Repair of Magnetic Cores in Generator Stators

When ELCID or the toroide loop test detect shorted laminations, hot spots or interlaminar insulation degradation — before rewinding the stator. Rewinding over a defective core destroys the new winding in a few years through localized overheating; core repair is a technical prerequisite when quantifiable defects exist. It also applies after severe events: phase short-circuit, lightning strike, or mechanical impact during handling.

With quantitative data. ELCID measures eddy currents in mA per zone; the toroide loop test measures hot spots in thermal gradients. If defects are localized and the specific core loss stays within tolerance after intervention, the core is recovered. If defects extend over more than 15 to 20 percent of the stator or if damage compromises the air-gap geometry, we evaluate major restacking or replacement. We never propose repair when the data supports replacement.

Mostly in the Tlajomulco workshop — the process requires rotor extraction, unobstructed access to the stator, heavy test equipment and a dedicated test bench for validation. For minor interventions on isolated, accessible hot spots, on-site service is possible under CFE LAPEM W4200-12. The choice is locked at scope definition after the initial diagnostic.

Yes. We repair magnetic cores of synchronous generators and turbogenerators up to 350 MW under CFE LAPEM W4200-12. For large-section cores we size the toroide loop test to induce flux close to nominal with high-resolution thermal imaging. The IEEE 56 and IEC 60034-26 methodology is preserved independently of machine size.

We work under IEEE 56 (recommended practice for stator core testing), IEC 60034-26 (effects of unbalanced voltages and currents) and IEC 60034-27 (off-line and on-line tests on stator winding). The quality management system is certified under ISO 9001:2015 and repair services are certified under CFE LAPEM W4200-12 for generators 1 to 100 MVA.