Statistical analysis of icing event data for transmission line design purposes

Abstract

Climatic loads on overhead transmission lines are random variables. Wind, icing, and combined loads of wind and ice vary greatly in time and space. Therefore, a statistical approach is most appropriate for their study and forecast. For this reason, statistical analysis of field data for icing events is very important at all stages of planning: design, construction, and operation of overhead transmission line networks, especially for lines that cross regions with severe icing conditions. Results from this analysis allow for forecasting climatic loadings; this determines the economic characteristics and operational reliability of the line and its principal components. Analysis of large-scale databases covering vast areas and long time periods also allows for a better understanding of the spatial and temporal evolution of icing events and the extent of their impact on the power network. The need for long-time series of available, reliable and pertinent field records of meteorological data containing historical information for icing events is increasing continuously, especially since probabilistic methods have been recommended in transmission line design (see IEC/CEI-60826 2003). While such databases for wind are, in general, relatively readily available, collecting data for icing on line equipment is a difficult, costly, and time-consuming process. In this chapter, we aim, first, at discussing issues pertaining to icing event data measurement and collection, and then at reviewing statistical analyses and modelling of icing using the ice data. This chapter is therefore subdivided into two main parts. The first part, 2.1 - Measurements and Database, gives some basic definitions pertaining to icing events (2.1.1), describes the sources for obtaining meteorological field data (2.1.2), and the principal measurement instruments: Passive Ice Meter (PIM) (2.1.3), Icing Rate Meter (IRM) (2.1.4), Load Cell (LC) (2.1.5), tubular-steelrod racks in Norway (2.1.6), and horizontal metallic rods at stand Studnice, Czech Republic (2.1.7). Section 2.1.8 is devoted to databases containing statistical information on icing events. The second part, 2.2 - Statistical Analysis and Modelling Ice Loads on Overhead Transmission Lines, is a brief review of the principal statistical distributions, models, and methods in use in transmission line engineering related to atmospheric icing: modelling freezing-rain data from the PIM network (2.2.1), extreme value analysis (2.2.2), combined wind-on-ice loads (2.2.3), modelling hourly icing rates on transmission line conductors (2.2.4), joint distribution of wind speed and air temperature (2.2.5), and modelling spatial and temporal evolution of icing events (2.2.6). © Springer Science+Business Media B.V. 2008.