El CID application phenomena

The Electromagnetic Core Imperfection Detector (El CID) was invented in the late 1970s as an additional tool in the field of electric machine condition monitoring. It is more convenient than the traditional full flux ring test for checking stator core interlaminar insulation. Initial application was to large turbogenerators but it is equally straight forward for industrial sized multipolar machines with one piece cores built in a continuous ring of segmental laminations. Anomalous results were obtained, however, when El CID was applied to large diameter, split stator cores which are typical of hydrogenerators. A range of the problems encountered are presented and it is shown how they may be understood, or, if possible, avoided. An exhaustive theoretical treatment is not attempted. The large number of illustrations necessitates only brief comment on each