Researchers at the Paul Scherrer Institute in Switzerland have used a technique called neutron grating interferometry to observe magnetic domains as they establish magnetic fields inside the iron core of transformers. The researchers say these observations are a significant step towards understanding how transformers work and towards developing more efficient transformers in the future.
Neutron grating interferometry bounces neutron beams off samples while marking the ultra-small-angle scattering that results. As neutrons scatter off inhomogeneities in the material being studied, the scattering leads to a measurable local decoherence of the neutron beam.
In the case of power transformers, the magnetic orientation of each tiny magnetic domain within the core is uniform. The boundaries between these magnetic areas are domain walls. When the iron core is magnetized, all domains point the same way; The domain walls disappear. Researchers say the decisive factor for an efficiently functioning transformer is domain-wall mobility because a transformer’s iron core is re-magnetized at twice the frequency of the ac it handles, being re-poled from north-to-south and vice versa in rapid succession. The greater the flexibility of the domains, the better the transformer performs.
So far researchers have only been able to observe domain-wall behavior indirectly. Use of neutron grating interferometry generates displays in which the domain walls appear as black lines.
In one study, researchers found that there were certain thresholds of ac voltage and current beyond which domain walls either disappeared or appeared to freeze. These insights do not lead directly to better transformers, but could improve their development process. Particularly in the development of transformers for power lines, it has not always been clear why one transformer functioned better than another. More accurate information on the magnetic processes taking place within the iron core should enable a more target-oriented optimization process.