| In the power system,the electric energy should be a perfectly symmetrical sine wave.Power quality mainly has the following several indexes: frequency deviation,voltage deviation,voltage fluctuation and flicker,three-phase unbalance,waveform distortion(harmonic),voltage sag,interruption,sag,etc.The problem of power quality will cause the loss of power when the power grid is running.Network loss(line loss)refers to the energy loss in the form of thermal energy,that is,the active power consumed by resistance and conductance.It has become an important part to evaluate the economic performance of the power grid through the size of the power loss.According to the data,about half of the power loss in China's power distribution network is caused by the medium-voltage power distribution network,and the power loss caused by the power quality problem occupies a large proportion.Therefore,it is very important for the economic operation of the power grid to calculate the network loss caused by the power quality problems in the medium-voltage distribution network and make a comprehensive evaluation of the power quality on this basis.Three important aspects of power quality problem causing power loss(harmonic,voltage deviation,three-phase unbalance)are analyzed in detail,and the calculation formula of power loss is derived in the article.MATLAB was used to build IEEE33 node model as a 10 kV medium voltage distribution network simulation model,and the network loss of three power quality problems was simulated and verified.Based on the structure and power flow data of the 10 kV medium-voltage distribution network in dayong line,songyuan city,jilin province,IEEE20 node model is established to calculate the network loss and make a comparative analysis with the measured network loss,which verifies the feasibility and accuracy of the model's network loss analysis.The comprehensive evaluation methods of power quality were analyzed in this article,it improves the analytic hierarchy process(AHP)and entropy weight method considering the power quality network loss,adjusts the weight according to the influence of network loss of different indexes,and analyzes the advantages and disadvantages of the traditional combination of subjective and objective weight,and proposes a new combination of subjective and objective weight.Dayong line,in anxian county,songyuan city,Jilin province,the tide of 10 kV medium voltage distribution network and the network loss data as the foundation,considering the distribution network loss of power quality comprehensive evaluation,the evaluation results with fuzzy mathematic method and did not consider network loss are analyzed in combination with objective and subjective evaluation result,verify the accuracy and completeness of this method.Some Suggestions on harmonic,voltage deviation and three-phase unbalance are put forward. |
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