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 ad-
vantages 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.