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INTERNATIONAL CIGRÉ SC A3 COLLOQUIUM
SARAJEVO 2003, Sep. 15–16 2003
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CIGRE SC A3 COLLOQUIUM – SARAJEVO 2003 TECHNICAL REPORT by Prof. Dr. Mirsad Kapetanovic on behalf of SC A3 Following an invitation from CIGRE National Committee for Bosnia and Herzegovina a decision to hold the International Colloquium ”Asset Management of Switching Equipment and New Trends in Switching Technologies” in Sarajevo has been reached by former CIGRE Study Committee 13 (Switching equipment). Its successor, the new CIGRE Study Committee A3 (High Voltage Equipment) organised the Colloquium in cooperation with CIGRE National Committee for Bosnia and Herzegovina on September 15 and 16, 2003. In such a way the event can be seen as the fifth and the last Colloquium of CIGRE SC 13 and as the first Colloquium of CIGRE SC A3. Just after the Colloquium, during the following two days, CIGRE SC A3 has held its annual meeting. Using a rare opportunity to have so many scientists and professors in one place, CIGRE SC A3 in cooperation with Faculty of Electrical Engineering of the University of Sarajevo organised a parallel running Tutorial. It was an intensive two-day course which covered high voltage circuit breakers technology and switching techniques through carefully chosen lectures:
In addition, a panel session “Ask the Expert” was also held with an excellent moderation by Chairman of CIGRE SC A3 Prof. Dr. Klaus Froehlich (Switzerland). Thirty two attendants have successfully completed the Tutorial. The dean of the Faculty of Electrical Engineering Sarajevo, Prof. Dr Melita Ahic-Djokic awarded Certificates. Three Preferential Subjects have been chosen for the 2003 CIGRE SC A3 Colloquium in Sarajevo. Twenty one papers have been submitted by authors from Australia, Brazil, France, Germany, Iran, Japan, The Netherlands, Pakistan, Switzerland, USA and Bosnia and Herzegovina. The Colloquium was very well attended by 83 participants and invited guests from 15 countries. The Preferential Subjects and the related papers are as follows: 1. „Asset Management“ of switching equipment: § Reliability of the different switching technologies (AIS, GIS, ...) § Life cycle cost assessment § Maintenance philosophies § Diagnostics and monitoring as tools to „manage the assets“ § Maintenance, retrofit, refurbishment (life extension) and replacement as elements of „Asset Management“ § Initial cost aspects § Clarification of terms around „Asset Management“ Papers # 05, 07, 09, 11, 16, 17, 19, 23, 24. 2. New trends in Switching Technologies: § SF6 and its future; Alternatives § From the circuit-breaker to the future „Switching Machine“ , including disconnectors and earthing switches and eventually other elements § Air insulated technologies versus encapsulated technologies § New switching principles Papers # 01, 03, 04, 12, 13, 14, 18, 20, 21, 22. 3. Increased fault currents and Fault Current Limiters (FLC) § Applications and FCL technologies § Interactions between the FLC and the system § Degree of current limiting needed in different application § Essential parameters that must be defined for a FLC specifications Papers # 02, 15. From the papers and discussions that came after their presentations by authors it is possible to emphasize some thoughts and considerations that has been prepared with many contributions by Prof. Dr Heinz-Helmut Schramm and by Prof. Dr. Klaus Froehlich: PREFERENTIAL SUBJECT 1: „Asset Management“ of Switching Equipment technical, financial and risk management approach Many utilities are in the process of establishing asset management as a separate function and responsibility in order to emphasize the new role of the network infrastructure in the new business environment. Asset management strategy has to include at least three approaches: technical, financial and risk management approach. There exists a certain discrepancy between the way of thinking of technical experts (long term solutions, less technical risk, large efforts for optimal results) and the way of thinking of economists (short term profit, less financial risk: lowest costs, less efforts for acceptable results). Asset management, by balancing technique, finances and risks, has to direct an adequate allocation of resources to get the best added value for costs. It is especially the asset managers job to find the proper balance between these three disciplines. different substation configurations in terms of investment and life cycle costs Due to liberalization of the electric energy market and the growing importance of economic considerations within electric utilities and the owners of transmission networks asset management is one of the key subjects, today. Several authors presented comparison analyses of different substation configurations in terms of investment and life cycle costs. However, it was found that the actual costs depend largely on conditions external to the substation, like availability and cost of land, location of the substation, environmental and ecologic constraints, etc. That means that each case has to be considered individually and no general guideline can be given concerning the choice of a substation configuration. shorter or longer term view in decision making Before liberalisation of electricity market, the main driving forces for the network development were the increase of demand, the connections of new power plants and the high reliability of the network. However during the last decade, with liberalisation, the emphasis is put on the economic performance of the networks and there is a tendency to consider the short term rather than the longer term view in decision making. The advantages of long term view are evident and many examples are available for solid solutions chosen some decades ago and still performing sufficiently, thus avoiding today extra costs for refurbishment, replacement or extension of capacity. time based, condition based or reliability centered maintenance Utilities are using computerized maintenance management support systems. Such systems are mainly used to schedule the time based maintenance activities. There is trend towards condition based maintenance. The establishment of a condition monitoring system that is integrated into corporate systems and asset management systems will enable condition monitoring to contribute to the reliability of electricity networks and business performance. Reliability centered maintenance is seldom applied and has to be implemented carefully. strategy for online monitoring A strategy for online monitoring with the aim of achieving the key outcomes will necessarily require analysis and justifications for installing each device. Factors influencing justification include: reduction in routine maintenance, improvement of defect response, early detection of equipment failure, increased equipment availability. Other possible considerations are improved decision making, staff safety, environmental considerations and social effects of loss of supply. The presence of an online monitoring system does not replace the careful thought given to parameters to be monitored, nor does it replace proper analysis and interpretation of the data obtained. However, it makes the data accessible for the appropriate asset management decisions. parameters to be observed and the criteria to be applied The development in diagnostic and monitoring technologies is tremendous. However, pieces of primary equipment in the substation are complex devices, made out of several hundreds parts with many parameters and functions that can be monitored. Pressure on costs (a significant share of monitoring system overall price is borne by the sensors), need for systems that are altogether comprehensive and simple (for reliability reasons), coupled with experience from field installation led to a limitation of main functions monitored. Defining the component which causes abnormal behaviour is often difficult, because many failures could lead to the same symptoms. Manufacturers of equipment can propose a certain parameters to be observed, but manufacturer’s failure databases are much restricted to factory and site commissioning problems because utilities usually do not share their failure database with the manufacturers. In the absence of any monitoring system, symptoms that announced the incoming problem were not detected, not recorded and thus never transmitted to the manufacturer. As a consequence, the knowledge about the parameters to be observed and the criteria to be applied are still limited. IT-based on-line monitoring systems Following the discussion it can be concluded that opinions on the usefulness of sophisticated, IT-based monitoring systems are quite diverse. Some users simply do not trust the systems reliability concerned about false alarms which in a worst case might initiate a false operation and/or because of a high network density and small geographical distance have not a strong need for on-line monitoring. Other users consider these complex und multifunctional systems as a powerful tool for optimisation of maintenance and service operation, in particular, if remote unmanned equipment has to be covered. So are the pro arguments, all of which contribute finally to cost savings:
diagnostics services and expert systems Natural complements of condition monitoring are diagnostics services. Diagnosis is still a difficult task and needs further research for better life time estimation as an important tool for asset management. Nowadays evolution of technology had led to a new generation of monitoring systems, mainly thanks to advances in communication technologies and implementation of expert systems. As a consequence, achieving a truly comprehensive expert system is a matter of time and co-operation: first step consists in installing monitoring devices on a large pool of primary equipment, building up a standardised event records database. Then as time goes by and failure database grows, manufacturer and utility joined efforts result in further diagnostics and prognosis being added to the initial system, in a continuous progress. Web-based technology Monitoring systems are intended to be web-based. Web-based technologies have given monitoring systems a significant boost because they greatly increased access to information on operating condition of primary equipment. Furthers steps to enhance their potential to drastically shorten response times and larger diffusion of information are under way. It is intention to integrate all the information into a single system with the same interface for all users. Such tools are now able to provide utilities with: · global and real time knowledge of their whole transmission system. · complete expert system to diagnose and prevent failures. · global installed pool of all kind of equipment installed all over the country. · direct links to manufacturers spare parts resources and maintenance teams. Today manufacturers of HV equipment offer a variety of monitoring devices for the different types of apparatus. Some of them are complete systems, monitoring numerous features of one or more devices. Data in modern systems are transported via internal networks (intranet), frequently connected through firewalls to the internet for further use. The tendency towards such procedures is well visible for the future. possibility that monitoring device reduces the reliability of the circuit breaker The possibility that the monitoring device will reduce the reliability of the circuit breaker causes a certain concern. This has occurred where the circuit breaker has locked out unnecessarily due to the incorrect operation of the monitoring device, where the monitoring device has been integrated into the control function. At this stage, some utilities are no longer allowing new forms of monitoring devices to be integrated into the trip and close functions of the circuit breaker. Utilities and equipment manufacturers consider diagnostics and monitoring to be important tools to reduce life cycle costs as well as to extend the life expectance of the equipment and thus to optimize asset management. However, many of the existing monitoring systems do not provide satisfactory service. False alarms and in particular problems with the computer software often necessitate more frequent visits to substations than in case of conventional apparatus. At this time one of the most advanced utilities could report on one manufacturer, only, who provided a diagnostic and monitoring system with good reliability. Yet, this shows the progress made in this field and that positive expectations are justified. wear processes The background of the erosion and ablation physics is extremely complex and current knowledge about it is still incomplete and not well shared, but the amount of eroded materials of arcing contacts and nozzles can be estimated with acceptable certainty through consideration of the energy balance in the arc column and using measure of its thermal stresses. Of special concern is the monitoring of arcing contacts and nozzles of the high-voltage circuit-breakers as these parts are not accessible for sensors. Several solutions of indirect condition assessment have been presented. The overall positive practical experience, however, make it questionable whether the parts exposed to arcing within the interrupter of SF6 circuit-breakers really need to be monitored. efforts to reduce SF6 emissions Many new emissions reduction techniques and opportunities are being explored and employed by electric power industry. The implementations of these practices by specific companies have resulted in significant achievements, both fiscal and environmental. The following provides a summary of the key steps taken by some utilities to reduce SF6 emissions: § SF6 inventory tracking (SF6 cylinders are identified, weighed, leak checked, and inventoried) § laser leak detection (laser leak detection systems exploit the strong infrared absorption characteristic of SF6) § SF6 recycling
PREFERENTIAL SUBJECT 2: New trends in Switching Technologies Interrupter chamber of HV Circuit-Breakers Today interrupter development of high voltage breakers is focused on SF6 only. Novel principles such as self-blast interrupter chambers and double motion contact systems allow a very efficient interrupter – drive cost balance and thus keeping LCC’s low as well. trend to combined functions For improvement of substation layout and space saving there is a clear tendency evident towards integrated functions at given transmission levels. Key components, such as:
are integrated into one piece of apparatus. Both, life tank and dead tank versions have been introduced by various major switchgear manufacturers. The advantages of such a design are not only cost saving by reduced space requirement and lower shipping costs; it may also increase the reliability as the entire unit can be factory tested and shipped to site more or less in one single piece. In addition the number of parts is reduced, such promising a higher reliability as well. Equipment with integrated combined functions is entering the global market. Basically, this concerns high-voltage circuit-breakers which serve as disconnectors, as well. The justification is based on the high reliability of modern circuit-breakers which in some cases make separate disconnectors obsolete. An extensively discussed problem is the more complicated procedure to make a busbar accessible for work if no line side disconnector is installed. trend to hybrid (mixed) solution New hybrid solutions based on not only GIS concept but also conventional AIS concept are now proposed by many manufacturers. The ongoing urbanisation, energy needs in highly populated or industrially developing areas, economical and ecological considerations are increasingly forcing the selection of smaller optimised switchgear. Utilities are looking for upgrade, refurbishment and extension of infrastructure with new solutions. The decisive factors are very different for new substations. Therefore a hierarchical classification of the solutions can not be done. Substation arrangements based on mixed technologies (hybrid) become a strong competitor to the established substations with air-insulated open terminal equipment (AIS) and to gas-insulated substations (GIS). Their advantage is the need of smaller space than for AIS solutions and lower costs compared to GIS. increased reliability of circuit breakers New types of SF6 interrupting chambers, which implement innovative interrupting principles, have been developed during the last two decades, based on the objective of reducing the operating energy of the circuit breaker. This has led to a reduced stress and wear of the mechanical components and consequently to an increased reliability of circuit breakers. reduction in the SF6 content of circuit-breakers If one looks further in the future, other technology developments could lead to a reduction in the SF6 content of circuit-breakers. trend to silicone housings for high voltage equipment Over the last decade the application of hollow core composite polymer insulators (CPI) in the area of high voltage electrical apparatus has made a big progress. Reasons for changeover towards polymer–housed equipment is related to improved electrical performance in polluted conditions (hidrophobicity), greater resistance to seismic forces of earthquakes, explosion safety for personnel and surrounding equipment, lower weight, reduced risk for transport, and safety against vandalism. Main reasons why, in spite of all compelling positive attributes of composite polymer insulators, some utilities have a conservative approach toward CPI’s application in their network are CPI’s shorter life expectancy and higher price. Silicone insulators have been widely used in different applications for almost 30 years, now. A presentation raised the question why there has been no breakthrough, yet, for circuit-breakers with silicone hollow insulators although a certain number is in service, already. A market shift is expected when they will be more economical compared to porcelain insulators and when some still existing technological constraints have been overcome. There are some opinions that the application of the technology of composite polymer insulators has not yet reached the level where these products are sufficiently cheap or technically attractive to the customer and that their advantages should be used only in specialist applications. polymeric-housed distribution arresters Traditionally, porcelain-housed distribution arresters have tended to fail due to problems with sealing. The benefits of a leak-tight design using polymers have been generally accepted leading to the almost wholesale changeover from porcelain to polymers as the housing material for distribution arresters. Another factor is that at present polymeric-housed distribution arresters are cheaper than those made with porcelain housing. possible future design principles Some interesting considerations have been presented from work on possible future design principles. One concerns the uprating of existing circuit-breakers through the insertion of opening resistors during the actual current interrupting process. Another applies the principles of low voltage switchgear to medium voltage by forcing the current through zero by means of a high arc voltage across a system of contacts. new digital measurement and analysis New, fast and high-resolution digital current zero measurement system for application in high-power laboratories and analysis techniques are now available as an aid to development, testing and selection of SF6 high-voltage circuit breakers. The arc conductivity very shortly (200 ns) before current zero pretends to be an indicator of the performance of the breaker under test. The increase of that value of arc conductivity from test to test, gives a clear indication of the number of short circuit currents that a given breaker can interrupt. Arc model parameters can be extracted out of every individual test and that enable to determine limit performance of the tested circuit breaker and to predict its performance under other conditions than tested. PREFERENTIAL SUBJECT 3: Increased fault currents and Fault Current Limiters development of fault current limiting devices The development of fault current limiting devices (so called FCL’s) is a future-oriented topic. Many principles have been introduced over the decades; however, none of them was able to match reasonable cost requirements. CIGRE WG A3.10 will publish soon a survey on the state of the art. Today the situation has changed somewhat as a certain demand for current limitation becomes stronger in distribution as well as in transmission systems. The reason is mainly coupling of systems thus increasing the short circuit currents, which would demand either limitation of the latter or investment in new equipment. So motivation for the developers is enhanced to create current limiting solutions. However, there is still this hen-egg situation where today’s practicable solutions (based on superconductors) are too expensive to experience a real breakthrough. The tendency towards current limitation can be noticed anyway. To be prepared, CIGRE WG A3.16 started to work in order to cover future problems such as the integration of FCL’s into the systems, mainly concerning protection and selectivity. For FCL’s also some visionary solutions for current limiting switches were introduced, which show that research is quite active in this field. presentation of the work of WG A3.10 Presentation of the work “Fault Current Limiters - Report on the Activities of CIGRE WG 13.10” was done during the Sarajevo Colloquium. Final version of the Technical Brochure “Fault Current Limiters in Electrical Medium and High Voltage Systems” is submitted to CIGRE CO for publication. A summary regarding the Technical Brochure has been prepared and will be published in ELECTRA. Work of WG A3.10 is finished and Study Committee disbanded the Working Group. Fault current limitation will gain in importance with the growing loads especially in medium voltage distribution networks. The preferred location will be the bus tie between two partial networks. When a fault in one of the networks occurs this fault current limiter will reduce the overall stress and help to maintain the generation stability. At present the application of this device is limited due to the relatively high costs for investment and, in some cases, for operation. This situation will change in future when the short-circuit currents in distribution systems rise above the limits of the installed equipment. Several solutions of various technologies are under consideration. LIST OF COLLOQUIUM PAPERS List of the Colloquium papers with abstracts is available on the Colloquium web site (List of Colloquium Papers) COLLOQUIUM PROCEEDINGS The Colloquium PROCEEDINGS including all the Colloquium papers is issued in the form of a bound volume and CD-ROM. The volume and CD-ROM are available for purchase from CIGRE Committee of Bosnia and Herzegovina (contact person: Mrs. Jasmina Jakic, e-mail: cigre@utic.net.ba ). |
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