Experimental Application of Leakage Flux to the Detection of Insulation Faults on Disc-Type Winding Transformers

Abstract

This paper presents an experimental study carried

out on a disc-type winding transformer. Although several

industrial methods exist for the on-line and off-line monitoring

of power transformers, all of them are expensive and complex,

and require the use of specific electronic instrumentation. In

this paper, an on-line analysis of transformer leakage flux is

tested as an efficient alternative procedure for detecting

insulating failures during their earliest stages. A power

transformer was specifically manufactured for the study. A

finite element model of the machine was designed to obtain the

transient distribution of leakage flux lines in the machine’s

transversal section under normal operating conditions and when

shorted turns are intentionally produced. Very cheap, simple

sensors, based on air core coils, were built in order to measure

the leakage flux of the transformer, and non-destructive tests

were also applied to the machine in order to analyse pre- and

post-failure voltages induced in the coils. Results point to the

ability to detect very early stages of failure. The asymmetry

produced by the failure generates an indicator (induced EMF in

the coils) that can be easily distinguished from the one obtained

for the healthy machine. In fact, diagnosis can be perfectly

achieved in spite of the variation of such an indicator with load