IEEE TRANSACTIONS ON POWER SYSTEMS, VOL. 20, NO. 1, FEBRUARY 2005 75 A Reliability-Centered Asset Maintenance Method for Assessing the Impact of Maintenance in Power Distribution Systems Lina Bertling, Member, IEEE, Ron Allan, Fellow, IEEE, and Roland Eriksson, Senior Member, IEEE Abstract—This paper proposes a method for comparing the effect of different maintenance strategies on system reliability and cost. This method relates reliability theory with the experience gained from statistics and practical knowledge of component fail- ures and maintenance measures. The approach has been applied to rural and urban distribution systems. In particular, a functional relationship between failure rate and maintenance measures has been developed for a cable component. The results show the value of using a systematic quantitative approach for investigating the effect of different maintenance strategies. Index Terms—Asset management, electric power distribution system, maintenance strategy, reliability evaluation, relia- bility-centered asset maintenance (RCAM). I. INTRODUCTION E LECTRIC power distribution systems constitute the greatest risk to the interruption of power supply [1]–[3]. Traditionally, however, distribution systems have received less attention than generation and transmission, evidenced by the difference in the number of publications [4]. However, focus is moving toward distribution as the business focus changes from consumers to customers. Deregulation of the power system market has led to a shift from technical to economic driving factors. The utilities that own and operate the power distribution systems now face various market requirements. On the one hand, customers are paying for a service (delivered energy) and the authorities are imposing regulation, supervision, and compensation depending on the degree to which contractual and other obligations are fulfilled, see for example Norway [5], Sweden [6], and the U.K. [7]. On the other hand, utilities must ensure that their expendi- ture is cost-effective. This means that electricity utilities must satisfy quantitative reliability requirements while at the same time minimizing their costs. One predominant expense for a utility is the cost of main- taining system assets, for example through adopting preventive measures, collectively called preventive maintenance (PM). PM Manuscript received June 29, 2004. This work was supported by the Com- petence Center in Electric Power Engineering at the Royal University of Tech- nology (KTH). Paper no. TPWRS-00271-2003. L. Bertling and R. Eriksson are with the Electrical Engineering Department, Royal Institute Technology (KTH), 100 44 Stockholm, Sweden (e-mail: lina.bertling@ets.kth.se; roland.eriksson@ets.kth.se). R. Allan is with the Electrical Engineering Department, Manchester Centre for Electrical Energy, University of Manchester Institute of Science and Tech- nology (UMIST), Manchester, U.K. (e-mail: RonAllan@iee.org.uk). Digital Object Identifier 10.1109/TPWRS.2004.840433 measures can impact on reliability by either improving the con- dition, or prolonging the lifetime of an asset. Reliability overall can be improved by lowering either the frequency or the du- ration of interruptions. PM activities could impact on the fre- quency by preventing the actual cause of the failure. Conse- quently, PM is cost-effective when the reliability benefit out- weighs the cost of implementing the PM measure. There is, therefore, a need for utilities to incorporate systematic methods which relate maintenance of system assets to the improvement in system reliability. This is part of the wider concept of asset management. Asset management involves making decisions to allow the network business to maximize long term profits, while delivering high service levels to the customers with acceptable and manageable risks. Reliability evaluation and maintenance planning techniques have separately been well developed, for example [1]–[4], [8], [9], with reliability assessment starting in the 1930s [10]. However, few techniques relate system reliability to component maintenance. Furthermore, the available techniques are not generally put into practice. The reason for this, according with the authors, is the lack of suitable input data and a reluctance to use theoretical tools to address the practical problem of maintenance planning. One method for relating reliability to PM is known as relia- bility-centered maintenance (RCM). RCM is a qualitative sys- tematic approach to organizing maintenance [11]–[13]. It origi- nated in the civil aircraft industry in the 1960s with the introduc- tion of the Boeing 747 series, and the need to lower PM costs in attaining a certain level of reliability. The results were suc- cessful and the methodology was developed further. In 1975, the U.S. Department of Commerce defined the concept RCM and declared that it should be used in all major military sys- tems [11]. In the 1980s, the Electric Power Research Institute (EPRI) introduced RCM into the nuclear power industry. Today RCM is used or being considered by an increasing number of electrical utilities [14], [15]. The main feature of RCM is its focus on preserving system function where critical components for system reliability are prioritized for PM measures. However, the method is generally not capable of showing the benefits of maintenance for system reliability and costs. This paper proposes a reliability-centered asset maintenance (RCAM) method, which provides a quantitative relationship between PM of assets and the total maintenance cost [2]. The method is developed from RCM principles attempting to relate more closely the impact of maintenance to the cost and reliability of the system. The method has been developed from 0885-8950/$20.00 © 2005 IEEE