Analyzing Ferroresonance Phenomena in Power Transformers Including Zinc Oxide Arrester and Neutral Resistance Effect

This paper studies the effect of zinc oxide arrester (ZnO) and neutral earth resistance on controlling nonconventional oscillations of the unloaded power transformer. At first, ferroresonance overvoltage in the power system including ZnO is investigated. It is shown this nonlinear resistance can limit the ferroresonance oscillations but it cannot successfully control these phenomena. Because of the temperature dissipation of ZnO, it can withstand against overvoltage in a short period and after that ferroresonance causes ZnO failure. By applying neutral earth resistance to the system configuration, mitigating ferroresonance has been increased and chaotic overvoltage has been changed to the smoother behavior such as fundamental resonance and periodic oscillation. The simulation results show that connecting the neutral resistance exhibits a great mitigating effect on nonlinear overvoltage. 1. Introduction Ferroresonance is a complex electromagnetic phenomenon which may be neglected in power system studies which is carried out for routine designs, planning, and operations [1]. A stability domain calculation of period-1 ferroresonance in nonlinear resonant circuit power system elements is given in [2]. In this case, quasistatic analytical approaches can be used to give a quick indication of the locations of domains of different ferroresonant states as a function of a set of parameters. Fast ferroresonance suppression of coupling capacitor voltage transformers (CCVT) is studied in [3]. This paper describes a procedure for fast suppression of the phenomenon of ferroresonance in CCVT without major change in the design. The design of a hall effect current transformer and examination of the linearity with real time parameter estimation is given in [4]. The aim of “blind source separation” (BSS) is to recover mutually independent unknown source signals only from observations obtained through an unknown linear mixture system [5]. Sensitivity studies on power transformer ferroresonance of a 400？kV double circuit are given in [6]. Novel analytical solution to fundamental ferroresonance in [7] investigated a major problem with the traditional excitation characteristic of nonlinear inductors. Application of wavelet transform and MLP neural network for ferroresonance identification was done in [8]. Impacts of transformer core hysteresis formation on stability domain of ferroresonance modes were done in [9]. The principle of AC current transformers (CT) based on the magnetic coupling principle is given in [10]. Current paper studies the effect of neutral resistance on