Distribution network planning, historically known as a ‘predict and provide’ process, seeks to determine a set of optimal network solutions for supplying electric demands spatially distributed over a geographic area. Today, the rapid development and deployment of distributed generation and smart grid products (e.g., control, communication, and new economic measures) call for urgent improvements in distribution network planning to allow the utilities to proactively modernize their existing distribution grids. This paper reviews the current practices in this area and the emerging trends towards smart planning. Some challenges with smart planning are identified and briefly discussed.

An overview of trends in distribution network planning: A movement towards smart planning

The electricity grid is undergoing significant changes as it paves its way towards a smarter grid. New technologies provide a much clearer view on the electricity grid and its processes, mainly due to the fine-grained and near real-time acquisition of data as well as assessment of it. The huge amount of information will include additional technical data beyond the traditional metering information for billing purposes. This may give rise to a new generation of tools that rigorously monitor residential endpoints. Such monitoring may assist towards rapidly identifying problems and decrease the time to resolve them. Currently, a real-time view of the grid state is done by specialized equipment, but their costs combined with their need to be widely deployed, is a limiting factor. Today's modern communication approaches coupled with high-performance analytics can be used in complex system monitoring and assessment. We argue how a large network of distributed smart meters can be used for analytics of the smart grid, based on our experiences in developing a smart metering platform that is currently monitoring approximately 5000 real smart meters. We analyse and discuss the results stemming from the data being streamed to the platform, and show how new insights can be obtained with respect to power quality.

Sensing in power distribution networks via large numbers of smart meters

This paper proposes the definition, model and algorithm of two quantitative indices named the Total Supply Capability (TSC) and Ideal Total Supply Capability (ITSC) for distribution planning. The TSC of a distribution system is comparable to Total Transfer Capability (TTC) in transmission systems, which is defined as the maximum load it can serve under the N-1 guideline for distribution systems, taking into account the capacities of the substation transformers, network link topology, link capacity, and other constraints. The ITSC of a distribution system is the calculated TSC which considers capacities of tie lines are large enough. Mathematical models for TSC and ITSC are set up and procedures to calculate TSC and ITSC are presented. Based on TSC and ITSC calculation, a concept named Potential Supply Capability(PSC) is proposed, which depicts the “potential” or “hidden” TSC of the distribution system. Finally, TSC and ITSC calculation have been performed in a test system with promising results. The case study has shown that TSC and ITSC algorithms are efficient approaches to analyze and evaluate the existing distribution system.

Total Supply Capability and Ideal Total Supply Capability for distribution system: Definition, model and algorithm

After Optimal distribution substation locating, distribution feeder line planning remains the main problem in distribution system planning. Therefore, a MST-based and new GA algorithm for distribution network optimal planning is presented. To reduce computational time and avoid infeasible solution, two new operators are introduced to ensure that all individuals are feasible solution. Meanwhile, an electricity distribution network structure and feeder cross-sectional area selection simultaneous optimization model is adopted to deal with the weight of the minimal-cost system tree. This Combinatorial coding guaranties the validity of solution towards globe optimum. Finally, The method is examined in one real MV distribution network example.

A MST-based and new GA supported distribution network planning

A model to solve maximum power supply capability of urban distribution network is proposed, which is based on linear programming model of DC power flow. In the proposed model the maximum load power is taken as objective function, and the power balance of network, rated capacity of all branches (including lines and transformers), power constraints at power source points and load points are basic constraint conditions. Taking the actual distribution network of a city in a certain domestic district for example, the effectiveness the proposed model are verified, and the accuracy of the proposed model is also verified by traditional power flow calculation method.

A New Algorithm to Evaluate Maximum Power Supply Capability of Urban Distribution Netwrok

The computer-supported decision-making system has become an essential tool for the sustainable growth and expansion planning of modern urban power distribution network. Current packages with planning functions are independent packages, which are limited in the academic research. Presently, in Shanghai Municipal Electric Power Company and its subordinate units, a geographic information system(GIS)-based production management system(PMS) has been applied successfully as the working platform in most departments, which makes the further research on the computer-aided decision-making system possible and feasible. Taking the PMS as the graphics supporting platform, this paper studies and develops a practical GIS-based decision-making support system for urban distribution network expansion planning, which establishes a primary foundation for information-based planning, daily-frequent planning and elaborate planning. Firstly, the physical structure of the system is designed with a four-layer hierarchical architecture, including the data layer, platform layer, application layer and performance layer, which is suitable for object-oriented development to ensure the security and stability of the system. Secondly, to satisfy the requirements of distribution expansion planning, the main functions of the system are divided into seven modules according to the planning process abstracted in the computer, including the module of current situation analysis, load forecasting, substation locating and sizing, network planning, cable channel planning, economic evaluation of planning and so on. There is at least one or one set of practical mathematical models and methods for planning adopted in each module to ensure the accuracy and reasonableness of the final planning results. Finally, an actual planning of Shanghai, China is accomplished with the expansion planning system. The practical application achievements show that the system can not only optimize the expansion planning results of urban power distribution network, but also reduce the workload of computation, analysis and graphics drawing dramatically.

A practical GIS-based decision-making support system for urban distribution network expansion planning

A partheno-genetic algorithm based on tree structure encoding method for distribution network optimal planning is proposed, and two new genetic operators such as shift operator and redistribution operator for tree structure encoding partheno-genetic algorithm are proposed in this paper, after the reason that the convergence of bintree structure encoding genetic algorithm can be generalized to tree structure encoding genetic algorithm has been given. Prim algorithm is employed to create initial radial networks, which are better than entirely random initial schemes. The advantages of partheno-genetic algorithm are fully utilized in distribution network optimal planning. All schemes in the solving process are always naturally being radial mode, no need for inspection of connectivity and being radial in connection of the networks. The determination of conducting wire section, the treatment of street bifurcate nodes and the method of expansion planning for distribution networks are discussed. The examples of distribution network planning show that the method is feasible and efficient. Finally, in the conclusion part, mutation operator has been proposed to perfect the tree structure encoding partheno-genetic algorithm.

Distribution network planning based on tree structure encoding partheno-genetic algorithm

Planning is vital for the development of power system; and the quality of planning has direct influence on security, reliability and economy of the power system in the future. Therefore, it is urgently needed to study quantitative evaluation method for distribution network planning. First, this paper proposes a practical comprehensive hierarchy and method on evaluation of distribution network planning. Second, the implementation steps for the evaluation of planning network are given, which include the determination of indices hierarchy and the evaluation of planning. In the end, this paper takes 10 kV network distribution planning of a district in China for example in order to illustrate the specific evaluation steps and methods based on the hierarchy, at the same time, the case shows that the evaluation method has strong feasibility and practicability. The planning evaluation hierarchy and method proposed in this paper can not only seize the key elements influencing the characteristics of network planning, but also describe the planning integrally and quantitatively, and possess significant engineering practicability.

Comprehensive method on evaluation of distribution network planning

A proper evaluation on the power supply capability of urban distribution system is of enormous social and economical significance. In competitive marketing environment, to satisfy the sustainable growth of distribution loads, electric utilities must judge whether the return of power supply capability is sustainable and valued against the certain amount of investment. Therefore, to make up the insufficiency of traditional methods referring from the concept of total transfer capability of transmission system, this paper proposes a straightforward method to evaluate the power supply capability of distribution system, which is based on “N−1” simulation analysis of interconnected main-transformers under the “N−1” guideline. Firstly, a series of interconnected main-transformer groups are drawn from the main-transformers' interconnection analysis after the topological simplification of distribution system. Secondly, the maximum average load rates of main-transformers are concluded through the “N−1” simulation analysis of every interconnected group. Finally, based on a comprehensive analysis of all the interconnected groups' results, the maximum permissible load rate of each main-transformer can be obtained, thus the power supply capability of the entire distribution system can be calculated. Through the application in a district of Shanghai, China, the effectiveness and the accuracy of the method are demonstrated. The application results suggest that, the method presented in this paper based on “N−1” simulation analysis of interconnected main-transformers is a simple and practical tool, to evaluate the power supply capability of a distribution system, which will need only once calculation with constraint to the “N−1” guideline. Moreover, the interconnection weak-points and the interconnection bottlenecks of the distribution system can be identified easily with this approach, thus providing effective references for urban distribution network planning and the following project investment decisions.

An evaluation method for power supply capability of urban electric power distribution system based on “N−1” simulation analysis of transformers

Combining the daily operations of the utilities, the latest computer technology and the professional technology of distribution network planning, a practical GIS (Geographical Information System) based computer decision-making support system with eight sub systems for urban power distribution network planning is introduced. The models and functions of the system are described. This system has been successfully applied in some real urban power networks. The results show that it cannot only optimize the planning results of urban power distribution network considering many complicated factors, but also reduce the work of computation, analysis and graphic drawing.

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Jianmin Wang

Papers

A practical GIS-based decision-making support system for urban distribution network expansion planning

Distribution network planning based on tree structure encoding partheno-genetic algorithm

Comprehensive method on evaluation of distribution network planning

An evaluation method for power supply capability of urban electric power distribution system based on “N−1” simulation analysis of transformers

Study and application of decision-making support system for urban distribution network planning of Shanghai