IEEE Transactions on Power Delivery, Vol. 11, No. 2, April 1996

Rubber-epoxy interface

Rubber-epoxy interface

XLPE insulation

663

Closed void Conductive contaminant Insulating contaminant Water Conductive contaminant Insufficient compression of interface (Knife) cut in cable insulation Conductive contaminant Insulating contaminant Conductive protrusion

STUDY ON DETECTION FOR THE DEFECTS OF XLPE CABLE LINES

Katsumi Uchida Hideo Tanaka Ken'ichi Hirotsu

'Ihe Furukwa Electric Co., Ltd. Shin'ichi Kobayashi Susumu Sakuma Hitoshi Inoue Taka0 Kawashima

Chubu Electric Power Co., Inc. Tokyo, Japan Osaka, Japan Nagoya, Japan

Sumitomo Electric Industries, Ltd.

Abstract - This paper is a report on the results of a basic study of testing methods to replace the dc after laying test that is presently most frequently used as an after laying test for XLPE cable lines. Chosen as the alternative waveforms for dc voltage were damped oscillating wave (OSW) and very-low- frequency wave (VLF) voltage. Experiments were conducted on the ability to detect various types of lme defects under these voltages. It was found that these alternative waveforms are promising as after laying te'st voltage waveforms to replace dc and that greater defect detection ability can be achieved by combining them when conducting tests.

L INTRODUCTION

After laying tests are essential to verify the soundness of an XLPE cable long-distance line, including its joints, after the lme has been laid. After laying tests are generally done using dc voltage. With dc voltage, the pwwer source for testing is compact, the test can be easily carried out, and fiied results are obtained even with a dc after laying test.

But the electric field distribution within the insulation when a dc voltage is applied is different from when an ac voltage is applied. There has therefore been some doubt as to whether the defects that occur in a lme when the operation voltage is applied can be efficiently detected by appllying a dc voltage.[l] Concern has also been expressed that a perfectly good XLPE cable might be damaged if a dc voltage is applied to it.[2] In addition there is a demand for the development of testing methods to replace the dc after laying test and provide improved screening ability.

From the standpoint of applying the same type of voltage as the operation voltage, it is desirable to apply a commercial-frequency ac voltage.[3] But this would require a large-capacity testing transformer, and such testing would not be easy to carry out.

The authors, tuming to damped oscillating wave (OSW) andl very-low- frequency (VLF) voltage,[4] carried out a study by model experiments to determine whether the various defects that occur in XLPE cable lines can be detected by tests using such voltages.

In this research we abstracted and modeled the defects in XLPlE cable and its various types of joints, determined the insulation breakdown voltage by OSW and VLF of samples of them, and compared the results with the characteristics obtained by ac and dc voltages.

As a result, it was revealed that there exist specific types of defect that can be better detected by either OSW or VLF and that the defect detection ability can be improved by combining both waveforms.

II. DEFECTS AND MODELING OF XLF'E CABLE AND VARIOUS TYPES OF JOINTS

a Types of joints and defects

The defects that occur when a line is laid often occur mainly ]in the joints and sealing ends of the XLPE cable line. Figure 1 presents a statistical summary of the state of insulation breakdown in XLPE cable lines ]in the 66- to 77-kV class. These joints and sealing ends can be divided into the following two broad categories.

Premold-type joints: As shown in Figure 2, these consist of a stress relief cone made of rubber used for buffering the electric field of the lioint, and an epoxy unit used for the material for a sealing end. Among the defects associated with construction are the voids, contaminants, insufficient compression, and water that is found in the interface between these dissimilar insulators, the rubber-epoxy interface, and the rubber-XLPE interface. Mold-type and tape-wound-type joints: As shown in Figure 3, the reinforcing insulation consists of material of the same type as the XLPE cable insulation. Among the defects associated with construction are

95 SM 490-3 PWRD A paper recommended and approved by the IEEE Insulated Conductors Committee of the IEEE Power Engineering Society for presentatlon at the 1995 IEEE/PES Summer Meeting, July 23-27, 1995, Portland, OR. Manuscript submitted December 28, 1994; made available for printing April 21, 1995.

contaminants in the insulation, protrusions in the semiconductor layer- insulation interface, and external damage to the insulation wife cuts).

Cable breakedown Sealing end breakdown (9.3%)

Joint breakdown Joint breakdown Cable breakdown

Fig. 1. Statistics on breakdown in 66- to 77-kV-class lines

Rubber-epoxy interface

I

Rubber-XLPE interface

Fig. 2. Example of cross-sectional view of a premold-type joint

Fig. 3. Example of cross-sectional view of mold-type, tape-wound-type joint

In the XLPE cable itself we can also have contaminants in the insulation, semiconductor layer protrusions, and external damage to the insulation. But because contaminants and protrusions are tested for when the cable is shipped from thefactory, we need consider only external damage as a defect that can occur during construction.

b. Selection of defects

A selection of types of defects to consider was made based on the above classifications. In making the selection, by preliminary tests we considered that they are defects that can occur during construction and that their occurrence is harmful, and we studied their size and types. As a result, the defects selected for study are as listed in Table 1.

Table 1. Types of defects selected

In the foregoing, we devised a model constructed so as to make it possible to test in the laboratory the types of defects that can occur in the selected XLPE cable lines, and we tested the model in experiments.

0885-8977/96/$05.00 0 1995 IEEE

664

Interface defects XLPE insulation defect

Ddfect Gm I Closed void Conductive Contaminant Insulating contammant

Insulauon shielding layer

ion

Conducta miv)

Conductive contaminant Conducnve prormsion (Knife) cut in cable mulation Conductive contaminant Insufficient compression of interface Water

Insulaung contaminant

III. HIGH-VOLTAGE GENERATORS FOR ALTEWATWE WAVEFORMS

For the altemative waveform generators to replace dc, OSW and VLF were selected, in consideration of the results seen in various literature as well as applicability to cable power transmission lines. These voltage generators were developed for laboratory use and were used in experiments.

a Damped oscillating wave generator

In an after laying test, it is important that a uniform voltage waveform be applied along the entire length of the line. We studied the results obtained in various countries,[4],[5] and keeping in mind that reflection at the sealing end does not pose a problem in long-distance lines of about 10 km length, we developed a generator having the following specifications. The OSW that can be generated with this device is a type in which there is no dc prestress. The basic specifications are listed in Table 2, the circuit is diagramed in Figure 5, the generated waveform is shown in Figure 6, and a picture of the device appears in Figure 7.

Table 2. Specifications for damped oscillating wave generator

Oscillation frequency 1 :;. Constant during damping Maximum output about 170 kV

WOOMR ZWOMR

0 Out put

1 Fig. 5. Circuit diagram of damped oscillating wave generator

500 ps -

Fig. 6. Waveform of damped oscillating wave

b. Very-low-frequency voltage generator

Here 0.1 Hz was selected as the frequency for the very-low-frequency voltage. The waveforms that suggest themselves include a sine wave, triangular wave, quasi-triangular wave, and rectangular wave. A triangular wave was selected as the very-low-frequency wave for this research because a quasi-triangular wave can be generated relatively easily by RC charging and discharging. The basic specifications are listed in Table 3, a block diagram of

the device is given in Figure 8, the generated waveform is shown in Figure 9, and a picture ofthe device appears in Figure 10.

Fig. 7. Appearance of damped oscillating wavegenerator

Table 3. Specifications for very-low-frequency wave generator

Oseiuation frequency I 0.1 Hz Generated waveform Maxi" outout 1 200kV

I Triangular wave (sine wave is also possible)

M&k" load canacitance I 5000 OF

0 + DC Out put E

775-

. . ! : ; ; ! , , i ; . . . . i_l,.-i_..-i- .... ..;.....a ....... j.. : : ; ; : : . ,

. . I i . . . '

Fig. 8. Block diagram of very-low-frequency wave generator ......... ~ .................... .......................... ...................... . .

; ....... . . . . . . . . . . I ....... : ....... i ....... i ....... ?+Ab!> ....

, . ' . .

, , / I ! . .

................ ....... . .

.......

...... ....... ....... ....... ............... ......... , . , . . . . : : : : : : ; : . . . . . . .

; ........ i ....... ; ...... .: ...... : ...... .i : ....... ; .......... ....: ....... i : ; ! ; : : : $ i ...... .: ,...___ J ....... i ....... i ....... I ....... ; ....... i ........................ : : ! ; : : ' ' ................ I . ... : ...... : ....... : ...... :. . .................I ...... j

. . I , / . ......

, . , . , .

, . , . , . , . . . . . . : ; . . . . . . , , . . . . . . , i

Fig. 9. Waveform of very-low-frequency voltage

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Insulation Rubber- XLPE Interface Rubber -Epoxy Interface

XLPE

Fig. 10. Appearance of very-low-frequency wave generator

IV. BREAKDOWN VOLTAGE CHARACTERISTICS BY VARIOUS VOLTAGE WAVEFORMS

a Number of samples and test outline for breakdown tests

Breakdown tests by ac, dc, OSW, and VLF voltage were carried out for the models described above. The test quantities chosen were 6 samples per model for ac, and 5 samples per model for the other wavefom. In consideration of actual after laying test conditions, the voltage was incremented every 10 minutes for ac, dc, and VLF, and for OSW the voltage was applied once per step. The voltage was innemented until sample breakdown or until the

. maximum output voltage of the power source used for testing.

b. Experimental results

The following is a summary of the results of breakdown tests conducted for the four voltage waveforms. Because the experiments are done by modeling, the breakdown voltage varies depending on the size of the model and the size of the given type of defect. Therefore the ratio of the breakdown voltage of each model is important as a characteristic value depending on differences in the voltage waveform.

Accordingly, the experimental results were evaluated as the ratio of each type of breakdown voltage to the ac breakdown voltage. The resdlts are given in Table 4 and Figure 11. For dc, the breakdown voltage ratio was corrected in consideration of differences in the dc electric field distribution between the model and the actual device.

Table 4. Ratio of dc, OSW, and VLF breakdown voltage with respect to ac voltage, for defects of various types

BD voltage ratio dc VLF OSW

Closed void 4.7 5.0 2.0 Conductive contaminant 2.0 1.9 1.1 Insulating contaminant 1.1 1.0 0.9 Water 2.7 1.5 1.6 Conductive contaminant 2.5 1.4 0.9 Insufficient compression of interface 3.0 2.2 1.3 (Knife) cut in cable insulation 2.8 1.0 2.1 Conductive contaminant 2.1 1.9 2.6

Type of defect

Insulation Insulating contaminant I 1.4 I 1.1 I 1.5 Conductive protrusion I 3.1 I 1.1 1 2.0

Closed Void -

DC -VLF O W

Compression of VF

Fig. 11. Ratio of dc, OSW, and VLF breakdown voltage with respect to ac voltage, for defects of various types

V. CALCULATION O F AIiTER LAYING TEST VOLTAGE BY ALTERNATIVE WAVEFORM

a Approach

according to the following approach. This is shown in Figure 12 as well. The after laying test voltage by alternative waveform is calculated

1) The voltage class considered is 77 kV. 2) A defect is defined as one that leads to breakdown of the line within two

years of its start of operation. 3) The ac breakdown voltage at the after laying test time equivalent to (2

years/operation voltage) is calculated according to the inverse power law. When this is done, the characteristic l i e exponent n for each type of defect is used.

4) The after laying test voltage for each waveform is set to the above voltage multiplied by the breakdown voltage ratio of each waveform with respect to ac that is shown in Figure 11.

log VT : ac test voltage . Vo: mat ion voltaEe

logt 4 IT Time 2years

'ITa,,: alternaave waveform test voltage k : breakdown voltage raho of altemaave waveform with respect to ac

Fig. 12. After laying test voltage calculation method by alternative waveform

b. Life exponent n for each type of defect The l i e exponent n for each type of defect listed in Table 1 was

determined in order to make a conversion to the equivalent voltage in ac voltage. Where such values are clear from the literature, those values were used. When not clear, they were determined through experiment.

1) Results for literature search: For rubber-XLPE interface closed voids, rubber-epoxy interface conductive contaminants, and knife cuts in the XLPE insulation, a life exponent of n=9[6] was adopted, with the idea of applying the void discharge degradation by causing void discharge in each case. For semiconductive protrusions and conductive contaminants in the XLPE insulation, the literature[7] reports n=22-25. Thus, to be on the safe side, a value of n=20 was adopted. For fiber contaminants in the XLPE insulation, n=9 was taken, following literature reference [SI.

2) Experimental results: Values were determined by experiments for conductive contaminants and insulating contaminants in the rubber-XLPE insulation and for insufficient interface compression and water in the rubber-epoxy interface. Three levels of voltage were selected for each type of defect, and long-term tests were carried out on five samples each. The results are given in Figures 13 and 14.

3 0 ' ' ' --! ' luUvl c 3 ~ 3 - t I - - , c r J

i o - ' i o o i o ' i o 2 l o 3 i o 4 Tiine until breakdown {hours]

Fig. 13. V-t characteristics of contaminants and insulating contaminants in rubber-XLPE interface conductive

' ' '"'7 &.

-.. x,e*~ I F 9 4 A.Water

Time until breakdown [hours]

Fig. 14. V-t characteristics of insufficient interface compression and water in rubber-epoxy interface

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Rubber-XLPE Closed void interface Conductive contaminant

Insulating contaminant

9 16 17

Conductive contaminant Insufficient compression of interface (Knife) cuts in the cable insulation

insulation Conductive contaminant Insulating contaminant 20 Conductive protrusion 20

c. Results of test voltage calculation

Based on the above considerations, a calculation was made of the voltage that would allow screening of defects that would cause breakdown within two years of start of operation. The results are presented in Figure 15 and Table 6.

Insulating Contaminant Insulating

Contaminant i W a t e r 1

I . Cutm Cable 1 Insulahon Insufficient

Compression ofI/F

Fig. 15, Results of calculation of after laying test voltage according to alternative waveform

Table 6. Results of calculation of after laying test voltage according to alternative waveform

VI. CONSlDERATION OF EXPERTMENTAL RESULTS

a Screening of defects by various veforms

summarized as follows.

1) dc breakdown characteristics: Except for insulating impurities, for dc a high voltage must be applied in order to detect defects. This indicates that the defect detection ability of dc is low.

2) OSW breakdown characteristics: For OSW the test voltage is relatively close to ac, and it is thought to be able to detect defects of various types with good balance. It is found to be particularly good for the detection of various interface defects. On the other hand, its test level with respect to impurities m XLPE and knife cuts is about the same as dc.

3) VLF breakdown characteristics: VLF offers superior ability to detect defects in XLPE insulation. But ifs ability to detect various types of interface defects is not very high. In particular, its test level is about the same as dc for rubber-XLPE interface defects.

As seen from the foregoing, dc has only inadequate ability for detecting defects.

OSW and VLF differ in the types of defects that they can detect well. l3us OSW and VLF are in a complementary relationship with each other concerning their ability to detect defects. This suggests that the ability to detect defects might be further improved by tests in which both voltage waveforms are combined.

b.

The resuIts of calculation of after laying tests by 4 voltage waveforms are

Voltage waveforms and breakdown mechanism

It was fomd that depending on the specific voltage waveform applied, there are specific Characteristics to the ability to screen for defects. The mechanism by which these characteristics arise were considered in relation to the breakdown mechanism.

1) The pattern of the breakdown process: It was confirmed that various interface defects and knife cuts in the XLPE insulation indicate a condition in which void discharge occurs and breakdown takes place. This is based on the fact that with ac and VLF, a steady partial discharge occurs at a voltage that is lower than the insulation breakdown voltage. With the other defects, the amount of discharge tended to increase rapidly, leading to breakdown, simultaneously with the occurrence of partial discharge.

The breakdown process with each type of defect is thought to be divided into the following WO broad pattems.

2) Relationship between tree inception and propagation and the applied voltage waveform: The following knowledge has been gained conceming the effect of the waveform of the applied voltage on the initiation and propagation of the electric tree.

&actors for acceleration of electric tree initiation> - Frequency is high,[9] and change of voltage waveform with respect to

time (dV/dt) is large[lO] - When the space charge accumulation in the vicinity of the defect and the

polarity reversal are superimposed[ll]

*acton for acceleration of electric tree propagaiion> - Frequency is high,[9] and the voltage with dV/dt is applied for a long

time - The gas pressure inside the tree pipe does not readily increase.[ll]

Table 7 summarizes the above characteristics for dc, OSW, and VLF.

<Type I> Each type of interface defect model, XLPE insulatton external damage defects: easy to detect with OSW

and propagation

<Type 2> XLPE insulation conductive contaminants, insulating contaminants, semiconductlve protrusions: easy to detect with VLF

+ Electnc tree mception and propagauon

Fig. 16. Insulahon breakdown process classified by type

Table 7. Various voltage waveforms and tree inception and propagation

dc

Polarity 2 Electric tree Waveform Electric tree reversal inception holding time propagation

no 0 Y long Y I I I I. I.

O s w I yes I large I 0 1 short I n I yes I s m d I A I long I 0

0: excellent x : inferior A: intermediate

c. Voltage waveform and breakdown mechanism

From the above considerations, the differences in defect detection ability according to applied voltage waveform are explained using Figure 17, which shows the typical breakdown process of type 1, which is characterized by void discharge, and of type 2, which is characterized by the direct inception of a electric tree.

1) Type 1: At V W voltage, void discharge takes place continuously from low voltage. But because the dV/dt is small, the electric tree conversion is slow. On the other hand, with OSW the dV/dt is large, so the charge with void discharge concentrates in the void ends. Here the irise of the waveform resembles an impulse voltage, and this is thought to be similar to the phenomenon in the impulse breakdown process.[l2] And with OSW, because there is polarity reversal, conversion takes place from low voltage to a electric tree.

2) Type 2 The initiation of an electric tree with VLF is slow. But once the tree gets started, it propagates quickly, so breakdown is reached at a relatively low voltage. With OSW, on the other hand, although the tree initiation voltage is low, the tree propagation every time voltage is applied is short. Thus some time (voltage steps) is needed until breakdown is reached, and the breakdown voltage is high.

Tree Inception Tree hopagation

VLF

o s w b BD I

<Type 1> + Breakdown voltage

Tree Inception Tree Propagation

<Type 2> 4 Breakdown voltage

Fig. 17. Breakdown process by damped oscillating wave and very-low- frequency voltage

The above mechanism can explain qualitatively the characteristic breakdown properties according to OSW and VLF.

d. Summary

As described above, it has become clear that OSW and VLF voltage selected as an altemative waveform for dc voltage exhibits better properties than dc for the ability to detect defects. This shows that these voltage waveforms hold promise as alternative test waveforms in dc after laying tests. Moreover, it has been shown that the breakdown characteristics of both alternative waveforms are in a mutually complementary relationship for detecting defects. This suggests that the defect screening ability can be further improved by after laying tests that combine both waveforms.

Keeping in mind tests on actual lines, it is very desirable to be able to detect defects with as low a voltage as possible. In this sense, considering applicability to actual lines, by taking full advantage of the properties of both waveforms it should be possible to come up with a method for aftex laying tests that is just better than a dc after laying test but even rivals an ac after laying test.

VII. BASIC 5v"Y OB AFTER LAYING TEST METHOD

FREQUENCY WAVE COMBINING DAMPED OSCILLATING WAVE AND VERY-LOW-

The above considerations suggest a testing method that makes use of the tree inception properties of OSW and the tree propagation properties of VLF. This is a method in which a tree is initiated at low voltage by applying an OSW voltage, and then, by applying VLF, at low voltage the tree is made to

667

propagate, leading to breakdown. This should make it possible to screen for defects at a lower voltage than would be required with either single waveform.

The results of breakdown voltage reduction by this combination were verified using block-type test samples.

a Experimental method

The discussion thus far predicts that the tree inception and propagation properties of OSW and VLF should be different between type 1, which is characterized by void discharge, and type 2, which is characterized by the direct inception uf a electric tree. Samples representing these two types of defects were tested in an experiment. They are shown in Figure 18.

(a) Type 1 (void type) sample (b) Type 2 (electric tree type) sample Semiconductive

Metal tree needle c.:; 0.5 mm

, electrode

Electrode tip radius : 5pm Electrode tip radius : 1 Fm : l m m

Gap length : 0.5 mm Gap length Void length : 05"

Fig. 18. Block samples for basic study of combination test method

The content of the experiment is as follows.

1) Measurement of the tree inception and breakdown voltage individually for OSW and VLF

2) Measurement of the tree repropagation voltage and breakdown voltage with VLF of samples in which tree inception is initiated by OSW

In this way, an evaluation was made of the (tree inception voltageisingle breakdown voltage) with OSW, and the (tree repropagation starting voltage/single breakdown voltage) and (breakdown voltage after repropagation/single breakdown voltage) with VLF.

b. Experimental results

The experimental results are shown in Figure 19.

Void discharge type samples Electric tree type sairiples

I I I I I I I

VLF OSW OSW VLF OSW OS+W

VLF VLF t

0 : tree inception vohage 0 : lree repropagation voltage

Fig. 19. OSW, VLF combination test: results of basic experiment

m: breakdown voltage U: breakdown voltage after repropagation

Summarizing these results, we have the following.

1) When only OSW is applied, with both models the tree inception voltage is much lower than the breakdown voltage.

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2) When only VLF is applied, with both models, breakdown is reached shortly after electric tree inception, so the tree inception voltage and the breakdown voltage agree.

3) In samples in which the electric tree was initiated with the application of OSW, the voltage from tree repropagation to breakdown with VLF is much lower than the breakdown voltage with VLF alone.

Thus it has been confirmed that in a test that combines OSW and VLF, breakdown can be made to occur at a lower voltage than with either applied singly. This suggests that a test that combines both waveforms comports with general principles and is desirable. At present, verification experiments on this point are being carried out using a model that closely resembles actual cable. Areport on this work is to be presented on another occasion.

VIII. SUMMARY

a Conclusions

The following has been learned as a result of above experiments and study.

1) A technique has been established for abstracting, modeling, and conducting experiments on the defects thought to occur in XLPE cable lines.

2) The breakdown properties of the above samples were investigated with respect to ac, dc, OSW, and VLF voltage. As a result, it was learned that the detection of defects with dc voltage requires a higher voltage than with ac, and that the detection of defects with OSW 01 VLF voltage can be done at a lower voltage than with dc.

3) OSW has a high capability of detecting defects that cause void discharge type breakdown. VLF has a high capability of detecting defects that cause electric tree direct inception type breakdown. Thus it has been leamed that the two waveforms are in a complementary relationship with respect to defect detection capability.

4) It has further been shown that defect detection capability is further enhanced by combining the two waveforms of OSW and VLF.

b. TasksAhead

following tasks.

1) Verification by cable model of the effects of combining OSW and VLF 2) Development of a small, lightweight OSW, VLF generator that can be used

on site 3) Determination of the after laying test conditions to be applied to actual

l i e s

On the basis of the results of the present study we will undertake the

E. REFERENCE

[l] W. Kalkner, R. Bach, R. Platch, Zhiyong. “Investigation of alternative after laying test for MV cables,” Jicable, B. 3. 2, 1994.

[2] G. S. Eager Jr., B. Fryszczyn, C. Katz, H. A. Elabadaly, A. R Jean. “Effect of DC testing on water tree deteriorated cable and preliminary evaluation of V.L.F as alternative,” IEEE T&D Conference, 1991.

[3] M. Ogino et al. “Recent development in Japan of insulation diagnostic technology for extra-high voltage XLPE cable lines,” CIGRE, 21-103, 1994.

[4] H. Auclair, W. Boone, M. S . Papadopulous. “Development of a new after laying test method for high voltage power cable systems,” CIGRE, 21-06, 1988..

[5] C. Aucourt, W. Boone, W. Kalkner, R.D. Naybour, F. Ombello. “Recommendation for a new after laying test method for high voltage extruded cable systems,” CIGRE, Session 21-105, 1990..

[6] F. H. Kreuger. “Endurance tests with polyethylene insulated cable,”

171 R. Jocteur et al. “Research and develoument in France in the field of CIGRE, 21-02, 1968.

. _ extruded polyethylene insulated high voltage cables,” CIGRE, 21-07, 1972.

[SI Tsuchiya et al, National convention of IEEJ (Institute of Electrical Engineers of Japan) paper No. 1549,1994 (in Japanese).

[9] IEEJ Technical Report part I No. 100 (in Japanese). [lo] IEET Technical Report part I1 No. 237 (in Japanese). [ll] P. Gonefeld et al, 5th ISH 21. 10, 1987. [12] Yasui et al, Transactions of the IEEJ vol. 90, No. 1, 1970 (i Japanese).

BIOGRAPHY

Katsumi Uchida was bom in Aichi, Japan, on November 18,1963. He received the B.E., M.E. and Ph D degrees from Nagoya University in 1986, 1988 and 1992 respectively. He joined Chubu Electric Power Co., Inc. in 1988. He has been engaged in research on under ground power transmission lines. Dr. Uchida is a member of Institute of Electrical Engineers of Japan (IEH).

Shin’ichi Kobayashi was bom in Nagano, Japan, on June 2,1966. He rceived the B.E. degree in electrical and computer engineering from Yokohama National University, Japan in 1989. He joined Chubu Electric Power Co., Inc. in 1989. He has been engaged in construction and research on the underground power transmission lines. Mr. Kobayashi is a member of IF‘EJ.

Taka0 Kawashima was bom in Aichi, Japan, on January 6, 1947. He received the B.E. degree in electrical engineering from Nagoya Institute of Technology, Japan in 1969. He joined Chubu Electric Power Co., Inc. in 1969. He has been engaged in construction and research on transmission l ies. Mr. Kawashima is a member of IEEJ.

Hideo Tanaka was bom in Tokyo, Japan, on October 21, 1963. He received the B.E. and M.E. degee in electrical engineering from Tokyo University, Japan in 1986 and 1988, respectively. He joined The Fumkawa Electric Co, Ltd. in 1988. He has been engaged in research on testing method of XLPE cables and development of 500 kV XLPE cables. Mr. Tanaka is a member of IEEJ.

Susumu Sakuma was born in Tokyo, Japan, on February 8, 1954. He received the B.E. degree in electrical engineering from Tokyo University, Japan in 1977. He joined The Furukawa Electric Co., Ltd. in 1977. He has been engaged in design, research and development of EHV cables, their accessories and their forced cooling systems. Mr. Sakuma is a member of the IEEJ, IEEE and CIGRE WG. 21-04.

Ken’ichi Hirotsu was born in Kyoto, Japan, on August 17, 1959. He received the B.E. and M.E. degrees from Kyoto University, Japan and the Ph. D. degree from Georgia Institute of Technology all in Electrical Engineering in 1982, 1984 and 1993 respectively. He joined Sumitomo Electric Industries, Ltd. in 1984. He has been engaged in development of EHV XLPE cables and their accessories, testing method, diagnosis method and application of neural networks. Dr. Hirotsu is a member of IEEJ.

Hitoshi Inoue was born in Osaka, Japan, on October 15, 1951. He received the B.E. degree in electrical engineering &om Hiroshima University in 1974. He joined Sumitomo Electric Industries, Ltd. 1974. He has been engaged in development on EHV oil filled and XLPE cables, their accessories, on-site testing method and diagnosis methods for XLPE cables. Mr Inoue is a member of IEEJ.