Mathematical Modeling of Passive Techniques Designed for PT Ferroresonance Suppression

Ferroresonance often inflicts severe damage on electrical equipment like potential transformers (PTs), surge arresters, and circuit breakers. In this paper, a new passive (P) technique using Cex (external parallel capacitor) is proposed and its performance is compared with the methods using Rex (parallel resistor), MOA (metal oxide arrester), Cn (grounding capacitance), Rn (grounding resistance), and Rcb (parallel to CB resistor) components. The mathematical models of the approaches are derived and their bifurcation diagrams for the peak voltage versus the method parameter are computed. The results indicate that the Rex, Rn, Cn, and Cex designs can effectively suppress the ferroresonance and limit the peak voltage to less than safe 2pu. However, since the Rex, Rn, and Cn methods disrupt the PT’s normal operation, those cannot be installed permanently and must be triggered by a ferroresonance detection module (FDM). Besides, the heat generated by the Rex and Rn methods is considered another disadvantage. As a result, the proposed Cex method with no heat generation, availability at power stations and not requiring FDM viewed as a prime choice. It is also shown that the level of the input voltage (E) that the method, under any initial conditions, can tolerate increases by the C_Tx/C_s ratio. The study was verified through numerous simulations where some have been presented as evidence.