Analysis method of feeder partition capacity considering power supply security and distributed generation

Transcription

1 The 6th Internationa Conference on Renewabe Power Generation (RPG) October 2017 Anaysis method of feeder capacity considering power suppy security and distributed generation Weifu Wang 1, Zhaojing Cao 2, Ke un 3,DeHe 1, Yanjun un 1, Chunxiao Li 1, Ming un 2, hufeng Dong 2 1 tate Grid haoxing Power uppy Company, haoxing, , Zhejiang Province, Peope s Repubic of China 2 Coege of Eectrica Engineering, Zhejiang University, Hangzhou , Zhejiang Province, Peope s Repubic of China 3 tate Grid Zhejiang Eectric Power Company, Hangzhou , Zhejiang Province, Peope s Repubic of China E-mai: dongshufeng@zju.edu.cn Pubished in The Journa of Engineering; Received on 12th October 2017; Accepted on 2nd November 2017 Abstract: Large-scae integration of distributed generation (DG) increases the stabiity of the distribution network which in turn makes the network structure more compex to anayse. Thus, this study proposes a feeder avaiabe capacity cacuation mode considering N 1 security verification and DG, in order to provide data support for distribution network s operation and panning. Firsty, the authors discuss DG s different categories and respective treatment in N 1 faut. econdy, a cacuation method of feeder avaiabe capacity is proposed for the distribution network with a high permeabiity of DG. Finay, the cacuation resuts of a practica distribution network prove the practicabiity and effectiveness of the proposed method.\ 1 Introduction The use of distributed generation (DG) is dramaticay being pursued due to its cean, green and eco-friendy feature. DG is instaed in the distribution network which utiises renewabe energy resources, such as wind energy or soar energy [1]. The integration of DG in the grids has brought about a new chaenge to evauation, panning and operation in the distribution network [2 6]. Integrating DG into eectric power systems is a significant approach to improve power quaity and stabiity [7 9]. It can improve the reiabiity and stabiity of distribution network power suppy to insta DG to the grid reasonaby and appropriatey. Future distribution network panning and reiabe operation need to consider the impact of DG. In the meantime, the access of the DG turns the distribution network from the origina radiation structure with singe power into a compicated network of mutipe power sources, which enhances the difficuty for reevant cacuation and anayses. N 1 security criterion must be met during an urban eectric network panning, which is an important and practica index for power suppy security [10]. Aso, evauation of feeder capacity is an important step in power system s reasonabe panning and safe operation. Therefore, we propose a method of cacuating the avaiabe capacity of feeder considering the N 1 security criterion of the distribution network which contains ots of DGs. Firsty, the distribution network is divided into feeder depending on the switch s position; meanwhie, DG finds its modes in the N 1 faut. econdy, distribution network topoogy is described based on the power suppy path by means of the power grid GI system. Thirdy, taking path states and avaiabe capacity as variabes, the mixed integer inear programming (MILP) is obtained to cacuate feeder avaiabe capacity considering the N 1 security criterion. Finay, the mode is soved by the branch and bound method. Furthermore, in this cacuation mode, the objective function is the maximum avaiabe capacity of feeder. Aso constraint conditions are four parts. (i) DG restriction: DG exists in three kinds of states when N 1 faiure occurs; (ii) distribution network radia operation: there is ony one path to the oad for power suppy; (iii) source restriction: the capacity of the power suppy must be greater than the sum of the oad; (iv) feeder restriction: feeder carrying capacity is enough to undertake its oad. The study has the foowing contributions: (i) Accurate feeder avaiabe capacity can be obtained by means of constructing the MILP and anaysing mutipe transfer paths. (ii) Compared to feeder avaiabe capacity without DG, the cacuation resuts quantitativey indicate how much stabiity the integration of DG can improve. (iii) The cacuation resuts have usefu instruction function to the panning and stabiity evauation of the distribution network in the future. This paper is organised as foows. ection 2 presents the process of estabishing the feeder avaiabe capacity cacuation mode. ection 3 shows a practica case of the distribution network and compares with grid without DG. A brief review and concusion of this paper are given in ection 4. 2 Cacuation method of feeder avaiabe capacity In this section, we present an anaysis method to cacuate feeder avaiabe capacity satisfied the N 1 security criterion with highy-penetrated DGs. Firsty, we discuss different DG s categories when there is a faut occurring in the power distribution network; secondy, we cacuate the max feeder avaiabe capacity by considering mutipe transfer paths; asty, we demonstrate the entire anaysis and computer fowchart of our proposed method.

2 2.1 DG operation modes in faut systems To conduct the DG after distribution network N 1 faut better, we shoud do some preiminary work about cassification based on DG s factors [11 13]. (i) According to whether DG can pay the roe of the stand-by eectric source after the N 1 faut occurred in the distribution network, it can be divided into two categories: back-start DG (DG) and non-back-start DG (NDG). The former can be used as stand-by power, whie the atter cannot. ince DG s output power can be artificiay controed; however NDG s output power is intermittent and non-controabe. DG mainy contains generating unit, micro gas turbine, fue ce, wind generation and soar generation with storage, etc.; NDG incudes wind power generation and soar power generation without storage, sef-excited machine type, etc. (ii) According to whether DG is in the faut zone or not when the N 1 faut happens in the distribution network, it can be cassified into faut area DG (FDG) and non-faut area DG (NFDG). FDG is in the area which gets into troube of suppy interruption due to the N 1 faut. In the same way, NFDG is ocated in the norma area of power suppy after the N 1 faut. Therefore the N 1 faut can ony have an effect on the FDG. Obviousy, the first kind of category is on the basis of DG s inherent invariabe feature. o it is confirmed as ong as DG is sure. However, the atter woud change as the faut occurs in different ocations of the distribution network. According to the above discussion, we cassify DGs based on their abiity to reserve power and ocation reative to the position of the faut. Then we adopt different treatment on DG s operation modes for different kinds of DG. pecific operation information is shown in Tabe 1. In genera, DG s operation modes contain two types: survived DG (DG) and non-survived DG (NDG). DG can sustain gridconnected operation to the utiity grid after the N 1 faut. At this point, DG is equivaent to the oad node whose capacity is negative. NDG has two conditions: (i) isanded operation: When the faut occurs, the grid containing the DG is separated from the pubic grid. Afterwards, DG continues to transmit its power to suppy its independent network. This kind of free-running operation mode is caed isanded operation; (ii) tripping operation: in the event of the N 1 faut, DG woud be out of service and no onger work as a power source. Aso, the distribution system undertakes the oad which was previousy supported by DG. uppose there is the N 1 faut in the main transformer or a feeder outet of the distribution network, we start to find the faut area downward from the faut point. If there is an NDG in the faut area, we make it quit running; if there is a DG, we take isanded operation. Aso, on the basis of ensuring the power suppy to oca users, DG shoud enarge the power suppy range as much as possibe to increase the reiabiity of the distribution network. On the other hand, DG in the non-faut area can continue to maintain interconnection operation to the utiity grid. Tabe 1 DG operation modes in faut systems 2.2 avaiabe capacity mode The soution to the feeder avaiabe capacity cacuation shoud assume that the topoogy of the distribution network is known. In this study, we describe the network topoogy by using the power suppy path. The topoogy description at the ow votage eve is more difficut due to its compex structure and numerous oads. Therefore, we first need to simpify the grid to get a brief and cear diagram. We consoidate oads between two automatic/manua switching devices which can isoate fauts and restore service of power. Then, ots of oads in one zone can transfer into a oad node, which we caed a feeder [14]. According to the above method, oad nodes, source nodes (substation nodes) and paths between them can make up for the tota distribution network. Compared to the network before the simpification, the new topoogy can enormousy decrease the number of oads and make distribution network s structure more concise. In genera, there are mutipe paths which can suppy power for any oad node in the grid. The structure of the distribution network usuay has the characteristics of cosed-oop design and open-oop operation. During the actua operation of the distribution network, any oad node has one and ony one suppy path with the hep of switching devices. Thus, it can be seen that we can describe the topoogy of the distribution network fuy by making use of a oad nodes and their tota possibe suppy paths. uppose oad node I has p possibe suppy paths. Obviousy, every path starts from one source and ends at oad node. We define p i k [ Pj as the kth possibe suppy path of the oad node i. Aso, this path is the coection of a branches which connect the oad node i with some source nodes. Then, we use the set P i N to gather the tota suppy paths of the oad node i, i.e. P i N = { pi 1, pi 2,..., pi k,..., } pi P (1) Just as the above discussion, there is ony one suppy path at work for one oad node. Aso, a oad nodes are capabe of being powered by a source. In other words, the distribution network uses the radia running mode. To ensure this condition, we use a binary variabe W i k to describe if path p i k is connected or not W i k { 1, connected, = 0, disconnected. The authors of [15] have proved that the foowing two constraints are sufficient conditions for distribution network s radia running mode: (i) There is ony one connected suppy path in the set P i N of every oad node, i.e. Wk i = 1, i. (3) p i [ i k N (ii) If path p i k is connected, p i m which is a part of p i k must be connected, i.e. (2) W i k W m, p m, pi k. (4) tand-by power Location Operation mode DG FDG isanded operation NFDG grid-connected operation NDG FDG tripping operation NFDG grid-connected operation esides the constraint of the radia running mode, the cacuation of feeder avaiabe capacity needs to consider the capacity of the source and the current carrying capacity of the feeder. To describe these two constraints, we define the foowing sets:

3 (i) P i = {a paths suppied by source j }. (ii) P i = {a paths through the branch b j }. (iii) If the two nodes connected by branch b are i and j, respectivey, then P bi P = {a paths through b with i as end point}; P bj P = {a paths through b with j as end point}. uppose there are n oad nodes, s source nodes and b branches in the grid, the constraint conditions of source and feeder can be expressed as (i) The sum of the oads suppied by source j sha not exceed its capacity of power suppy node in a distribution network is as foows: MaxC s.t. W p i [ k i = 1, i, i k N Wk i Wm, p m, p i k, W i p i [ k L i + Z j p k [ k j, j k W i p i [ k L i + Z m p k [ k m, m k Z k MW k, Z k ( ) C M 1 W k. (10) p i k [ j W i k L i + p k [ j W k C j. (5) (ii) The actua current carrying capacity of feeder m sha not exceed its maximum vaue where p i k [ m W i kl i + p k [ m W kc m, (6) W i n represents the state of suppy path. j and m are the capacity of source and the current-carrying capacity of feeder. L i and C are oading amount of the oad i and avaiabe capacity of the oad node, i.e. feeder. A suppy paths need to satisfy (5) and (6): p i k [ Pj. A oad nodes need to satisfy (5) and (6): i=1,2,3,, n. A sources need to satisfy (5) and (6): j =1,2,3,, s. A branches need to satisfy (5) and (6): m =1,2,3,, b. y means of introducing variabe Z k, we convert origina probem into an easiy-soved question 2.3 Agorithm fow The N 1 safety criterion requires the safety of power suppy can be ensured by transfer oad to other norma feeders when a faut occurs at any position. In this study, we buid the 0 1 inear programming mode for N 1 safety certification in ausion to the feeder outet faut which is the most serious faut in a feeder faut. When any feeder outet generates faut, we use the foowing fow path to cacuate the avaiabe capacity of feeder C (Fig. 1). The concrete soution process is reaised by java anguage. uppose there are F feeder outets in the distribution network, we need to repeat the above process F times to get F cacuation for feeder. Then, the minimum vaue in the F cacuation is the avaiabe capacity of feeder considering DG and N 1 safety criterion. 3 imuation resuts 3.1 asic situation According to the simpified method of ection 2.2, a practica distribution network is reduced to a network wiring diagram consisting of oad nodes and source nodes, which is shown in Fig. 2. There are five feeders, 25 feeder s, and 29 switching devices. 1 5 are circuit breakers of feeder outets. Aso, k1 k24 are circuit breakers of power ines. esides, the instaed capacity of each feeder of the network is shown in Tabe 2. Z k = W k C. (7) Then in order to obtain the genera form of inear programming, we change the above equation into foowing inequaities: Zk MW k, (8) Zk ( ) C M 1 W k. (9) The aim of our mode is to cacuate the feeder avaiabe capacity, so we take max C as the objective function. In summary, the MILP mode for the avaiabe capacity of oad Fig. 1 Agorithm fow of feeder avaiabe capacity cacuation mode

4 Fig. 2 impified diagram of distribution with DG Tabe 2 Instaed capacity of feeder Instaed capacity, Instaed capacity, increase the reiabiity and stabiity of the distribution network. DG3 DG6 in the non-faut area retain grid-connected operation. tep 3: when cacuating the feeder avaiabe capacity satisfied N 1 security criterion, the distribution network shoud be in a norma radia operation state. o we describe the topoogy of distribution network fuy by making use of a oad nodes and their tota possibe suppy paths. tep 4: suppose that the oad node has an accessibe capacity of C, we take the maximum vaue of C as the objective function and use operation mode which can satisfy ong-term norma operation of the distribution network after N 1 faut as constraints. Then the MILP mode is constructed to cacuate the feeder avaiabe capacity. tep 5: the above method can be soved by the branch and bound method to get the maximum avaiabe capacity of feeder L1. Meanwhie, the corresponding state of the grid s suppy paths can be obtained, i.e. the transfer feeder and switch operation can be certain. tep 6: suppose a faut happens on the outet of feeder -E, respectivey, we repeat the above step 1 step 6 and can get the maximum avaiabe capacity of feeder L1 for every faut. Obviousy, the minimum vaue of the above a cacuated avaiabe capacity vaues is the fina avaiabe capacity of the oad node. Aso, the corresponding transfer program after N 1 faut is aso obtained at the same time. L L L L L L L L L L L L L L L L L L L L L L L L L Tabe 3 pecific information of DG Number Access position Capacity, Category DG NDG DG2 7 1 DG DG DG DG DG DG NDG DG DG DG1 DG6 are distribution generations, which specific capacity, access position, and category are shown in Tabe 3. Take the oad node 1 for exampe, the detaied soving process is shown as foows: tep 1: suppose there is a faut in the outet of feeder A, we can find the switch k8 is the boundary between the faut area and the nonfaut area. s L1 L8 are affected by the faut, and other feeder s are in norma operation. tep 2: there are two DGs, i.e. DG1 and DG2, in the faut area. According to Tabe 1, DG1 is a DG, so it woud be isanded operation; DG2 is an NDG, so it woud be out of service. esides, DG1 in isanded operation ought to expand the scope of power suppy as much as possibe based on its capacity, which can 3.2 Anaysis of simuation resuts The agorithm proposed is impemented in Java anguage. Firsty, we set up a the DGs in the distribution network with 0 output. Aso, the cacuated resuts of every oad node are shown in Tabe 4. According to the cacuation resuts of Tabe 4, we can find that there is a great difference between different feeder s. For exampe, the avaiabe capacity of feeder L22 is However, for feeder L23 which is cose to the L22, its avaiabe capacity is There are two reasons to expain the difference: (i) Own oad ratio of the feeder : the greater the proportion of instaed oad to its capacity, the smaer the avaiabe capacity of feeder is. (ii) Load ratio of the adjacent feeder : the smaer the instaed capacity of the adjacent feeder, the more transfer oad it can undertake. To expore the infuence of DG to the distribution network, we anayse the distribution network with DG. Then the avaiabe capacity of feeder satisfied with N 1 security criterion in the distribution network with DG can be cacuated by the above method. Tabe 4 Avaiabe capacity of feeder satisfied with N 1 security criterion in distribution network without DG Avaiabe capacity, Avaiabe capacity, L L L L L L L L L L L L L L L L L L L L L L L L L

5 Tabe 5 Avaiabe capacity of feeder satisfied with N 1 security criterion in distribution network with DG significance to the panning and operation of the smart grid with a high permeabiity of DG. Avaiabe capacity, Avaiabe capacity, 5 References L L L L L L L L L L L L L L L L L L L L L L L L L y comparing the two cacuation resuts in Tabes 4 and 5, we can obtain the foowing concusions: (i) The integration of DG can increase the grid s power quaity and stabiity, which our simuation resuts can prove numericay. For exampe, the feeder L22 increases its avaiabe capacity from to 5.025, which can guarantee the reiabiity of the eectric power system when a faut occurs. (ii) The access capacity and ocation are essentia factors to increase the avaiabe capacity of feeder satisfied with N 1 security criterion. The optima pacement of DG can improve the distribution network s stabiity effectivey. 4 Concusion This study has presented an anaysis method of feeder capacity considering power suppy security and DG. The integration of DG can increase the grid s stabiity by a fexibe network structure and more capacity margin, which is proved by our simuation resuts quantitativey. ased on anaysing mutipe transfer paths, the mode we proposed is appreciated for its accuracy of feeder avaiabe capacity and quick in computation. The cacuation resuts are of great [1] Ackermann T., Andersson G., öder L.: Distributed generation: a definition, Eectr. Power yst. Res., 2001, 57, (3), pp [2] Lu Z., Dong Y.: ervice restoration strategy for the distribution system with DGs, Autom. Eectr. Power yst., 2007, 1, p. 019 [3] Moravej Z., Akhaghi A.: A nove approach based on Cuckoo search for DG aocation in distribution network, Int. J. Eectr. Power Energy yst., 2013, 44, (1), pp [4] Papathanassiou.A.: A technica evauation framework for the connection of DG to the distribution network, Eectr. Power yst. Res., 2007, 77, (1), pp [5] Wan C., Xu Z., Pinson P., ET AL.: Probabiistic forecasting of wind power generation using extreme earning machine, IEEE Trans. Power yst., 2014, 29, (3), pp [6] Wan C., Xu Z., Pinson P., ET AL.: Optima prediction intervas of wind power generation, IEEE Trans. Power yst., 2014, 29, (3), pp [7] E-Khattam W., aama M.M.: Distributed generation technoogies, definitions and benefits, Eectr. Power yst. Res., 2004, 71, (2), pp [8] Lopes J.P., Hatziargyriou N., Mutae J., ET AL.: Integrating distributed generation into eectric power systems: a review of drivers, chaenges and opportunities, Eectr. Power yst. Res., 2007, 77, (9), pp [9] Pepermans G., Driesen J., Haesedonckx D., ET AL.: Distributed generation: definition, benefits and issues, Energy Poicy, 2005, 33, (6), pp [10] Luo F., Wang C., Xiao J., ET AL.: Rapid evauation method for power suppy capabiity of urban distribution system based on N 1 contingency anaysis of main-transformers, Int. J. Eectr. Power Energy yst., 2010, 32, (10), pp [11] Chen X., Chen D., Liu J., ET AL.: Fast service restoration of distribution system with distributed generations IEEE Power and Energy ociety Genera Meeting, 2012, pp. 1 6 [12] Choi J.-H., Kim J.-C., Moon.-I.: Integration operation of dispersed generations to automated distribution networks for network reconfiguration IEEE Power Tech Conf. Proc., oogna, 2003, vo. 2, p. 5 [13] Xianchao H., Lizi Z., Tayor G.: ervice restoration of distribution system with distributed generation Int. Conf. on Power ystem Technoogy (POWERCON), 2010, pp. 1 5 [14] Kersting W., Phiips W., Doye R.C.: Distribution feeder reiabiity studies, IEEE Trans. Ind. App., 1999, 35, (2), pp [15] Ramos E.R., Expósito A.G., antos J.R., ET AL.: Path-based distribution network modeing: appication to reconfiguration for oss reduction, IEEE Trans. Power yst., 2005, 20, (2), pp