Economic Research Of On-load Capacity-adjusting Transformers Under Unbalanced Three-phase Condition

In recent years,driven by the concept of energy and power transformation,my country is vigorously implementing electric energy substitution to promote the electrification of terminal energy consumption.Electric energy substitution increases the peak-valley difference of the power supply load,which is not conducive to the economic operation of distribution transformers(referred to as distribution transformers).On-load capacity-adjusting distribution transformers are suitable for areas with large load peak-valley differences.It can solve the problems of high no-load loss and low voltage caused by seasonal or periodic changes in the distribution network.It is to reduce the loss caused by electric energy substitution.Important technical methods have been widely used in 27 provinces and cities including Beijing,Shandong and Zhejiang.However,the three-phase load imbalance in the distribution network will have a greater impact on the economic operation of the capacity adjustment.This paper considers the actual distribution network three-phase imbalance problem and carried out S11 and S11 with different capacity levels of 10kV according to the total ownership cost(TOC)method.Economic research on operation of S13 type On-load capacity-adjusting distribution transformers.First,consider the actual load situation of the distribution network,and study the loss calculation model of on-load capacity-adjusting distribution transformers under three-phase unbalanced conditions suitable for engineering applications.The composition of the distribution transformer loss is analyzed,and the theoretical loss calculation model of the on-load capacity-adjusting distribution tranaformers under the three-phase unbalanced condition is derived.Considering the actual data status of the electricity consumption information collection system of the distribution network,a phase estimation model of the voltage and current on the low voltage side of the distribution transformer is proposed.The two operating modes(Dyn11 and Yyn0)of the on-load capacity-adjusting distribution transformers were verified by simulation and physical experiment respectively on the low-voltage side current phase,sequence current and loss results.Then,based on the loss calculation model of on-load capacity-adjusting distribution transformers,the economic capacity-adjusting strategy of on-load capacity-adjusting distribution transformers under three-phase unbalanced conditions is studied,and the dynamic loss of capacity adjustment is calculated.Introduced the current threshold value adjustment method adopted by the on-load capacity adjustment transformer,and calculated the dynamic loss of the on-load capacity adjustment transformer based on the unbalanced load data of the actual area according to the threshold value method.Based on the loss calculation model of on-load capacity-ajusting transformers under three-phase unbalance,an economic capacity-ajusting strategy of on-load capacity-ajusting distribution transformers is proposed and compared with the sequential capacity regulation state of the threshold value method.The correctness of the proposed method is verified.Using MATLAB software to calculate the dynamic loss of on-load capacity-adjusting distribution transformers based on economic capacity-adjusting strategy,and compare and analyze the dynamic loss based on threshold value method to verify the energy saving of the proposed method.Finally,based on the loss calculation model and economic capacity-adjusting strategy of the capacity-adjusting transformers under the three-phase unbalanced condition,the economics of the existing S11 and 13-type capacity-adjusting transformers are studied.Under the condition of three-phase balance,the economics of S11 type capacity-adjusting transformers are higher than that of ordinary distribution transformers.The economics of the S13 type capacity-adjusting transformer with rated capacity of 315 and 400kVA are lower than that of ordinary distribution transformer.The economic difference between the remaining capacity-ajusting and ordinary distribution transformers is negligible.Under three-phase unbalanced conditions,the economics of S11 and S13 type capacity-ajusting transformers are lower than Dyn11 distribution transformers.