Single and Multiple Outage Statistics in Turkish National Power Transmission System

Transcription

1 Single and Multiple Outage Statistics in Turkish National Power Transmission System Aydogan Ozdemir, Mustafa Bagriyanik, Ilim Erden Department of Electrical Engineering Istanbul Technical University Istanbul, TURKEY (ozdemiraydo, Yener Akkaya APK Devision Turkish National Power Transmission Company Ankara, TURKEY Abstract Detection of failure propagation and prevention of cascading outages is crucial to maintain power system reliability and security. Multiple outage and cascading failures have been one of the most important problems of Turkish National Power transmission system. Past records show that the Thrace part of the system has suffered from this multiple outages. This paper presents the initial phase of the project involving analysis, mitigation and prevention of multiple outages in the region. It is a statistical outage analysis of a 7 year period between It is concentrated on the occurrences and the durations of the outages. Keywords-outage, outage duration, multiple outage, cascading failures I. INTRODUCTION Network interconnections over the years due to economical development and the population growth have increased the steady-state operational efficiency of the system. In addition, non-utility generators, independent power producers and several reactive power control devices have brought the system to a new stage. However, all those improvements have also increased the operational uncertainty, making the system dynamic behavior more complicated, and expanding the impact of local power grid failure into region electrical network nearby, which is more likely to lead to blackouts caused by cascading outages. Right-of-way restrictions and limitations on building new transmission lines have increased transmission line loading and such an operation close to the stability limits have increased the probability of cascading event occurrences as well as system blackout risks. Cascading outages in a power system occur when one or more of the partially or completely failed element shifts their load to nearby elements in the system. Those nearby elements are then subjected beyond their capacity so they become overloaded and shift their load onto other elements. These events are rare events and it is generally difficult to predict combinations of individual events such as single line outages. There have been several efforts to estimate the rare-event probabilities and to develop new methods, technologies and tools in order to better understand, predict, prevent and restore the cascading outages as well as to mitigate the effects of cascading outages [1-4]. Risk based reliability studies has been conducted due to the number of severe blackout events occurred across the globe in the recent years Power systems are normally designed to maintain the secure operating state in case of all N-1 contingencies as well as in case of some N-2 contingencies. However, incorrect settings of protective relays as well as protection system maloperations may destroy this secure operation and result in cascading events. Recent studies show that the power protection system plays an important role not only in any possible initial triggering, but in further propagating the disturbances. Since the protection system outages have critical impact on power system reliability, the researchers have concentrated on the reliability of protection systems to identify the protection outage effects on power systems, and to enhance power system reliability considering the protection failures. [5,6] It is clear that data collection is the initial phase of development of new models, methods, technologies and tools in order to better understand, predict prevent and restore the cascading outages [9,10]. This study presents single and multiple outage statistics of Turkish National Power Transmission System-Thrace Part. It is the initial part of an ongoing project involving analysis, mitigation and prevention of cascading events. The data belongs to a 7 year period between Single outages and their classifications were later followed by multiple outage statistics. II. TURKISH NATIONAL ELECTRIC POWER SYSTEM AND THE THRACE SECTION Turkish electricity transmission system has a total transmission capacity of MVA. It is composed of 154 kv and 380 kv sub-systems. In addition there are some 220 kv Interconnection lines connecting Turkish system to Georgia, to Armenia, to Bulgaria and to Greece. Thrace part of Turkish National Power Transmission System is the most power consuming part of Turkey (30-35 %). There are 174 buses, 267 transmission lines/hv cables, 65 transformers. 154 kv system comprises 4-5 islands under normal operating conditions. This project is supported by Turkish Electricity Transmission Company

2 The protection system includes 40 line differential relays for cables, 453 distance relays and 447 overcurrent relays. The system is fed at several locations by the Turkish National Electric Power Transmission System and there are some internal power plants. Past records showed that the number of outages in this part of Turkish National Power Transmission system was more than it was expected and also more than the number of outages at the other parts of the system. In addition, several cascading events were also experienced, especially in adverse weather conditions. Therefore, LOLE and the other reliability indexes were greater than the similar indexes for this type of systems. III. OUTAGE STATISTICS Outage data statistics were collected for the following categories: kv power transmission lines/cables, kv power transmission lines/cables, - 66 kv sub-transmission lines, - HV/Medium Voltage Power transformers, kv/154 kv auto transformers. Transmission line/cable outages include both the failures along their length and the station oriented failures at both ends. The number of outages and outage durations are summarized in Table I-II for each category. The tables include both the single and the multiple outages. Note that the outages include both the momentary and the sustained outages, whereas outage durations are the average values of sustained outages. Outage numbers and the outage durations include all the single outages and the multiple outages. It is clear that both the number of outages and the outage durations are high in 2001 and Actually this is because of multiple outages occurred in these years is the best year, showing the minimum number of outages and outage durations. On the other hand, the number of outages shows more uniform variation when compared with outage durations. 6 different conductor configurations and 9 different conductor configurations are used in 380 kv system and 154 kv system, respectively. Average failure numbers per year per 100 km line length and average outage durations per outage are illustrated for each type of transmission lines/cables are illustrated in Figure 1-4. Figure 1. Number of outages per year per 100 km of each 380 kv transmission line types TABLE I. NUMBER OF OUTAGES DURING PERIOD σ 380 kv lines kv lines/cables kv subtr.lines Power Transf Autotrf TOTAL Figure 2. Average outage durations per outage for 380 kv transmission lines TABLE II. OUTAGE DURATIONS DURING PERIOD [HOURS] σ 380 kv lines kv lines/cables kv subtr.lines Power Transf Autotrf TOTAL Figure 3. Outages per year per 100 km of each 154 kv transmission line/cable types

3 versus transmission line/cable lengths is illustrated in Figure 5 and 6 for 380 kv system and 154 kv system respectively. Note that all the single and multiple outages are taken into account while constructing the regression lines. Both the 154 kv and the 380 kv transmission line/cable outage rates are much greater than the conventional values used in power transmission reliability analysis. Figure 4. Average outage durations for several 154 kv transmission lines and cables Both the annual failures per 100 km and the average outage durations show a uniform distribution for 380 kv system. However, there are significant differences between the outage durations and annual outages per 100 km of 154 kv transmission components. It is mainly because of cable (K1000) failures and multiple outages Average outage duration of sustained outages is illustrated in Table III for the transmission lines and the transformers. Outage durations of transformer outages are greater than the outage durations of the transmission lines/cables. It is interesting that the outage duration of a 154 kv transmission line/cable is greater than the outage duration of 380 kv transmission line. Figure 5. Annual outage numbers versus transmissin line/cable length for 380 kv system TABLE III. AVERAGE AUTAGE DURATION OF SUSTAINED OUTAGES [HOURS:MINUTES] Σ 380 kv lines 2:04 4:04 4:06 3:59 2:50 2:04 1:32 2:57 1: kv 3:05 5:01 3:43 lines/cables 2:57 6:41 2:15 3:31 3:53 1:23 66 kv 1:23 2:52 0:48 subtr.lines 4:22 4:33 2:00 2:00 2:34 1:19 Power Transf. 4:51 6:21 4:56 10:42 12:20 15:38 8:12 9:00 3:46 Autotrf. 3:22 1:30 0:54 2:38 4:32 3:22 3:57 2:53 1:12 The outage rates of transmission lines/cables are estimated by using the scatter diagram-regression analysis method [7]. The regression method provides a means for making confidence statements about line outage. Number of outages Figure 6. Annual outage numbers versus transmissin line/cable length for 154 kv system It is well known that there is strong correlation between the outages, outage durations and the atmospheric conditions. Outage numbers and outage durations for each month are illustrated for the transmission lines and the transformers in Table IV and V. TABLE IV. AVERAGE NUMBER OF PERMANENT OUTAGES DURING PERIOD Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec AVG 380 kv lines kv lines/cables kv subtrans. lines Power Transformers Autotransformers TOTAL

4 TABLE V. PERMANENT OUTAGE DURATIONS DURING PERIOD [HOURS:MINUTES] Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Σ AVG 380 kv lines 50:08 58:48 36:02 19:47 28:16 68:21 76:10 51:08 29:00 20:57 24:06 115:07 577:56 48: kv lines/cables 438:59 161:46 53:40 81:41 136:45 101:11 108:48 170:38 86:57 178:08 266:02 284: :35 172:27 66 kv subtrans. lines 40:16 26:23 101:37 3:10 2:42 20:19 5:10 9:37 15:45 2:20 63:25 58:44 349:32 29:07 Power Transformers 245:47 154:04 117:03 61:23 51:57 111:22 123:55 139:08 103:06 186:26 69:07 231: :43 132:53 Autotransformers 20:27 5:50 13:17 6:33 9:58 16:29 18:50 10:13 17:18 5:51 8:03 26:34 159:28 13:17 TOTAL 795:39 406:53 321:40 172:37 229:39 317:43 332:56 380:45 252:08 393:45 430:45 716: :16 395:56 It seems that there are two critical periods for the outages; namely, winter period (November, December, January) and summer period (July and August). Summer outages are more than the winter outages. However, outage durations are much longer in winter time. The followings can be written for the outages. - Both the outage numbers and the outage durations are greater than they should be. - The system experiences more failures in Summer time, but the outage durations are much longer in winter times. - Annual outage duration is 4585 hours which corresponds 52% of overall operating period. Therefore, (N-1) criteria is not a secure operation condition. - The insufficiency is more clear during winter period. Total outage duration in January is 107% (795 hours) of operating time. - It is obvious that the system reliability level will be more critical if periodic maintenance tasks are taken into account. - The number of related (dependent) outages is high. They should be minimized by using improved protection coordination. IV. SINGLE AND MULTIPLE OUTAGES A multiple outage event is defined as the outages in which one outage occurrence is the consequence of another outage occurrence, or in which multiple outage occurrences were initiated by a single incident, or both [8]. High outage numbers and long outage durations in the region were assigned to be one of the indications of intensive multiple outages in the system. Therefore, outage records are classified as single and multiple outages. Table VI and VII illustrates the number and the duration of single and multiple outages in the region during period. Multiple outages are grouped with respect to the number of outages in the event. For example represents the multiple outage events including 4, 5 or 6 single outages. Table VIII shows the average duration of single and multiple outages. Table VI and Table VII show that 60% of overall outages are single (independent) outages and 75% of total outage duration comes from single outages. On the other hand, average duration of multiple outages decrease with increasing outage numbers in a multiple outage. TABLE VI. SINGLE AND MULTIPLE OUTAGES AVG Single Total TABLE VII. TOTAL SINGLE AND MULTIPLE OUTAGE DURATIONS [HOURS] Single Total TABLE VIII. AVERAGE DURATION OF SINGLE AND MULTIPLE OUTAGES [HOURS:MINUTES] Single 3:16 4:55 3:54 4:56 7:43 6:13 4:02 5: :44 6:26 2:46 2:31 2:20 1:13 1:26 2: :55 1:43 2:16 2:02 4:25 0:45 0:41 1: :46 0:36 0:46 0:10 1:28 2:36 0:36 1: :34 1:06 0:40 1:07 0:57 0:31 1:16 1:02 Single outage statistics that will be used for chance outage modeling of power transmission components can better be constructed from single outage data. Table IX and X illustrates the single outage statistics of 154 kv and 380 kv power transmission systems. The followings can be derived from the comparison of Tables IX and X with Tables I and II. Average single outages are approximately 60% of overall outages. All components show more uniform distribution besides 66 kv sub-transmission lines and autotransformers.

5 66 kv sub-transmission lines show more multiple outages due to their radial structure. 154 kv power transmission lines/cables are more effected from multiple-outages when compared with 380 kv transmission lines. Multiple-outages of 66 kv sub transmission system are longer. Duration of multiple outages is shorter. TABLE IX. NUMBER OF SINGLE OUTAGES DURING PERIOD 380 kv lines kv lines/cables kv subtr.lines Power Transf Autotrf TOTAL TABLE X. DURATION OF SINGLE OUTAGES DURING PERIOD [HOURS] 380 kv lines kv lines/cables kv subtr.lines Power Transf Autotrf TOTAL Final statistics regarding seasonal variation of cascading outages are illustrated in Table XI. Here cascading outages are assumed as the multiple outages including 10 or more outaged components. TABLE XI. SEASONAL VARIATON OF CASCADING OUTAGES (10+ OUTAGES) J F M A M J Jl A S O N D T TOT Table XI shows that there are again two critical periods for cascading outages; namely, summer and winter periods. Although the table shows that there are more cascading outages during the summer time, the duration of winter cascading periods are longer. This is a global result and more quantitative information will be given whenever outage duration statistics of cascading outages are finished. V. CONCLUSIONS AND DISCUSSION This study has presented single and multiple outage statistics of a critical part of Turkish national power transmission system. First, all outages and outage durations are presented on a component basis. Their seasonal variation and outage number versus transmission line/cable length were introduced. The results have showed that the system was seriously affected from multiple outages. Then, multiple outage statistics were introduced. The followings can be derived from this initisl attempt. Outage numbers and the outage durations are greater than they should be. (N-1) criteria cannot be accepted as a secure operation condition. (N-2) criteria should be satisfied, especially for winter period. The system experiences more failures in Summer time, but the failure durations are much longer in winter times. High number of outages and long outage durations don t give enough chance for periodic maintenance tasks. The number of related (dependent) outages is high. Radial structure of 66 kv sub-transmission system is the most critical one from related outages. High multi-outages are because of insufficiency in 154 kv system. 154 kv system should be extended buy additional transmission facilities. In addition, protection system should be improved, if required. The authority prefers multi-island operation under normal operating conditions because of high short circuit currents. Such an operation decreases the steady state security of the system as well as increases the number of local-cascading outages. Improved protection coordination and better islandingmode configuration is required to minimize the multiple outages in the system. ACKNOWLEDGMENT The authors would like to thank the Turkish National Electric Power Transmission Company for their support and encouragement for the study. References [1] H. Hu, X. Du, C. Xu, F. Zhao, X. Lin, Z. Bo, Risk Assessment of Cascading Failure in Power Systems Based on Uncertainty Theory, IEEE PES General Meeting, pp.1-5, July 2011, Detroit, USA. [2] J. Chen, J. S. Thorp, I. Dobson, Cascading dynamics and mitigation assessment in power system disturbances via a hidden failure model, Electrical Power and Energy Systems, vol. 27, no.4, pp , 2005 [3] S.P. Wang, A. Chen, C.W. Liu, C.H. Chen, and J. Shortle, Rare-event Splitting Simulation for Analysis of Power System Blackouts, IEEE PES General Meeting, pp. 1-7, July 2011, Detroit, USA

6 [4] H. Ren, I. Dobson, Using transmission line outage data to estimate cascading failure propagation in an electric power system. IEEE Trans.Circuits and Systems Part II, 2008, vol. 55, no. 9, pp [5] A.Ozdemir, M.Bagriyanik, I Ilisu, O. Gul, A.Kaypmaz, Y.Akkaya, Impacts of protection system misoperation on the reliability of Turkish National Power Transmission System, International Conference on Advanced Power System Automation and Protection APAP2011, October 16-20, 2011, Beijing-CHINA [6] J.S. Thorp, A.G.Phadke, S.H. Horowitz, S.Tamronglak, Anatomy of power system disturbances: importance sampling, International Journal of Electrical Power & Energy Systems, vol. 20, no. 2, pp , February [7] A.D.Patton, Determination and Analysis of Data for Reliability Studies, IEEE Transactions on Power Apparatus and Systems, Vol. PAS-87 no. 1, pp , January [8] IEEE Standard Terms for Reporting and Analyzing Outage Occurrences and Outage States of Electrical Transmission Facilities, IEEE Std [9] R. B. Adler, S. L. Daniel, C. R. Heising, M. G. Lauby, R. P. Ludorf, T. S. White, An IEEE Survey Of U.S. And Canadian Overhead Transmission Outages At 230 kv and Above, IEEE Transactions on Power Delivery, vol. 9, no. 1, pp , January [10] Data Analysis Task Force, Working Group on Statistics of Line Outages, General Systems Subcommittee, Transmission & Distribution Committee, R. B. Adler (Chairman), S. L. Daniel, Jr., C. R. Heising, M. G. Lauby, R. P. Ludorf, T. S. White, vol. 9, no. 1, pp , January 1994.