Power Transformer Hysteresis Measurement

The state-of-the-art in power transformer condition assessment includes different electrical measurement to assess the condition of e.g. the windings, bushings or the transformer core. This work proposes a hysteresis measurement to supplement the available diagnostic for transformer cores. When dealing with hysteresis measurements, remanent flux in the transformer needs to be reduced to a minimum in order to reduce e. g. inrush currents or the transformer sound level after energizing. Different laboratory and field measurements of a DC hysteresis showed that the available demagnetization procedures are not sufficient for all the tested transformer cores. As a consequence, two additional demagnetization procedures are proposed. These demagnetization procedures are based on an established demagnetization algorithm implemented in portable transformer test devices. A supplement saturation/hysteresis is proposed to mitigate the inter-phase magnetic coupling of multi-limb multi-winding power transformers. This saturation/hysteresis test can be performed at rated
frequency with a sufficient large power source or as DC measurement with a portable transformer test device. In addition to the condition assessment the hysteresis measurement could also be used for power transformer modelling. The DC hysteresis measurement approach was tested with four different transformer types and different rated power from 50 kVA to 300 MVA.