STATISTICS OF FAILURES ON UNDERGROUND HIGH VOLTAGE POWER CABLES IN BRAZIL

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1 21, rue d Artois, F PARIS B1_110_2010 CIGRE 2010 http: // STATISTICS OF FAILURES ON UNDERGROUND HIGH VOLTAGE POWER CABLES IN BRAZIL C. D. PEIXOTO * E. K. FILHO LIGHT Serviços de Eletricidade S.A. EDS Engenharia e Consultoria Brazil Brazil N. H. G. R. de LOUREDO EDS Engenharia e Consultoria Brazil SUMMARY Underground power transmission systems are extremely reliable since they are not vulnerable to winds, storms and other environmental factors. But it s subject to others agents, and when it happens, generally, the time repairs takes too long and so does the interruption of energy. In this way, the establishment of previous diagnosis helps underground transmission owners to avoid undesirable failures, then it reduces the great costs involved in each solution. Referring to underground power transmission systems, it is difficult to perform statistics related to insulated power cables reliability levels. That s because not all the companies participate of this survey, since the replies weren t receive from all areas of the country. However the data collected was representative since the participating companies have the greatest high voltage underground power system. In 2003, the Brazilian Study Committee B1 created a Working Group B1.10 Statistics of Failures of Underground Cables and Accessories to perform a survey among Brazilian utilities and compile the results in a technical report. The collected data in this original survey by this WG goes from 1999 to In 2008, the WG was reactivated and updated the data up to The terms of reference of this WG was to collect statistics for the lengths of underground cable systems at a range of voltages. The collection of the number of failures, the extension of the cables damaged and the total duration of each failure was included in this report. The failure causes and accessories involved were objects of this survey also. This paper shows the results of this WG and details about the already mentioned survey that brings the quantity of failures and the power outage causes on underground high voltage cables in the Brazilian energy utilities. The time of the analysis encompasses the two surveys in the last eleven years, from 2000 to The questionnaires elaborated to the survey could be summarized in the following two basic groups. They were sent to the Brazilian companies that have high voltage underground cable systems. carladam@light.com.br

2 Group 1: collect the data about the total transmission system length observed, the quantity of failures, total length of the damaged lines and its duration out of service, totalizing them per each year; Group 2: informs the identification of each line that failed per year, with its voltage, length, cable type, failure duration, type of cause and its effects. The company could choose from a selected list the type of causes like: system operation, overvoltage, overload, protection equipment problems, external mechanical damages, environmental damages, fire, oil leakage, abnormal oil pressure, installation problems, moisture penetration, manufacturing problems, material stress and ageing. The companies also described the failure effects and their localizations. The participants of this survey totalize four companies named Light, AES Eletropaulo, CTEEP and CEMIG. They are located in the most urban Brazilian area and counted on the cities of Rio de Janeiro, São Paulo and Belo Horizonte. The data was summarized and compared in two tables and graphics indicating frequency, duration, unavailability, quantity of faults per year and its identification. They were analysed including the medium values. 2. KEYWORDS High Voltage, Underground System, Oil Filled Power Cable, Cable Failure, Statistic 1

3 STATISTICS OF FAILURES ON UGHV It consists on a survey of the number of failures and causes of power interruptions in the annual highvoltage cable transmission system underground in the national level. The analysis was extended among 2000 to Data Here we have the collected statistics at a range of transmission lines. Each energy utility company filled two tables like as it follows. Table 1 - The total extension of the underground transmission system observed the amount of faults, total extension of the line involved in the failure and the total annual duration to every year of the period in subject. VOLTAGE (kv) YEAR SYSTEM LENGTH (circuit km) NUMBER OF FAILURES CIRCUIT FAILURE LENGTH (circuit km) DURATION (h) Table 2 - Identification of the affected line and failure cause and the consequently effect VOLTA GE (kv) YEAR LINE ID. CABLE TYPE LINE LENGTH (circuit km) FAILURE DURATION (h) CAUSE EFFECT 2

4 Table 3 - Summarized data with the outage calculation in terms of frequency and average duration VOLTAGE (kv) NUMBER OF FAILURES PER YEAR ANNUAL DURATION OF THE FAILURES (h) EXTENSION IN 10 YEARS (km.ano) TOT TOT FREQUENCY 1/100km.ano AVERAGE DURATION (h) UNAVAI LABILITY (%) AES Eletropaulo (1) CEMIG (2) CTEEP (3) LIGHT (4) , , , , , ,52 88/230/ , , , , , ,68 AES Eletropaulo (1) CEMIG (2) CTEEP (3) LIGHT (4) VOLTAGE (kv) EXTENSION IN 10 YEARS (km.ano) Table 4 - Faillures and causes NUMBER OF FAILURES PER YEAR CAUSES TOT INTERNA EXTERNA SECUNDÁRIA 88, , ,00 172, /230/ , , ,

5 FREQUENCY 5,00 4,00 3,00 2,00 1,00 0, Energy Utility Figure 1 - Comparison of the Frequency Results for each Utility Company UNAVAILABILITY 70,00 60,00 50,00 40,00 30,00 20,00 10,00 0, Energy Utility Figure 2 - Comparison of the Unavailability Results for each Utility Company 4

6 Number of Failures per Year 10 Number of Failures AES Eletropaulo CEMIG CTEEP LIGHT Analised Year Figure 3 - Comparison between the utilities TYPE OF FAILURE CAUSES 2% 40% 1Internal 2External 3Secundary 58% Figure 4 - Failure Causes Identification EXTERNAL CAUSES 4% 4% 1Termite attack 22% 2External enviroment 8% 3Third part mechanical damage 4Installation/maintenance problems 62% 5System protection problems Figure 5 - External Causes Detail 5

7 CONCLUSIONS Considering all the data obtained, it s observed that the annual frequency on underground transmission lines has a reduced value. In spite of the unavailability of the affected line is very high. It is important observe that 99% of the analyzed cables are self contained oil filled power cables. In the case of the analysed failures, the most frequent cause observed was the mechanical damages from third party. In this way, the excavation activities of the other utilities companies were responsible for the majority of the underground cable failures. This point shows the importance of inspections on a regular basis along the cable route to check for evidence of third part activities. Other important action is to establish procedures to exchange information (e.g. cable route records) between utilities and another companies contracted to carry out the underground service. The necessity of to install visual signalizations along the traffic ways and/or side walks that will show the presence of Underground systems represents very important tool referring to UGHV protection. Another relevant cause also verified was termite attack. This cause showed problems occurred when contractors didn t take the correct procedures after cable installation that was to remove all the wood used during the service. Then it is also relevant the existing of external sheath with termite repellent. In despite of the initial high cost involved on underground high voltage cable installations, the usage of this system is compensated by its higher performance and reliability when compared with overhead transmission lines. BIBLIOGRAPHY [1] XVI SNPTEE Group III GLT/029 - Probabilistic Index of Performance in Transmission Lines (National Seminar on Production and Transmission of Electrical Energy, Brazil 2001) [2] XVI SNPTEE Group III GLT/030 - Probabilistic Index of Performance in Transmission Lines (National Seminar on Production and Transmission of Electrical Energy, Brazil 2001) [3] Brazilian Working Group B1 TF nº 12 CIGRE - Statistcs on Underground Transmission Systems (Brazil, 2003) 6