Equivalent Impedance Parameter Calculation of Three-phase Symmetrical Loads for Harmonic Source Location

The equivalent impedance parameters of loads have been widely used to identify and locate the harmonic sources.However,the existing calculation methods suffer from outliers caused by the zero-crossing of the denominator.These outliers can result in inaccuracy and unreliability of harmonic source location.To address this issue,this paper proposes an innovative method of equivalent impedance parameter calculation of three-phase symmetrical loads that avoid outliers.The correctness and effectiveness of the proposed method are verified by simulations on Simulink using actual monitoring data.The results show that the proposed method is not only simple and easy to implement but also highly accurate.

Effects of Coal Metakaolin on the Mechanical Properties and Microstructure of High-belite Sulphoaluminate Cement

The effects of coal metakaolin on the mechanical properties of high-belite sulphoaluminate cement under compressive loading were investigated.The composition and microstructure of hydration products at different hydration times were analyzed by X-ray diffraction and scanning electronic microscopy.The hydration process of blended cement was studied via electrochemical impedance spectroscopy.In particular,replacing a part of cement with CMK(10%,20%,and 30%)was found to promote the hydration process,to refine the pore size,and to improve the compressive strength of the composite.The best compressive strength of the cement was achieved at a CMK content of 30%after 28 days hydration,being improved by 20.13 MPa,or1.44 times relative to that of undoped specimens.Furthermore,the compressive strength is shown to correlate with the impedance parameter R_(CCP),which allows the latter to be used for nondestructive assessment of the compressive strength of blended cement materials.

On-Line PMU-Based Transmission Line Parameter Identification

China Southern Power Grid Company(CSG)recently developed and implemented an online PMU-based transmission line(TL)parameter identification system(TPIS).Traditionally,TL parameters are calculated based on transmission tower geometries,conductor dimension,estimates of line length,conductor sags,etc.These parameters only approximate the effect of conductor sag and ignore the dependence of impedance parameters on temperature variation.Recent development in PMU technology has made it possible to calculate TL parameters accurately.The challenges are that such an application requires highly accurate PMU data while the accuracy of PMU measurements under different working/system conditions can be uncertain.With a large number of PMUs widely installed in its system,CSG plans to improve and update the EMS database using the newly developed TPIS.TPIS provides an innovative yet practical problem formulation and solution for TL parameter identification.In addition,it proposes a new metric that can be used to determine the credibility of the calculated parameters,which is missing in the literature.This paper discusses the methodologies,challenges,as well as implementation issues noticed during the development of TPIS.