Abstract :
The development of systems for the transmission of telegraphy, telephony, music and television over lines has made increasingly exacting demands on magnetic materials and cores for transformers. Published data appropriate to the frequencies and inductions usual in line communication are inadequate and largely unreliable as a basis for design; moreover, the characteristics of some materials vary considerably from batch to batch, and with difficult designs this leads to excessive factory rejections. The paper first sets out the theoretical performance for homogeneous magnetic material at very lowinductions and then compares this with test results on typical specimens of materials and cores; most of the data, unfortunately, are not statistical. Results are first given for the initial permeability and eddy-current losses of single ring stampings, and the effects of stacking are examined. Corresponding measurements follow on single turns of typical strip and on spiral cores wound with strip down to 0.0006 in thick; this leads to an investigation of inter-laminar insulation and the effect of cutting to form C-type cores; measurements on some flat laminations are then given. Finally, some typical measured values of hysteresis coefficients and residual loss coefficients are given for the materials concerned.
