Computation of electro-magnetic transients using dual or multiple time steps

When computing transients with the EMTP (the Electro-Magnetic Transients Program) a single time step is selected for the trapezoidal integration all over the system. When this step is small because of the presence of a “fast” component, the simulation may be significantly slowed down. This paper presents a procedure by which the computations at selected fast buses can be performed with smaller time steps than at the rest of the system. The linkage of the variables at two different time steps is achieved in a simple way at the line-bus interface by a small addition to any existing implementation of an electro-magnetic transients program. Significant computational savings can be obtained without any loss of accuracy.