dd1.1 DEMO 1 Advanced MV network operations using a multi agent system

Transcription

1 Advanced MV network operations using a multi agent system

2 ID & Title : dd1.1 Specification and requirements Version : V1.0 Number of pages : 72 Short Description This deliverable details for Demo 1: 1) Procedures for KPIs validation and measurement 2) Inputs to GWP2 for risk management 3) Description of requirements and functionality of the overall system Revision history Version Date Modifications nature Author V0.1 04/04/2012 First draft René Lorenz V0.2 25/07/2012 New Layout Peter Noglik V0.3 27/08/2012 Writing of sections Dr. Jendernalik V0.5 07/09/2012 Final draft ready for external review Dr. Jendernalik V1.0 11/10/2012 Integration of ENEL s comments. Dr. Jendernalik Accessibility Public Consortium + EC Restricted to a specific Group + EC Confidential + EC If restricted, please specify here the group Owner / Main responsible Name (s) Function Company Visa Dr. Lars Jendernalik Technical Manager DEMO1 DSO WWE Dr. Lars Jendernalik Author (s) / Contributor (s) : Company name (s) Westfalen-Weser-Ems Verteilnetz GmbH (DSO WWE) RWE Deutschland AG RWE Westfalen-Weser-Ems Netzservice GmbH ABB Deutschland AG TU Dortmund Reviewer (s) : Company name (s) Company Visa DSO WWE, ENEL Approver (s) : Company name (s) Company ERDF, VATTENFALL, ENEL, IBERDROLA, CEZ DSO & RWE Work Package ID: DEMO1 Review validated by Technical Committee on October 29 th 2012 Visa Approved by Steering Committee on October 29 th 2012 Task ID: dd October /72

3 Executive summary This document describes the activities of the demonstration project DEMO1 Advanced MV network operations using a multi agent system in the period of the first project year. The high share and still massive increasing amount of distributed generation, predominantly wind and photo-voltaic set new challenges to the DSO s. In order to provide hosting capacity to integrate these resources huge investments in grid infrastructure are required. Grid operation and grid observation becomes more complex since power flows become less predictable. At present in Germany there are hardly any surveillance facilities or grid automation in place in medium voltage networks. DEMO1 addresses these challenges with the demonstrator to be built up in the area of Reken, located in North-Rhine-Westphalia. The considered grid is well selected since it shows already today a balance between installed generation power and maximum demand. Further increase in renewables to be connected is forecasted. The grid focused on consists of around 120 stations of which around 15 are going to be equipped with switching facilities so called switching agents. The following objectives are targeted: Integrating an increasing number of decentralized energy resources (DER) in the mediumvoltage (MV) network and underlying low-voltage (LV) networks Achieving higher reliability, shorter recovery times after grid failures Avoiding unknown overloads and voltage violations Fulfilling the needs of surveillance and remote-control in MV-networks Reducing network losses Regarding the demonstrative character of this project the main activity of this period was the preparation of all necessary requirements to ensure the construction of an automated multi agent system in the field in the next project period. To fulfil this objective, several subtasks were solved. Besides a general description of the principle of the multi agent system, systematic approaches to position the agents have been elaborated and the associated information to be exchanged between the different entities was defined. The principle idea of a multi agent system is based on an autonomous interaction between these agents and their responsibility for a defined part of the MV network. The agents are divided into the two groups: Switching Agents and Measuring Agents. Switching Agents can use the switch gear of their secondary substation whereas Measuring Agents provide measured values to the Switching Agents. The possibility of autonomous switching provides dynamic topology reconfiguration which is a new concept of operation. The advantages and goals of this approach were analysed and led 30 October /72

4 to main principles of the agents behaviour and their necessary capabilities. Two main objectives were solved to ensure this new concept. First two different approaches for the positioning of Switching Agents were analysed and combined in a multi-step method to assure an optimized location and minimized number of Switching Agents within a real MV network. Both approaches provided very similar and comparable results which are depicted in section Special attention was led to the applicability of these approaches on any other MV-network in order to enable full exploitation of the replication potential. Second the basic communication principles between the agents were developed and tested by means of generic network structures. Furthermore detailed technical requirements for hardware and software of the agents were defined and the communication structure was principally described. The risk management was implemented and will be detailed in the next period regarding the upcoming field construction subtasks. In section 2 of this report a first set of Key Performance Indicators have been elaborated. In summary, the basic algorithms and methods to build up a demonstration multi agent system are described. The next steps include laboratory tests and the step-by-step practical implementation in the demonstration grid. 30 October /72

5 Table of Contents EXECUTIVE SUMMARY... 3 LIST OF FIGURES & TABLES INTRODUCTION AND SCOPE OF THE DOCUMENT Scope of the document Structure of the document Notations, abbreviations and acronyms Definitions and Explanations PROCEDURES FOR KPI VALIDATION AND MEASUREMENT DEMO1 KPIs INPUTS TO GWP2 FOR RISK MANAGEMENT Elaboration risk management DESCRIPTION OF REQUIREMENTS AND FUNCTIONALITY OF THE OVERALL SYSTEM Development of rules to position the agents Development of generic MV-network Data collection of demo field (today/2030) Development of an algorithm to place the agents Multi agent system description Technical requirements for operating MV-network Hardware specification of the multi agent system Software specification of the multi agent system Detailed software structure of the single agent Example: MV-Load application Communication structure General communication structure Peer-to-Peer Communication RTU SCADA communication RTU RTU communication Redundancy Adding and removing agents Analysis of different communication technologies REFERENCES Project Documents External documents ANNEXES dd1.1_detailedrisk_demo1_rwe_ October /72

6 6.2 dd1.1_detailedrisk_demo1_rwe_ dd1.1_detailedrisk_demo1_rwe_ dd1.1_detailedrisk_demo1_rwe_ dd1.1_detailedrisk_demo1_rwe_ dd1.1_detailedrisk_demo1_rwe_ dd1.1_detailedrisk_demo1_rwe_ dd1.1_detailedrisk_demo1_rwe_ dd1.1_detailedrisk_demo1_rwe_ dd1.1_detailedrisk_demo1_rwe_ List of figures & tables Figure 1: List of deliverable dd Figure 2: Detailed Ring topology Figure 3: Ring topology Figure 4: Ring topology - results Figure 5: Ring topology after relocating the circuit breakers Figure 6: Generic topology conclusions Figure 7: Map of the distribution grid of WWE Figure 8: The active power distribution in the Reken MV-Network Figure 9: Flow chart of the heuristic method for position of the breakers Figure 10: Normal state of the grid Figure 11: Breakers in step T Figure 12: The frames for the Reken topology Figure 13: Circuit breaker eliminations according to the worst case principle Figure 14: Final placement of the breakers of Reken Network Figure 15: Grid topology with closed cut-off switches Figure 16: Cut-off switches to contiguous grids Figure 17: Grid section with tagged branches Figure 18: Conductor parameter in NEPLAN Figure 19: Direction of load flow Figure 20: Overview of separation points after method Figure 21: Final selection of separation points Figure 22: Secondary substation Figure 23: Typical secondary Substation with actors Figure 24: Agent Infrastructure Figure 25: MAS hierarchy and interdependencies Figure 26: Cluster principle and communication between clusters and control centre Figure 27: detailed agent software structure Figure 28: states of the overload elimination process October /72

7 Figure 29: Simple ring topology with 4 possible 'solutions' Figure 30: Communication process - forward information flow Figure 31: Communication process - backward information flow Figure 32: Communication overview Figure 33: Communication layer Figure 34: Redundancy Table 1: Grid4EU KPI Family Table 2: List of risks Table 3: Generic MV-Topologies Table 4: Factors for future situation Table 5: Summary of the used breaker Table 6: RWE-specific diversity factors Table 7: Factors for loading case Table 8: Factors for feeding case Table 9: Element results in NEPLAN Table 10: Element results in MS-Excel Table 11: Conductor selection with the minimal current load Table 12: DIN EN Table 13: M-Agent Signal list Table 14: S-Agent Signal list October /72

8 1 Introduction and scope of the document 1.1 Scope of the document The scope of the document is the description of Specifications and requirements and of DEMO1 documentation. The delivery date of the document is M12 (end of month 12). Task number Deliverable number Deliverable Deliverable description and responsibilities Delivery date dd1.1 Specification and requirements 1) Procedures for KPIs validation and measurement 2) Inputs to GWP2 for risk management 3) Description of requirements and functionality of the overall system M Figure 1: List of deliverable dd1.1 Figure 1 shows that the deliverable dd1.1 Specification and requirements consists of different tasks. All the tasks will be described separately in the document. 1.2 Structure of the document The structure of the document, according to the tasks listed in (Figure 1), is: 1) Procedures for KPI validation and measurement 2) Inputs to GWP2 for risk management 3) Description of requirements and functionality of the overall system 30 October /72

9 1.3 Notations, abbreviations and acronyms CC-Agent DER DG DSO EU IAF KPI MAF M-Agent MAS PC PLC PLC PV RES RTU S-Agent SCADA SCC SGAM SGCG SSS TM VPN Control Centre-Agent Distributed Energy Resources Distributed Generators Distribution System Operator European Union Infrastructure Agent Function Key Performance Indicator MV-Agent Function Measuring-Agent Multi Agent System Project Coordinator Programmable Logic Controller Power Line Carrier Photovoltaic Renewables Remote Terminal Unit Switching-Agent Supervisory Control and Data Acquisition Special Contract Customer Smart Grid Architecture Model Smart Grid Coordination Group Secondary Substation Technical Manager Virtual Private Network 30 October /72

10 1.4 Definitions and Explanations Circuit Breaker - A circuit breaker is an automatically operated electrical switch designed to protect an electrical circuit from damage caused by overload or short circuit. Generic Networks Generic Networks are theoretically assumed structures, which are common in MV-networks of a Distribution System Operator (DSO). The generic network consists of typically used equipment. The network is tested with various scenarios of load and feed-in, especially the possible location of the circuit breakers has to be analysed. Scenario A certain constellation of different parameters of load and feed-in. Different scenarios have to be mastered by the tested network. Also a development of load and feed-in over several years give multiple scenarios. Switch state This state represents the actual topology of the grid, depending on the actual circuit breaker state. For example a ring structure with three breakers could have three practical switch states, which give a radial structure and not a meshed structure (closed ring topology and / or islanding needs to be avoided). Limit value violation under/over crossing of an allowed operative state value. Allowed state values are: voltage limits: +/- 10% from the nominal voltage current limits: the current in a line must not exceed 100% of the nominal current 30 October /72

11 2 Procedures for KPI validation and measurement The scope of this task is the definition of Key Performance Indicators (KPIs), which will allow measuring the success of the project in relation to its overall technical objectives. The KPIs, in accordance with the ERGEG definition of Smart Grid benefits, are identified as: 1) Increased sustainability; 2) Adequate capacity of distribution grids for collecting and bringing electricity to consumers; 3) Uniform grid connection and access for all kind of grid users; 4) Higher security and quality of supply; 5) Enhanced efficiency and better service in electricity supply and grid operation; 6) Coordinated grid development through common European, regional and local grid planning to optimize electricity grid infrastructure. The chosen indicators must be measurable and show clear dependencies on the demonstrators results, taking into account the boundary conditions of the demonstrations (i.e. their specific geographic, network, regulatory and customer environment). The KPIs have been chosen to emphasize the synergy between the six demos in order to achieve GRID4EU scalability/replication assessment objectives. There are two different kinds of KPIs, General KPIs and Specific KPIs. The list of Grid4EU Project KPIs is provided below: Grid4EU KPI Family Energy losses Fault Awareness, Localization and Isolation Time Network Hosting Capacity Line voltage profiles KPI ID KPI TYPE KPI Description GWP2.2_KPI_1 GWP2.2_KPI_2 GWP2.2_KPI_3 GWP2.2_KPI_4 Technical The monitoring and in some cases minimization of energy losses through different solutions presented in DEMO projects. Faster reaction time to grid failures and faults Increased hosting capacity of RES in the MV and LV grid Power Quality improvements (in this case voltage quality) Islanding GWP2.2_KPI_5 Voltage deviation during islanding 30 October /72

12 Use of standards Recruitment Active participation GWP2.2_KPI_8 GWP2.2_KPI_6 GWP2.2_KPI_7 Social Actual use of standards in different DEMOs with respect to initially described use. Fraction of consumers and producers accepting participation in the different demos Fraction of consumers/producers actively taking part in the different demos Table 1: Grid4EU KPI Family 2.1 DEMO1 KPIs The following RWE DEMO KPIs are also Grid4EU Project KPIs (i.e. other DEMOs also monitor these indicators): Energy losses Fault awareness, localization and isolation time Network hosting capacity Use of standards For more detailed information about the KPIs, please refer to the GWP2.2 document Project KPIs definition and measurement methods. 30 October /72

13 3 Inputs to GWP2 for risk management 3.1 Elaboration risk management This task deals with the setup of a risk management to ensure a successful project. The setup will be handled by Westfalen-Weser-Ems Verteilnetz GmbH. RWE Westfalen-Weser-Ems Netzservice GmbH will give additional support due to operational risks. The main risks are: Obviously the approach of the multi agent system is quite complex. Nevertheless the risks during the project can be considered as moderate. There is already a lot of theoretical and practical work done at TU Dortmund as well as at ABB. A useful hardware-tool for modeling network topologies is already built up at the Dortmund University. Some algorithms are already developed for some applications in the HV network. These algorithms have to be adapted for the requirements of a MV network. The main risk in this project is a delay until the field-trial can be started. As far as there is a R&D component this risk cannot be eliminated completely but minimized. Since there is a well-described multi-step approach for the system integration tests also the risks while operating this new system can be considered as moderate. Regarding scalability and potential replication under cost aspects it needs to be checked with the regulators (national, EU) whether the costs for these new and innovative solutions will be accepted by the regulators. 30 October /72

14 Actually there are a few points for risk management in the different sections of the first deliverable d.d.1.1. ID Description Action Plan D1-001 The successful implementation of the agent intelligence depends on the intensive cooperation between TU Dortmund (process description) and ABB (software implementation in practice). Responsibilities, processes and tools are defined by TU Dortmund and ABB before starting WP DEMO D1-002 The process description has to be transformed into software capable for the hardware agents (capability of agents, run-time, response time). D1-003 The decentralized communication structure of the hardware agents is too complex in practice. Capacity of hardware agents must be compatible to process demands. One alternative could be, that the agent system intelligence will be transferred to the control centre (also a decentralized approach from the SCADA system view). D1-004 D1-005 D1-006 The agent system can be applied only in the Reken grid. General requirement for scalability and replication cannot be fulfilled. Timeline and budget of the hardware upgrade of substations may be critical. The substation housing is not suitable for additional components (especially compact substation). Actual the agent system can only be applied in the demonstration area of Reken. The next step is the standardization for usage in other MVnetworks. Generic methodology to position the agents. The hardware upgrade will be carried out in 2013 with DEMO1.2; practical change of selected substations may be possible; budget restrictions may lead to a lower amount of upgraded substations. Additional components will be housed inside an external additional package (cost impact). D1-007 The housing temperature of the substations is too high for the additional (mostly electronic) components. Additional components will be housed inside an external additional package (cost impact). D1-008 The RWE security standards must be fulfilled by the complete communication structure. RWE security standards can exceed the regular project requirements, which results in higher development effort. Early involvement and strong collaboration with RWE s IT security department 30 October /72

15 D1-009 The network penetration with decentralized energy resources (DER) will not be high enough within the project run time to show measureable KPI effects of the multi-agent-system. KPIs may be determined by (hardware) simulation to show a long-term effect (e.g. DER penetration of the year 2025). D1-010 System integration tests and operation are carried out on a real network with the risk of failures. This working package includes a welldescribed multi-step approach for tests and operation. Table 2: List of risks 30 October /72

16 4 Description of requirements and functionality of the overall system 4.1 Development of rules to position the agents This chapter has the purpose to develop the methods and the rules to position the switching agents (S-Agents) entities of the overall Multi Agent System (MAS). This task is linked with the placement or relocation of the circuit breakers. The purpose of the positioning of the agents is to maintain the stability of the distribution grid under the influence of the distributed generation (DG). In this step a short network analysis is made and two methods to position the agents are developed. For the used medium voltage (MV) network area Reken some specific scenarios are constructed. The current and future values of the loads and the DG are considered. Two types of agents were defined in the project: the switching agent (S-Agent) and the measuring agent (M-Agent). The S-Agents are combined with the circuit breakers to enable the network topology reconfiguration. The M-Agents are considered to make additional measurements in some nodes of the grid. The focus of this chapter is to place the active MAS entities (S-Agents). The main criterion for positioning of the M-Agents is to extend the observability of the grid and monitor the most critical nodes. This process has no influence on the number and placement of the S-Agents Development of generic MV-network This section concentrates on the development of the rules for relocation of the circuit breakers which are equipped with S-Agents. To find the rules to relocate the breakers, it is necessary to develop and use generic MV-networks. The generic network structures are typical topologies which are frequently used in the network planning. With the approach of generic networks the replicability for other networks with similar structures is ensured. The next table depicts these topologies which represent some features for the real grid. This subchapter can also be called generic topology analysis. The analysis provides necessary information and generates the rules for the optimum relocation of the circuit breakers with the active MAS. The presented topologies have the following characteristics: the lines have the same length; the loads/generators are connected at the same node of the lines; and they are operated as open radial networks. The active power of the components is the value at each node (the sum of the active power of the loads and DGs). 30 October /72

17 Generic Network Topology Graphic Ring Topology Ring Topology, Interconnected Triple Network Two neighboured rings Table 3: Generic MV-Topologies In order to find the position of the breakers, different scenarios have been defined. In all scenarios a major role is played by the DG s. The installed power of them is much higher than the loads. This situation can be observed throughout the analysis. Two types of scenarios are used: time series using standard load and generation profiles as one type of scenarios and maximum values scenarios as a second. The time series scenario is presented in the example below, where the generic network is explained. Because of the higher computational time of the time series scenarios and the difficult application of the analysis for the complex topologies, the maximum values scenarios are applied mainly. For monitoring the influence of the DG groups, their locations are varied in some structures. These scenarios deliver the same results as the extreme values of the time series scenarios. The maximum overloading of the components and the voltage limits are two parameters which help to define the relocation of the circuit breakers. These parameters determine the switching state of the grid: allowed or not allowed states. An allowed state represents the state of the grid in which the limitation parameters are not violated. Not allowed state represents the state of the grid in which the one or both parameters are exceeded. Also closed radial loop network and meshed structures operational states are not allowed. When a violated state is reached, the network topology has to be reconfigured. Every new topology state corresponds to a combination of several opened circuit breakers. The violation limits for the parameters are defined as: 100% the maximum overloading limit for lines, and +/-10% for the voltage limits for all the components of the grid. The analysis follows a simple calculation principle. In the first step the DG groups and their locations are set. Loads are assumed at each node of the network. They have low installed capacities, therefore their influence on the parameters violation is small. The major influence is given by the DG groups. To determine the operation state for each generic topology, load flow 30 October /72

18 calculations are performed. The results of the simulations determine different operational states. These states, allowed or not allowed, display the limiting parameters of the grid. The allowed states are representing the stability of the grid and they are most important for the placement of the breakers (see Figure 4 and Figure 5). The second step of the analysis is to determine the scenarios. As described in the first step, the grids are simulated and the obtained results are processed in relation with the operational states. After interpreting the results, important rules for determining the placement of the breakers respectively the breakers with the active MAS are defined and demonstrated. To understand the principle of this analysis an example of ring topology is shown in the followings. In the Figure 2 a detailed model of the ring structure used for the generic analysis is presented. Figure 2: Detailed Ring topology Applying the steps of the generic analysis, the results for this topology showed that the overloading and voltage were between the standard limits. That means just allowed states were obtained, therefore the circuit breaker remains in its original place, in the middle of the ring topology. No other breakers were necessary. Because of the parameters of this grid structure are homogenous, it is needed to expand the structure to get a significant effect. It was considered a 30 nodes ring with 3 major distributed generator (DG) groups and short lines, as in the next figure: 30 October /72

19 circuit breaker? Figure 3: Ring topology After determining the components of the grid and the scenarios for the DG s a time series calculation is made. The results are shown in Figure 4. In this figure the allowed switches with green and not allowed switches in red are shown. As told before the not allowed switches are the overloading and voltage violations. On the X axis the time is represented. On the Y axis the allowed/not allowed states of the network for each time step are represented. It can be observed that in this topology there are 3 allowed topology states which permit to avoid the violations. These 3 states impose the relocation of the circuit breakers. Using these results the needed breakers position and switching times can be obtained. In Figure 6, the circuit breaker points are depicted and the corresponding time periods (in integer timesteps) of opened switch states. Here after the switching operations, the not allowed states are avoided and the grid is operated in stable state. The switching provides dynamic topology reconfiguration which is a new concept of operation. 30 October /72

20 Allowed state Not allowed state Voltage violations Needed breakers Figure 4: Ring topology - results The time series scenario example shows why the need for dynamic reconfiguration exists. For finding the optimal circuit breaker positions only the extreme scenarios are of the main interest. Different generation scenarios were applied to the generic structures from Table 3. For the ring topology following conclusions can be made: - Ring topologies require only few breakers - Short rings can be managed with only one static breaker - Longer rings need several breakers: Bigger load groups need breakers DG groups have to be separable 30 October /72

21 The generic analysis using the principle and the aspects from the example and applying it to all structures delivers the followings: 1. At least 5 breakers are needed in some structures to provide all possible configurations (Figure 6.a), applicable just at topology 2 2. DG groups have to be separable from each other through breakers (Figure 6.b) 3. The influence of the DGs near the primary substation is not critical. Bigger loads also can be separated with breakers (Figure 6.c) 4. Low feed-in ring 1 has no influence on ring 2; therefore both rings are independently operated (Figure 6.d). High feed-in s need a connected operation (Figure 6.e) 5. The breakers placement is strongly coupled with the DG s location (Figure 6.f) t = t = t = Circuit Breaker Figure 5: Ring topology after relocating the circuit breakers This subchapter presents the first of two methods to develop and place the agent systems. In addition, the operational circuit breaker placement method is described in Application of the generic results is used in The resulted postulations have been applied to the model of the real network Reken, where a number of 35 circuit breakers for the S-Agents has been obtained. 30 October /72

22 a) b) c) d) e) f) Figure 6: Generic topology conclusions Data collection of demo field (today/2030) The grid section out of the WWE distribution network (Figure 9) shows our demonstration area. The community of Reken is supplied by the transformer station Groß Reken. As you can see in Figure 7, at the moment there is a load of approximately 25,5 MW and a feeding capacity of 25,9 MW which means the ratio between both is well balanced. The feed-in does mainly consist of renewable energy sources like wind power, solar power and biomass. Currently in the demonstration area there is approximately a feed-in of 9,1 MW wind power, 14,6 MW solar power and 2,2 MW biomass. 30 October /72

23 Figure 7: Map of the distribution grid of WWE The reference values for the actual situation at the demonstration area Reken were taken from the RWE-data pool. To consider the increased influence of the decentralised generating plants in the analysis, the generating plants have to increase their power in the respective scenarios. The scaling factors for the various types of renewable energies were taken from the study "Prognose der Versorgungsaufgabe". The study was realized by the Research Association FfE commissioned by RWE. The forecast is done in a time interval of 5 years until 2030 for a county level. Table 4: Factors for future situation 30 October /72

24 Figure 8: The active power distribution in the Reken MV-Network Development of an algorithm to place the agents Heuristic method for relocation of the circuit breakers with active MAS This method helps to determine the final number of the circuit breakers with the active MAS needed to maintain the stable state of the selected grid. The method and the results are developed in reference to the network model of Reken, because the mentioned generic network structures in this grid. The method is structured in 3 steps: 1. Selection of the normal state topology 2. Selection of the breakers using the generic network analysis (see 4.1.1) 3. Validation of the step 2 using the frame analysis The following chart shows the procedure of the heuristic method for relocation of the circuit breakers: 30 October /72

25 Figure 9: Flow chart of the heuristic method for position of the breakers Step T1. This step covers the normal state of the grid, which has the today s configuration of the network. The number of the breakers is calculated by the classic planning methods and is approved by the DSO. The method is described in the next subchapter ( ). The breaker numbers are used as base structure in the following steps (Figure 10). In this step the set of breakers T1 is obtained. Step T2. The generic structures and their conclusions (to see 4.1.1) are determining the number and the position of breakers for the Reken grid (set T2). The main basis for these placements are generation locations depicted and highlighted in the Figure 8. Some new breaker locations are relatively near to the breakers from step T1. The others are completely new. These breakers are useful for the grid operation in the stable state for critical load and generation scenarios. To verify the validity and usefulness of the breaker set T2 it is necessary to process with the so-called frame analysis. 30 October /72

26 normal state opened circuit breakers nodal feed-ins in MW Figure 10: Normal state of the grid circuit breakers after performing step T2 Figure 11: Breakers in step T2 Step T3. In this last step T3, the entire selected number of the breakers in the other steps is verified. The step T3 has the purpose to eliminate some of the breakers from the previous steps. All possible combinations of the breaker states ('closed'/'opened') from the step T2 lead to an extremely high number of the hypothetical possible topological variations. For example, the set of 30 October /72

27 35 switches results in topologies. Many of these topologies are islanded or meshed, so the final set of valid topologies is relatively small. Still the procedure to filter out the unmeshed and unislanded topologies is difficult and takes too much time. Also this way would lead to a high number of load flow computations. In order to reduce the computational time the 'frame analysis' is applied. Two main assumptions are made for the suggested frame analysis method: separation points variation in a specific local area doesn t strongly affect voltages and currents in the distant regions only the area of the at most 3, in some special cases 4, neighboured feeders is relevant for the topological variations (e.g. 'moving' of the separation point along the ring topology) The frame analysis consists of the sequential analysis of the selected grid. The network is fractioned in frames. The frames are simple structures, as the generic networks, and they are operated as open radial structures. In this way fewer computations have to be performed. The frames are calculated sequentially on the network plan. The length of the frames includes at least 2 neighboured feeders, in some cases two neighboured ring topologies. An example of some frames and of their movement is given in the Figure 12. The frame analysis includes the following steps: 1. Definition of the single frames 2. Definition of the topology states for each frame 3. Definition of the scenario relevant nodes for each frame 4. Definition of scenarios (high loads / high feed-in of the DG) 5. Power flow computation for every combination {topology state scenario}, violations check 6. Evaluation of the results from 5 and the following elimination of some breakers In the first step 21 frames for the Reken grid model have been obtained (compare with the Figure 12). Following, the possible topological states and the relevant nodes for applying the scenarios are defined. In the fourth step the scenarios are defined. Although different generation scenarios were presented in the previous subchapter, only the generation scenario for 2030 is considered as the one with the most impact. 30 October /72

28 Figure 12: The frames for the Reken topology After all the preparations, in the fifth step, the power flow computations are carried out. In order to monitor only the frame relevant results, the increased scenario power values are applied only to the nodes within the current frame. The nodal power values in the rest of the network are taken from the base case. While performing the computations, the violated cases are flagged. Especially the corresponding opened circuit breakers get an individual statistics about their usage. Finally, every breaker exhibits a rating, which specifies the number of the violated state and the number of the useful state participations. In principle unused (or rarely used) breakers can be removed and not further considered. Unfortunately, the absolute number of the breaker participations can t be directly used for the elimination process. The reason for this is the different frame s complexity and thus different number of topological states. Especially the case should be considered where a breaker is only once being useful for the frame X and is never being useful for the frame Y. This would suggest that the breaker should be removed. Considering that this breaker would provide the only not violating constellation for X, its usefulness increases extremely, though not represented in the rating. From the above considerations, the idea for filtering the breakers is based on the worst case principle. Most breakers will either be useful or needed to avoid violated grid conditions. For these, no direct filtering can be applied. The breakers which do not have any useful participations, but some violating participations, are filtered out (worst case). As illustrated in the Figure 13, seven breakers (#5, #8, #10, #12, #17, #22, #23) are eliminated in this way. Breaker #18 is eliminated by the comparison of the violation behaviour in some relevant frames (compare with the Figure 12, frames B / BQ and B2 / BQ2 ). Using #18 means applying the interconnected ring topology (compare with the Table 3). For the given scenario there is no benefit in the usage of this breaker. 30 October /72

29 Figure 13: Circuit breaker eliminations according to the worst case principle Another benefit of the frame analysis is the evaluation of the critical network areas. After performing the load computations to the topological variations, it can be easily seen which frames exhibit the most violated states. The other frames appear as not critical due to the increasing generation feed-in. For these network regions the addition of new breaker may not be very beneficial. That s why, in these areas, the breakers from the step T2 can be eliminated as well. For the Reken topology this is the case for the region of breakers #28 to #35. In the Figure 14 the final reduced set of the circuit breakers (22 in total) is presented. Also the summary of the resulting breaker set is given by the Table 5. Figure 14: Final placement of the breakers of Reken Network 30 October /72

30 # usage notes 1 special customer breaker, always operated opened in normal state 2 x 3 x 4 x 5 6 x 7 x 8 9 x x x 14 x 15 x 16 x existing breaker, always operated opened 19 x 20 x 21 x x 25 x 26 x x 29 x not needed according to the frame analysis, but could be useful for fault cases 30 x x x Table 5: Summary of the used breaker 30 October /72

31 Operational method for relocation of the circuit breakers The determination of disconnection points is performed by the network simulation software called NEPLAN. (NEPLAN is the standard grid planning tool at RWE) For the following described process it is not necessary to use NEPLAN, but the chosen software should be able to simulate the load flow of a grid. In order to design a set of separation points for an optimized grid operation, one needs to review the characteristic cases of interest, which are our worst cases. The worst cases are the loading case and the feeding case. For these cases the RWE-specific diversity factors, which can be seen in Table 6, should be used. Also, for the grid calculations the scenarios in Table 4 will be used. Table 6: RWE-specific diversity factors a) Loading case In the loading case, all feeders will be set to zero and all loads reach their maximum. The load of the substations will be set to a diversity factor of 0,65. This is an internal experience of RWE, since not all consumers reach their maximum power at the same time. For special contract customers a diversity factor of 1 is assumed. Table 7: Factors for loading case b) Feeding case In the feeding case, all generating plants feed in their maximum. The loads are weighted with a factor of 0,25. The diversity factors remain unchanged. For PV a factor of 0,8 is assumed, wind power and biomass remain unchanged. Table 8: Factors for feeding case 30 October /72

32 Arrangements for the simulation In order to start the simulation to determine the separation points, all of the existing separation points and also all rings have to be closed. The result of this is a continuous network topology which can be seen in Figure 15. Figure 15: Grid topology with closed cut-off switches Definition of the grid borders The chosen grid is considered to be independent, because special contract customers and the transition to surrounding grid sections are not contemplated for the agents placement, as you can see in the following figure. 30 October /72

33 Figure 16: Cut-off switches to contiguous grids Renaming the offshoots Lines that are not arranged in a ring, and thus they won t be considered for the determination of the separation points, will be renamed. This is necessary for a filtering of the lines, which will be done later. 30 October /72

34 Figure 17: Grid section with tagged branches In this case the line labels from those offshoots are marked with an A in front of the original name. Figure 18: Conductor parameter in NEPLAN After closing the separation points and marking the offshoots, the calculation of the load flows and the currents can be executed. The results of the calculation appear in a list and are imported to MS-Excel. 30 October /72

35 Table 9: Element results in NEPLAN 30 October /72

36 Table 10: Element results in MS-Excel 30 October /72

37 Filtering the data (set) For the further procedure all the irrelevant data is faded out. The required data is filtered for element, type and the outgoing line of a bus bar in the transformer station. Type: line Element: doesn t start with A Outgoing line: starts with the label of the bus bar of the transformer station As a last step the lines are filtered for the individual current load. The line with the least current load will be selected and displayed in the list (Table 11). Table 11: Conductor selection with the minimal current load Determining the separation points The optimal position of the separation point is the result of the calculation of the load flow and lies within a ring at the line with the least current load. After opening a switch a new calculation has to be made, and the next switch at the line with the least current has to be opened. Using this method, the meshed grid is transformed into a radial grid. As a result, for the chosen load and feedin-situation, the best separation points are determined. 30 October /72

38 determined line line with the least current flow optimized separation point direction of load flow Figure 19: Direction of load flow After the determination of the line with the least current load, the ring will be opened at this or at the next possible switchable point. Here the local conditions need to be considered. Afterwards the calculation with the new grid situation will be executed. Lines, which turn into offshoots due to new integrated separation points, must not be used for the next data analysis. The whole process will be repeated until the entire grid topology no longer shows a closed-ring structure. As a result of setting a new separation point, overloads or voltage variations can appear at certain segments of lines. So it is easy to determine the weak points of a grid. As you can see in Figure 20, some of the separation points out of the different scenarios are congruent. Other separation points differ only by one or two substations and some separation points are driven only by load-dominated (black arrow) or feed-in-dominated (yellow arrow) scenarios. To get a final number of separation points, the congruent and the singular separation points are set, the near-by separation points are combined reasonable. By numbering the separation points at the determination it is possible to do a prioritization. For example, if there is 30 October /72

39 just a certain budget for the upgrade of a substation to a switchable substation, a prioritization can be very helpful. Shift to near SP SP feed-in-case SP opt. load-case Chosen SP Figure 20: Overview of separation points after method 2 The increase of DER and with that the increase of the feed-in will have an effect on the location of the optimized separation points within a distribution grid. 30 October /72

40 Conclusion and selection of the positioning of the circuit breakers A comparison between both described methods shows, that most of the separation points are similar. The number of separation points, determined by the first method ( ), exceeds the number of separation points determined by the second method ( ) significantly. Shift to near SP SP Method 1 SP Method 2 Chosen SP Figure 21: Final selection of separation points Due to a limited budget, it is reasonable to choose the smallest possible number of separation points. Therefore the second method is favoured. Also a better replicability to other distribution grids in Europe is given by the second method. It makes sense to use the first method as a reference procedure afterwards. One can improve the setting of the separation points easily. In Figure 21 a synthesis of both methods is shown. To increase the operability of the grid, separation points of both methods are combined. The experience of the DSO has to be considered in setting the separation points. 30 October /72

41 4.2 Multi agent system description Technical requirements for operating MV-network The topic Technical requirements for operating MW networks is really complex. There are many different issues you can expect under this point, for example operating rules, system ruggedness, operation fundamentals etc. One essential technical requirement for the simulations of the grid calculations with the software tool NEPLAN is handled in the DIN EN The DIN EN defines the maximum level of the voltage restrictions in MV and LV networks. Table 12 shows the valid values for both voltage levels. Character Medium voltage Low voltage Slow voltage variation 95 % of the 10-min-average values: ± 10 % supply voltage 95 % of the 10-min-average values: ± 10 % supply voltage Table 12: DIN EN For safety reasons the agents, that were described in chapter 4.1, have to be equipped with a service-modus for work on the grid, e.g. maintenance. If service or maintenance works are in progress, earthed parts of the grid have to stay earthed. The agents aren t allowed to switch in this case. The agents should observe the grid and estimate an optimal loadflow-situation. If the loadflowsituation results in one or more off-limit-conditions, the agents have to evaluate if a possible solution violates the off-limit-condition at one point of the grid. If one off-limit-condition is violated, the solution is not permissible. At any possible grid-state the grid-protection has to work in normal state. Any switching possibility should result in an acceptable state for protection devices. In case of a communication failure, it is necessary to know the actual or last state of the separation points in the control centre and the SCADA system. If it s not possible to communicate the actual status to the control centre or SCADA system, the grid-normal-state is the initial situation for a safety grid operation. 30 October /72

42 4.2.2 Hardware specification of the multi agent system The agents are distributed along the MV-network in several secondary substations. There are two types of agents: Agents with sensors only, M-Agents Agents with sensors and actuators, S-Agents Figure 22 shows a secondary substation structure. In Germany usually the secondary substations are not equipped with any active measurement; therefore it is necessary to integrate new equipment. In case of M-Agents at least sensors for MV-currents must be added. If possible also the voltage and the status of the switches should be monitored. MV MV Current/Voltage transformer RTU LV LV Current/Voltage transformer N S Communication Figure 22: Secondary substation The following signals are used: Signal name Signal Type Range 3 Phase yes/no MV_U_1 Analog value 0-24 kv Yes MV_I_1 Analog value 0-?? A Yes MV_P_1 Analog value 0-?? Yes MV_Q_1 Analog value 0-?? Yes MV_U_2 Analog value 0-24 kv Yes MV_I_2 Analog value 0-?? A Yes 30 October /72

43 MV_P_2 Analog value 0-?? Yes MV_Q_2 Analog value 0-?? Yes MV_SW_1 Double Indication On/off No MV_SW_2 Double Indication On/off No Table 13: M-Agent Signal list The measurement ranges of the signals are not defined at this moment. They will be set later in the project. S-Agents are equipped with sensors and actors. The only difference with respect to a M- Agent is the possibility to operate the installed switches/circuit breakers. MV MV Current/Voltage transformer RTU LV LV Current/Voltage transformer N S Communication Figure 23: Typical secondary Substation with actors Signal name Signal Type Range 3 Phase yes/no MV_U_1 Analog value 0-24 kv Yes MV_I_1 Analog value 0-?? A Yes MV_P_1 Analog value 0-?? Yes MV_Q_1 Analog value 0-?? Yes MV_U_2 Analog value 0-24 kv Yes MV_I_2 Analog value 0-?? A Yes 30 October /72

44 MV_P_2 Analog value 0-?? Yes MV_Q_2 Analog value 0-?? Yes MV_SW_1 Double Indication On/off No MV_SW_2 Double Indication On/off No Table 14: S-Agent Signal list Hard- and Software platform of the single agent The complete agent-software will run on the ABB-RTU560 platform. To meet the performance requirement of such a multi agent system, a more powerful CPU will be used as in the standard product up to now. The development of the agents will be done in the PLC environment of the RTU560. The reason of this approach is to avoid creating new firmware versions in case of changing the MV-agent algorithms. If during the development a lack of performance and/or functionality will be identified, it is possible to implement these complex parts in libraries which are programmed in C and linked to the firmware. These libraries can be used as function blocks in the PLC environment. From the software point of view, the agent system is divided in three main parts: RTU560 Firmware Agent-Infrastructure Agent-MV-Network-Application As already said, the agent infrastructure, as well as the MV-Network-Application, will be implemented in RTU560 PLC. This implies that the PLC interface of the RTU560 must have not only access to signals, but also to an interface for message exchange between different agents. Figure 24 shows the basic structure and data flow within the agents. The idea behind this picture is to clarify some basic functions and communication issues. This is a special view on the system to make it easier to understand what must be implemented. 30 October /72

45 Figure 24: Agent Infrastructure The RTU560 Firmware contains all necessary software to run the complete RTU560. Basically everything what is needed to start up RTU, monitoring I/O-signals and finally all communication stacks are parts of the firmware. The interface between firmware and PLC is mainly an interface to exchange signals. To exchange data between firmware and PLC those signals must be used. Despite that, to implement an agent system at least two data streams are necessary: Signal-Information stream Agent-Information stream The signal information stream contains the required information about the actual status of the MVnetwork like currents/voltages and breaker status. Together with basic topology knowledge it is possible to run network applications on this data. The result of such a calculation may lead into the necessity to inform other agents about the result. This is done over the agent-stream. The agentstream is mainly needed to coordinate the actions of all agents among the system. Both streams are controlled by the agent infrastructure actor. This piece of software is responsible to sort out the information coming from the protocol handler and either transfer to the MV-network application or build up and update the network topology. The agent interface provides the interface 30 October /72

46 between agent infrastructure actor and MV-network application. This can also be seen as a part of the infrastructure. For more details please refer to chapter Software specification of the multi agent system Agent hierarchy The suggested MAS system exhibits a functional architecture: three different types of agents are assigned. The control centre (CC-Agent) agent, switchable agents (S-Agents) and measuring agents (M-Agents) are responsible for their special tasks in the framework of the overall system. CC-Agent is a single central instance. It plays the supervisory role and provides the gateway to the SCADA system. Main tasks of the CC-Agent are: information acquisition from the MAS, deactivation/activation of the agents and manual operation of the agents. CC-Agent is placed at the primary substation. A CC-Agent is not essential. It could be useful, but depends on the final communication structure. Also alternatively an S-Agent can be used as the CC-Agent and provide the link to the SCADA. S-Agents are inferior to the CC-Agent. These actors are able to perform control actions by activating their switching devices. Furthermore they collect local information and exchange it among each other in order to perform cooperative coordination actions. Another role of the S- Agents is the information acquisition from their own measurements. In this respect, an S-Agent covers the same functionality as an M-Agent. S-Agents are placed at switchable secondary substations. M-Agents mainly perform measurements at the non-switchable secondary substations. They are sending this information to their supervisory S-Agents. In emergency situations, i.e. exceeding of set thresholds for voltage or current, M-Agents have to alert them immediately. In the following figure the hierarchy of the MAS is depicted. CC-Agent management / information-base S-Agent S-Agent S-Agent execution / coordination M-Agent M-Agent execution Figure 25: MAS hierarchy and interdependencies 30 October /72

47 Grouping of agents cluster principle After defining the overall functional roles, a more precise system architecture concept is described. For optimal using of the considered agent hierarchy an appropriate agents grouping have to be developed. Regarding a network fragment between two switchable secondary substations, the group of the M- Agents in this area can be understood as a local monitoring group. These agents only see what happens in their neighbourhood. Also for the other agents, outside this area, there is no direct information visible. They only see a cluster with input and output characteristics. For each cluster a supervisor a S-Agent is defined. Every cluster supervisor is responsible for data collection, interpretation and redirection. Furthermore, only the supervisor is able to perform actions in its local environment. As shown in the Figure 26, the S-Agent SA1 is performing the cluster supervisor role. M-Agents MA1 and MA2 collect information and send it to SA1. A communication act is only carried out between neighboured cluster supervisors e.g. between SA1 and SA2 feeder primary substation CC SA1 MA1 MA2 SA2 control centre S-Agent M-Agent M-Agent S-Agent regular communication reserve communication Figure 26: Cluster principle and communication between clusters and control centre The overall system, consisting of cluster groups, can act as a bare observer or perform some switching operations. In both cases the measurement and topology information has to be passed to the control centre. Information transport is carried out from cluster to cluster. In case SA1 couldn t operate, the inferior agents MA1 and MA2 should send their information directly to SA2 (reserve supervisor assignment). More detailed cases of the failed agent communication treatment can be found in chapter October /72