Non-invasive alternating and direct flux sensor for power transformers

This paper presents the measurement results of a flux sensor prototype, which can be used in power transformers for non-invasive flux sensing. The flux sensor uses the fluxgate principle to measure alternating, direct and mixed flux. The sensor can be located between two limbs on the transformer yoke and produces a flux proportional voltage signal output. The sensor uses two nanocrystalline cores, which offers several advantages over ferrite cores. The operation principle is explained for the two core arrangement and demonstrated on a 60 kVA laboratory transformer with superimposed DC. The analysis of the measurement signal reveals that alternating, direct and mixed flux can be detected and measured by the sensor prototype.