ࡱ> z|y5@$Lbjbj22 vXXI $ &&&&< 5----;-b15$6R8&5- % % % &5 S5%'%'%'% b  -%'% -%'F%'k(VN+ + @:l&"+ y- i505+ 9-#9+ 9 +v^%'L &5&5 d&' &Simplified reliability data collection and analysis in the power system M.Stojkov HEP group, Distribution, Area Slavonski Brod, Croatia R.Kova evi DT, Croatian Telecom, Slavonski Brod, Croatia S.Nikolovski Faculty of Electrical engineering, University of Osijek, Croatia ABSTRACT: Business activities analyzing and decision making in all organization levels of the nowadays company become the starting point for further success like productivity improving or losses reducing. It is a questionable what part of the company activity is the most important, probably that one with the most money savings. But some of these activities, like human resources, education and motivation - that are basics for further company development cant be recognized at any moment. However, there are many activities in the power system companies that can be analyzed and exactly named by history data. Maintenance of the system, dispatching electric loads to the end users, planning new systems development (new buses and branches or replacing a present component with new one of greater transmission capacity) are only some of these activities that are described here. Introduction The power system The power system is a very complex structure, with great number of components and kilometers of power lines connected together, which make it possible to get electric energy in all towns, villages, factories, hotels and almost in every household and farm. Electric energy has significant importance in nowadays life because of continually energy supply to end-users. System development There is two viewpoints on the power system: end-users view and power company view. Sometimes, they are not in harmony, even they are diametrically opposite. But, in every moment both of them are aware of the continually load supply process importance. Often, it is unchangeable energy source need for production to any users. On the other hand, power system companies try to find new load consumption in order to increase lines capacity using due to extra profit. Decades ago, the first customers and system engineers common idea was to get connection on power system network at desired voltage level depending on energy amount and user-network distance. After starting production period with accelerated production growth, electric input capacity problem was the main preoccupation. The capacity problem was either in factory connection or even more in the distribution network following by voltage drops. Some of these problems were solved by higher capacity cable replacement or by building new connection on higher voltage level network with new designed industrial transformer substations. Sometimes, new power plant had to be built to meet all load demands. Now, the power system reliability has high impact on user productivity in companies and on user life standard satisfaction for regular people. As times go by, electricity consumers market was born and now - there are reliability rules and power quality recommendations written by the pool. Present system problems The power system with a number of states Existence of two or even more selected feeding lines for almost every transformer substation in the network gives a variety of load flows in different switching system states. Basic system load flows are time dependant functions based on day period, season, temperature etc. Because of such a sophisticated structure, it is hard to reach all data needed for a reliability evaluation. Although there is several control centers, studiously situated for better system controlling, inspection and management covering, it becomes very hard to work there, with high level of mind intention and responsibility for these educated people. It is expected that the power system is very reliable, with only a few non-voltage periods of negligible duration. When the power system fault occurs in higher voltage level of the power system - more electricity consumers are injured; energy non supplied damages and public reasoning become more important. Also, stuff function (switching, fault locating and repairing) has to be of higher quality. It is required to design and install several tools to ease a system state overview and to forward target achievement. the Systems database Database incorporation Sometimes, usually after a system malfunction in the past, new improvement approach has been born. Engineers and even scientists have something to say about problems in the system, about human faults and absence of human education or learned skills, or about unprepared reserved component. It is forgotten that we cant say even a word without knowing the system configuration, architecture and components and their parameters build-in the system, and also knowing about detailed power load flows. If we have all needed above-mentioned data, almost all answers of better and reliable system function come instantaneously. Power system data archiving, editing and storing is permanent and important data handling, although hard process. The real benefits of that process lie in easy and fast selection and filtering of some specific data that can lead to technical or manager decision making. The technical data interchange between the power supplier companies, between electricity board and electricity components producer or electricity components designer or even scientific institution come very easy and with high speed by standard table formats using e-mail. Database design Here, the power system is well designed by two main (Power Line and Transformer Substation) and three helpful interrelated tables (Location of Power Line, Power Line Characteristic and Power System Components). It is very easy to get connections (feeding points and power lines load flow) between transformer substations and power lines. Each transformer substation is described with a set of next properties: Identification mark of transformer substation, name and voltage ratio (35/10 kV) is the basic transformer substation data. Total installed transformers load on primer voltage 35 kV and number of installed transformers in transformer substation keep the information of possible load sources in that point of the power system. Numbers of feeding inputs and outputs on primer voltage, numbers of outputs on secondary voltage 10 kV give importance and position of that feeding node in the network. Total installed transformers load on secondary voltage; number of installed transformers 10/0.4 kV, real measured peak load and number of consumers describe load characteristics on secondary voltage level. The main properties of each power line are identification mark, name and incident transformer substation. The other attributes that give important load data are total installed load of transformers 10/0.4 kV, number of installed transformers, real measured peak load, average night peak load and average day peak load, number of customers and type of consume. Protection current boundaries and location of power line, length of main line, total length and length of power line without load describe power line architecture. Reliability data that give line position in the network are number of interconnections with neighbour power lines and number of other power lines connected. The identification mark of power line has 5 characters where the first two characters are the ID mark of feeding transformer substation. user friendly application New friendly Visual Basic Code is designed as useful tool, serves connection between faults database inside present power system state and real variables that are feed by user after a fault. It is very easy to choose a power line and simultaneously get total number of end consumers at determined power line or substation by helpful selection from the Power line of Transformer substation data tables. At the same time, automatic controls choose and distinguish a load curve of selected power line, depending on daytime and season. Even if a fault is only on part of a radial power line, it can recognize number of customers depending on an opened line disconnect switch location. These devices are used for easy fault detection localization and cost reduces during the maintenance actions. Disconnect switches make possible power lines to be sectionalized or reconfigured. Some other calculations are performed during faults data input process. The code offers a number of useful lists such as faults causes, faulted component, and fault type in the power system from data tables designed in the database. Here, the application is an attempt to improve reliability of electricity supply and increase flexibility of the power system. It also reduces time for calculating reliability indices to ease choice of the most profitable and effective power line for further reconstruction or even replacement with brand new line. Selection model is based on power line comparison under known criteria usually used in energy market all over the world. After the main variables were input, the code calculates total faults time duration, duration of preparing time, failure location time and repairing time (depending on organization and staff education), and also non supplied energy. Some power lines reports can be done depending on chosen monitoring period in data base query. Statistics report calculates duration of monitored period, total up-time and total down- time (Tdown), number of failures, mean time to failure (MTTF) and mean time to repair (MTTR), failure intensity, failure frequency and statistical availability (StAv). The energy report gives total energy (ENS), average energy per failure (ENSF), average energy per year (ENSY), cumulative product of unsupplied consumers number and duration of non-voltage period (Cum) and average of cumulative product (AvCum). The last two variables are brand new, introduced here in this paper, very significant and important in selecting process of the power line under reconstruction or planning new systems development. Period report results in basic and derived periods variables: mean values per year and mean values per failure. The following periods are contained: reaction, location, fault and repairing periods. After all, beside the better way to store and edit faults data, user can do some analysis at any time after it. Some queries are designed to reduce data base records in desired criteria, example all faults in power line 0407 I.Antunovica 10 kV which happened in period between 16.08.1998. - 25.04.2000.; where the fault component was an insulator and where the fault cause was thunderstorm or fire. There are thousands of combinations in data request by designed queries; so a range of sensitivity analysis can be done. application examples User can easy compare the same power lines indices during different periods in the past. By that way maintenance engineers can evaluate their activities in the last period and maybe decide on any corrections in the policy. The comparisons of power lines faults during two periods (whole 1998. and 1999.) for radial underground power line Ljudevita Posavskog, marked 0403, are given in Table 1 and Table 2. On the base of presented data in table 1, it is easy to see that there was increased profitability during 1998. for power line 10 kV 0403. The main cause was probably because of weather conditions that results in different numbers of faults and duration of down-time. Anyway, the maintenance of that power line improved during 1999. due to decreased value of MTTR (Table 1) and time period of reaction (Table 2). Table 1. Power line 10 kV 0403; faults indices during whole 1998. and 1999. _____________________________________________ Year 1998. 1999. _____________________________________________ Tdown (minutes) 1839 2023 MTTR (hours) 2.043 1.983 MTTF (hours) 581.956 513.310 StAv 0.9965011 0.9961511 Fail. Intensity rate 5.967E-3 6.765E-3 Fail. Frequency 15 17 ENS (MWh) 26.4118 31.5588 ENSF (MWh/fault) 1.7608 1.8564 AvCum (minutes/fault) 2780.607 3242.102 _____________________________________________ The other measured faults periods are better in 1998. If there are reserved power supply for all customers dependant on power line, time period of a repair (Table 2) can be longer without negative influence on availability. Table 2. Power line 10 kV 0403; faults periods during whole 1998. and 1999. _____________________________________________ Year 1998. 1999. _____________________________________________ Treaction (minutes) 507.00 420.00 Tlocation (minutes) 623.00 1047.00 Tfault (minutes) 1839.00 2023.00 Trepair (minutes) 484.00 7401.00 AvTreaction/fault 33.80 24.70 AvTlocation/fault 41.53 61.59 AvTfault/fault 122.60 119.00 AvTrepair/fault 32.27 435.35 _____________________________________________ After detailed analyses of power lines faults have been done, it is easy to see the most important maintenance activities in the system and important deep faults problems power lines. Table 3 and Table 4 show a basic selection data on two selected power lines. It is obvious that the power line 0407 (underground) has significantly less number of all faults time periods. The underground part of the power system is built in the city area and most of the transformer substations are interconnected with a several power lines. Quality of supply mainly depends on time reaction period and time location period. Table 3. Several power lines 10 kV faults indices _____________________________________________ Power Line 0407 0801 _____________________________________________ Tdown (minutes) 2610 7367 MTTR (hours) 1.673 3.721 MTTF (hours) 783.865 615.188 StAv 0.9978702 0.9939883 Fail. Intensity rate 11.720E-3 10.694E-3 Fail. Frequency 11 14 ENS (MWh) 21.2858 9.1493 ENSF (MWh/fault) 0.8187 0.2773 AvCum (minutes/fault) 1896.000 1103.900 _____________________________________________ Table 4. Power lines 10 kV faults periods _____________________________________________ Power Line 0407 0801 _____________________________________________ Treaction (minutes) 286.00 2501.00 Tlocation (minutes) 1125.00 3326.00 Tfault (minutes) 2610.00 7367.00 Trepair (minutes) 2754.00 1611.00 AvTreaction/fault 11.00 75.78 AvTlocation/fault 43.27 100.79 AvTfault/fault 100.39 223.24 AvTrepair/fault 105.92 48.82 _____________________________________________ Radial overhead power lines in rural areas have not reserved power supply and they are usually on greater distance from maintenance and control center. So, power supply quality directly depends on time repairing period. Power line 0407 has higher importance due to deep faults problems a greater power load and number of consumers, so following variables show power lines importance: Energy not supplied (ENS), energy not supplied per failure (ENSF) and average cumulative product of unsupplied consumers number and duration of non-voltage period. The faults database is a source of benchmark data used for any additional analysis of their drawbacks. This tool is very powerful in weakness detection or for further development of system planning and prevention strategies. Finally, some simple reliability calculations for all power lines (or for exact defined power lines) are achieved - performed by a form (Visual Basic code): number of failures, SAIFI (System Average Interruption Availability Index), SAIDI (System Average Interruption Duration Index), ASAI (Average Service Availability Index), AENS (Average Energy Not Supplied Index), ENS (Energy not supplied), ENSY (average value per year) and ENSF (average value per failure). All power system faults data are presented in Table 5. It is good starting point for further, more detailed analysis of the power system. Special expert team has to continually monitor all system states to make seasons power lines faults reports. Table 5. Power system reliability indices in period between 01.01.1998 and 30.04.2000. __________________________________________________ Number of faults 401 SAIFI 838.6 SAIDI (hours) 666.38 ASAI 0.997044 AENS (MWh/customer) 1.470765 ENS (MWh) 548.478 ENSY (MWh/year) 235.246 ENSF (MWh/fault) 1.36777 __________________________________________________ conclusion The first idea of faults time period monitoring and analyzing have been performed during 1998. to 2000. Simplicity of described approach and fast data retrieval gives practical improvement in power system reliability studies. Distinction possibility of faults causes, failure component or time period (date to date for determining month, season, year) results in systematically data collection and valuable quantitative reports. We recognize some components with serial fault (ceramic insulators 10 kV), improve response time in one maintenance team with the worst call back results, add surge arrestors on some specific points in the system and make new reconstruction plans by using this application. New buses, branches design and building or present component replacement with new one of greater transmission capacity are consisted parts of systems planning investment. Described code is successfully applied to help power system design and load dispatching. Now, further implementation is run on the distribution power system of Slavonski Brod; our present objective is interaction of faults on power lines feed from the same transformer substation. Further step in research will be a connection between SCADA (System Control and Data Acquisition) system and statistical data about faults. Real faults initial and duration time, actual load before the non-voltage period and number of consumers are the main variables that will be taken from SCADA system. references Stojkov, M. & Mravak, I. & Nikolovski, S. 1999. The reliability evaluation of distribution power system, Proceedings of ESREL, Munich-Garching, Germany, Volume I, pp. 341-346. Stojkov, M. & Nikolovski, S. & Mravak, I. 2003. Improved methods of power systems availability indices determination, Proceedings of ESREL, Maastricht, The Netherlands, Volume 2, pp. 1503-1509. Vv  ! 5 D   ! 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