Probabilistic Modelling Of HarmonicCurrents Produced By AC Locomotives

Abstract

The effective design and analysis of a modern ac electric railway requires a knowledge of system harmonics. Modern locomotives generally contain power electronic drives which generate substantial ac current harmonics. Conventional analysis of these harmonics involves the calculation of worst-case levels from a deterministic calculation. In practice, however, railway operation is such that a wide range of system conditions can exist, with locomotive demand, speed and position all contributing to the harmonic levels. On this basis, probabilistic analysis has been considered to give a more informative overview of system harmonics. Previous researchers have carried out a probabilistic analysis of traction system harmonics, based upon measurements taken from an operating railway. However, such measurements inherently include the combined effects of locomotive demand, speed and position, and to identify the effects of each of these parameters is not an easy task. This paper describes the development of an object-oriented software model used to calculate operating levels for an operating locomotive. The model is used to calculate the input current harmonic levels for an ac, thyristor-bridge, locomotive. A probabilistic analysis of locomotive operation is then developed to give probability functions of demand, speed and position for an example railway. These are used in conjunction with the traction system model to perform a Monte Carlo probabilistic analysis of locomotive harmonics, from which harmonic limits may be derived. Transactions on the Built Environment vol 7, © 1994 WIT Press, www.witpress.com, ISSN 1743-3509 364 Railway Operations