GB751037A - Improvements in or relating to inductance coils having ferromagnetic cores - Google Patents

Abstract

751,037. Inductors. LIGNES TELEGRAPHIQUES ET TELEPHONIQUES. March 30, 1954 [April 23, 1953], No. 9324/54. Class 38 (2). An inductor, especially a loading coil for telecommunications circuits, has a magnetic core of ferrite material having values of permeability Á. of at least 2400, a Curie temperature of approximately 190‹ C. and values of F n /Á, h/Á<SP>2</SP>, t/Á and αÁ lower than 0.0005, 0.001, 0.001 and 0.002 respectively, where F n , h, t and αÁ are eddy current loss, hysteresis loss, residual loss and temperature coefficient of permeability as defined. A suitable material is that forming the subject of Specification 730,703. The core may be a pot with a central stem having an air gap, either built up from parts, Fig. 1 (not shown), or made in two halves either moulded or machined in the manner described in Specification 737,068, Fig. 10. The halves may be bolted together, Fig. 9 (not shown), or cemented together. They may be arranged for mutual rotation to vary the effective length of an oblique air gap. The windings may comprise single wires distributed in two or four compartments of a plastic former for side and phantom circuit coils respectively, Figs. 3, 4 (not shown). For better balance the windings may be wound together, Figs. 5-7 (not shown). The number of turns and size of wire may be less than in conventional coils, thus reducing mutual capacitance. The conductors may be insulated with enamel, varnish or plastic material which welds together, and the coil may be embedded in plastic such as polyamide or polystyrol, no former being needed. The windings may be insulated with vinyl chloride or polyethylene and surrounded by a polystyrol band cemented to the former: If preferred the windings may be impregnated or immersed in oil, or coated or filled with polyesters such as Araldite (R.T.M.) afterwards polymerized. Alternatively the coil may be filled with nitrogen. Two side-circuit and one phantom-circuit coil units may be clamped together between flanges 47, Fig. 11, or cemented together. To reduce magnetic coupling between adjacent units they may be separated or surrounded by a screen such as an iron washer, sheet of Permalloy C, or Mumetal (Registered Trade Mark), Figs. 12, 15-25 (not shown). They may be coated by injection moulding with an external cylindrical or octagonal plastic coating, Fig. 13 (not shown). The loading coils may be located inside the cables or joints, without external casings. A number of composite arrangements are described in detail and their properties tabulated. Specification 730,703 also is referred to.