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Tereza Cristina Leite Galindo Tereza Cristina Leite Galindo C

Compaompanhinhia hida hidroelétroelétririca do Sca do São Francisco – Chesão Francisco – Chesf f

Participants: Adolpho Calazans, Augusto Miranda, Eduardo Luiz, Esdras Rodrigues, João Domingos, Josué Beltrão, Max Norat, Marcos Venício, Participants: Adolpho Calazans, Augusto Miranda, Eduardo Luiz, Esdras Rodrigues, João Domingos, Josué Beltrão, Max Norat, Marcos Venício, Companhia hidroelétrica do São Francisco - Chesf

Companhia hidroelétrica do São Francisco - Chesf

ABSTRACT

In this paper we present evaluation

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

problems indicated by thermograms. INTRODUCTION

INTRODUCTION

Chesf (Companhia hidroelétrica do São Francisco) has been applying the thermographic inspection technique Chesf (Companhia hidroelétrica do São Francisco) has been applying the thermographic inspection technique in its substations for more than 30 years, initially in connections and later for equipment evaluation, including in its substations for more than 30 years, initially in connections and later for equipment evaluation, including surge arresters.

surge arresters.

The methodology applied for the surge

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

types of evaluations:

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Quantitative evaluation – considers the difference between Quantitative evaluation – considers the difference between the absolute temperature of the objectthe absolute temperature of the object and the room temperature of the same;

and the room temperature of the same;

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Comparative evaluation – considers the temperature difference between siComparative evaluation – considers the temperature difference between si milar surge arresters.milar surge arresters.

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The numeric criteria are established from the

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

Ligntening Normal Ligntening Normal ((∆∆TT°°C)C) Critical Level 1 Critical Level 1 ((∆∆TT°°C)C) Critical Level 2 Critical Level 2 ((∆∆TT°°C)C) Comparative Comparative ≤≤3 3 33<< ∆∆TT≤≤77 >>77 Quantitative Quantitative ≤≤5 5 55<< ∆∆TT≤≤1010 >>1010 DEVELOPMENT DEVELOPMENT

Some samples were selected to better analyze

Some samples were selected to better analyze the applied criteria and the the applied criteria and the errors associated to the measuringerrors associated to the measuring process in the field:

process in the field:

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To carry out laboratory analyses after field iTo carry out laboratory analyses after field i ntervention;ntervention;

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To monitor the field work through interventions of porcelain surface cleaning.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: The following case studies give examples of our work. Units taken to the laboratory: Case 1: Case 1: 230 kV Surge Arrester.Substation: MRR 230 kV Surge Arrester.Substation: MRR Description of occurrence: Description of occurrence:

Inspection in 04/19/05, at 18:45h. Room temperature of 29

Inspection in 04/19/05, at 18:45h. Room temperature of 29ooC and relative humidity of 73 %.C and relative humidity of 73 %. Thermal critical state level 2.

Thermal critical state level 2.

Action: removal of operation equipment. Action: removal of operation equipment. Thermogram carried out in the field during

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17,9°C 49,8°C 20 30 40 J6: 41,9°C

Figure 1. Thermogram of surge arrester in critical condition Laboratory analyses:

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Measurement of losses – it wasn’t possible to carry out this analysis due to the instability at the measuring bridge, indicator of high losses;

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Measurement of leakage current:

Tension (kV) 1ª. Reading I (µA) 2ª. Reading I (µA) 3ª. Reading I (µA) 2.5 84.7 87.4 88.9 5.0 58.1 53.4 46.8

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

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Case 2:

230 kV Surge Arrester. Substation: MSD Description 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

17,1°C 45,8°C 20 30 40 ase A*: 33,3°C

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

Laboratory analyses:

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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.

Internal Corrosion

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Case 3:

230 kV Surge Arrester. Substation: PRD Description of occurrence:

Inspection in 12/18/01, at 19:00h. Room temperature of 22oC and relative humidity of 74 %. Inspection in 01/15/2002, at 21:00h. Relative humidity of 73 %.

Thermal critical state level 2.

Action: removal of operation equipment

Thermograms carried out in the field during inspections:

21,2°C 32,7°C 25 30 A: 24,9°C 18-12-2001 16,9°C 43,3°C 20 30 40 A: 45,8°C

15-01-2002 - 28 dias após a ins

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

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Measurement of leakage current: Superior Section: Current Voltage (kV) _I P-P (mA) IP÷√2 (mA) 3°h (%I60Hz) 5°h (%I60Hz) 7°h (%I60Hz) 2.5 0.18 0.06 0.00 0.00 0.00 5 0.32 0.11 0.00 0.00 0.00 10 0.61 0.21 0.00 0.00 0.00 20 1.20 0.42 1.28 0.00 0.00 30 1.72 0.60 1.69 0.00 0.00 40 2.24 0.79 1.31 0.00 0.00 50 2.72 0.96 1.54 0.00 0.00 60 3.24 1.14 1.36 0.00 0.00 70 3.72 1.31 3.42 0.00 0.00 80 4.28 1.51 7.57 2.21 0.00 90 5.28 1.86 15.05 5.10 1.28 100 9.40 3.32 26.87 10.97 3.29 105 14.6 5.16 32.96 14.13 3.46

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Inferior Section: Current Voltage (kV) _I P-P (mA) IP÷√2 (mA) 3°h (%I60Hz) 5°h (%I60Hz) 7°h (%I60Hz) 2 2.5 0.88 0.00 0.00 1.79 5 6.5 2.30 0.00 0.00 2.08 7 9.8 3.46 0.00 0.00 2.32 10 13.8 4.88 0.44 0.00 2.18 12 16.0 5.65 0.47 0.00 2.46 15 20.0 7.07 0.22 0.15 3.29 17 21.2 7.50 0.00 0.14 4.21 20 29.2 10.32 0.84 0.52 5.79 25 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: MSD Description of occurrence:

Action: removal of operation equipment.

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18,3°C 40,2°C 20 30 40 Ø B1: 33,5°C Lado NORTE 18,3°C 40,2°C 20 30 40 B*: 32,7°C Lado SUL

Figure 7. Thermogram of problem arrester, north side

Figure 7b. Thermogram of problem arrester, south side

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Measurement of leakage current and dielectric losses:

Superior Section -2 Inferior Section -1 Voltage (kV) Leakage Current (mA) Dielectric Loss (W) Leakage Current (mA) Dielectric Loss (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 10.9255 50 70.20 9.2001 95.00 18.5763 60 111.70 167.00 70 208.30 350.00

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Case 5:

230 kV Surge Arrester. Substation: PRD Description of occurrence:

15,1°C 49,2°C

20 40 33,4°C

Figure 9. Thermogram carried out during field inspection.

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Measurement of leakage current and dielectric losses:

Superior Section Tension (kV) Leakage_Current (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

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Figure 10. Opening of the inferior unit. Case 6:

13, 8 kV Surge Arrester. Substation: FTZ Description of occurrence:

19,2°C 41,8°C 20 30 40 ase B*: 36,0°C

Figure 11. Thermogram carried out in the field during inspection. Laboratory analyses:

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

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The equipment was submitted to a tension of 15 kV/

√

3 in the laboratory and monitored with the IR Camera:

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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: MTT Description of occurrence:

Action: removal of operational equipment.

19,3°C 40,1°C 20 30 40 Fase C: 31,1°C

Figure 14. Thermograms carried out in the field during inspection.

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Measurement of lickage current and dielectrical l osses: they were not carried out.

Figure 15. Opening of the unit.

Case 8:

230 kV Surge Arrester. Substation: NTD Description of occurrence:

Inspection in 02/16/2005, at 19:30h. Room temperature of 23oC and relative humidity of 71 %. Action: external cleaning of porcelain and posterior inspection

18,4°C 38,1°C 20 30 30,1°C 18,4°C 38,1°C 20 30 25,3°C

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18,4°C 38,1°C 20 30 29,6°C 18,4°C 38,1°C 20 30

Figure 17. Phase B Figure 17b. After cleaning

18,4°C 38,1°C 20 30 FC: 31,1°C 18,4°C 38,1°C 20 30 25,3°C

Figure 18. Phase C Figure 18b. After Cleaning

SUMMARY

To characterize heating “rings” in the body of the equipment it is necessary to do a study of the different phases from different angles; Whenever possible, the cleaning procedure of the porcelain and repetition of the 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 operational background, same maker and type; in all cases the cause is the loss of estanqueity with humidity penetration, increase of internal leakage current and heating.

REFERENCE

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