C I R E D INTRODUCTION OF CONDITIONED BASED

CIRED 17th International Conference on Electricity Distribution Barcelona, 12-15 May 2003 INTRODUCTION OF CONDITIONED BASED MAINTENANCE AT WIENSTROM USING THE KNOWLEDGE-BASED EXPERT SYSTEM MABI Franz REISINGER Wienstrom GmbH - Austria franz.reisinger@wienstrom.at INTRODUCTION The deregulation of the electric power market in Austria and the resulting reorganization at WIENSTROM have entailed fundamental changes of the framework conditions for the maintenance of our switchgear and controlgear. While in the past funds were invested primarily in power network expansion and power network renewal, the increasing cost pressure brought about by the ongoing deregulation of the electric power market has led to a great reticence in the investing behavior. As a consequence, there have been significant changes in the age structure of the various switchgear units. And it is the increasing age of the existing devices in particular that calls for an analysis and the optimization of the maintenance to be carried out. Accordingly, an efficient maintenance needs to utilize the available resources as suited to the needs and cost-effectively. Its aim is to obtain the best possible value added from the existing switchgear potential. Scope and contents of measures must be archived well, evaluated, and questioned. WIENSTROM accomplish this aim by introducing MABI, a modular plant evaluation and maintenance package. ACTIVITIES OF THE DEPARTMENT The authors of this report are active in WIENSTROM's NT4 Department ("Erection and Operation of Substations, Switching and Traction Substations"). Just the name of this department already tells you that the tasks of this department focus primarily on substation-related matters – from the installation to the operation of high- and mediumvoltage switchgear. More specifically, the switchgear can be subdivided into three 400/110kV, 39 110/20kV and 110/10kV, and 97 d.c. systems used for the supply of Vienna's subways and trams as well as into four hydroelectric power plants. It must be noted that the area supplied by WIENSTROM comprises not only the conurbation of a city having a total population of 1.8 million, but also its surrounding regions. PREVIOUS MAINTENANCE STRATEGIES The foremost goal of the previous maintenance strategy was to achieve a high degree of reliability of the switchgear, the cost not being of primary relevance. No Risk-oriented Strategies The aim of past maintenance measures was to prevent any faults and disturbances as much as possible and to refrain from using risk as a control parameter when planning maintenance measures. Yet, in spite of the objective of achieving the highest possible reliability, it was not possible to fully prevent errors and resulting outages. Time-based Maintenance As is customary in power engineering, in the past we have serviced our switchgear according to the "round robin“ principle. Depending on the type of switchgear, it, or certain elements of it, were serviced according to a sequential pattern, the time since the last maintenance job serving as the basis for the planning of further maintenance measures. System Type and Technology Determined the Maintenance Intervals Especially in the case of high-voltage switchgear, the maintenance intervals would be specified by the manufacturer and mostly adopted by the power network operator. Typically, the same maintenance measures and cycles would be applied to the entire switchgear and its devices, even though the devices involved were of a different importance, in different technical conditions, and at different stages of wear, etc.. The biggest downside of this method was that not only elements in need of maintenance but also elements that were still reliable and fully functional would be subjected to maintenance. An example of this is a 110kV switchgear with line feeders, transformer feeders, and a shunt reactor feeder. The power network operation results in a staggered sequence of circuit breaker switching cycles of these feeders. Thus, a shunt reactor is operated daily, a transformer several times a month, but a line feeder almost never. This demonstrates that, due to the number of switching operations and the load to be switched in this process, the circuit breaker of a shunt WIE_Reisinger_A1 Session 6 Paper No 69 -1- CIRED 17th International Conference on Electricity DistributionBarcelona, 12-15 May 2003 reactor needs to be inspected and serviced more frequently than that of a transformer or a line feeder. Equipment Data In the various specific segments (h.v. technology, secondary technology, etc.) separate small decentral databases have emerged. There were no competencies for a higher-level concept of maintenance-relevant equipment databases. In the past, for lack of necessity, data were not centralized and no appropriate computer environment was created. Engineering knowledge was not integrated when the data contents were created, the data remaining limited to "index card“ character. Therefore, the creation of useful parameters for modern maintenance strategies was hardly possible. Maintenance-oriented Investments "Maintenance begins with the procurement!". This sentence is increasingly gaining in importance. Maintenance-relevant aspects in the procurement of new technical systems or investments in replacements only become important in full-fledged state-of-the-art maintenance strategies and had so far hardly ever been taken into account. Technical quality used to be regarded as much more important than pure costefficiency considerations. In order to make optimum use of financial and human resources, WIENSTROM now aims at incorporating such considerations into its maintenance concept and at basing its measure planning, inner organization, and distribution of competencies thereon. FUTURE MAINTENANCE STRATEGIES Prioritization of Switchgear Segments For a new, more intelligent maintenance tool, it is necessary to also contemplate the desired scope of maintenance. It must be evaluated which devices need to be considered, and with which data depth such consideration should take place. In addition, switchgear components are to be prioritized, based on their type of use and importance [1]. It is also useful to take individual switchgear segments and incorporate them step by step into a maintenance system, thereby gathering experience from easy-tosurvey detailed segments and also collecting aspects specific to power supply companies. Such a procedure makes sense in particular in the event of WIE_Reisinger_A1 Session 6 complex data contents which can be found where a commercial & strategic maintenance tool is used. Condition-based Instead of Time-based Maintenance When managing a large number of switchgear units, a simple time schedule is all it takes to schedule these jobs and the costs incurred in connection therewith for several years in advance. In this case, the devices involved will undergo maintenance at certain predefined time intervals. However, to obtain the same quality of switchgear condition and the same reliability of the various switchgear units with fewer resources, the technical condition of the devices is acquired and action intervals adapted accordingly are defined. So far, the best possible safety had been the uppermost priority in maintenance cycle scheduling. In the most cases, it can be expected that in a condition-oriented maintenance regime the intervals for maintenance measures will become longer and that, consequently the costs incurred can be reduced. The best-case objective would be to service the devices only shortly before they break down. However, to do so, maintenance manager would also have to be "psychics". The more intelligent the maintenance tool, the closer one can get to achieving this goal. Strategic Evaluation of Devices Apart from the purely technical acquisition of the condition of devices, a modern maintenance planning tool should also factor in commercial and strategic targets defined by the enterprise and permit suitable action planning and expense budgeting. For such "strategic evaluation" of the devices, wear, significance, as well as economic efficiency are the decisive factors. Each of these variables is determined by several relevant subparameters as shown in Table 1. Risk-oriented Maintenance As capital costs (investments and replacement investments) can only be reduced on a long-term basis, the cost pressure power network operators are faced with will in the future mainly affect variable costs. Risk-oriented considerations also need to be integrated into the strategic evaluation of devices. [2] The cost-saving adaptation of maintenance measures will in most cases reduce reliability and system Paper No 69 -2- CIRED 17th International Conference on Electricity DistributionBarcelona, 12-15 May 2003 availability only to such an extent where it is still acceptable for customers. The shift from a technology-oriented to a customeroriented strategy of the company in maintenance is reflected by the introduction of risk management for switchgear systems. For successful risk management it is necessary to determine the reliability and thus the probability that a fault or an error will occur in TABLE 1 - Parameters for strategic evaluation devices. This calls for a full-fledged fault management and fault statistics tool. Faults must be detected, and fault analyses and the interpretation of the error type – performed by experts – constitute the basis for ascertaining the reliability of devices. Low economic efficiency degree of standardization availability of service availability of spares maintenance cost reliability Wear location air quality short-circuit currents/operating currents fault incidence age/technology Significance/Importance importance of bay importance of switchgear type of use WIE_Reisinger_A1 Session 6 Paper No 69 -3- CIRED 17th International Conference on Electricity Distribution Barcelona, 12-15 May 2003 devices of the same technical type. Type of Maintenance Measures Finally, it must be noted that the type of maintenance measures implemented needs to be reconsidered. The further development of system technology and changes in legislation make it necessary to reevaluate long-standing maintenance measures. Besides, terms for measures (e.g. "revision") have in part become obsolete and need to be superseded by new nomenclature resulting from technical provisions. Continuous Transition toward New Maintenance The transition to this new kind of maintenance is a continuous process. Once a company decides to take this step, data must be collected, edited, and integrated. Then, as the data pool keeps growing, it will be possible to conduct increasingly finer evaluations, simulate more detailed scenarios, and more accurately implement desired strategies. TECHNICAL IMPLEMENTATION OF NEW STRATEGIES BY MEANS OF MABI Data Structure and IT Environment Database features. For the applications defined hereinabove, requirements as regards the database can be formulated. It should be the goal of a servicing body to compile a central database containing master data of all maintenance objects, in order to not only avoid data redundancies but also to be able to carry out data maintenance in the specific technical department. In the case of MABI, we opted for a central, relational Oracle database. Data structure. For such applications, e.g., the management of switchgear and equipment, an open, object-oriented structure of the data is what makes sense. In workshops, WIENSTROM and SAG Energietechnik GmbH jointly elaborated specific object levels for the transformer substation segment: location level switchgear object level bay level equipment level additional equipment level In order to implement the technical and strategic evaluation of devices, the data structure must be prepared accordingly. In addition to regarding the devices as individual objects, a grouping was implemented in the database structure, whereby the devices are sorted according to their technical types. This makes it possible to perform various analytics functions on WIE_Reisinger_A1 Session 6 Software architecture. The persons who will access this database will have undergone different levels of training and schooling and have different levels of previous knowledge. To render the screens familiar to the user, the database is superposed on an underlying web-based application. The pages of an Internet browser (in our case, Microsoft's Internet Explorer) form the user interface. The CGI script pages opened in the browser (Common Gateway Interface is a classical method for such applications) are filled with the respective data from the current database. The maintenance and care of the browser client software is carried out by the company. Thus, no maintenance effort will have to be incurred by the "Maintenance" department. The entire software also supports interfacing to existing systems such as SAP, documents, pictures, etc. User interface. The above-mentioned features of the client software permit the implementation of dynamic, interactive elements. A striking feature of the user interface is the use of a tree structure (directory structure) similar to that of the Windows Explorer and used for navigating between the maintenance objects on the various object levels. The use of familiar controls and buttons represents an additional advantage for the user. Mobile data acquisition. The mobile data acquisition system permits the automated recording and transfer of data when detecting faults and when performing maintenance jobs. It is to be used in the place of the previous paper-based process and seeks to accomplish the greatest possible minimization of administrative processes. Fig. 1: Tree structure in MABI Paper No 69 -4- CIRED 17th International Conference on Electricity Distribution Barcelona, 12-15 May 2003 Functions of the Expert System Modular system. MABI stands for "Modulares AnlagenBewertungs- und Instandhaltungspaket" (Modular Plant Evaluation and Maintenance Package). It is comprised of various software modules representing the areas "Master Data, Technology, Maintenance, Evaluation, Faults, and History". These parameters are introduced into the maintenance reports recorded in the system. The compilation of these reports permits the detailed visualization of the processes of the various measures. The process-oriented perspective makes cost-boosting factors and flaws in organization transparent. This module comprises not only planning but also budgeting, cost targeting and tracking, and the cost-effective use of human and material resources. Evaluation of technical condition. In MABI, the technical evaluation of a device is supplemented with the additional implementation of a strategic evaluation. The expert knowledge required for the evaluation of the technical condition is provided in the Knowledge Editor [3]. The Knowledge Editor contains stored technical limit values and reference values ("fingerprints“ of the maintenance individual concerned) to be used in detecting the condition and defined based on the experience of the technical expert. A function generator calculates the required values from the raw measured values. For example, SF6 gas pressure values from the Maintenance module are standardized to 20° C and compared to the limit values applicable to the respective gas compartment. If certain absolute limits are undershot, a message to the technician in charge will be generated. Similar to a traffic light, these messages are available in three steps ("green“, "yellow“, and "red“). The traffic-light states are to be interpreted as follows: Red: immediate action required! Yellow: device fulfills its tasks, however, needs to be serviced! Green: no action required, everything OK! Furthermore, it is possible to indicate negative developments. An example is a creeping gas loss in a gas-insulated (GIS) switchgear. The need for action will be signaled even before the absolute limit values are undershot. Strategic evaluation. The subparameters referred to in Chapter 4.3., i.e., Importance, Economic Efficiency, and Wear, are implemented in MABI and can be weighted as needed, depending on the company's strategic targets. It is possible to define limits for these variables. A threedimensional representation shows the range in which devices must remain so as to not require any maintenance measures. These functions permit the fast adaptation of the MABI system to any changes in the company's strategic orientation. In addition, it is possible to simulate various scenarios so as to help the management in its decision-making process. Fig. 2: Implementation of the modular concept via tabs in the MABI Information on equipment. The information on equipment is implemented in the Master Data and Technology modules. In the Master Data module, the switchgear, bay, and equipment is inventoried. The various maintenance objects are embedded in the respective object levels and their individual data stored. In the Technology module, the relevant technical data of the various devices is type-coded and defined, statements as regards the degree of standardization being possible. These modules also feature integrated intelligent search functions and a user-friendly navigation. Acquisition of the history of devices. In this module, all technically and commercially relevant events in the lifecycle of a device are recorded. Typical milestones of a maintenance object in switchgear engineering are: procurement, startup, change of location, damage, modifications of the device, maintenance, scrapping. These data are also used as a basis for determining the lifecycle costs. Fault acquisition and evaluation. The fault acquisition takes place in two steps, implemented in the form of two reports: the operating report and the expert report. During the initial acquisition of the fault, essential fault data, as defined in the operating report, are entered on site by the fault complaint service. In the second step, an expert report is completed providing for a more detailed analysis of the fault, where the cause of the fault is determined by the technical expert and the severity of the fault is evaluated. In addition, the expert report includes fault parameters necessary for analyzing the reliability of the devices involved. More specifically, it is possible to conduct an analysis of defects and flaws. The effects of influencing factors on the emergence of a defect can be analyzed. Hazard potentials can be derived and forecast. Maintenance planning and implementation. This module represents a planning module for cyclic inspection measures, a condition-based and network-oriented adaptation of inspection intervals being possible. This is also where the technical condition of the switchgear and the technical input parameters for condition evaluation are acquired. WIE_Reisinger_A1 Session 6 Paper No 69 -5- CIRED 17th International Conference on Electricity Distribution REFERENCES: Barcelona, 12-15 May 2003 MABI-Evaluation Wear Limits for adaptation of the company’s strategy orientation [1] Balzer G.; Schmitt O.; Halfmann M.; Hößle A., 2001, “Maintenance And Refurbishment Strategies For Medium Voltage Substations”, 16th International Conference and Exhibition on Electricity Distribution, CIRED 2001, Amsterdam [2] Schreiner W., Rieder T., Haslauer F., Wagner O., Heinz F., 2002, “Risiko-orientiertes Anlagenmanagement”, Energiewirtschaftliche Tagesfragen, 52. Jg., Heft 11, 776-779 [3] Junglas K., Haschke J., Vennegeerts H., 2000, “Effiziente Instandhaltungsplanung”, Energiewirtschaftliche Tagesfragen, 50. Jg., Heft 3, 164-169 Importance Low economic efficiency Fig. 3: Three-dimensional representation of strategic evaluation WIE_Reisinger_A1 Session 6 Paper No 69 -6-