Estimating the line performance of voltage upgraded lines

Abstract

The Norwegian Transmission System Operator, Statnett, operates a network of over 10,000 km of overhead lines from 132 to 420 kV. Around 5500 km of these overhead lines are, per today, operated on 300 kV and around 2200 km are, per today, operated on 420 kV. Recent changes in power flow have made it necessary to increase capacity so, like many transmission system operators worldwide, Statnett is now working towards building the next generation grid. This will be accomplished by building new overhead lines in the same right of way, and by upgrading existing lines. By the time this work is completed (in 2030) 1500 km of the 7500 km 420 kV lines will be upgraded 300 kV lines and because of this it is important to keep an eye on the line performance of these upgraded lines. One of the reasons for this is that statistical dimension tools have been used for the dimensioning of these lines. Statistical dimensioning was necessary because the margins in upgraded lines are very small and therefore the engineering needs to be done more precise than for new lines. To be able to perform the required engineering for voltage upgrading, Statnett has performed a number of R&D projects. Different types of insulators have been studied, as well as pollution and lightning performance of the most used glass insulator. The precise gap factors have been determined theoretically and practically in full scale. Besides that, tools for the determination of the exact air clearances have been taken into use. A tool for determination of the total line performance with accurate gap factors and insulator performance has been developed. This paper covers the tool for the determination of the total line performance, how it is used, how it works together with PLS CADD and a practical example is given.