Experimental study of eddy currents induced in the solid shells of d.c. machines carrying undulating currents

Eddy-current density distributions in the solid yoke of a specially designed d.c. machine were measured with and without main poles in position, with the compoles alone excited from a variable frequency source. From the measured eddy-current density distribution curves and from the flux-density distributions in the airgap at the back of the compole, the eddy-current flow pattern around the shell is obtained. The instrumentation of the test machine, the layout of the current density probes and search coils in different parts of the magnetic circuit, and the various measurement techniques are also discussed.