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Energy and Power Engineering, 2013, 5, 36-41 doi:10.4236/epe.2013.53B008 Published Online May 2013 (http://www.scirp.org/journal/epe) Three-defense Line Coordination Strategy of the Guizhou Power Grid with the New Security Situation Wencheng Zheng, Tao Yu South China University of Technology, Guangzhou 510640, Guangdong, China Email : epwenche n gzheng@hotmail.com Received 2013 ABSTRACT In order to meet the requirements of Decree of the State Council of the People's Republic of China (No.599), this paper presents a three-defense line coordination strategy based on the Decree of the State Council (No.599). Taking the Guizhou power grid o f 220 kV&500 kV as an example, the security and stability problem of th e Guizhou po wer grid is analyzed. The strategy using three-defense line coordination for lowering the level of electricity safety accidents is re- searched. The analysis results show that the proposed coordination strategy is feasible, which can lower the level of electricity safety accidents under the same fault in same operation mode. Through studying the three-defense line of the Guizhou power grid, this paper presents a basic idea of the three-defense line coordination strategy based on the Decree of the State Council (No.599). The three-defense line coordination strategy provides reference for other provinces power grid . Keywords: Security and Stability; Three-defense Line; the Guizhou Power Grid; Decree of the State Council (No.599) 1. Introduction With the development of th e smart grid, the power struc- ture presents more and more complicated. The coordina- tion problem of machine and network become increas- ingly prominent. The grid dynamic characteristics as well as the security and stability issues are increasingly com- plex. It also increases the grid stable operation of the control difficul t y . Along with the introduction of the Decree of the State Council (No.599), the security and stability of the power system is more and more attention. The security defense system of Power system must be established to ensure the system safe and stable operation. It mainly includes reasonable grid, reliable equipment, sound and effective three-defense line, efficient scheduling operation and management. Among all above, Setting three-defense line is a successful experience to run a security and sta- bility power grid in China. The provisions of China's electric power system to withstand large disturbance ability of the security and stability standards are divided into three levels [2-4]. In order to meet the requirements of the three standards of security and stability, a reasonable grid structure should be first built. The foundation of power system safe and stable operation needs a good system grid. Correspond- ing to the three standards, China has formed three-de- fense line concept. The construction of the grid is plan- ning and configuration by three-defense line as well as the grid’s scheduling operation and management. Over the years, China’s power grid didn’t appear a large area blackout. It benefited from the construction of three-de- fense line in accordance with the claim of the power sys- tem security and stability’s guide [5 -6]. The first line of defense is the most basic requirements of system safety performance. It generally doesn´s not need to take measures. It achieves by the system auto- matically adjust device or the dispatching automation system’s preventive controls. The accidents belong to the second line of defense happen with low probab ility, bu t it will harm system deeply. If effective measures do not be taken after the accident, it would expand the range of the system accident, even lead to the collapse of the system. So it needs to set emergency control device and take measures to guarantee the system’s stability. The third line of defense is preventive measures that prevent the system appearing large area blackout and whole grid crash accident. The res earch has been tak en on the measu res and con- trol of grid security and stability of Guizhou main grid and the regional solitary power grid [7-8]. Base on the Guizhou Power Grid’s configuration of three-defense line analysis in 2012, the paper analyses the adaption of the Guizhou Power Grid’s three-defense line to the De- cree of the State Council (No.599) and modifies the un- suited part. Then it proposes the basic idea of three-de- fense line coordination strategy under the Decree of the Copyright © 2013 SciRes. EPE W. C. ZHENG, T. YU 37 State Council (No.599). 2. Guizhou Power Grid Security and Stability Analysis In 2012 Using PSD-BPA and PSD-SSAP, the paper analysizes five typical operating modes of the Guizhou power grid in 2012. The five typical operating modes is summer maxi- mum & peak & light load operation mode and winter peak & light load operating mode. 2.1. Small Signal Stability Analysis In three peak load operating mode, there are weakly damped oscillation mode in the grid. The main oscilla- tion points are concentrated in the Tongren Area and Zunyi Area. It illustrates that these patches lack electrical damping. In order to improve area damping levels, the crucial generator sets such as Xiangziyan generating sta- tion in Tongren or Qianbei generating station in Zunyi may be considered to install PSS device or re-tuning the PSS parameters. Overall, in most cases, the small signal interference problem in Guizhou power grid isn’t in a prominent place. 2.2. Security and Stability Analysis of the 500 kV Main Grid The prominent stability problems in Guizhou 500 kV main grid are following. (1) The double circuit line of 500 kV from Anshun to Gaopo occurs short-circuited. It may lead the line of 500kV from Nayong Power Plant II to Gaopo overload. (2) When 500 kV Shibing transformer substation and Tongren transformer substation operates in open-loop, the double circuit line of 500 kV from Shibing to Tongren occurs short-circuited. It will lead Tongren regional power grid and the main grid separate. Then the eastern part of Guizhou may appear frequency in stability. 2.3. Security and Stability Analysis of the 220 kV Main Grid Guizhou 220 kV grid centres in the each 500 kV trans- former substation. Each area runs independently. In 2012, there are sixteen 500kV transformer substations in Guizhou grid. That forms 16 regional grids. The prominent stabil- ity problems in Guizhou 220 kV main grid are following. (1) Siling power station send channel serious failure will lead transient instability problem in Tongren grid. (2) Shatuo power station send channel serious failure will lead transient instability problem in Songtao grid. 3. Three-defense Line Coordination Strategy Base on the Decree of the State Council (No.599) in Guizhou Power Grid 3.1. Accident Classification Base on the Decree of the State Council (No.599) in Guizhou Power Grid The Decree of the State Council (No.599) has published the ordinance of electrical safety incidents emergency disposal investigation and processing. The Ordinance is composed of six chapters. They are general principles, the report of the accident, emergency disposal, accident investigation an d hand ling, liab ility, an d ann ex. Th e most critical is divided accident level. (1) The level of accidents is mainly determined by the proportion of the redu cing load supp ly an d the prop ortion of urban electricity customer outage. (2) Grading standards of electrical safety accidents is a supplement on the basis of The Decree of the State Council (No.493). The core is defined four types of ac- cidents. They are especially significant accident signifi- cant accident larger accident and generally accident. Table 1 shows the accident corresponding level of Guizhou power grid. It can be drawn from the load dis- tribution of all cities and counties in Guizhou Province Table 1. Accident level of Guizhou power gr id. Accident level Judgment Especially Significant Accident 1 More than 40% load supply of the whole grid r educe 2 More than 60% loa d supply of the Gui yang City reduce Significant Accident 1 Load supply reduc i ng o f t he wh o l e grid is am on g 16 % t o 4 0 % 2 Load supply reducing of Gui yang grid is among 40% to 60% 3 More than 60% load supply of the Zunyi grid Liupanshui grid Anshun grid Tongren grid and Bijie grid reduce Larger Accident 1 Load supply reduc i ng o f t he wh o l e grid is am on g 12 % t o 1 6 % 2 Load supply reducing of Gui yang grid is among 20% to 40% 3 Load supply reducing of Zunyi grid Liupanshui grid Anshun grid Tongren grid and Bijie grid is among 40% to 60% 4 More than 60% load supply of the Kaili grid Duyun grid Xingyi grid Qingzhen grid and Fuquan grid reduce Generally Accident 1 Load supply reduc i ng o f t he w ho le grid is am o n g 6% to 12% 2 Load supply reducing of Gui yang grid is among 10% to 20% 3 Load supply reducing of Zunyi grid Liupanshui grid Anshun grid Tongren grid and Bijie grid is among 20% to 40% 4 Load supply re ducing of Kaili grid Duyun grid Xingyi grid Qingzhen grid and Fuquan grid is among 40% to 60% 5 More than 40% load sup p l y of the Chishui grid and Renhuai grid reduce Copyright © 2013 SciRes. EPE W. C. ZHENG, T. YU 38 and the dividing standards of accident level in the Decree of the State Council (No.599). 3.2. The Coordination Strategy of the First Defense Line and Second Defense Line Research Power system operating st at us can be di vi ded i nt o: normal, alert, emergency, extreme urgency, collapse and recovery. Corresponding system run state changes, setting three- defense lines to ensure the safe and stable operation of power system encounters a variety of accidents. Figure 1 shows the relationship between the grid operating state conversion and th ree-defense line setting. The coordination of the first defense line and second defense line refers to the system normal operation that preventive measures can't maintain effective system safety performance. Then the emergency control device take timely measures to maintain system stability. The coordination of the first defense line and second defense line is directly related to the system whether it can deal with low probability of o ccurren ce of large fault o r not. It is very important to the safe and stable operation of the system. Especially for system operation of the weak link, it should pay more attention. The weak link of power system operation is the grid key transient stability section . Also it is the key object of the power grid stability analysis and monitoring. One of the important premises to guarantee the stability of the power grid is to control transmission section operating within transient stability limit. In normal mode, there are three electromagnetic loop networks in Guizhou 500 - 220 kV power grid. So Tab le 2 confirms seven sections that need t o control the power flow. Table 2. Section need to control the power flow. Section Control Value(MW) Double circuit line from Xifeng to Guiyang 2200 Double circuit line from Yaxi to Nanbai 480 Double circuit line from Zunyi to Nanbai 330 Double circuit line from Fuquan to Wenlang 280 Circuit I from Zhudong to Zhuling and Double circuit line from Qingyan to Zhudong 500 Line from Anshun to Xiayun and Double circuit line from Anshun t o P uding and Line from Anshun to Yao pu 400 Double circuit line from Qinzhen to Zhanjie 410 Figure 1. The constraint of three-defense line coordination in The Decree of the State Council (No.599). Copyright © 2013 SciRes. EPE W. C. ZHENG, T. YU 39 3.3. The Coordination Strategy of the Second Defense Line and Third Defense Line Research The second defense line needs the emergency control device that is configured in the system to take a cutting machine, load shedding, plan splitting and other meas- ures to ensure the stab ility of the system. And it needs to take appropriate control measures in accordance with pre-established control strategy. In normal operation mode, the Guizhou power grid needn’t take stability control measures when the grid appears single fault. It maintains the stability of the pow er system operation and power supply through control power flow. In the 500 kV line N-1 maintenance mode, a circuit line happens three-phase disconnect fault. If the influ- ence of transmission limit is big, measures such as cut- ting machine, load shedding, cutting down DC transmis- sion power should be taken to maintain the stability of the power system operation and the integrity of the main grid. Opposite, if the influence of transmission limit is small, it just needs to control power flow. When the Guizhou power grid appears single serious fault, measures such as cutting machine, load shedding should be taken to maintain the stability of the power system operation and the integrity of the main grid. There are some weak links in the grid those happen sin- gle serious fault will cause the system instability. So the stability measures such as cutting machine, load shed- ding of the second defense line should be configured. When the system appears multiple serious faults, it couldn’t maintain the integrity of the whole grid. The system should be set measures such as system splitting, frequency and voltage emergency control to avoid sys- tem collapse and large area blackout. The protective de- vices of generating unit and line should avoid taking mi- soperation to prevent generating unit and line cascading trip when the system appears frequency oscillation. Gui- zhou power grid splitting point should be set based on the situation of the entire southern power grid system oscillation center. And it should guarantee the consis- tency of the splitting device action in the same section. In order to restore stability of the system frequency after splitting, the system should configure enough cut- ting machine capacity and set the operating frequency and round reasonably. The emergency control of the fre- quency and the voltage mainly includes the low-frequency and low-voltage load shedding device [9,10]. Guizhou power grid should configure the low-frequency and low- voltage load shedding device based on the grid situation of the section and the grid splitting. 4. Three-defense Line Adaptive Analysis and Coordination Strategy Correction Base on the Decree of the State Council (No.599) in Guizhou Power Grid In 2012, the regional power grid of Xifeng, Guiyang, Jinzhou, Bijie, Anshun, Yaxi, Tongren and Songtao in Guizhou power grid appearrs all kinds of fault in each kind of operation mode. It will cause different effects after controlling of three-defense line. Table 3 shows that the most serious fault in each of these areas in Guizhou power grid is classed based on the Decree of the State Council (No.599). Table 3. The electrical safety accidents grading of the Guizhou Power Grid in 2012. Area Operation Mode Fault Stable Strategy The Proportion of the Amount of Load Shedding Accident Level Guiyang Guiyang substation one transform er is overhaul and the other one is tripping 1.Shedding 569 MW load 2.Low-Frequency Load Shedding 45MW in first round 14.41% Generally Accident Xingyi Jinzhou substation one transformer is overhaul and the other one is tripping Shedding 84 MW load 0.06% --- Bijie Shexiang substation on e transformer is tripping 1. Shedding 204 MW load 2. Low-Frequency Load Shedding 42MW in first round 24.12% Generally Accident Zunyi Yaxi substation one transformer i s overhaul and the other one is tripping Shedding 600 MW load 24.19% Generally Accident Tongren substation on e t ransformer i s overhaul and the other one is tripping Shedding 233 MW load 12.94% --- Tongren winter peak load operating mode Songtao substation one transformer is overhaul and the other one is tripping Shedding 184 MW load 10.22% --- Copyright © 2013 SciRes. EPE W. C. ZHENG, T. YU 40 (1) In winter peak load operating mode, Anshun sub- station operating in single transformer appears the fault of transformer tripping when the transformer transmis- sion power is 630 MW. Then Anshun grid becomes an isolated network. The bus frequency deviation of the isolated network is shown in Figure 2(a). After shedding 620 MW load, the bus frequency deviation of the isolated network is shown in Figure 2(b). The total load of Anshun grid is 780 MW. The accident load accounts for 79.50% of the total load. It reaches significant accident according the Decree of the State Council (No. 599). Through correcting the coordination strategy of three- defense line, it will not reach the accident level when the same fault occurred. The correct strategy is that when Anshun substation operating in single transformer, then the operation mode becomes electromagnetic loop net- work and controls the section power flow to meet N-1 operation mode won’t overload in electromagnetic loop network. (2) In winter peak load operating mode, Xifeng sub- station operating in single transformer appears the fault of transformer tripping when the transformer transmis- sion power is 972 MW. Then Xifeng grid becomes an isolated network. The bus frequency deviation of the isolated network is shown in Figure 3(a). After shedding 932 MW load, the bus frequency deviation of the isolated network is shown in Figure 3(b). The total load of Gui- yang grid is 4261MW. The accident load accounts for 21.87% of the total load. It reaches larger accident ac- cording the Decree of the State Council (No. 599). Through correcting the coordination strategy of three- defense line, it will not reach the accident level when the same fault occurred. The correct strategy is that when Xifeng substation operating in single transformer, then the operation mode becomes electromagnetic loop net- work with Guiyang substation and controls the section power flow to meet N-1 operation mode won’t overload in electromagnetic loop network. (a) (b) Figure 2. (a) The 220 kV bus frequency deviation of Anshun; (b) The 220 kV bus frequency deviation of Anshun after shed- ding load. (a) (b) Figure 3. (a) The 220 kV bus frequency deviation of Xifeng; (b) The 220 kV bus frequency deviation of Xifeng after shedding load. Copyright © 2013 SciRes. EPE W. C. ZHENG, T. YU 41 . Co5nclusions nalysis, it shows the configu ration of de ent or generally ac lo udy were included in the pla of REFERENCES [1] State Councilic of China, “The epublic of China State Economic and Trade e's Republic of China State Economic and Trade for rk for De- Security and Stability m- Automatic Low-frequency Load Shed- and Q. H. Wu, “A Review on Op- Through the above a three-defense line of the Guizhou grid in 2012 adapts to the Decree of the State Council (No.599). But there are some areas that don’t set three-defense line or the exist- ing coordination strategy can’t reduce the accident level, operation mode should be adjusted to fix and improve. Then the high level accident could be avoided. So the configuration of three-defense line coordination strategy should take full consideration to the Decree of the State Council (No.599) that assesses accident level. (1) The fault that will lead especially significant acci- nt or significant accident should take protective meas- ures such as the section power flow control in the first defense line to guarantee the significant accident or sig- nificant accident wouldn ’ t h appen. (2) The fault that will lead larg er accid cident should take the coordination strategy of the second defense line and the third defense line. The self-healing of the system should be used as much as possible to reduce the capacity of the cutting machine and shedding load. Then it can reduce the accident level. (3) In some maintenance mode, the measures such as ad supply control and operation mode adjustment should be taken to prevent the accident level worse when the fault happens. The result of the stnning ding Technology Provisions,”Chinese Ministry of Energy, 1991, pp. 428-1991. [9] Y. S. Xue, X. C. Ren the safety and stability control device extension and rebuilt in the 2012 Guizhou grid. 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Sun, “Study on Measures of the Isolated Grid Operation of the Guizhou Power Grid and Area Power Grids,” Power System Pro- tection and Control, Vol. 36, No. 19, 2008, pp. 29-33. [7] H. D. Sun, X. D. Wang and S. Y. Ma, “Measures to I prove System Security and Stability for Isolated Opera- tion of Guizhou Main Power Grid and Its Regional Power Networks,” Power System Technology, 2008, Vol. 32, No. 17, pp. 35-40. [8] “Power System timi Zation and Coordination of under Frequency Voltage Load Shedding,” Automation of Electric Power System, Vol. 33, No. 9, 2009, pp. 100-107. Copyright © 2013 SciRes. EPE |