Fluxgate Sensor for Power Transformer Monitoring

This paper presents the experience from a laboratory setup with a prototype sensor for measuring alternating and directional flux in power transformers during regular operation and during offline state. The sensor is based on the fluxgate principle, which allows the continuous monitoring of the alternating and direct flux inside the transformer core. With knowledge of time-dependent alternating and direct flux, the transformer operation can be optimized, mitigating high inrush currents, and enabling direct flux compensation. The sensor functionality was validated in laboratory measurements on a five-leg 60kVA transformer, where direct flux and mixed alternating and direct flux conditions were tested. The proof-of-concept laboratory tests reveal the qualitative measurement of alternating and direct flux. From the laboratory measurements, we conclude that the measurements of the absolute amplitude and phase of the mixed flux requires a calibration of the sensor on the transformer core and characterization of measurement setup for different magnetic field strengths.