Study On The Mechanism Of Power Quality Disturbance Affecting Distribution Network Loss

With the wide application of impulsive and non-linear loads and the emergence of a large number of single-phase users in low-voltage distribution network,power quality problems such as harmonics,three-phase unbalance and voltage deviation become increasingly prominent.Power quality problems make distribution network produce more additional losses,and distribution network losses are the main economic and technical indicators that comprehensively reflect the level of planning,design,production,operation and management of power network.For the whole power grid,power loss mainly distributes in 10kV and 0.4kV low-voltage distribution network,accounting for about 80%of the total distribution network loss.Therefore,it is of great significance to study the additional losses of key equipment in low-voltage distribution network under complex power quality disturbances.The paper first discusses the definitions,basic properties,and characterization indexes of the three most common power quality disturbances(three-phase unbalance,harmonics and voltage deviation).On this basis,the influence mechanism of each single power quality disturbance on the loss of key equipment in low-voltage distribution network is studied.Then,this paper theoretically deduces the formula for calculating the additional loss caused by the single power quality disturbance of key equipment in low-voltage distribution network,and verifies the accuracy of the theoretical deduction in the simulation platform of MATLAB/SIMULINK.Secondly,based on the derived additional loss calculation formula under single power quality disturbance,the concept of harmonic three-phase unbalance is introduced to deduce additional loss under the combined action of harmonic and three-phase unbalance,which is verified by simulation platform.In addition,the simulation data comparing the two power quality disturbances at the same time and the additional loss when they exist alone are analyzed and compared,and the results show that the additional losses under the complex power quality disturbance do not meet the superposition theorem.Since the additional loss does not satisfy the superposition theorem,and the increase of the additional loss in low-voltage distribution network is caused by the interaction of power quality disturbances,it is difficult to obtain the exact correlation between the additional loss and a single power quality characterization index.Therefore,this paper proposes a decoupling method of composite power quality disturbance,which lays a theoretical foundation for quantitative analysis of the relationship between single power quality indicators and additional losses of key equipment.Finally,in the decoupling analysis process of power quality disturbance,in order to prevent the power quality disturbance signal from being overwhelmed by noise,the signal needs to be denoised.Therefore,the basic principle of wavelet transform is expounded in detail.Based on this,the characteristics,principles and steps of wavelet denoising are introduced.Based on the typical noisy harmonic disturbance signal,the effect of wavelet soft and hard thresholds on the signal denoising is compared and analyzed.