| As the distributed generation accessing to the distribution neywork speedily and the expectations of the quality and reliability of the power supply are growing,the construction and operation of distribution network are facing a great challenge.Due to low reliability,small power supply capacity,difficult access to distributed generation and other drawbacks,the traditional open-loop operation mode of 10 kV distribution network is facing the bottleneck of development.A new operation mode of 20 kV closed-loop distribution network will be an effective way to solve the problems above.However,10 kV open-loop distribution network has been adopted in domestic for a long time and the traditional evaluation system and control method cannot meet the requirement of 20 kV closed-loop distribution network operation mode.The key theory and technology supporting system for the optimization of 20 kV closed-loop distribution network operation mode has not been formed yet,which restricts the popularization and application of 20 kV distribution network.Considering the application need of the construction and operation for 20 kV,the key theory and technology supporting system for 20 kV distribution network are studied in this paper in order to realize the optimization of operation and improve the reliability of power supply for 20 kV distribution network.A power flow analysis method is proposed and a reliability evaluation model is established for the closed-loop distribution network.Also,an optimization method for reactive power configuration in 20 kV distribution network,a suitable protection and control strategy as well as a communication scheme based on wide area protection and control system are put forward.Major work includes:(1)A method of power flow analysis and a model of reliability evaluation are established for the closed-loop distribution network operation.Considering the branch of the feeder line,the calculation method of the closed-loop power flow is improved,which helps to evaluate the safety of the closed-loop operation mode under extreme operating conditions and typical operating conditions.A reliability model including the system network,the feeder trunk and the feeder branch is established,which describes the influence on the closed-loop distribution network so as to provide reference for the quantitative assessment of the network reliability.A preferred closed-loop distribution network is finally recommended combining with the power flow analysis and reliability evaluation of a certain regional.(2)A reactive power planning method is put forward based on the modeling approach from point to surface and the correlation analysis,taking accounts of the rate of reactive power allocation,in order to offer a reference range for the distribution transformers with different characteristics to optimize the reactive power allocation,which provides solutions for the limited optimal research on the rate of reactive power allocation and the over-generalized guidelines neglecting the differences in 20 kV distribution network.Also,the method avoids the limits of generality of other approaches,considering every feeder's optimal reactive power planning.The effectiveness of the method is verified by example results.(3)The protection and control plan for 20 kV closed-loop distribution network is put forward: the framework of the wide area protection and local protection system are built from the perspective of protection coordination,communication efficiency and the expansive functional demands.Then,the current differential protection algorithm and the local protection algorithm with adaptive function are studied to improve the adaptability of protection scheme for the closed-loop distribution network.Finally,aiming at the problem of closed-loop feeder overload,the corresponding load shedding strategy and its algorithm are given.(4)A communication network scheme based on wide area protection and control system of distribution network is proposed,including the communication network framework,networking and the scheduling strategy.Followed by the study of communication network description method based on IEC 61850 standard.The models for wide area protection and control system and the scenes for simulation of OPNET are established to provide the quantitative evaluation method for the network performance with the help of a simulation case.Different communication network schemes for the wide area protection and control system are tested in the simulation cases.(5)Comparing with the conventional protection scheme,a wide area protection and control scheme is designed for a 20 kV closed-loop distribution network in a certain area.Followed by the rationality evaluation of the wide-area protection and control scheme from the aspects of investment scale and performance. |
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