Overload Detection of Distribution Transformer by Magnetic Flux Leakage Measurements /

Abstract

Distribution transformers commonly referred to as utility transformers are one of the fundamental block of power distribution system, serving to provide the final voltage transformation in the electric power distribution network, by stepping down the voltage used in the distribution lines to the level urged by the end customer. In developing countries, utility transformers are frequently overloaded, especially in peak load seasons. This beckons the need of a monitoring system for overload detection, which is both contactless and easy to install. Magnetic flux linkage from coils find its way as flux leakage in vicinity of transformer tank. This magnetic flux when quantified can be an indicator of transformer loading condition. In this paper, a method to measure and interpret these variations into transformer overload detection by means of magnetic field sensing has been developed. For this, firstly a finite element analysis has been conducted for 200 kVA distribution transformer in normal and overloaded states. Then, magnetic flux leakage is sensed at 27 different positions so that an optimal position with the highest magnetic flux density yield can be determined for magnetic sensor placement. Afterwards, an optimal sensor placement position has been determined for magnetic sensor placement in vicinity of transformer for measuring the magnetic flux density at different loading states. Further, an experiment has been performed where a non-contact magnetic sensor along with its processing circuitry is placed at optimum position to analyse the effect of overloading by means of variation in the magnetic field density produced outside the steel tank of transformer. Based on the findings, a contactless method has been validated for transformer overloading detection by means of state of the art magnetic sensor.