Electromagnetic field effects on EL CID tests

EL CID (electromagnetic core imperfection detector) monitors the condition of large AC rotating machine stator cores. Applications cover turbogenerators, industrial-sized machines and hydrogenerators. The basic principle is that of detection by a Chattock potentiometer of the electromagnetic field set-up by circulating current from inter-laminar insulation defects. The test provides an indication of core insulation faults, remedial work progress, a satisfactory condition before, and after winding, and also on-going service condition (as a guide to the necessity for core renewal). A quantitative analysis of some unusual EL CID results, further confirms the soundness of the EL CID technique