[8] Gorur, R.S, E.A. Cherney, et al, "The AC And DCPerformance Of Polymeric Insulating MaterialsUnder Accelerating Aging In A Fog Chamber",IEEE Trans. On Power Delivery, Vol. 3, No. 4,pp.1892-1902, Oct.1988

[9] Amarh Felix, et al, " Level Crossing Analysis ofLeakage Current Envelope of Polluted Insulators",IEEE Power Engineering Review, August 2001

[10]Piah, M. A. M, "Modelling Leakage Curent andElectric Field Bahavior of Wet ContaminatedInsulators", IEEE Trans. On Power Delivery,Vol.19, No. 1, pp.432-434, January 2004

[11]Yong Zhu, et al, "Mechanism for Change inLeakage Current Waveform on a Wet SiliconeRubber Surface-A Study using a Dynamic 3-DModel", IEEE Trans. On Dielectrics and ElectricalInsulation, Vol.12, No.3, pp.556-565, June 2005

[12] IEC 507, "Artificial pollution test on high-voltageinsulators to be used on ac systems", 2nd edition,Geneve, Suisse, 1991

[13] Gorur, R.S., et al, Outdoor Insulator, Ravi S.Gorur, Inc., Phoenix, USA, 1999

[14]T. Sorqvist and S. M. Gubanski, "Leakage currentand flashover of field-aged polymeric insulators,"IEEE Trans. Dielect. Elect. Insul., vol. 6, pp. 744-753, Oct. 1999.

[15]A. de la and Gorur, R.S., "Flashover ofContaminated Nonceramic Outdoor Insulators in aWet Atmosphere", IEEE Trans. On Dielectrics andElectrical Insulation, Vol.5, No.61, pp.814 -823,December 1998

[16] George G. Karady, "Flashover Mechanism of Non-ceramic Insulators", IEEE Trans. Dielect. Elect.Insul., vol. 6 no.5, pp. 718-723, Oct. 1999.

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