INFORMATION SYSTEM SOLUTION FOR RELIABILITY BASED ANALYSIS AND DEVELOPMENT OF DISTRIBUTION NETWORKS

Transcription

1 INFORMATION SYSTEM SOLUTION FOR RELIABILITY BASED ANALYSIS AND DEVELOPMENT OF DISTRIBUTION NETWORKS Pekka VERHO, Pertti JÄRVENTAUSTA, Antti MÄKINEN, Kirsi NOUSIAINEN Tampere University of Technology - Finland Pekka.Verho@tut.fi Markku POUTTU Koillis-Satakunnan Sähkö Oy Finland Pentti JUUTI ABB Oy Finland Summary Cost efficiency and reliability of power distribution are of great importance in the modern society. The most challenging task for electrical utilities is to reduce costs and improve power supply reliability at the same time. This can be achieved with advanced IT-solution, which provides reliability analysis as part of network planning process. This paper presents the basic ideas of the practical solution, reviews the history and introduces the ongoing development. INTRODUCTION The deregulation of electricity market in Finland in the middle of 1990 s changed power distribution to be more business oriented than utility oriented. Due to the liberalization the price of electricity was reduced and the processes are now more efficient, which was also the original target. The rationalization of the processes has been successful because it has been a driving force and remarkable efforts have been put into the process development. Despite of the deregulation it must be emphasized that all processes are not part of competition. The network management is still monopoly business and resembles the utility business. Such business requires regulation and because of the liberalization in the neighbouring business the need is very critical compared to the old times when the whole business was utility-driven monopoly. Especially it is important to ensure that reducing the level of power quality is not the way of making money in the network management business. Thus the term re-regulation could be used to describe the public controlling of the network management business. In Finland the public control model is becoming established, which means that the utilities (i.e. network management companies) must be aware on the monitoring and in order to success it is better to be proactive instead of reactive. In the current situation, there are two important driving forces in utility s life: Asset management and power quality and the information system solutions supporting the processes. Asset management is a new approach introduced for the use of electricity distribution business. It implies that the most important factor in the distribution management is the maximization of revenues by optimal use of all assets. Asset management means a comprehensive way of thinking covering all activities in power distribution: Investments, maintenance, operation etc.. The consideration of lifetime costs of the components is becoming more and more important due to the aging of the networks. In Finland huge renovation processes are waiting in the near future. The situation is getting worse because at the same time a significant amount of the skilled staff is coming to the age of retirement. Power quality is all the time becoming more and more important. The uninterrupted electricity distribution is of great importance to the society and new computer based devices and electronic appliances are critical regarding to the power quality, which means not only interruptions but also voltage quality. The harms due to voltage dips, harmonics etc. are becoming more important factors. In order to be aware of the existing power quality level in the network there must be methods to measure and monitor the power quality: there must be comprehensive outage statistics and monitoring of the voltage quality. The modern power quality monitoring has been presented in [1] and [2]. The driving forces asset management and power quality are linked to each other in two senses in two senses: The regulator should create a control model which motivates the utilities to improve or at least maintain adequate power quality and at the same time aims for optimal asset utilization. Regarding to the network calculations and planning the two driving forces are linked in reliability analysis: methods to estimate e.g. the number and duration of outages in the distribution network. In order to be ready for coming control model the proactive utility should use reliability analysis as part of its network planning and development process. The concept asset management is quite new in power distribution and also power quality seems to be in fashion. Nevertheless, an obvious drawback of these new concepts is the discrimination of the traditional and still relevant solutions. One aim of this paper is to point out that many TUT_Verho_A1 Session 5 Paper No

2 traditional solutions (both the methods and information system integration) are more or less in line with modern asset management and power quality philosophy and provide a good basis for new methods and comprehensive approach. In this paper the development of the solutions used in Finland since the 1980 s are shortly reviewed in order to illustrate the evolution from separate systems to the integrated information system entity. The evolution process is made more concrete by introducing a case study representing a 15-year development in one Finnish utility. Finally the paper presents the recent research and development activities and the further development ideas. The main focus is in the development of reliability analysis to better fit in today s and future requirements and to better utilize the existing possibilities provided by the distribution automation and information systems. UTILITY S INFORMATION SYSTEM ENVIRONMENT The information systems and their mutual integration are of great importance for the power distribution companies. In this chapter integrated information system entity is presented covering network information system (NIS), distribution automation (DA), distribution management system (DMS) and some other related systems. The integrated information system entity is illustrated also in figure 1. CIS Network monitoring Customer database Distribution management system Network Documentation Operations planning & Optimization Network Information System Figure 1. The integrated information systems Network Information System Network planning & Optimization Network database Fault management SCADA Distribution process The core of the integrated information system is formed by network database and the data management application. Traditionally the background of such systems lied in the Automated Mapping (AM) system and the Facilities Management (FM). Originally they were separate systems but are nowadays integrated into one system referred as AM/FM/GIS or simply GIS. In Finland the evolution has been slightly different generating a concept of network information system (NIS), which means a system with network calculations taking into account technical restrictions (e.g. voltage variations and network protection) and planning integrated with network database (AM/FM/GIS). This tradition originates from the 1980 s and includes also another special form of integration: The use of customer energy consumption data available in customer information systems (CIS) in load assessment. The methods for distribution network planning purposes were actively developed in Tampere University of Technology (TUT) in the 1980 s. The foundation of those methods was the consideration of total costs in long term as an obective including investments and losses. Looking now back it can be after wisely said that those methods were actually elements of power quality and asset management. In addition to the traditional planning methods the methods developed included also a quantitative reliability analysis, which could be used to ensure the adequate power quality improvements with optimised total costs. The practical implementation of the methods in a PC based environment was also the basis for NIS [3]. Nowadays, the developed methods and the associated PC-based implementations are widely used in Finnish utilities as part of ordinary processes. Distribution Automation and Distribution Management System Another important characteristic of power distribution in Finland is the long tradition and high level of distribution automation at MV level. The use of SCADA systems also in distribution became common already in the 1980 s and not only in the substations but also in the network level together with remote controlled disconnectors. The basic philosophy in feeder automation has involved centralized instead of local automation, which forms a good basis for the development of new solutions, such as Distribution Management System (DMS). In 1990 s there was intensive development of DMS at TUT together with system suppliers and a rural utility, Koillis- Satakunnan Sähkö Oy. As a result an advanced DMS was developed to integrated environment, where SCADA and NIS are the main information sources (figure 1). The system provides application functions for network monitoring, operations planning and fault management purposes. The foundation of most functions lies on the system integration, which means utilizing of process data together with network information to generate more information and knowledge. The application provides advanced functionality for network monitoring, fault management and operations planning. The DMS concept is presented in more detail in reference [4]. One of the best examples of integration-based functionality is short circuit fault location. In the case of faults in distribution network the fault current data registered by modern microprocessor based relays and the indications of fault detectors are transferred from the substations. This information is combined with the network data and the calculated fault currents in the DMS by applying fuzzy reasoning. As a result the possible fault locations are shown TUT_Verho_A1 Session 5 Paper No

3 to the system operator together with the instructions for operations to be carried out in order to isolate the fault and restore the supply to the non-faulted parts of the network. The remote controlled part of the sequence can even be automated, which is extremely useful in an unmanned control centre (e.g. at night). When the fault has been repaired DMS is used to support the outage reporting. The interruption time for each customer is calculated and stored to database. Also the total values are calculated together with the amount of non-delivered energy. Reliability Analysis In principle, the reliability analysis of distribution networks is quite easy thanks to the radial operation of the networks. The basic input data is the failure rate of each component and network configuration. The determination of outage time in different parts of network due to faults is not so simple. Some parts of the network are restored (repair rate from the reliability point of view) using remote control in some minutes, some other parts are restored manually in some tens of minutes and in a fairly small part of the network the outage time is the same as real repair time. As a basic result of the reliability analysis the outage number and duration in different parts of the network is calculated. These parameters can further be combined into SAIFI, SAIDI and CAIDI, which provide average reliability indices for the whole system without any consideration of the importance of the customers. Instead of the mere overall indices the measuring of reliability level of distribution network should be based on the customer outages and reliability worth evaluation, which can be achieved by modelling the inconvenience of the customers by outage costs. By this means it is possible to make reliability commensurable with other operational costs. The evaluation of the outage costs met by customers is based on the value of non-distributed energy. In Finland some studies have been carried out to determine this value for different customer groups. Depending on customer the value of non-distributed energy may be even over one hundred times greater than the unit price of distributed energy. The reliability analysis is based on the following formulas: f U = f k k K = k K f t k k C = f ( a + b t ) P k K i I k i i k where f = total outage rate of load point f k = failure rate of component k K = set of components whose failure results in an outage at load point U = total outage time of load point i t k = outage time of load point caused by a failure of component k C = total outage costs of load point a i =outage cost parameter for demand not supplied for customer group i [ /kw] b i = outage cost parameter for energy not supplied for customer group i [ /kwh] P i = outage power of customer group i at load point I = set of customer groups In the model, developed at TUT six different switching times are applied and each outage time depends on how faulted component, load point, and remote controlled and manually operated disconnectors are situated. The reliability analysis has been further described in [5]. REALIZATION OF UTILITY S DEVELOPMENT PROCESS The overall development can also be considered from another point of view by studying the process in the pilot utility, Koillis-Satakunnan Sähkö Oy. In the middle of the 1980 s the utility was in a situation typical in Finland. The level of automation was rather low and old-fashioned as well as the overall organization of network operations. However, the situation was favourable for remarkable changes. The construction manager and the operation managers were new and open to new ideas and the organization was small enough for flexible changes. The situation was analysed and a longterm development plan considering the network operation was made. According to the plan the important strategic investments should be focused on distribution automation instead of primary network. This decision can be seen as a strategy, which was implemented together with broad-minded use of latest technology and intensive co-operation with partners; i.e. system suppliers and a university. In practice the implementation of the DA strategy meant intensive automation investments in logical order. A new Network Information System (NIS) was acquired already in The system was PC-based offering an inexpensive solution for data management and network calculations. The old-fashioned SCADA system was replaced in 1988 with a modern and reasonable PC-based system. In this context the revolutionary selection was the remote terminal technology. Instead of traditional remote terminal units (RTU) a new concept was chosen; integrated secondary technology. This means use of new feeder terminals for both relay protection and remote control. The shifting to the new technology was made step-by-step in , so that in the end all relays (feeder terminals) in all substations were identical. In addition to the substation control the building of remote controlled disconnector stations was intensive especially during the turn of the decade, but the process has been continued throughout the years. Reliability analysis tool described above was of great importance in the selection of the locations on the remote control. Nowadays there are more than 100 remote controlled disconnectors while the total number of line TUT_Verho_A1 Session 5 Paper No

4 disconnectors is about 600. An important part of the overall development was co-operation in DMS development with the university (TUT) and system suppliers. At first a fault location application was developed as a pilot proect, which eventually resulted in the DMS concept. One of the results achieved by the implementation of the DA was the decrease of the mean outage time (in hours) per a fault (also referred as CAIDI, Customer Average Interruption Duration Index), which is a good measure for the operational efficiency (figure 2). The figure shows that the mean outage time per fault has decreased into half in ten years. At the same time remarkable labour cost savings were achieved because of the lightened duty practice. Meanwhile, along with the higher automation level (especially thanks to remote controlled disconnectors and fault location application) the number of the needed duty crew was decreased into half. Remote control of disconnectors has also affected to labour cost savings and outage time reduction during the scheduled outages. hours 1,4 1,2 1 0,8 0,6 0, year Figure 2. The development of mean outage time per a fault in pilot utility A more detailed description of the development process is presented in reference [6]. At present the focus is in fault prevention (including transient and permanent faults), preventive fault indication and other new applications. Network renovation includes also challenging planning tasks. The utility is still very active in piloting the new ideas based on the system integration, both in power quality monitoring and asset management area. RECENT DEVELOPMENT As indicated above, there is a long tradition in Finland in the utilization of the system integration in the development of power distribution process. Characteristic for the process is the fruitful co-operation between utilities, companies and research partners (i.e. university). At present the co-operation continues at least as active as earlier. In addition to information system integration and methodological development the good competence available in high voltage engineering, condition monitoring and diagnostics in TUT has now been integrated into the development of new IT applications. The driving force in the past few years has been using the same philosophy as used in the development of DMS (i.e. integration of process data and network information) further for new applications: Power quality monitoring, preventive fault indication and condition monitoring. Power Quality Monitoring One new possibility is the utilization of integration in the collection of data of system performance, e.g. in power quality monitoring. There is a constant need to improve or at least maintain the quality of electricity distribution. At present there is also a dramatically increasing need for power quality monitoring. For the power companies the primary requirement arises from the obligation to prove the adequacy of power quality, including outages and voltage quality. The same information can also be applied in network planning and reliability analysis in order to allocate the investments to the right parts of network. The basic ideas of using distribution automation and information systems in power quality monitoring are presented in [1] and [2]. Preventive Fault Indication and Condition Monitoring The integration of condition monitoring and asset management functions into the information system entity provides new possibilities also to the utilization of on-line condition monitoring and condition based maintenance. The future on-line condition monitoring applications will indicate at least some part of faults before they cause a trip and consequently an interruption to any customer. Other elements of preventive fault indication are the overall condition assessment and the optimisation of maintenance and investments. At present most of the maintenance is still carried out time based regardless of the new trends for condition-based maintenance. In practice this means sometimes too much and sometimes too rare maintenance. With comprehensive utilization of condition-based maintenance remarkable cost savings can be achieved. Examples of the applications developed so far are the monitoring of distribution transformer temperature and ageing and condition monitoring based on partial discharge (PD) measurements [7]. Extended Reliability Analysis In addition to the development in power quality monitoring and condition monitoring the reliability analysis itself have recently been extended to cover also voltage dip analysis. Because the dips are affecting larger number of customers than an interruption they are of great importance and should be taken into account in the comprehensive network analysis. In the dip analysis faults are simulated to different parts of networks based on the failure rates and the resulting voltage dip is calculated and its affection area is determined. As a result the voltage dip distributions in the busbars are determined and the number of deep dips (e.g. residual voltage lower than 60 %) and low dips are calculated for each load point. By having cost functions for dips in the same way as for outages the harm caused by dips can be added to the overall reliability analysis. TUT_Verho_A1 Session 5 Paper No

5 With the existing tool the basic task is the analysis of an existing network considering a one-year period. As a result of the analysis the following results are given: For each load point The number of outages The duration of outages The number of voltage dips The outage costs For each component The outage cost due to one failure The total outage costs caused by the failures of the component For the whole network General indices (SAIFI, SAIDI, CAIDI) Total outage costs List of the load points having largest outage costs List of the components causing the largest outage costs In graphical user interface the results can also be illustrated in geographic view, e.g. the load points having largest outage costs or the components causing largest outage costs. Based on the analysis of existing network the alternative network development strategies can be studied in planning mode by making changes to the network and running the analysis. The same analysis results are available in the planning mode, but the study period may be for example 20- years. As a result of interactive study the most cost efficient network development strategy resulting required quality level should be found. Examples of possible studies are: The analysis of the effect of distribution automation (e.g. remote control of disconnectors) Reduction of voltage dips in a certain area (e.g. an industrial area) The effect of re-routing the overhead lines form forests to along the roads during renovation Calculation example The possibilities of the extended reliability analysis are demonstrated by the following case study. Let s assume that there is a need to make a renovation of certain part of network and there are two alternatives: Keeping the existing 5 km line route in the forest or building the new line using new route along a road, which is a little bit longer but has lower failure rate (failure rate less than half of the original). The calculated faults and dips caused by the whole 120 km feeder are summarized in the table below. TABLE 1. Results of calculation example Original New route line in the forest along the road Reliability costs /year/feeder outage costs re-closing costs work outage costs Outages [number/year] Re-closings [number/year] Customer outage time [h/year] Deep voltage dips [number/year] Low voltage dips [number/year] Voltage dip costs [ /year] The results show that the re-routing affects more to the costs caused by the voltage dips than the outages, when cost of deep dip equals to the short interruption cost. Because the studied line section is rather near the primary substation the re-routing affects only to deep voltage dips. The profitability of re-routing the line depends on the reliability cost savings and the renovation and re-routing costs of the line. The final selection of the route should be based on the utility s strategy and the cost difference of the alternatives. FURTHER DEVELOPMENT The recent development provides good basis for further development of reliability analysis. Although the existing reliability analysis methods are rather comprehensive there are a lot of possibilities to further develop them. The failure rate modelling and the analysis itself can be enhanced and the outage cost modelling can be developed. Also the information system solution can be developed in order to better utilize of the possibilities available. Traditionally the failure rate modelling has been based on constant failure rates for each component type. In practice, however, the operational and environmental circumstances and the age have an effect on the failure rate of the components. Especially the route of overhead lines affects strongly to the failure rate. The probability of a fault in the lines in forests is much higher than for those in the fields. Another development of failure modelling deals with the improved classification of the faults. Traditionally, the reliability analysis has handled mainly the permanent faults, but nowadays the harms due to the temporary faults and dips are of great importance and they should also be taken into account. Thus, there should be failure rates for both temporary faults and permanent faults. There should also be classification depending on the repair time. Some faults are easy to repair (e.g. removing a tree from the line), but some requires longer repair time (e.g. changing a pole or transformer). Also the over-voltage protection should be added into the analysis. Both the failure and repair rates should even be time and weather dependent, which makes the modelling even more challenging. The outage cost modelling is one of the most difficult subtasks in the comprehensive reliability based network analysis. In the traditional way of modelling fictive costs were used, TUT_Verho_A1 Session 5 Paper No

6 which cannot be part of business driven process development. Due to compensations due to outages as well as the regulation model, in which better power quality ustifies increased permitted profits, the outage costs become real costs. In the reliability analysis the outage cost modelling must be flexible, in order to provide tool for proactive development of networks. The appropriate modelling of voltage dip costs is also a big challenge in the future. In addition to the improved modelling the information system solution is of great importance. Today s information technology provides good possibilities for development and the existing basis in the utilities is quite good as described earlier. However, the real utilization of the huge amount of data available in utilities is a big challenge in the future development. The basis of the information system solution is network information system, providing the detailed network data. Maintenance and operational data is needed in order to determine the condition of the components. The environmental data of the line routes is needed in order to determine the failure rate of lines. The power quality measurements and outage statistics are needed in order to fix the failure rate parameters and to check that the results of reliability analysis are in line with the realized events. The future development described above is part of ongoing development proect in Finland. The proect partners include several utilities and system suppliers as well as research partners. The aim of the proect is to implement the ideas described above as part of reliability analysis tool. The utilization of the tool under development will in future support the network planning process of the utilities. CONCLUSIONS In the traditional long-term planning of distribution system the obective is to minimize the costs due to losses, operation and investments subect to technical constraints. In Finland, in the 1980 s reliability analysis and outage costs were added to the planning tools, which were successfully used for example in optimisation of distribution automation investments. REFERENCES [1] Mäkinen A, Järventausta P, Parkki M, Kortesluoma M, Verho P, Vehviläinen S, Seesvuori R, Rinta-Opas A. Power Quality Monitoring as Integrated with Distribution Automation. International Conference on Electricity Distribution (CIRED 01), Amsterdam, Netherlands, June 2001 [2] Mäkinen A, Järventausta P, Verho P, Rinta-Opas A. Comprehensive Development of Power Quality Managemetn and Evaluation of Voltage Dip Problems. International Conference on Electricity Distribution (CIRED 03), Barcelona, Spain, May 2003 [3] Partanen J, Juuti P, Lakervi E. PC-Based Network Information System for Power Distribution Companies and Cosultants. International Conference on High Technology in the Power Industry. Tainan, Taiwan, March [4] Verho P., Järventausta P., Kärenlampi M., Partanen J., Intelligent Support System for Distribution Management. International Journal of Engineering Intelligent Systems for Electrical Engineering and Communications, Vol. 4, No. 4, December 1996, pp [5] Mäkinen A., Partanen J., Lakervi E., A Practical Approach for Estimating Future Outage Costs in Power Distribution Networks. IEEE Transactions on Power Delivery, Vol. 5, No. 1, January 1990, pp [6] Verho P., Luoma P., Järventausta P., Pouttu M., Rinta- Opas A., Distribution Automation as the Core Strategy in Koillis-Satakunnan Sähkö Oy. Proceedings of DistribuTECH '99 Europe. Madrid, Spain, September [7] Verho P., Nousiainen, K., Distribution network asset management based on integration of information systems and distribution automation. 6th International Transmission and Distribution Conference and Exhibition, November 2001, Brisbane, Australia The recent development has been focused on power quality monitoring and condition monitoring and integration of those new applications as part of information systems. The reliability analysis methods have also been extended adding voltage dip analysis as part of the program. The existing situation provides good basis for further development of the methods. The average and often inaccurate fault and repair rate values can be adusted using new models and analysing huge amount of available data. The outage cost modelling should be improved to better fit in today s business-oriented management of distribution process. A new solution taking into account the tasks mentioned above is under development in Finland in cooperation between utilities, system providers and research partners. TUT_Verho_A1 Session 5 Paper No