Mitigating potential transformer ferroresonance in a 230 kV converter station

A wound potential transformer failed catastrophically on the Manitoba Hydro system. The failure was attributed to excessive current flow in the primary winding due to a sustained ferroresonance between the circuit breaker grading capacitance and nonlinear magnetizing inductance of the potential transformer. In order to prevent future occurrences, switching guidelines have been revised and permanently connected damping resistors were installed. Modern nonlinear techniques of analysis are evaluated for their suitability of defining safe and unsafe zones of operation. A new two-dimensional bifurcation diagram is proposed as a new visualization tool.