Investigation of Ferroresonance Physical Behaviours on Three Phases Transformer with Unsymmetrical Core Leg

Ferroresonance still become a confusing phenomenon since its non-linear response and very high sensitivity to parameter system and flux condition of transformer core. The existence of such greatly destructive phenomenon is basically caused by an interaction among different inductances (non-linear) with a capacitance. This paper investigated the physical characteristic of ferroresonance on three phases transformer with different dimension of core leg in which the greatest dimension was at the second phase (S-phase). A variation capacitance was given in order to observe the ferroresonance behaviours, that were 10 uF, 50 uF, and 100 uF. The transformer primary voltage and its total harmonics distortion (THD) were then analyzed. The results showed that the capacitance value was not linear with the ferroresonance effect level on transformer. The highest overvoltage level was seen on the test with a capacitance of 50 uF, namely about 180 %, whereas the greatest THD value was observed on the test with a capacitance of 10 uF, namely about 18 %. Moreover, the S-phase with the greatest core leg dimension was the most susceptible to ferroresonance as the highest overvoltage level and THD value was seen on this phase.