Online Optimal Transmission Line Parameter Estimation for Relaying Applications

Transmission line protective relaying algorithms usually require transmission line parameters as inputs and thus accuracy of line parameters plays a pivotal role in ensuring the reliable performance of relaying algorithms. Online estimation of line parameters is highly desirable and various methods have been proposed in the past. These methods perform well when the measurements utilized are accurate; they may yield erroneous results when the measurements contain considerable errors. Based on nonlinear optimal estimation theory, this paper puts forward an optimal estimator for deriving the positive sequence line parameters, capable of detecting and identifying the bad measurement data, minimizing the impacts of the measurement errors and thus significantly improving the estimation accuracy. The solution is based on the distributed parameter line model and thus fully considers the effects of shunt capacitances of the line. Case studies based on simulated data are presented for demonstrating the effectiveness of the new approach.

I. Introduction

Transmission line parameters including series resistance, series reactance, and shunt susceptance are critical inputs to diverse power system analysis programs. Precision of line parameters is thus essential in ensuring the accuracy of the obtained analysis results. Especially in areas of power system protection, many distance relaying algorithms entail line parameters for determining appropriate relay settings, calculating fault distance, and making a sound tripping decision [1]–[3]. It has been established that the value of line resistance, inductance, and capacitance is frequency dependent [4]–[6]. This paper is concerned only with estimating line parameters at the fundamental frequency, which are usually required by relaying applications.