This study is concerned with improved power system models for use in the development of high and super speed distance protection. New protection techniques indicate the need for a precise system model which takes into account any distortions produced by both the source and transmission lines. The effect of unexpected and/or delayed zero-crossings of the voltage and current waveforms due to travelling and fully offset current waves are studied. A new technique utilising symmetrical components and the Fourier transform to analyse a system containing a large turboalternator, generator transformer and a distributed parameter transmission line is developed and compared with time domain phase coordinate solutions.