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.

Regulating reserve with large penetration of renewable energy using midterm dynamic simulation

A novel renewable energy intermittency model and a new midterm dynamic simulation tool in power systems are developed for examining dynamic behavior along the load curve for different combinations of the system operation reserves and renewable portfolio standard(RPS)rates.The system’s import limits are considered.It is concluded that ignoring intermittency and governor effects is an inadequate method to assess intermittency impact.The intermittency midterm dynamic impact must be studied.For the studied system,the instability is expected to be about 25%RPS with current reserves.Besides,the most vulnerable peak hour to instability is the afternoon peak hour when solar begins to drop off.This article stimulates further dynamic intermittency studies on the issues caused by renewable intermittency.The studies on the issues caused by renewable intermittency have not been revealed because of inadequate/incomprehensive study methodologies so that effective,mitigative solutions can be developed to guarantee the reliability of power grid when incorporating higher RPS if high operation reserves are impractical.

An Efficient Substation Placement and Sizing Strategy Based on GIS Using Semi-supervised Learning

As load and renewable penetration continues to grow,optimal placement and sizing of substations is becoming increasingly important in distribution system planning.This paper presents an improved methodology to solve the substation siting and sizing problem based on geographic information and supervised learning.The proposed approach can optimize the locations,capacities,and power supply ranges of substations with minimum investment and annual operation costs.Capital cost of land adds complexity and difficulty to the substation placement problem,especially for highly developed urban areas.This paper presents a theoretical framework to determine the optimal location of substations considering the cost of land.The state-of-the-art parallel computing techniques are employed so that co-optimization for substations of multiple voltage levels can be directly conducted in a computational efficient way.Case studies are presented to demonstrate the effectiveness of the proposed approach.