Modelling of Capacitive Loads for the Study of Transients in Synchronous Machines

There is often a temptation to model the reactive power loads on a synchronous machine as an equivalent lumped capacitor or reactor for the purposes of transient simulations. Significant errors can result from such an approach, especially in the simulation of fast rotor transients in machines connected to HVdc systems. This paper attemps to show where such simplified representations are allowed, and where they are not. The results indicate that a long and unloaded transmission line may be represented by an equivalent capacitor, but that other loads such as HVdc filters may not. Certain other modelling aspects such as breaker opening are also discussed.