Asset Management and Maintenance in Transmission and Distribution Networks

Transcription

1 Asset and Maintenance in Transmission and Distribution Networks S. Surender Reddy Department of Railroad and Electrical System Engineering, Woosong University 171 Dongdaejeon-ro, Jayang-dong, Dong-gu, Daejeon, Republic of Korea. Abstract In this paper, asset management strategies in transmission networks are presented based on short-term, medium-term and long-term time scales. Asset management is the process of guiding the acquisition, use and disposal of assets to make the most of their future economic benefit and manage the related risks and costs over their entire life cycle and it has gained more importance in monopoly transmission and distribution sectors. Aging assets, uncertainty in power system load profile and renewable energy resources, and demand management create a challenge for the optimal operation and maintenance of the electrical grid. This paper addresses the challenges and opportunities to improve transmission and distribution systems asset maintenance. This paper also presents the asset replacement alternatives. This paper also presents the costbenefit analysis of asset management using the information/ real time data from the utility company. This paper will serve a guide for doing the asset management to the benefit of world's electrification process, investment and recovery to sustain reliable and efficient power delivery. Keywords: Asset management, aging assets, uncertainty, renewable energy resources. INTRODUCTION The CIGRE Australasian Asset Working Group defines asset management for electricity industry as Asset is a set of business processes concerned with developing, operating and maintaining the assets of an organization to meet the desired requirements of the customers and the shareholders of the business. These desired requirements usually encompass cost, performance, safety and environmental outcomes as well as a secure electricity supply. Aging assets and uncertainty in power system load profile and demand management create a challenge for the optimal operation and maintenance of the electricity grid. Asset will reduce the risk of equipment failure, extend the life of equipment, and minimize the occurrence of costly unplanned outages. Asset management can be applied to help electric utilities address aging power transmission and distribution infrastructure, reliability and business risk challenges in an organized and orderly fashion. Applied correctly, asset management explicitly recognizes that the utility's equipment exists to serve its customers and that all decisions regarding its use and care are made on the basis of business needs and profitability in performing the utility's mission. When one is interested in knowing how asset management works to benefit their companies, it is very important to get to know how asset management really works. This includes the services that asset management employs to handle assets, the costs of utilizing asset management services, the available software designed to manage assets, even the qualifications of certified asset management advisors. Most electric utilities in North America have significant portions of their electrical infrastructure that are aged composed mostly of equipment that has been in service so long that wear and tear have an obvious effect, but not so deteriorated that immediate replacement is needed. Asset management focuses on all aspects of managing aging assets well, from a far-reaching look at aging and its impacts on transmission and distribution system, customer reliability, and the utility s bottom line, to the various means through which utilities can manage aging, it s costs and effects in an efficient manner. Asset management includes: comprehensive inspection programs, condition assessment and tracking, maintenance management, life-extension technologies, strategic planning and prioritization, and refurbishment and replacement policies. It is very important to know that the asset lifecycle has four broad stages that asset management firms take into consideration. Planning and procurement includes carefully considering which to procure, ordering these and even receiving and testing these are salient features of asset management. Managing the daily operations of assets enabling companies to maximize productivity is also an important feature of asset management. Knowing how much it costs to operate the company and comparing it to the profits and the existing assets make for balanced returns and even more commonly returns to the part of the companies. The restructuring and liberalization developments worldwide have increased the incentives for a cost effective and efficient use of available assets in generation, transmission and distribution segments of the electricity industry [1]. Essentially, asset management, which is the process of guiding the acquisition, use and disposal of assets to make the most of their future economic benefit and manage the related risks and costs over their entire life cycle, has gained more importance in naturally monopoly transmission and distribution sectors than before, like in the competitive generation industry [2]. Asset management plan summarizes the intended maintenance, asset replacement and contingency plans for each asset, and provides detail on the expenditure associated with each of these plans. Transmission assets operate at very high voltages and the consequence of their failure has the potential to affect many customers. Equally, compared to distribution, there are relatively few transmission assets, and their age and condition are generally well understood. The age of the network provides a useful indication of the need for 9735

2 asset renewal. While there are other factors that will determine the need to renew a particular asset including physical location, loading, suboptimal maintenance and any design faults, age provides a useful trigger to consider the need for replacement. Asset management for most utilities today is handled using run-to-fail strategy. Particularly in the distribution network, where asset value is generally low, many utilities have not incorporated sensing or monitoring technology into their networks. However, with the advent of the smart grid and the deployment of communications networks that enable advanced metering infrastructure and distribution automation programs the inclusion of sensing or monitoring is starting to make more economic sense. Nowadays, transmission owners and operators face new challenges due to stringent regulatory mandates, system security concerns and inherent capacity limitations in the face of increased transfer demands. Additionally, they are facing growing cost pressures for minimizing or curtailing operational or capital investments in the transmission asset arena. Asset management processes are described in Figure 1. Network Planning Process Customer, Shareholder and Community Expectations Planning Criteria Technical Code Load and Generation Forecasts Asset Plans Demand Side Capital Expenditure Forecast Regulatory Requirements and Obligations Networks Vision and Objectives Network Investment Strategy Expenditure Forecasts Trade offs Regulatory Requirements and Obligations Demand and Generation Growth Operating and Maintenance Expenditure Demand Side Opportunities Figure 1. Overview of Asset Processes. In [3], an application-based distribution network asset management is discussed by proposing a dynamic network rating approach to facilitate low carbon network operation. A two-step methodology for scheduling electric vehicle charging while limiting the burden on distribution and transmission assets is proposed in [4]. Reference [5] develops a model for determining the number and location of automatic switches in distribution networks with the objective of minimizing the investment, operation, and unreliability costs. In [6], an intelligent framework for condition monitoring and assessment of power transformers is proposed while using data from online sensor measurement and historic database. Multi-objective decision-making condition based maintenance model is proposed in [8]. A cascading failure risk assessment method based on the reliabilities model of circuit breakers and protective relays is proposed in [9], where a fully physical mechanism is utilized to illustrate the evolution of cascading failures. Frequent condition assessment with asset audit enables a comprehensive assessment of the asset in question and includes objective and transparent asset condition information recommendations for the improved environmental sustainability. Based on the individual maintenance schedules or on the assessment and inspection findings, maintenance operations are planned to ensure the reliability of the system. The Asset Plan describes the intended maintenance, asset replacement and contingency plans for each asset, and provides detail on the expenditure associated with each of these plans. Transmission assets operate at very high voltages and the consequence of their failure has the potential to affect many customers. Equally, compared to distribution, there are relatively few transmission assets, and their age and condition are generally well understood. The age of the network provides a useful indication of the need for asset renewal. While there are other factors that will determine the need to renew a particular asset age provides a useful trigger to consider the need for replacement. Asset management for most utilities today is handled with what is commonly called a run-to-fail strategy. Particularly in the distribution network, where the asset value is generally low, many utilities have not incorporated the sensing or monitoring technology into their networks. However, with the advent of the smart grid and the deployment of communications networks that enable advanced metering infrastructure and distribution automation programs the inclusion of sensing or monitoring is starting to make more economic sense. Transmission owners and operators face new challenges due to stringent regulatory mandates, system security concerns and inherent capacity limitations in the face of increased transfer demands. Additionally, they are facing growing cost pressures for minimizing/curtailing operational/capital investments in the transmission asset arena. TRANSMISSION ASSET MANAGEMENT As mentioned earlier, the transmission owners and operators face new challenges due to stringent regulatory mandates, system security concerns and inherent capacity limitations in the face of increased transfer demands. Additionally, they are facing growing cost pressures for minimizing or curtailing operational or capital investments in the transmission asset arena. The need for practical, effective and reliable tools to help manage these important assets in real-time has never been stronger. Figure 2. Energy System (EMS) Platform. 9736

3 Effective management of these assets involves efficient and holistic monitoring of the complex transmission network, intelligent and reliable security analysis tools for developing effective strategies to avert, mitigate and cope with system emergencies, and well-rehearsed scenarios and well-trained operators to deal with localized or system-wide emergencies, blackouts, voltage collapse, loss of critical equipment, etc. The Blackout of August 14, 2003, and other similar collapses in various grids in Europe and the Americas, have greatly underlined the need for strong and reliable transmission monitoring and management tools as well as effective and realistic operator training systems. Efficient algorithms, effective on-line maintenance tools, intuitive graphics and user interface techniques provide for a powerful security monitoring and analysis environment for transmission operators. Transmission and EMS applications will help transmission operators of various size and grid complexity worldwide. From China's fast growing and challenging transmission systems to overly burdened transmission systems in Australia, Europe or the Americas, EMS applications have been the reliable nucleus of many companies' real-time security analysis strategy. Using detailed dynamic modeling of the power system and an exact replica of the Control Center environment, system operators can rehearse a full spectrum of system events, emergencies and restoration techniques in the most realistic settings. To maximize the operating life of electricity generation, transmission, and distribution equipment, one need to strike the right balance between preventative maintenance and condition-based monitoring. Figure 3 depicts the condition monitoring using the balanced approach. Figure 3. Condition Monitoring using Balanced Approach. DISTRIBUTION ASSET MANAGEMENT The distribution system asset management can be categorized as short-term asset management is related with the operational issues of the network, mid-term asset management is associated with the maintenance of system assets, and longterm asset management is concerned with the strategical planning of distribution systems [2]. Operational The main tasks of a Distribution Utility Enterprise (DUE) in short-term include the operation and control of the network ensuring the security and reliability of the power supply. Security of supply is the ability of the network to meet customer demand without suffering an interruption in the first instance, and secondly, where an interruption develops it is the ability to restore power more quickly via alternative supply options. Power system assets are monitored through the Supervisory Control and Data Acquisition (SCADA) systems which help system operators monitor and control the system in real-time. SCADA collects real-time data from Remote Terminal Units (RTUs) installed in substations and power plants, and distributed throughout the power system. These data are transmitted to the system control center and stored in the Distribution System (DMS) realtime database. The DUE tracks and manages loads, maintains voltage profiles and maximizes the efficiency of the distribution system by the DMS. Sub-transmission and distribution networks have a geographical reference. Geographic Information System (GIS), which stores spatial information about a utility s assets for representing the location and condition of assets including switches, relays, transformers, poles, cables, provides a variety of functions for asset management in all time scales. Demand type, outage information and customer complaints are among the information that give important feedbacks to asset management decisions. Future developments of GIS technology may include SCADA processes technology. Maintenance Mid-term asset management associates with the maintenance of assets. Since there is a cost involved in the maintenance (the cost of the service plus the cost of possibly interrupting load), many research works have been presented on maintenance scheduling optimization, under the objective of providing a focused management framework, intended to ensure that the condition and performance of distribution assets continue to effectively meet the requirements of customers in the most economic manner. Maintenance in a utility may be divided in three main categories: emergency, preventive and predictive. Emergency maintenance occurs after a fault, where the preventive and predictive maintenances intend to keep equipments and installation in proper working conditions, avoiding failures. Preventive maintenance can be divided in two categories further: Timebased Maintenance (TBM) and Condition based Maintenance (CBM). TBM is performed at regular and scheduled intervals, loosely based on the service history of a component and/or the experience of service personnel. CBM periodically determines the state of equipment deterioration, and maintains equipment when the condition falls below acceptable thresholds. Many numerical approaches have been developed in literature to prioritise distribution maintenance activities based on system reliability and cost-effectiveness [2]. Mathematical models, which represent the effects of maintenance on reliability, are needed in those approaches to find the optimal RCM strategy. Indeed, a comprehensive asset database, which consists of all necessary information based on periodic inspections, diagnostic tests, or other means of condition monitoring, is 9737

4 mandatory to develop an RCM strategy. This database can be included in existing IT applications such as GIS. In fact, since there is no unique product of system that covers all the facets of the asset management, the supporting IT applications have to be built on existing systems. This points out a need for applications and system integration over a robust IT infrastructure. Therefore, favouring open standards that facilitate data and message exchanges among different utility systems and provide the framework for extensibility is quite important in the context of asset management in all time scales. Strategical Planning Asset management in the long-term associates with identifying asset enhancement and development programmes required to meet target levels of service. The choice of a particular planning solution has traditionally been determined by performing network analysis considering the load growth and calculating the economic and financial implications associated with each possible solution. The solution that provides the minimum economic and financial impact would then be selected for implementation. In today s demanding environment, issues such as distributed generation, reliability and quality of supply and environmental issues are now becoming as important as load growth and must also be included in the distribution planning activity. Owing to the radial operation of power distribution networks, the reliability of distribution systems generally depends on the worst reliable equipment existing in the system. Therefore, decision-making techniques that applied to electricity distribution system planning should assess the conditions and performance of the system assets. ASSET MANAGEMENT IN SMART GRID As smart grid technologies began to be deployed rapidly at utilities through the last parts of the 2000s in the predominant forms of advanced metering infrastructure, distribution automation technologies and control room software such as distribution management systems (DMS), few companies understood that adding those assets to a companywide asset management strategy portfolio would be as important as it now is. Asset management involves optimizing and prioritizing investments in assets to maintain or improve performance and life expectancy throughout the asset s life cycle. Smart Asset uses smart grid data to improve asset management results through the use of backend integration and data analytics. Asset management applications are heavily data driven requiring data from across the enterprise from GIS, the work management system, the maintenance management system, outage management system, on-line monitoring system(s), meter data management systems, equipment catalogs, standards, planning and archived operational histories. Often such information is lacking altogether or inaccurate. This is because information is siloed within various utility departments without adequate integration at the backend. Manual data transfers and processes involving copy-paste and single point-to-point integrations make the process of asset management error-prone and in most cases very time consuming. Smart grid data when collected and analyzed provide a rich resource for asset management allowing utilities to better understand their deployed assets and manage performance. Smart Asset may be realized by providing backend data integration so that data may be used effectively in building a knowledge-based program. Some of the benefits of implementing Smart Asset include cost savings and a better understanding of risk; asset life cycle and procurement planning; improved performance from existing equipment; a vigorous, defendable, repeatable platform for justification of asset decisions with advanced auditing capability; improved system reliability with increased longevity of asset life by maintaining operation within asset specifications; and compliance with regulations and improved customer satisfaction through better power delivery and reliability. CONCLUSIONS Asset management describes the intended maintenance, asset replacement and contingency plans for each asset, and provides detail on the expenditure associated with each of these plans. Aging assets, uncertainty in power system load profile and renewable energy resources, and demand management create a challenge for the optimal operation and maintenance of the electrical grid. This paper addresses the challenges and opportunities to improve transmission and distribution systems asset maintenance. This paper also presents the asset replacement alternatives. This paper serves as a guide for doing the asset management to the benefit of world's electrification process, investment and recovery to sustain reliable and efficient power delivery. REFERENCES [1] M. Shahidehpour, R. Ferrero, Chronological Strategies for Power System Asset, IEEE Power and Energy, Vol. 3, No. 3, May [2] O.B. Tor, M. Shahidehpour, Power Distribution Asset, IEEE Power and Energy Society General Meeting, Montreal, [3] J. Yang, X. Bai, D. Strickland, L. Jenkins, A.M. Cross, Dynamic Network Rating for Low Carbon Distribution Network Operation A U.K. Application, IEEE Trans. Smart Grid, vol. 6, no. 2, pp , [4] V. Aravinthan, W. Jewell, Controlled Electric Vehicle Charging for Mitigating Impacts on Distribution Assets, IEEE Trans. Smart Grid, vol. 6, no. 2, pp , [5] O.K. Siirto, A. Safdarian, M. Lehtonen, M.F. Firuzadad, Optimal Distribution Network Automation Considering Earth Fault Events, IEEE Trans. Smart Grid, vol. 6, no. 2, pp , [6] H.Ma, T.K.Saha, C. Ekanayake, D. Martin, Smart Transformer for Smart Grid-Intelligent Framework and Techniques for Power Transformer Asset, 9738

5 IEEE Trans. Smart Grid, vol. 6, no. 2, pp , [7] H. Wang, D. Lin, J. Qiu, L. Ao, Z. Du, B. He, Research on Multi-objective Group Decision making in Condition-based Maintenance for Transmission and Transformation Equipment Based on D-S Evidence Theory, IEEE Trans. Smart Grid, vol. 6, no. 2, pp , [8] X.Liu, M.Shahidehpour, Y. Cao, Z. Li, W. Tian, Risk Assessment in Extreme Events Considering the Reliability of Protective System, IEEE Trans. Smart Grid, vol. 6, no. 2, pp ,