Analysis of the influence of outside equipments on the online deformation detection of transformers

Abstract

The Frequency Response Analysis (FRA) method is increasingly used in the diagnostics of power transformers, especially for the identification of winding integrity. For online FRA the signal is injected from the bushing tap by a capacitor, and the response is measured at the neutral point. Recently, an online method was put forward, in which sweep frequency signal or impulse signal was injected into the windings from the neutral point and its response was measured at the bushing both by magnetic coupling. But the influence of the outside equipments that connect with the transformer is unknown. In this paper a method to eliminate the influence of outside devices is put forward. Through the analysis of the two-port network equivalent of transformer winding, in which the outside equipment is equivalent to a impedance, we find that the zeros of the transfer function is not affected by the influence of this impedance. In this paper, the detail of this method is introduced, and is proved on a 220kV test transformer. The experiment results showed that when the outside equipment changed, the amplitude frequency response curve of the winding was different, but the minimum point location of the curve almost did not change. So we can use the minimum point to eliminate the influence of outside equipments.