MODELING AND ANALYSIS OF FERRO-RESONANCE IN TRANSFORMER

Abstract

Ferroresonance is a type of nonlinear resonance characterized by overvoltage whose waveforms are highly distorted and which can cause power quality problem and equipment damage in power distribution and transmission system. In most cases, ferro resonance occurs when one or two of the source phases are disconnect while the transformer is lightly loaded or unloaded. This type of situation occurs due to the clearing of single phase fusing, or single phase switching procedures. In these cases, if, only two phases of the transformer were energized and one of the three switches was open, it would leads to a voltage induced in the "open" phase. This induced voltage will "back feed" the distribution line, back to the open switch. if the capacitance of distribution line is sufficient to cause ferro-resonance, ferro-resonance will occur. Also in simple words ferroresonance is an LC "resonance" involving a nonlinear inductance and a capacitance. For ferroresonance to occur in power networks, the system must have a voltage supply (generally sinusoidal), capacitance (due to lines), a nonlinear transformer or inductance coil (including saturable ferromagnetic materials), and low losses. A detailed analysis of many simulation results show that the probability of system goes into chaos as losses decrease and the nonlinearity of the transformer magnetization rise. The effect of varying the transformer core losses, the value of the source voltage and the length of transmission line on the chaotic solution of the system has been studied.. With detailed analysis of many simulation results, to simulate ferro-resonance and to obtain Poincare maps, phase plane diagrams and bifurcation diagrams the Electromagnetic Transient Program (EMTP) and matlab is used. In this work the results in investigating the effect of different sets of circuit parameters and different magnetization characteristics of the transformer on the behavior of the ferro-resonant circuit have been presented. It was seen that changing in the exponent of the nonlinearity (n), transformer core losses (R), length of the transmission line(C), and applied voltage (E) can leads to different modes of behavior, which may be chaotic or periodic. For example, when the applied voltage is gradually increased, the responses may be period one, then period two, and then chaotic. A more accurate representation of the q -i characteristic of the transformer leads to chaos at a much lower magnitude of the source voltage.