Designing and Implementation of Overhead Conductor Altitude Measurement System Using GPS for Sag Monitoring

Abstract

Background: For efficient operation and reliability of power systems, continuous monitoring of power line sag is needed. The dynamic thermal line rating of a power transmission system at any instant may also be evaluated if power line sag information is available at that time. The smart grid also encourages sag measurement technologies so that the operator can take immediate corrective action whenever power line ground clearance exceeds the maximum allowable limit. Aim: The purpose of this paper is to design and implement an overhead conductor altitude measurement system using Global Positioning System technology with accuracy enhancement techniques for sag monitoring in power transmission lines in real time. Method: The observed Global Positioning System (GPS) measurements are found inaccurate by the comparison of observed GPS measurements with physical measurements taken at the field site. Therefore, various combinations of accuracy enhancement techniques such as Bad Data Identification/Modification (BDIM), Least Square Parameter Estimation (LSPE), and Haar Wavelet Transform (HWT) are used. Results: The field test has been conducted successfully on 11 kV power line by using the designed system to measure the altitude of overhead conductor at mid-span as well as at the pole to evaluate conductor sag of power lines in real time. Conclusions: It is found that HWT after LSPE and BDIM combination of accuracy enhancement techniques improves the accuracy of GPS measurements significantly and hence conductor sag can be monitored on-screen directly.