Some effects of clamping pressure on localised losses and flux distribution in a transformer core assembled from POWERCORE strip

POWERCORE strip is a consolidated form of magnetic amorphous ribbon exhibiting low power loss and high magnetic permeability at power frequencies. A three-phase, three-limb model core was assembled from POWERCORE laminations with 45° mitred joints. Conventional yoke clamps were used to study the effect of flattening stress up to 0.45 MPa when the core was magnetized up to 1.4 T, 50 Hz. Localized losses were measured at selected points without the core using thermistor techniques and internal flux density variation was measured with the aid of small search coils. The main effect of pressure on the flux distribution was to increase the rotational flux at the joints between yokes and center limb. The localized loss increased by up to 70%. The total loss increased by 35% at a clamping stress of 0.45 MPa. The variation in localized loss is related to the clamping stress and the resulting flux distribution to show how its magnitude can be controlled