IR SA Case Study

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InfraMation 2006 Proceedings ITC 115 A 2006-05-22

Monitoring of Surge Arresters through Thermographic Inspection Case Studies

Tereza Cristina Leite GalindoCompanhia hidroeltrica do So Francisco Chesf

Participants: Adolpho Calazans, Augusto Miranda, Eduardo Luiz, Esdras Rodrigues, Joo Domingos, Josu Beltro, Max Norat, Marcos Vencio,Companhia hidroeltrica do So Francisco - Chesf

ABSTRACTIn this paper we present evaluation cases of surge arrester operational conditions, through thermographicinspections, criteria applied in the field, and analysis carried out in units removed from operation due to theproblems indicated by thermograms.

INTRODUCTION

Chesf (Companhia hidroeltrica do So Francisco) has been applying the thermographic inspection techniquein its substations for more than 30 years, initially in connections and later for equipment evaluation, includingsurge arresters.

The methodology applied for the surge arrester inspection is based on a structure of possibilities from twotypes of evaluations:

Quantitative evaluation considers the difference between the absolute temperature of the objectand the room temperature of the same;

Comparative evaluation considers the temperature difference between similar surge arresters.

The numeric criteria are established from the evaluations according to the table below:

Ligntening Normal(T C)

Critical Level 1(T C)

Critical Level 2(T C)

Comparative 3 3 7Quantitative 5 5 10

DEVELOPMENTSome samples were selected to better analyze the applied criteria and the errors associated to the measuringprocess in the field:

To carry out laboratory analyses after field intervention; To monitor the field work through interventions of porcelain surface cleaning.

The following case studies give examples of our work. Units taken to the laboratory:

Case 1:230 kV Surge Arrester.Substation: MRRDescription of occurrence:Inspection in 04/19/05, at 18:45h. Room temperature of 29

oC and relative humidity of 73 %.

Thermal critical state level 2.Action: removal of operation equipment.Thermogram carried out in the field during inspection:


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17,9C

49,8C

20

30

40

J6: 41,9C

Figure 1. Thermogram of surge arrester in critical condition

Laboratory analyses:

Measurement of losses it wasnt possible to carry out this analysis due to the instability at themeasuring bridge, indicator of high losses;

Measurement of leakage current:

Tension (kV) 1. Reading

I (A)

2. Reading

I (A)

3. Reading

I (A)

2.5 84.7 87.4 88.9

5.0 58.1 53.4 46.8

It was not possible to progress with the leakagecurrent measurer due to high current indication.

Figure 2. Opening of the unit.


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Case 2:230 kV Surge Arrester. Substation: MSDDescription of occurrence:

Inspection in 04/02/05, at 22:15h. Room temperature of 25oC and relative humidity of 96 %.Thermal critical state level 2.Action: removal of operation equipment

17,1C

45,8C

20

30

40ase A*: 33,3C

Figure 3. Thermogram carried out in the field duringinspection indicating significant problem.


Measurement of leakage current and dielectric losses.It was not possible to carry out the analyses due to high losses.

Figure 4. Opening of the unit. Figure 4b. Internal Corrosion.

InternalCorrosion


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Case 3:230 kV Surge Arrester. Substation: PRDDescription of occurrence:Inspection in 12/18/01, at 19:00h. Room temperature of 22


Inspection in 01/15/2002, at 21:00h. Relative humidity of 73 %.Thermal critical state level 2.Action: removal of operation equipmentThermograms carried out in the field during inspections:

21,2C

32,7C

25

30

A: 24,9C

18-12-2001

16,9C

43,3C

20

30

40A: 45,8C

15-01-2002 - 28 dias aps a ins

Figure 5. Thermogram of problem arrester Figure 5b. Thermogram of critical problem arrester


Measurement of leakage current:

Superior Section:CurrentVoltage

(kV) IP-P(mA)

IP2(mA)

3 h(%I60Hz)

5 h(%I60Hz)

7 h(%I60Hz)

2.5 0.18

0.06

0.00 0.00 0.005 0.32

0.11 0.00 0.00 0.00

10 0.61

0.21 0.00 0.00 0.0020 1.20 0.42 1.28 0.00 0.0030 1.72 0.60 1.69 0.00 0.0040 2.24 0.79 1.31 0.00 0.0050 2.72 0.96 1.54 0.00 0.0060 3.24 1.14 1.36 0.00 0.0070 3.72 1.31 3.42 0.00 0.0080 4.28 1.51 7.57 2.21 0.0090 5.28 1.86 15.05 5.10 1.28

100 9.40 3.32 26.87 10.97 3.29105 14.6 5.16 32.96 14.13 3.46


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Inferior Section:CurrentVoltage

(kV) IP-P

(mA)

IP2

(mA)

3 h

(%I60Hz)

5 h

(%I60Hz)

7 h

(%I60Hz)2 2.5 0.88 0.00 0.00 1.795 6.5 2.30 0.00 0.00 2.087 9.8 3.46 0.00 0.00 2.3210 13.8 4.88 0.44 0.00 2.1812 16.0 5.65 0.47 0.00 2.4615 20.0 7.07 0.22 0.15 3.2917 21.2 7.50 0.00 0.14 4.2120 29.2 10.32 0.84 0.52 5.7925 40.0 14.14 2.68 0.84 7.61

What became evident was the inferior section deteriorated faster with the increase of the losses, in

comparison with the superior section.

Figure 6. Opening of the inferior unit. Figure 6b. Bottom of inferior unit.

Case 4:230 kV Surge Arrester. Substation: MSDDescription of occurrence:Inspection in 11/09/2005, at 19:20h. Room temperature of 29


Thermal critical state level 1.Action: removal of operation equipment.

Thermograms carried out in the field during inspections:


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18,3C

40,2C

20

30

40

B1: 33,5C

Lado NORTE

18,3C

40,2C

20

30

40

B*: 32,7C

Lado SUL

Figure 7. Thermogram of problem arrester,north side

Figure 7b. Thermogram of problem arrester, southside


Measurement of leakage current and dielectric losses:

Superior Section -2 Inferior Section -1

Voltage(kV) Leakage

Current(mA)

DielectricLoss (W)

LeakageCurrent(mA)

DielectricLoss (W)

10 2.37 0.3481 4.60 0.6204

20 6.70 1.3934 9.90 2.6058

30 26.63 3.1751 23.90 5.9656

40 37.83 6.0296 52.40 10.925550 70.20 9.2001 95.00 18.5763

60 111.70 167.00

70 208.30 350.00

Figure 8. Opening of the inferior unit.


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Case 5:230 kV Surge Arrester. Substation: PRDDescription of occurrence:Inspection in 09/28/2005, at 19:14h. Room temperature of 25



15,1C

49,2C

20

40

33,4C

Figure 9. Thermogram carried out during field inspection.


Measurement of leakage current and dielectric losses:

Superior SectionTension(kV)

LeakageCurrent

(mA)

Dielectric

Loss (W)10 1.5 0.1168

20 6.2 0.4946

30 24.0 1.2179

40 32.1 2.4803

50 73.2

60 136

70 250.3

It was not possible to analyze the inferior section due to high losses.


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Figure 10. Opening of the inferior unit.

Case 6:13, 8 kV Surge Arrester. Substation: FTZDescription of occurrence:Inspection in 06/21/2005, at 19:20h. Room temperature of 26



19,2C

41,8C

20

30

40ase B*: 36,0C

Figure 11. Thermogram carried out in the field during inspection.


Measurement of leakage current and dielectric losses: It was not possible to carry out the analyses

due to high losses. The equipment was submitted to a tension of 15 kV/3 in the laboratory and monitored with the IRCamera:


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Ar1:max 67.3

29.1

76.9 C

40

60

FLIR Systems

Figure 12. Thermal profile similar to that in the field.

Figure 13. Opening of the unit:

Case 7:13, 8 kV Surge Arrester. Substation: MTTDescription of occurrence:Inspection in 08/06/2002, at 18:30h. Room temperature of 23


Thermal critical state level 2.Action: removal of operational equipment.

19,3C

40,1C

20

30

40

Fase C: 31,1C

Figure 14. Thermograms carried out in the field duringinspection.


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18,4C

38,1C

20

3029,6C

18,4C

38,1C

20

30

Figure 17. Phase B Figure 17b. After cleaning

18,4C

38,1C

20

30FC: 31,1C

18,4C

38,1C

20

3025,3C

Figure 18. Phase C Figure 18b. After Cleaning

SUMMARYTo characterize heating rings in the body of the equipment it is necessary to do a study of the differentphases from different angles; Whenever possible, the cleaning procedure of the porcelain and repetition ofthe measurement is recommended, as a way to reduce doubts regarding apparent heating due to pollution;The comparative evaluation proved to be more efficient, considering as premises the similar operationalbackground, same maker and type; in all cases the cause is the loss of estanqueity with humidity penetration,increase of internal leakage current and heating.

REFERENCEITC Infrared Training Center - Level II Course;


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