How to Avoid Unstable Time Domain Responses Caused by Transformer Models

Modeling a three-winding transformer occasionally gives a negative reactance that may result in an unstable circuit. This unstable condition can be eliminated by neglecting the magnetizing losses or taking them into account in a different way, as shown in this paper. Unstable responses are under certain conditions extremely dependent on the time step when using EMTP or similar programs. This paper shows why simulated terminal voltages do not always reveal an unstable circuit condition.