The Power Quality Characteristics Analysis And Evaluation Of Typical Nonlinear Loads Connected To The Grid

With numerous non-linear load and intermittent new energy connected to the grid, power quality problems have been the focus of both electricity setor and electricity parties in recent years. In-depth understanding power quality features of different interference sources and doing the power quality assessment of nonlinear loads access to the grid can provide the basis for power company to manage loads and develop appropriate governance compensation measures.For the power quality characteristics of typical non-linear loads, the paper studies the five common typical nonlinear loads in the grid, including Chemical rectifier load, Rolling Mill, Electric arc furnace, Electrified railway and IF furnace. The power quality indicators’calculation method of various types of load are given through the research on load characteristics, mainly power quality problems and solutions of compensation governance, as well as the proposal content value of each characteristic sub-harmonics generated by the five loads. For the electrified railway traction load, give the fitting function of typical vehicle’s speed (pole position)and the harmonics as the impact for the locomotive speed (pole position) to the load. For the compensation of mill load, give four main design factors including compensation effec, the cost of investment, reactive changes and load conditions. In consideration of four factors, give the proposed selection method of mill harmonic governance program.On the side of interference comprehensive assessment of nonlinear loads, the paper do the assessment of interference load lessons for the method of power quality comprehensive evaluation for the system side. Calculate the each index weight values impacted to the grid based on the Analytic Hierarchy Process (AHP) and DS evidence theory at first, and do the improvements as the lack of its heavy subjectivity so that downplay the human subjectivity in algorithm process and simplify the calculation process. Then give the correlation between the nonlinear load and the standard load combined gray relational analysis and index weights, which can be used to represent the interference degree of loads to the grid.