Three-dimensional theory of eddy-current couplings with copper-faced loss drums

The paper gives a 3-dimensional theory of eddy-current couplings with solid-iron drums, with a layer of copper at the airgap surface. It is shown that the iron has a significant effect on performance and that this effect can be adequately accounted for using linear theory. General double-Fourier series are derived to describe the field distributions in the drum and airgap. These are then successively simplified by taking account of the practical range of values for the permeability and resistivity of copper and iron to give design equations from which power loss and torque can be easily calculated. It is demonstrated that, under limiting conditions, the 3-dimensional theory agrees with existing end-effect theories, and that these are special cases of the more general theory presented. Experimental and theoretical torque/slip curves are compared and shown to agree. Generalised curves are deduced from the theory, which are also shown to agree closely with test results.