Iec 62217 Paper-e-13 2x3fi

ISBN 978-0-620-44584-9

Proceedings of the 16th International Symposium on High Voltage Engineering c 2009 SAIEE, Innes House, Johannesburg Copyright °

TRACKING AND EROSION OF COMPOSITE INSULATORS AND SPACERS – A COMPARATIVE STUDY OF TEST METHODS Darcy R. De Mello1*, Ricardo W. Garcia1 and Jorge R. de Mendonça1 1 CEPEL – Electrical Energy Research Center, Av. Olinda s/n, Adrianópolis, Nova Iguaçu, RJ, Zip Code 26053-121, Brazil *Email: [email protected] Abstr act: A comparison among the results obtained with the application of the tracking wheel test and 5000 h test to the same composite insulators for overhead lines and a discussion about approval criterion are presented. The 5000 h tracking and erosion test in a small compact distribution line is also presented. The results obtained are discussed principally with reference to three phase polymeric spacers and, as a result, a new tracking and erosion test for three phase spacers is presented.

1.

of them for 15 kV, to be tested at the same time, as can be seen in Figure 1.

INTRODUCTION

The necessity to make tracking and erosion tests on composite insulators as design tests following several IEC standards (IEC 61109 [1] and IEC 61952 [2]) obliged the test laboratories to mount special structures to fulfil the standards. There were two possibilities to make this test: the 1 000 h test and the multiple stresses test that was better known as 5 000 h test. Due to the long time of the 5000 h test, a special test chamber was built in order to testing, at the same time, several 15 kV composite insulators for overhead lines, composite line post insulators, polymeric pin post insulators and polymeric lightning arresters. When IEC 62217 [3] was published, it presented one new test method (wheel test) and changed the test arrangement and the voltage level of the 5 000 h test, reducing the number of the samples to be tested at the same time. These modifications made the laboratories to mount the wheel test and, during its implementation, several tests were made on the same composite insulators for overhead lines that had been tested with the 5 000 h test. The results obtained with this comparison are presented in this paper and permit an evaluation of what test is the best to evaluate the tracking and erosion characteristic of a polymeric insulator.

Figur e 1: Plan view of the 5000 h test facility

This paper also presents a 5000 h test made on insulators and cables for distribution compact lines to evaluate the tracking and erosion characteristic between them. The necessity to evaluate polymeric three phase spacers for compact distribution lines made the laboratory to develop a new tracking and erosion test with a three phase energization that is presented in this paper. 2.

2.1.

2.2.

Wheel test facility

The testing was conducted at the same special chamber of the 5000 h test as seen in Figure 2.

COMPARISON BETWEEN TRACKING AND EROSION TEST METHODOLOGIES 5000 h test facility

This test was mounted at the CEPEL’s High Voltage Laboratory, in a chamber with 5.20m x 4.60m x 4.60 m height, that let to install 24 composite insulators for overhead lines and 63 composite line post, polymeric pin post insulators or polymeric lightning arresters, all

Figur e 2: View of the wheel test facility Pg. 1

Paper E-13

Proceedings of the 16th International Symposium on High Voltage Engineering c 2009 SAIEE, Innes House, Johannesburg Copyright °

ISBN 978-0-620-44584-9

2.3.

Test samples

2.4.

The main characteristics of the 15 kV composite insulators for overhead lines used in the comparison test can be seen in Table 1.

The photos showing the results after the 5000 h test and after the wheel test can be seen in Figures 3 to 5. At each figure, the sequence showed is: A) first, the insulator when new (1 sample);

Table 1: Composite insulators main characteristics. Insulator number

Dry arc distance [mm]

Creepage distance [mm]

Voltage for wheel test [kV]

1 2 3

260 240 224

682 524 590

23.,8 18,3 20,6

Test results

B) second, the insulator after 5000 h test (1 sample); C) third, the insulator (4 samples).

after

wheel

test

B)

A) C)

4 Figur e 3: Insulator number 1

Pg. 2

Paper E-13

Proceedings of the 16th International Symposium on High Voltage Engineering c 2009 SAIEE, Innes House, Johannesburg Copyright °

ISBN 978-0-620-44584-9

A)

B)

C) Figur e 4: Insulator number 2

A)

B)

Sample 1

Sample 2

C) Sample 3

Sample 4

Figur e 5: Insulator number 3 Pg. 3

Paper E-13

Proceedings of the 16th International Symposium on High Voltage Engineering c 2009 SAIEE, Innes House, Johannesburg Copyright °

ISBN 978-0-620-44584-9

2.5.

system and propagates on the cable semiconducting housing.

Test comments

The insulators number 1 and number 2 were approved in 5000 h test but all samples of the same insulators submitted to wheel test were disapproved. The insulator number 3 presented non conductive erosion with 1 mm depth in 5000 h test and can be considered approved but in the wheel test all samples failed. The test results permits to consider that the use of the creepage distance, in the determination of the test voltage value, is the factor that makes a test able to best evaluate the tracking and erosion characteristics of a polymeric insulator. The revision of IEC 61109 and IEC 61952, published in 2008, indicates the use of IEC 62217 for tracking and erosion tests. This standard considers the leakage distance also for the 5000 h test but considering the test duration (more or less 7 months for 5000 h test and 1600 h for wheel test), the wheel test can be considered the best option. Another option for tracking and erosion test, presented by IEC 62217, is the 1000 h test that uses also the creepage distance but an inquiry made by IEC consider it the less severe among the three test options as can be seen in Figure 6.

Figur e 7: Compact line test arrangement

Figur e 6: Results of IEC inquiry 3.

COMPACT LINE EROSION TEST

TRACKING

AND

The electrical companies had related several failures in the assemblages polymeric pin insulator + cable and polymeric spacer + cable. Figur e 8: Test result with XLPE cable, polymeric ring and polymeric pin insulator

As there are no standards for polymeric pin insulators and polymeric spacers, it was decided to make 5000 h test to evaluate the tracking and erosion withstand capability of the assemblages. To do this test, a small compact distribution lines using the arrangement present in Figure 7 was mounted. Some test results are presented in Figures 8 to 10 and one can be seen that the main problem is the dielectric compatibility between the cable, the polymeric insulator and the tie system or between the cable and the tie system (in the case of porcelain insulators). The tie system must have its resistivity similar to the cable resistivity to avoid the current circulation in their interface due to the potential difference between them. It was also observed that the failure begins on the tie

Figur e 9: Test result with HDPE cable, polymeric preformed tie and polymeric pin insulator Pg. 4

Paper E-13

Proceedings of the 16th International Symposium on High Voltage Engineering c 2009 SAIEE, Innes House, Johannesburg Copyright °

ISBN 978-0-620-44584-9

4.2.

•

the circuit is heated until 60º C by induction using a current transformer;

•

to refresh is used rain (precipitation of 1 mm/min and conductivity of 750 µS/cm) in a cycle of 5 min with rain and 15 min without rain. Test results

The results obtained showed tracking similar the observed in field with the spacers (see in Figure 13), including also its destruction by flame due to a short circuit between phases (see Figure 14). With the pin post insulators it was observed a tracking similar to the result obtained in 5000 h test made with cable (see Figure 15) and the appearance of tracking signals in the region where the metallic pin is introduced into the pin post insulator, as can be seen in Figure 16. This type of tracking was observed in the field and is a great problem to the maintenance team due to its position.

Figur e 10: Test result with XLPE cable, polymeric preformed tie and porcelain pin insulator The results obtained in laboratory showed fails similar to the fails obtained in field for the cable – insulator arrangement (see in Figure 11) but the results with polymeric spacers were not the same because it has a three phase configuration and the test has only a one phase test source.

Figur e 11: Cables mounted with polymeric insulators danified in field 4.

TRACKING AND EROSIN POLYMERIC SPACER

TEST

ON Figur e 12: Compact line test arrangement. Where: 1 → three phase test transformer

A test circuit to evaluate the capacity to withstand tracking and erosion of three phase polymeric spacer and the dielectric compatibility between spacer, cable and tie was developed when was verified that there are no international standards for this equipment. To the results the same polymeric pin insulators and cable tested in 5000 h were mounted in a configuration similar to a small 15 kV compact distribution line. 4.1.

2 → voltage divider 3 → rain structure 4 → polymeric pin insulators 5 → voltage regulator 6 → current transformer 7 → composite line insulators 8 → auxiliary cables for heating 9 → cable under test 10 → polymeric spacer

Test facility

The first problem is the necessity to use a three phase test transform to energize the test circuit in order to the leakage currents between phases, as can be verified in the field. The second problem is the necessity to heat and refresh the test object and the third problem is the dimension of the test circuit. After several trials the test circuit showed in Figure 12 was approved with the following test methodology: •

the test voltage is twice the nominal voltage of the compact line;

•

test duration of 30 days continuously;

(a) in field (b) in laboratory Figur e 13: Tracking in polymeric spacers Pg. 5

Paper E-13

ISBN 978-0-620-44584-9

Proceedings of the 16th International Symposium on High Voltage Engineering c 2009 SAIEE, Innes House, Johannesburg Copyright °

The dielectric compatibility between cable - insulator tie and between cable - spacer - tie is a problem that must be evaluated in the future for compact lines. The new tracking and erosion test permits to represent the failures observed in the field and in the 5000 h test. It is the single test that can be made with three phase polymeric spacers and can represent the leakage current movement between phases. Although the new tracking and erosion test had obtained good results in the fail representation for pin post insulators its use with this insulator is only advisable for dielectric compatibility evaluation.

Figur e 14: Polymeric spacer burning during a test

6.

REFERENCES

[1] IEC 61109, “Composite suspension and tension insulators for a.c. overhead lines with a nominal voltage greater than 1 000 V - Definitions, test methods and acceptance criterion”, 2004. [2] IEC 61952, “Composite line post insulators for a.c. overhead lines with a nominal voltage greater than 1 000 V - Definitions, test methods and acceptance criterion”, 2004. [3] IEC 62217, “Polymeric insulators for indoor and outdoor use with a nominal voltage greater than 1 000 V – General definitions, test methods and acceptance criterion”, 2004. [4] D. R. de Mello, R. W. S. Garcia, C. E. M. Malheiros and R. L. Silva, “Evaluation of compact distribution networks”, ISH, 2003.

Figur e 15: Damage in the connexion cable - insulator

a)

b) Figur e 16: Polymeric pin post insulators danified (a) in field (b) in laboratory 5.

CONCLUSIONS

The results obtained permits to consider that the wheel test is more rigorous than the 5000 h test and 1000 h and it can be considered the best tracking and erosion test. Considering the its duration, the tracking wheel test needs much less time than 5000 h test and a few more time than 1000 h test, but as theirs costs are the same due the automation the tracking wheel is the best choice.

Pg. 6

Paper E-13