Light Sensors as Detectors of Tracking Deterioration

IEEE Transactions on Electrical Insulation Vol. EI-22 No.4, August 1987

LIGHT SENSORS As DETECTORS OF TRACKING DETERIORATION

M. Nishida, N. Yoshimura, and F. Noto

Department of Electrical Engineering,Akita UniversityTegata GakuenchoAkita City, Japan

ABSTRACT

This paper describes the result of light-pulse measurementwith light sensors for detecting the tracking deterioration on

the surface of organic insulating materials by means of the IEC587 tracking test method. Three kinds of light sensors were

used for detection of the discharges generated on the insulatorsurface. Each of the sensors can respond to ultraviolet (Su),visible light (Sv) and infrared (Sr), respectively.

An Su sensor continuously counted the light pulses from thestart of the test until it came to final tracking breakdown, inwhich case an almost constant rising rate of total number TN ofthe light pulses was observed. On the other hand, the risingrate of TN curves with Sv and Sr sensors during the trackingdeterioration were classified into three regions according toa transition from one discharge state to another with trackingdeterioration. Therefore, it was found that the measurementof the rising rate of the TN curves with Sv and Sr sensors was

a suitable means for detecting the transition of the trackingdeterioration.

The time required and the occupied rate for respective regionswere measured using the light sensors. The time required andthe occupied rate for respective regions depended on both thesample and the applied voltage. It also was clarified that thetest conditions have a significant influence on the main processwhich determines the time of the final tracking breakdown.

INTRODUCTION

A great variety of organic insulating materials are

being used for electrical insulations in cables, ma-

chines, switch boards and outgoing lines. Since thesedevices are being used under severe ambient conditions,tracking deterioration on the surface of organic in-sulating materials has become a serious problem. Thetracking breakdown phenomenon on organic insulatingmaterials has a strong influence on the safety and thereliability of electrical equipment. Many studies con-cerning tracking deterioration under wet conditionshave been reported [1-5]. However, a lot of researchesput stress on the result for the final breakdown [1-5].Therefore, the mechanism of tracking deterioration andthe aging characteristics of the organic insulatingmaterials have not yet been clarified.

Recently, it has been reported also that trackingbreakdown seemed to be a mixture of the processes ofdischarge inception, carbon formation, and propagation

of the carbon path under the influence of several fac-tors [6-7]. The difficulty of the investigation on

tracking deterioration lies in the complexity of thedegrading factor and the uncertainty in the detectionof the transitional property on the tracking deterio-ration process. In order to clarify the possible proc-ess of tracking deterioration, it is necessary to es-

tablish a method for detecting the transitional statesin tracking deterioration. Authors have already re-

ported that the spectra of the discharge generated on

the insulator surface depended on the types of the dis-charge such as corona, scintillation, or arc discharge[8-9]. Those results suggested the possibility of op-tical separation of the scintillation from the remain-ing two types of the above stated discharge.

In this paper, a count system for light pulses withthe light sensors was proposed as a detector of trackingdeterioration. The characteristics of the tracking re-

sistance for the sever4l materials were also discussedby means of the newly proposed method.

0018-9367/87/0800-0509$01 .00 @ 1987 IEEE

509


TRACKING TEST PROCEDURE AND MEASURINGSYSTEM WITH LIGHT SENSORS

Sample and Tracking Test Procedure

Polyvinyl chloride (PVC), polystyrene (PS), polycar-bonate (PC) and phenolic paper laminate (PL) were usedas samples in this test. The samples prepared have inthe same size 120x50 mm. The samples were dried in a

desiccator with silica-gel for 24 h or more after thesurface was cleaned with gauze dipped into methanol.

The experimental circuit used in this test is thesame as the IEC (International Electrotechnical Com-mission) 587 test method [10-11]. Fig. 1 shows the ex-

perimental circuit. The criterion employed for the

s VT T

S:VT:T :

R :.

V :

Sa:F :

power supply switchvariable ratio transformer

high-voltage transformerseries resistorvoltmetersampleovercurrent relay

25j

Is"" "..;--28 ->

all dimensions in mm Q)for Sv

for Sr

D[):rest sample (5):U.V. tron (Su).(2):Top electrode i® :Class f iber for SPD

(G:Bottom electrode M:Long-wave pass fiIter04:Filter-paper(contaminant feed) : Measurement area of SPD

t....................................................................................................................:....................................................................................... ...

Fig. 2: Arrangement of the electrodes and opticalmeasurement system.

3 shows the relative spectrum sensitivity of the re-

spective sensors. The sensors are UV radiation detec-tor (Su), silicon photodiodes (SPD) for visible light

Fig. 1: Schematic circuit diagram of IEC 587test method.

final tracking breakdown in this test is the same inthe IEC 587 test method. An over-current relay was setat 60 mA with a tripping time of 2 s. Fig. 2 shows thearrangement of the electrodes and the optical measure-

ment system. Stainless steel electrodes were used.The solution employed contains 0.1% NH4Cl and 0.02%non-ionic wetting agent (TRITON X-100) in deionizedwater, giving a resistivity of about 396 Qcm at 230C.

The contaminant was fed into the filter paper padwhich was clamped between the top electrode and thesample. Table 1 shows the relation between the flowrate of the contaminant and the test voltage.

>1.4-,

4-i

U)U)

4)

4J

(d

Table 1

Test voltage and contaminant flow rate.

Optical Measurement System

Three types of light sensors were used to measure the

light pulses of the discharge generated on the samplesurface. Referring to the previous paper [8-9], the

sensible range of the respective sensors was set. Fig.

Fig. 3: ReZativesensors.

Wavelength (nm)

spectral sensitivity of Zight

(Sv) and IR radiation (Sr). The Sv-sensor could respondslightly to the UV radiation below 400 nm; the UV regioncould be removed with a long-wave length color filter(LWPF), as shown in Fig. 2. The 10% edge position ofthe LWPF was 405 nm. The transmission was 90% above 500nm. The response range of three sensors are 700-1140 nm405-680 nm, and 185-260 nm for the Sr, Sv, and Su sen-

sors, respectively at 5% cut-off wave lengths. Themaximum sensitivity for radiation, which is the ratio ofthe amount of introduced light to the output current ofthe sensors, lies around 0.5 A/W for Sr and 0.3 A/W forthe Sv sensor.

Test vol tage(KV)Contaminant flowTestvolageKV) rate(ml/min)

1.00 to 1.75 0.0752.00 to 2.75 0.153.00 to 3.75 0.304.00 to 4.75 0.605.00 to 6.00 0.90

sin

-T

Lo--

Nishida et a1.: Light sensors as detectors of tracking deterioration

The SPD is connected to an optical glass fiber (OF).The transmission range of the OF is from 0.4 to 2.1 pm,so that it does glot invluence the measured wave lengthof the Sv and Sr sensors. The OF also has an inlet andtwo outlets (see also Fig. 2). The aperture of the OFis 67 degrees. The area observed on the sample surfaceis a circle about 28.0 mm in diameter, as shown in Fig.2. On the other hand, the Su sensor has a wide aper-ture, so that the measurable area covers the completesurface between the electrodes.

Count System for Light Pulses

Fig. 4 shows the block diagram of the measuring sys-tem for the light pulses. The electric signal is fedinto an electric counter (threshold level: 50 mV, gateduration: 30 s) through an amplifier (gain: 60 dB,high frequency cut-off 200 kHz). Fig. 5 shows the out-put waveforms of Sr and Su sensors at several positions

,ig'-Z' Long-wave Photodiodeliht pass filter Gasf

5ms/d i v.(1):Out put of pre-amp:lV/div.(2):Out put of differetial

circui t:1V/div.(3):Out put of shaping

circuit:2V/div.( a ) Srb

2V/div, Z2s/div.(b3) Su

Fig. 4: Block diagram of the light pulse measurementsystem.

in the electric circuit. As the noise level was lessthan 50 mV, the threshold level was set at 50 mV. Thislevel corresponds to a light current of 3X10-10 A. Theamplifier gain of the preamplifier is 1. 7x108, and thecut-off frequency is 6 kHz. On the other hand, thepulse width of the Su sensor is about 8 ps, and the in-terval between pulses is 250 ,us. In the experiment, anaccumulated number (APN) through a 30 s interval andthe total number (TN) of the light pulses until thefinal tracking breakdown was reached were measured.

CORRELATION BETWEEN OBTAINED RESULT OFLIGHT PULSES AND TRACKING DETERIORATION

Lischarges on Sample Surface in Tracking Breakdown

Various discharge modes to be observed during theprocess of tracking breakdown are shown in Fig. 6. Fig.6(a) shows a corona discharge with purple color. Itcontinues throughout between the top and the bottomelectrode until the carbon particles are deposited onthe sample surface. The corona discharge degrades thesample surface so that the wettability of the samplesurface decreases [6]. Carbon particles were depositedon the sample surface during the corona discharge. Af-ter the initiation of the carbon deposit, red and/orwhite colored scintillation (minute arc discharge)

Fig. 5: Waveforms of SPC and U. V. tron.

occurs near the bottom electrode, as shown in Fig. 6(b).The incipient carbon was washed away by the flowing con-taminant, so that the scintillation tends to occur atrandom near the bottom electrode.

A conductive carbon path is formed at the bottom elec-trode due to the repeated scintillation and, subsequent-ly, thermal radiation due to Joule heat in the carbonpath is observed, as shown in Fig. 6 (c) . Then, thescintillation continues to occur at the top of the con-ductive carbon path [see also Fig. 6(d)]. The conduc-tive carbon path develops toward the top electrode dueto the continuing scintillation, and finally leads tothe tracking breakdown.

Accwnulated Number (APN) and Total Number (TN) of LightPuZses

Figs. 7 and 8 show typical experimental results for theaccumulated number (APN) at 30 s intervals and the totalnumber (TN) of the light pulses with three types of sen-sors. The marks which correspond to the photographs inFig. 6 are shown also on Figs. 7 and 8. According to theresult in Fig. 7, the APN with Su sensor shows the samevalue at each interval. Also, the TN curve constantlyincreases with elapsed time after the start of the testto tracking breakdown. Therefore, it appears that theresult of the light pulses obtained with Su sensors doesnot coincide with the transitions of the tracking deter-ioration process.

On the other hand, the count rate of the APN and theslope of the TN curve with Sv and Sr sensors change re-markably at two critical points. The first point occursat the start of the count with Sv and Sr sensors. Thesecond point indicates the change of the count rate of

51


(xl

- 104J

: 80.! 6z4at 2

O

'100 12

.4J

C

.lr_

'0

r)8

v,

4.)

.a4c

l.

1-6

:I

~' C.,,

\ c. / \ I /

(a): Corona discharge (8 minutes)(b) Inception of scintillation discharge (8 minutes)(c): Formation of conductive carbon path (14 minutes)d Propagation of carbon------------pat ----------(17 -------minutes)d): Propagation of carbon pathi (17 minutes)l

Fig. 6: Photographs of discharges (PC, 2.5 kV).

APN or the slope of the TN curve. Two critical pointscorrespond with the initiation of the scintillation andthe formation of the conductive carbon path. Therefore,it follows that the count of light pulses with Sv andSr sensors is suitable for detecting accurately thetransition point of the tracking deterioration.

Correlation Between Measurement Result of Light Pulsesand Tracking Breakdown Process

Fig. 9 shows a general model of the TN curves with Svand Sr sensors. The TN curves with Sv and Sr sensorsare divided into three regions (I, II and III) at twocritical points along the time axis (A and B). The in,,tervals between the start point of the test and thecritical time A or B, also, depend on the kinds of sam-ple, the applied voltage, etc. As a result of Figs. 6and 9, a relationship between three regions and thetracking deterioration of the sample surface is deducedas follows:

In region I before the critical time A, no light pulsewas counted with Sv and Sr sensors in spite of the oc-currence of the corona discharge on the sample surface.

103)- a _ b

.-.liF*;

3

I-

I

C

: - - . X -- - -.- - --- 7

~-- --- ---*- -.- - - - --- J. L

1u 11

77..

12 13 (x102)Application time of voltage (sec)

Fig. 7: Measurement result of APN (PVC, 2.5 kV).

This fact indicates that carbon deposit and scintillationdo not occur in region I.

In region II from time A to B, Sv and Sr sensors beganto count the light pulses. Region II, also, indicatesthat the scintillation occurs intermittently. The countrate of the APN and the slope of the TN curve, however,were smaller than those in region III after time B. Itis found that the conductive carbon path is not yetformed due to the intermittent scintillation on the sam-ple surface in spite of the deposition of the carbonparticles.

In region III after time B, the count rate of the APNand the slope of the TN curve show an abrupt change andthen increase, as compared with region II. These re-sults mean that continuous scintillation occurs in theregion III. Therefore, the conductive carbon path rapid-ly grows towards the top electrode after time B, andfinally leads to tracking breakdown.

According to many results of the optical measurementmethod with light sensors, the possible process to thetracking breakdown after the start of the test is de-fined and then classified as follows (see also Fig. 10).

It

512

:=-j=_-j=j=__F "7:Sul-= ---

r..t._ -r :- _= . :

513Nishida et al.: Light sensors as detectors of tracking deterioration

202

0

C) 120 24 d2

3 /m

o JTrack ing~~~~~~~~~i

4444) I 0 E b4

44~ ~~~~~~~~~~~~~~~4~0 _ _0

Tracking~~~~E-'4

.44 brekdwn

Application time of voltage

Fig. 9: Model of TIN curve with Sv and Sr.

Application of voltagReg i on I

Carbon deposition andintiation of scintillation

Region II

Formation of conductivecarbon path

Region m

Track ing breakdown

Fig. 10: Possible process to final tracking breakdown.

Region I is the required time (Ts) for the initiationof the scintillation and the deposition of the carbonparticles. Region II is the required time (Tf) for theformation of the conductive crabon path and continuousscintillation. Region III is the required time (Tg)for the propagation of the conductive carbon path fromthe bottom electrode to the top one. The criticalpoints along the time axis A and B, therefore, indicatethe transition points of respective processes duringthe tracking deterioration.

The conventional methods [6-7] for the detection oftracking deterioration are based on observations withhuman eyes, the measurement of the leakage current,and the change of the current waveform. These methodscaused many problems in accurate discrimination of thetracking deterioration processes. On the other hand,the proposed method in this paper has many excellentcharacteristics, such as the possibility of automatedmeasurement, continuous measurement, no error caused bypersonal influence, etc. Therefore, it can be clearlystated that the optical measurement with light sensorsis suitable for detecting the transition process oftracking deterioration.

REQUIRED TIME AND OCCUPIED RATEOF THREE REGIONS

M4easurement Method of Required Time for Three Regions

The scintillation and the formation of the conductivecarbon path were mainly observed near the edge of thebottom electrode. The optical arrangement of Fig. 2sometimes caused a pulse count error. Therefore, whenaccurate measurement of the required time for three re-gions had to be performed, the inlet of the OF wasmodified to the inverse direction, as shown in Fig. 11.

I2 5

wwW

_(

InIf)

all dimensions in mm

".......... ........................................................................................

k():Test sample i:U.Y.tron (Su)Q2:Top electrode (®:G lass fiber for Sr-21I:Bottom electrode icb:Glass fiber for Sr-I®04:Filter-paper(contaminant feed)KV:Long-wave pass filterl.................... ...... ....................................................................................... .......................................................................................

Fig. 11: Arrangement of light sensors for measure-

ments of three regions.

Two Sr sensors were used because the Sr sensor has a

high sensitivity compared to the Sv sensor. They were

optically connected with the OF. The inlet of the OFwas attached at two positions, near the bottom electrode(Sr-l) and between bottom and top electrode (Sr-2) (seealso Fig. 11) . The Sr-1 sensor was attached near the

4

.4

t

r,

tl

M)w


bottom electrode for the purpose of the measurement ofscintillation initiation and the formation of the con-ductive carbon path. On the other hand, the Sr-2 sen-sor was attached between two electrodes for the purposeof the measurement of the propagation stage of the car-bon path.

Fig. 12 shows a typical result of the TN curve withthe optical measurement system of Fig. 11. The TNcurve in Fig. 12 gives the same tendency as that shown

(X105) 400 800 (X104)

5.0- 5.0 °,

4.0- 0 Su -4.0

c *Sri13.0 Sr.2 D .0

C C~~~~~~~~~~11)020 a)O~~~2.0-0

Z -.1.-

1.0 10 t~

2000 \ *~~~~~~~~~-- - PC2000-

1500 ~ \0

' 1200

o°\. 800 \

cc 400 -

1.5 2.5 3.5 4.5Test voltage (KV)

Fig. 13: Measurement results of required time forregion I.

00..

400 800 1200

Application time of voltage (sec)

Fig. 12: TypicaZ resuLts of the TN curves with themodified set position of Zight sensors (PVC, 3.5kV).

in Fig. 8. It is another interesting fact that thetime for the critical point B with the Sr-l sensor dif-fers from that with the Sr-2 sensor. This might becaused by the discrepancy between the measurement areaand the attached positions between the two sensors.This is because the Sr-2 sensor, which is attached be-tween two electrodes, cannot detect the scintillationoccuring at the top of the conductive carbon path under6 mm in the length from the bottom electrode. There-fore, the time discrepancy between Sr-1 and Sr-2 sen-sors indicates the propagated speed of the conductivecarbon path. It was also confirmed that the propaga-tion of the carbon path was increased with increasinglength from the bottom electrode.

Measurement ResuLt of Required Time for Ahree Regions

Figs. 13, 14, 15, and 16 show the voltage dependenceof the required time for three regions and the time to

tracking breakdown (lb), respectively. The results inFigs. 13-15 were obtained by the TN curve of the Sr-lsensor. Each dot in the Figures shows the averagevalues of 5 to 7 samples. The curves for Ts, Tf, andTg decrease by increasing the applied voltage, so thatthe Tb curve does not become the V-shape which has usu-

ally been found in the IEC 112 test method [6].

On the other hand, both the required time for threeregions and Th (time to tracking breakdown) depend onthe types of samples, and the relationship among theused samples are given as follows:

t)U,C-

C._0a)

t-

o

. _

aL)

.-_c0

aL)

11

O-PSO-PVC*- -PCO- PL

1.5 2.5 3.5Test voltage (KV)

4.5

Fig. 14: Measurement resuZts of required time forregion II.

.5 4000 _ t PSO-PVC

0 ~~~~*---PC.°2000 \', -Pc

; 800 _ X

OX

-n 400

aOI)

2.5 3.5 4.5Test voltage (KV)

Fig. 15: Measurement results of required time forregion III.

51t4

515Nishida et al.: Light sensors as detectors of tracking deterioration

PS PVC PC

Fig. 17: Occupied rate oftracking breakdown.

gi ~~~~~~~Rg i on

volI tage1.5 (KY)

three regions in time to

2.5 3.5Test voltage (KV)

4.5

Fig. 16: Measurement results of time to trackingbreakdown.

Ts: PS > PC > PVS > PL

Tf: PC > PVC > PL > PS

and the rate of Tg increases inversely. This resultsuggests that the main factor for PVC changes with theapplied voltage from the initiation process of thescintillation to the propagation process of carbonpaths.

For PC, the rate of Tg <1.'5 kV shows a very largevalue. The rates of Tf and Ts, also, decrease slightlyby increasing the applied voltage >2.5 kV. This resultsuggests that the main factor for PC slowly changes withthe applied volrage >2.5 kV from the initiation and theformation processes of the scintillation to the propa-gation process of the carbon path.

at 1.5 kV.

above 2.5 kV.

Th: PS > PC > PVC > PL

where Th is the total time (Ts+Tf+Tg) of the threeregions.

From the above results, the degree of tracking re-

sistance among the four samples correlates with that ofTs, as compared with Tf and Tg. However, it is anotherinteresting fact that Ts for all samples is not alwaysthe main factor in determining Tb. For example, the Tsfor PS is twice as much as that of PC, in spite of a

slight difference for Th (Figs. 12 and 16). This factsuggests that the main factor for determining the Th

value is dependent on the type of sample.

Occupied Rate of Three Regions

When the value of Tb was normalized to 100%, the oc-

cupied rate among three regions could be calculated.Fig. 17 shows the calculated result of the occupiedrate for three regions. It shows that the occupiedrate for three regions correspond to both the sampletype and the applied voltage.

For PS, the occupied rate of Ts shows the largestvalue comparing with the other samples. The occupiedrate of Ts also increases remarkably by increasing theapplied voltage. On the other hand, the occupied rates

of Tf and Tg are smaller than that of other samples.This fact for PS indicates that the process for the in-itiation of the scintillation becomes the main factorfor determining the tracking breakdown.

For PVC, the occupied rates of Ts and Tf show therelatively large value under the low voltage applica-tion. However, it is observed that the occupied rates

of Ts and Tf decrease by increasing the applied voltage,

(1) On the other hand, the rate of Ts for PL tends to in-crease with the applied voltage, similar to the case ofPS. The rate of Tg, however, gives a value above 50%under all voltage ranges. Therefore, it is suggestedthat the main factor which decides the time to the finaltracking breakdown of PL is different from that of PS.

When the degree of the tracking resistance for thematerials is examined, the details of some states ofthe aging characteristics and the degrading factor un-

der the respective test conditions have to be under-stood. This is because the final tracking breakdown isobserved as a result of mixed processes under severalfactors; the proposed system will become an effectivemethod for the investigation of tracking deterioration.

CONCLUS IONS

The method for detecting tracking deterioration withthree types of light sensors was investigated by means

of the IEC 587 test method. The light sensors usedcover ultraviolet (Su), visible light (Sv) and infrared(Sr), respectively.

Su sensors, continuously count the light pulses fromthe start point of the test until the final trackingbreakdown. Therefore, the count rate of APN and theslope of the TN curve with Su sensor were not correlatedwith the transition of the tracking deterioration.

On the other hand, when the Sv and Sr sensors were at-

tached near the bottom electrode, the slope of the TNcurves changes at two critical points along the timeaxis (A and B), and the tracking process was dividedinto three regions (I, II, and III) at two criticalpoints. It was found that these three regions corre-

sponded to the state of the tracking deterioration proc-

ess. Therefore, it was confirmed that the measurementmethod of light pulses with Sv and Sr sensors gave an

accurate correlation with the transition of trackingdeterioration. Namely, it was shown that the proposedmethod of this paper is suitable for detecting accurately

O-PS0- PVC*--- PC

---PL

-

a'

, 4000B

30-0

09

02000

to:* _

0a 1000

o 500. _

Tg: PC > PS > PL > PVC,

PC > PVC > PS > PL,


the transition of the deterioration process in track-ing breakdown.

In order to study the tracking process in detail, twoSr sensors were used because Sr sensors have a highsensitivity comparing to Sv sensors. The inlet of theOF was attached at two positions, near the bottom elec-trode (Sr-l) and between bottom and top electrodes (Sr2). The Sr-1 sensor was attached for the purpose ofthe measurement of initiation of the scintillation andthe formation of the conductive carbon path. On theother hand, the Sr-2 sensor was attached for the pur-pose of the investigation against the propagationprocess of the carbon path. The time discrepancy be-tween Sr-1 and Sr-2 sensors indicated the propagationvelocity of the conductive carbon path. It was alsoconfirmed that length of the carbon path increased withincreasing the length from the bottom electrode.

The required time and the occupied rate for each re-gion were measured by the proposed method with thelight sensor. The required time for three regions de-pended on both the kinds of samples and the appliedvoltage. It was also shown that the test conditionssignificantly influenced the main process which decidedthe time to the final tracking breakdown.

ACKNOWLEDGMENT

The authors wish to express their thanks to Mr. S.Takahashi and Mr. H. Ninomiya for their experimentalhelp in this work. This work was supported in part bythe Grant-in-Aid for Encouragement of Young Scientistfrom the Ministry of Education, Science and Culture.

[6] N. Yoshimura, M. Nishida and F. Noto, "Influenceof the Electrolyte on Tracking Breakdown ofOrganic Insulation Materials", IEEE Trans.Electr. Insul., Vol. EI-16, pp. 510-520, 1981.

[7] S. Nakamura, J. Kawai, M. Ieda and G. Sawa,"Resistance to Tracking of Polyethylene Dopedwith Flame Retarding Agent Containing Bromine",Trans. IEE of Japan, Vol. 103, pp. 103-110,1983. (in Japanese)

[8] N. Yoshimura, M. Nishida and F. Noto, "LightEmission from Tracking Discharges on OrganicInsulation", IEEE Trans. Electr. Insul., Vol.EI-19, pp. 149-155, 1984.

[9] N. Yoshimura, M. Nishida and F. Noto, "LightEmission Characteristics of Discharge Associatedwith Tracking Deterioration of Organic Insula-ting Materials", Trans. IEE of Japan, Vol. 105-A,pp. 373-380, 1985. (in Japanese)

[10] IEC Publication 587, First edition, "Testmethod for evaluating resistance to trackingand erosion of electrical insulating materialsused under severe ambient conditions", 1977.

[11] IEC SC 15A (Central Office) 44, Draft for anamendment to IEC publication 587, 1981.

Manuscript was received on 16 September 1985, infinaZ form 16 December 1986.

REFERENCES

[1] D.J. Parr and R.M. Scarisbrick, "Performance ofSynthetic Insulating Materials under PollutedConditions", Proc. IEE., Vol. 112, pp. 1625-1632, 1965.

[2] T. Tanaka, K. Naito and J. Kitagawa, "A BasicStudy on Outdoor Insulators of Organic Materials",IEEE Trans. Electr. Insul., Vol. EI-13, pp. 184-193, 1978.

[3] A.G. Day and D.J. Stonard, "Creepage and Clear-ance Discharges in Electrical Equipment forShipboard Use", IEEE Trans. Electr. Insul.,Vol. EI-12, pp. 191-199, 1977.

[4] F. Noto and K. Kawamura, "Tracking and IgnitionPhenomena of Polyvinyl Chloride Resin under wetPolluted Conditions", IEEE Trans. Electr. Insul.,Vol. EI-13, pp. 418-425, 1978.

[5] M.G. Weller, "Variation in the Results ofInclined Plane Tracking Test", IEE Conf. Publ.,No. 177, pp. 282-286, 1979.

516

Documents

Light Sensors as Detectors of Tracking Deterioration