Online detection approach for direct current flux of power transformer

Abstract

Direct current (DC) flux in power transformer initiates its abnormal operation, and can eventually lead to the transformer damage. A new fluxgate sensor structure to detect the transformer's DC flux is presented. A magnetic shunt path is designed to extract fractional flux from the transformer's core limb. The DC flux can be obtained by measuring the demodulation outcomes of the output signal from the sensor's detecting coil, for there is a monotonic relation between them. The DC flux can be measured by the demodulation of output from the sensor's detecting coil. As verification, the experiment has been implemented with a 10 kVA power transformer. Measurement results show that when the external DC current, used to produce the DC flux in the transformer, varies from 0.2 to 2.5 A, the magnetic modulated output signal changes significantly and the RMS value is monotonously changing with the excited DC current.