Comprehensive Evaluation Of Reliability And Economy Of Load Transfer Schemes For Distribution Network With Micro-grid

Load transfer is one of effective measures to guarantee the security of power supply under distribution network fault or N-1 maintenance. According to different objective functions, different load transfer schemes can be got. The feasibility is analyzed before each load transfer scheme is implemented. One of the most important things is comprehensive evaluation of reliability and economy. As micro-grid access to distribution network, network structure, operation mode, manipulative mode and evaluation system of distribution network will changed in different extents. When maintenance or fault of distribution network happens, micro-grid may turn grid-connected operation to islanded operation. The existing evaluation system of reliability and economy has been no longer applied. In order to achieve comprehensive evaluation of reliability and economy of load transfer schemes for power system more accurately, impacts of micro-grid on distribution network are quantified more comprehensively.When reliability and economy of distribution network with micro-grid are evaluated, the probability of micro-grid operating in the island, uncertain output of micro-grid and their functions on distribution network are considered. Islanded micro-grid uses the new reliability indices, which are chose and designed from the availability and interruption rations of hybrid power source and the short expectation and lack of probability of islanding operation. When power is shortage and the load needs to be cut, the nearside priority is employed. The load which is distant from power is given priority to cut down. And the ratio of load curtailment is considered. Distribution network with grid-connected micro-grid is evaluated by using the Monte-Carlo method and traditional reliability indices. The major distribution network and islanded micro-grid are on the basis of traditional economy evaluation indices, the impacts of micro-grid are considered from new energy development, economical power of combined power system and value of lost load on distribution network.Reliability and economy of distribution network with micro-grid no longer show up as two separate indices in the market environment. There exist the contradiction and coordination between the two. Reliability and economy cannot be considered separately. Keeping a certain level of reliability, the comprehensive optimization of reliability and economy is sought.The relationship and the relative importance between evaluation indices are analyzed and grasped and fuzzy analytic hierarchy process is used to confirm weight coefficient. The contradiction and coordination of reliability and economy are considered and different evaluation principles are delimited under different conditions. If reliability levels of all the schemes are higher, advantages and disadvantages of economy will directly determine the level of comprehensive evaluation of reliability and economy. If the reliability level of a scheme is too low and can no longer meet demands for the safety, economy is no longer discussed. The comprehensive evaluation is evaluated poorly. To test the capability of withstanding load fluctuation of different load transfer schemes, the comprehensive evaluation system is again performed in the maximum operation. At last, the effectiveness and feasibility of the evaluation system proposed in the paper are verified through comprehensive evaluation on two operation modes of modified IEEE33 node system.