Transmission Line Sequence Impedances Identification Using PMU Measurements

An online TL （transmission line） impedance TPIS （transmission line parameter identification system） using PMU （phasor measurement unit） was recently developed and implemented at CSG （china southern power grid company）, Traditional approaches for TL impedance calculation only approximate the effect of conductor sags and ignore the dependence of impedances on temperature variation. Utilizing PMU measurements may improve the accuracy of TL parameters calculation. The challenge is that the parameters identified are very sensitive to noise and errors in PMU measurements, which are difficult to quantify and can be uncertain under different system operating/loading condition, TPIS provides an innovative yet practical problem formulation for TL sequence parameter estimation based on least-squares with linear constraints. A bootstrapping-based resampling technique is developed and a new metric is proposed to determine the credibility of the estimated sequence impedances. This paper discusses the proposed methodologies, challenges, as well as implementation issues identified during the development of TPIS.

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.