A New Online Method Based on Leakage Flux Analysis for the Early Detection and Location of Insulating Failures in Power Transformers: Application to Remote Condition Monitoring

Power transformers figure to be amongst the most costly pieces of equipment used in electrical systems. A major research effort has therefore focused on detecting failures of their insulating systems prior to unexpected machine outage. Although several industrial methods exist for the online and offline monitoring of power transformers, all of them are expensive and complex, and require the use of specific electronic instrumentation. For these reasons, this paper will present online analysis of transformer leakage flux as an efficient alternative procedure for assessing machine integrity and detecting the presence of insulating failures during their earliest stages. A 12-kVA 400-V/400-V 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 and simple sensors, based on air-core coils, were built in order to measure the leakage flux of the transformer, and nondestructive tests were also applied to the machine in order to analyze pre and post failure voltages induced in the coils. Results point to the ability to detect very early stages of failure, as well as locating the position of the shorted turn in the transformer windings.