Electromagnetic Core Imperfection Detection (ELCID) Test

Electromagnetic Core Imperfection Detection (ELCID) was developed in the late 1970’s by the Central Electricity Generating Board (CEGB) in the UK to enable it to readily test machines where a high power source for traditional ring flux test was not available. The technology is now well established in many parts of the world as an easier means than the traditional ring flux test of checking the integrity of interlaminar insulation for stator cores of large rotating electrical machines. The ELCID test uses a similar excitation winding but at a very low flux level, typically four percent of rated flux. Hence the heat produced by faults is negligible and not detectable, but the fault current is detectable by electromagnetic means and it is this fault current, when scaled up to the appropriate rated flux level, which would give rise to the local generation of heat and associated hot spots.

Because of a large number of laminations and thin insulation layer there is a high probability of insulation breakdown. The fault currents induced can be large and cause excessive local core heating. If not detected and repaired at an early stage, faults could be catastrophic. Low power core testing can be performed more quickly and easily than using traditional ring flux test method. Only 4% of rated flux needs to be applied to the stator core.

Additionally advantageous benefits of the ELCID include reduced downtime, ease of use and safety for both machine and personnel. Recently, the tendency to reduce major outages has given rise to ELCID tests being carried out without removal of the rotor, where Ring Flux tests are not possible. This is sometimes achieved by the removal of one or two poles (hydro generators) and the rotor then rotated to allow inspection of the complete machine.

Application includes: Generators, Motors