Taking Power Transformer FRA Interpretation to the Next Level

Lecture / Panel
Open to the Public



L. Satish
HV Lab, Dept. of Electrical Engineering, Indian Institute of Science, Bangalore, INDIA


Irrespective of the type of winding damage FRA shows a left or right shift of natural frequencies. Interpretation of FRA has so far been confined to capturing these frequency shifts by statistical indices, followed by establishing a mapping between fault-type and a range for each index. Establishing this forward mapping seems to work on lab-scale experimental setups but is hard to generalize in practice. This is because it is a many-to-one mapping, and so a unique diagnosis becomes difficult. Thus, FRA remains a monitoring tool. Literature analysis reveals that this predicament of FRA is perhaps due to the lack of a suitable mathematical basis. Taking this cue, author’s research group developed a unified mathematical basis – which relates the harmonic sum of squares of winding natural frequencies to winding’s inductances and capacitances. These formulae can be manipulated to indirectly measure high-frequency inductance (L eff ) of an iron-core winding, and thereafter, the same can be reworked in conjunction with measured total shunt capacitance (C G ) to identify which winding has suffered an axial displacement (AD) or radial displacement (RD).
In this talk, the author will discuss much more challenging fault scenarios – viz., where more than one winding (in Y or Δ configuration) suffers more than one AD or RD or both, each of them occurring at different positions and in different windings. The goal is to find faulted windings and identify if it has suffered an AD or RD or both. Only quantities measurable at winding terminals are used. Experiments conducted on a hand-assembled 33kV, 3.5MVA, HV winding (Y or Δ) containing 22 double-disks/phase are presented.


L. Satish (1964) received his B.E. in Electrical Engineering in 1987 from U.V.C.E, Bangalore University. Thereafter, he completed M.E (1989) and Ph.D. (1993) from Department of High Voltage Engineering, Indian Institute of Science (IISc),
Bangalore. He was in Swiss Federal Institute of Technology (ETH), Zurich, Switzerland, from 93-95 pursuing post-doctoral research. He joined Dept. of High Voltage Engineering, IISc in May 1995 as an Assistant Professor, and became a Professor in May 2007, in the Dept of Electrical Engineering. During summer of 1998 he was a visiting professor for four months at HV Institute, Helsinki University of Technology, Finland. His current research interests are – studies on transformer windings, condition monitoring and diagnostics,FRA, testing of high-speed high-resolution ADCs, and PD measurements. He was conferred “Young Engineer Award 1999,” by Indian National Academy of Engineering. He is an Associate Editor of IEEE Trans on Power Delivery since Feb. 2020 and served as Associate Editor of IET High Voltage from 2017-2023.