Electro-magnetic transients on overhead transmission lines — An overview

The paper is essentially an overview presenting an outline of how Electro-Magnetic Transients (EMTs) are calculated in power system networks for means of an EMT Program based on travelling wave modelling of transmission lines. This paper presents the following steps: (1) For circuits with lumped parameters, the individual branches are modelled by different equations which are discretized to provide Norton equivalents. These are assembled producing nodal equations, to be solved step-by-step. (2) Transmission lines are modelled by time lags and Norton equivalents, even if their parameters are frequency dependent or multi-phase, in which case model decompositions are used. This paper uses state equations for transmission line modelling. Inclusion of transmission line Norton equivalents in the nodal equations does not complicate the system problem due to the effective time-decoupling of the computations. Some recent developments such as Z-transforms, s-domain analysis and corona modelling are also described.