Performance of various magnetic core models in comparison with the laboratory test results of a ferroresonance test on a 33 kV voltage transformer

Ferroresonance is a nonlinear phenomenon and occurs in all voltage levels of power systems. One of the main elements of a ferroresonance circuit is saturable inductance. Existing electromagnetic transient programs such as EMTP present various models of magnetization characteristics of saturable cores. However, to study ferroresonance phenomenon, many papers have used single-valued characteristics for magnetic cores and ignored hysteresis effects. In this paper, some modeling methods of magnetic core characteristics are reviewed and the results of a ferroresonance test on a 33 kV voltage transformer are presented. Using the results of the voltage transformer no-load test, the magnetization characteristic is obtained and the magnetic core is modeled by various methods. The comparison between the experimental and simulation results shows that in analysis of some ferroresonance cases, the aspect of inherent variation of inductance in hysteresis loops is more important than the power loss introduced by these loops. Therefore, in such cases, the core characteristic must be represented by a hysteretic model. Otherwise, the simulation results may present significant errors.