Overhead lines Asset Management in the Belgian network. S. GERMAIN K. VAN DAM B. RISSE JF. GOFFINET Elia Belgium

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1 21, rue d Artois, F PARIS B2-208 CIGRE 2012 http : // Overhead lines Asset Management in the Belgian network. S. GERMAIN K. VAN DAM B. RISSE JF. GOFFINET Elia Belgium SUMMARY The Belgian Transmission System Operator Elia is accountable to operate overhead lines and underground cables between 30 kv and 380 kv. The overhead electrical network has been built between years 1920 and today with different towers and conductors technologies with a big peak of investments in the years 60 and 70. In some situation the ageing of those equipments can be important and requires their replacements with different priorities in function of the investments possibilities that take into account the political decisions (for instance the integration of the renewable energies), the electrical needs, the financial constraints, etc. To determine those priorities, it is necessary to know the reliability of existing overhead lines. This paper describes the first step of the methodology implementation to determine those priorities by using different technical information. The following steps should be developed: - A briefly description of the problem and the general principle of the methodology will be explained by introducing the probability of failures and the failures consequence to calculate the risk matrix. - To obtain this risk matrix, it is needed to obtain different technical information from the visual inspection, robots inspection, destructive tests, etc. This chapter will describe in broad lines the actually used parameters to determine the two axes. - Finally a small description of the used tool will be described. KEYWORDS Asset Management, Overhead lines, Replacement policy [email protected]

2 1 INTRODUCTION The Belgian Transmission System Operator Elia is accountable to operate overhead lines and underground cables between 30 kv and 380 kv. The overhead electrical network has been built between years 1920 and today with different towers and conductors technologies with a big peak of investments in the years 60 and 70. In some situation the ageing of those equipments can be important and requires their replacements with different priorities in function of the investments possibilities that take into account the political decisions (for instance the integration of the renewable energies), the electrical needs, the financial constraints, etc. To determine those priorities, it is necessary to know the reliability of existing overhead lines. 2 SITUATION OF THE PROBLEM If we look at the age pyramid of the existing overhead lines owned by Elia, we see different parts in this curve: - The start of the curve where the number of overhead lines is limited. - One or more peaks which depend on investments - The end of the curve that corresponds to the obsolescence of the existing equipment (new generation equipments available, etc). The following picture gives an age pyramid for one of the equipment that fit out the existing overhead lines on the Elia electrical network Maintenance ELIA Zone (All) Electrical span 350 Sum of L km Class Electrical span Année_MSI Two situations must be envisaged to determine when the equipment should be replaced: - If we are in the first part of the curve, a technical audit should be made to determine the state of the existing overhead line. Based on this inspection either no work should be needed because the line is in a good state or an important maintenance should be needed to replace the damaged material and in finality to increase the reliability. In this situation, the cost should be included in the investment cost with a limited impact on the investment; 1

3 - If we are in a peak of the curve, the precedent process shouldn t be only used because the financial impact on the investment is very important and probably bigger than the investment capability of the TSO. Another complementary methodology should be developed. 3 USED METHODOLOGY To determine the priority of the investments, Elia has decided to apply the risk matrix at the overhead lines. This risk matrix has two axes: the technical state of the asset (probability of failure) and the consequence (operation, image ) if we loose them. As indicated in the following picture, the determination of the technical state is a combination of different information: ASSETS INSPECTIONS TECHNICAL INFORMATION FAILURES ANALYSE INSPECTIONS ANALYSE PROBABILITY OF FAILURE - The technical information about the overhead lines (age, type of steel, type of towers, type of conductors, ); - The failures analyse (date of the failure, type of failure, type of material concerned, ); - Analyse of the assets based on different visual inspections, audits, destructive analyse, painting maintenance, etc The second axis of the risk matrix is the consequence of the asset failure. The estimation of this axis is based on a combination of different impacts: ELECTRICAL IMPACT SAFETY IMPACT ENVIRONMENTAL IMPACT... CONSEQUENCE OF FAILURE - The importance of the electrical flow through the asset on the electrical network; - In some situation, the breakdown of the asset has a serious impact on the safety (explosion of a porcelain terminal for example); - The environmental impact; - Eventually other information. The estimation of these different elements must be made with a program that collects all information and calculate the different values. So it is important that each asset, that composes the electrical network, has one and only one reference. Indeed, the different information is stored in various data banks (technical data bank, financial data bank, environmental data bank ) and must be compiled asset by asset. 2

4 4 DETERMINATION OF THE RISK MATRIX 4.1 Probability of failures Since 1990, Elia owns an information data bank with all electrical failures observed on the networks 380 kv to 70 kv. For each incident, a technical analyse is made and the results are stored in it. Today, from this data bank, it is possible to extract all failures observed on overhead lines in function of the date, the type of failures (internal cause, meteorological cause, human cause ) and the electrical circuit number. In parallel, since 2005, a data bank with all technical characteristics of overhead lines is being filled in. For each line asset, it is possible to find the commissioning date, the type of used material, the principal characteristics By combination of the two data banks and by using the internal failures it is possible to determine the probability of failure of different equipments (Aluminium-steel conductor, steel tower, concrete pole ) via the Weibull curves. The obtained curves are conformed to the actual knowhow and the field experience. However, if we consider the internal failures, the number of incidents is fortunately very limited. So it is not possible to determine the curve for each section of a conductor family. Besides these curves don t take into account the environmental effect (sea, land ), the chemical aggression To adjust these curves in the future, Elia has started different actions to determine a health index: - During the routine and legal inspections, the agent writes a malfunction report for each observed damages. This report is written directly in a maintenance tool to plan the curative intervention. However this report contains a lot of important technical information that can be used to determine eventually a local problem on a component. To increase the quality of this report and to use directly the observations conclusion in the asset management tool, Elia has started the implementation of standard cards where the following information is available: the type of equipment where it is possible to observe the degradation, the degradation name, the degradation picture, the cause, the risk, the intervention time and if a monitoring of the installation is needed. 3

5 - For the Aluminium-steel conductor, Elia has been measuring for about 20 years the loss of the Zn galvanisation on steel wires without removal of a conductor sample. With this measure, it is possible to classify the different lines from the good to the bad. However, this measure doesn t give technical information on the rust steel and indirectly on the steel section reduction. Today with the evolution of the technology, it is possible to determine the steel section loss and then the residual mechanical tension of the conductor. This methodology enables a better tuning of the lines based on the state of the conductor without removal of a sample. This technology has been tested, for the first time in 2011, on one line and the results are promising. - To follow the evolution of the tower and fitting degradation, the reinforcement of the climbing patrol has been decided two years ago in order to follow the mechanical degradation in the time. For this purpose 10 to 20 % of the towers have been identified as reference towers. If each reference tower is climbed each 5 years, and the same technical points are observed, it is possible to follow the evolution of the mechanical degradation on the time. For each obtained report, a score is given. It is decomposed in 4 levels that translate a severity status: - RED: correspond to a major loss of mechanical and/or electrical characteristics; - ORANGE: correspond to a medium loss of mechanical and/or electrical characteristics; - YELLOW: the first small degradations are observed; - GREEN: the equipment is in a very good state. These scores should be used to determine the health index. 4.2 Consequences The failure of an overhead line in an electrical network can have different consequences in function of its location and the time of failure. To quantify theses consequences in a first time, Elia has decided to determine the following parameters: - Normally the electrical network is dimensioned for the N-1. In consequence, the loss of an overhead line has no consequence for the operation. When a second failure appears, the loss of the first equipment can be important and eventually drives to a switch off of a customer, a city and eventually to a local or global blackout. However the determination of the consequence of the loss of a line is very difficult because it depends on the configuration of the electrical network at one moment. The solution is very difficult and it is for this reason that Elia has standardised the load of each line in function of a maximum load defined. The result of this calculation gives the first consequence. 4

6 - The second used consequence parameter is the impact on the public. Indeed if we observe a failure of a conductor on a road or in a city, the impact on the public is very higher than in a situation where the breakdown is observed on a field. Moreover if during the incident a people is injured the image of the society is impacted. To take it into account, it has been decided to relate the number of crossing with roads and cities with the maximal number of crossing. With these two parameters, it is possible to compute a global consequence for each overhead line. 4.3 Example of a risk matrix When electrical equipment in high voltage, low voltage or power links has reached his expected life time, Elia writes a replacement policy that defines the reasons of the replacement, the condition of the replacement, the financial impact and the duration of this action. In each policy, it is needed to determine the priority of the replacement because the financial capacities are limited. To obtain these equipments classification, the precedent methodology is used and gives a risk matrix. Each point of the following picture corresponds to an overhead line or a part of an overhead line. RISICO MATRIX ß= 5 80% Legende: draadstelnummer - leeftijd (jaar) - geografische lengte (km) - * indien aardkabel 70% 60% 50% Relatieve gevolgschade 40% 30% 20% 10% 0% 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% Relatieve faalkans The red circle on the picture gives the critical of overhead lines where the risk is above an acceptable risk for the company. This graph gives the priorities for the investments. 5

7 5 ASSET MANAGEMENT TOOL In many situations, the technical needed information is stocked in different data banks (technical data bank, failures data bank, financial data bank, etc) where the information is stocked equipment by equipment. So it is needed a unique identification for each asset that composes the different links, substations, etc. In this situation, it is easy to compile this information to obtain the different components of the risk matrix, for example. Since 3 years, Elia has decided to start the implementation of an asset management tool to manage the different assets those compose the electrical network. Today this program enables the following tasks: - For each asset, this program compiles the different available technical information and gives the basic reports. Those reports must be used to write different documents and to control the data quality by crossing different information. - When the data are compiled, it is possible to estimate the Weibull curve to estimate the expected life time of the asset by using health index. - Another application of this program is the simulation calculation to determine the different components of the risk matrix, the optimal time for the investment, etc - By the using of this tool, it appears that the results are very sensitive to the data quality and should induce bad decisions in some situations. It is for this reason that a specific action is started to increase the data quality via inspection, training of the people, automatic data check, etc. Today, this tool is operational and possesses different methodologies that evolve with the time, with the technology evolution and with evolution of investigations. 6 CONCLUSIONS When the financial resources are limited, it is needed to determine a methodology to find where the money should be the best invested. To reach this goal for the electrical lines and substations, it is needed to determine a risk matrix based on technical information on one side and consequences for the society and the public on the other side. The result is obtained by compilation of much information that comes from one or more data banks. The quality of these data is very important because all errors could lead to a bad investment decision. Finally this methodology is not fixed in the time and may evolve in the future in function of the technical investigation evolution. This asset management is a long-term work. 6

8 BIBLIOGRAPHY [1] Working Group B2.08 CIGRE. Assessment of existing overhead line supports (Technical Brochure 230 June 2003) [2] Working Group B2.15 CIGRE. Life cycle assessment (LCA) for overhead lines (Technical Brochure 265 December 2004) [3] Working Group B2.20 CIGRE. Management of risks due to load-flow increases in transmission OHL (Technical Brochure 385 June 2009) [4] Working Group B2.30 CIGRE. Engineering guidelines relating to fatigue endurance capability of conductor/clamp systems (Technical Brochure 429 October 2010) [5] Working Group B2.33 CIGRE. Working Safely while Supported on Aged Overhead Conductors (Technical Brochure 471 August 2011) [6] Working Group B2.32 CIGRE. Technical Brochure on Evaluation of Aged Fittings (Technical Brochure 477 October 2011) 7