Polar mode of frequency response analysis used for observation of transformer condition

Abstract

Several tests are now available to estimate the state of insulation and mechanical integrity of transformers following major short circuits faults without opening the transformer tanks. Frequency response analysis is one of such a test currently used by utilities to estimate the state of transformers. However, analyzing graphs of amplitude and phase responses in the form of 'bode plot' is quite difficult and requires lot of experience, as every single type of transformer would have quite different frequency response. It is not unusual that significant deformation of windings or cores following severe short circuit faults could not be revealed by the bode-plot method. Another form of graphs that is easier to interpret the internal condition of transformers would then be useful. This paper offers a method of visualizing the frequency response scanning data in polar forms. This is done by simply converting the amplitude and phase graphs into nyquist-like plots, or polar plots, where amplitude response and phase response are drawn on the same frame. This method have been used to analyze for some new type transformer which to it applied by short circuit type test, then compared the scanning result before and after test.