Current Transformers with Nickel-Iron Cores

There has been developed recently a nickel-iron alloy called hypernik which has especially low hysteresis loss and high permeability at low inductions. Due to these properties the material is particularly suitable for the cores of current transformers. A ring-type series transformer with a core of hypernik has approximately one-third of the ratio and phase-angle errors exhibited by a similar transformer having a core of ordinary silicon steel. The relative performance of transformers with cores of the two kinds of material are shown by test and by calculation for various burdens and ratios. The minimum ratio for which satisfactory performance can be obtained with a through-type transformer having a hypernik core is about 200 to 5. This new material is relatively expensive but its use will undoubtedly be warranted for certain applications.