Service · Magnetic Core Repair
Repair of Magnetic Cores in Generator Stators
Diagnostic, restoration and reconstitution of stator magnetic cores in synchronous generators, turbogenerators and hydrogenerators. The core is the heart of the generator — damaged laminations, hot spots from eddy currents, displacement of the lamination stack or degraded interlaminar insulation compromise efficiency and accelerate winding failure. We diagnose first with ELCID plus toroide loop test, treat defects with controlled technique, recompact the lamination stack and release the core against the acceptance criteria agreed in writing with the client before any rewind. Service in the Tlajomulco workshop with document traceability.
ELCID + Toroide · Quantitative diagnostic
IEEE 56 (general guide)CIGRE TB 257 (ELCID)Loop testService overview
What a magnetic core repair includes
The process is sequential — quantitative diagnostic, mechanical-electrical intervention, post-repair validation. Each stage is documented with document traceability with quantitative data that justifies every technical decision.
- Initial diagnostic with ELCID reduced-flux test — Chattock-sensor mapping of interlaminar fault currents
- Complementary loop test (ring flux) when required
- Treatment of shorted laminations with controlled knife technique
- Application of modern interlaminar coatings — class F/H epoxy varnish
- Recompaction of the lamination stack and verification of clamping torque
- Restoration of slot wedges, blocking, pressure fingers and structural support
- Partial restacking when localized damage requires lamination substitution
- Final acceptance test against criteria agreed in writing with the client, with synchronized thermography before rewind
When to apply it
Scenarios that trigger magnetic core repair
Utilities, EPCs and plant managers who hit any of these scenarios save a rewind investment when the core is restored and validated against agreed criteria before any new winding is installed — rewinding over a defective core destroys the new winding in a few years.
- Before stator rewind — to validate that the core is recoverable
- After a severe electrical event: phase short-circuit, overtemperature, lightning
- Diagnostic ELCID shows anomalous eddy currents in specific stator zones
- Toroide loop test reveals hot spots above acceptable thermal gradient
- Legacy generator with several decades of service and progressive efficiency loss
- After mechanical impact during rotor extraction or insertion movements
Standards and certifications
Standards we apply to magnetic core work
Diagnostic methods are documented, IEEE 56 serves as a general reference and acceptance criteria are agreed in writing with the client. Quality management is certified with document traceability.
- IEEE 56 — Guide for insulation maintenance of large AC rotating machinery (general reference)
- IEC 60034-1 — Rotating electrical machines: rating and performance
- IEEE 95-2002 — Insulation testing of generators with HV direct current
- — Quality management system
Why TEMISA Power Gen
Six differentiators for magnetic core repair
ELCID plus toroide loop test in the same test bench — definitive diagnostic
Documented methodology, IEEE 56 as general reference and criteria agreed in writing
Recovery of cores competitors declare a total loss when ELCID data supports it
Quantitative decision: repair, partial restack or replace — never opinion-based
traceability with raw data available for independent verification
Related services
Services sequenced with magnetic core repair
Service
ELCID test for stator cores
Non-destructive diagnostic at about 4% of nominal flux with Chattock-sensor mapping of interlaminar fault currents; method documented in CIGRE TB 257, acceptance criteria agreed in writing. The diagnostic step that drives every magnetic core repair decision.
See serviceService
Stator and rotor rewind
After a magnetic core is repaired and validated against the agreed acceptance criteria, the stator is rewound with class F/H insulation and vacuum impregnation.
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Rehabilitation and life extension
Magnetic core repair is the prerequisite for life-extension projects on legacy generators. We sequence both services under a single project.
See serviceRelated equipment
Equipment with magnetic cores we restore
Illustrative example
Not a published project record.
Stator core repair on a cogeneration plant generator
Agreed in writing
Acceptance criteria
Localized repair
Option evaluated
Restack or replacement
Alternative compared
On a synchronous generator with recurrent thermal start-ups, ELCID can identify localized fault currents and the toroid loop test can confirm hot spots in the slot zone. If the damage is localized, the option evaluated is to treat the shorted laminations, apply interlaminar coating, recompact and repeat ELCID and the loop test with thermography before releasing the stator for rewind.
FAQ
Frequently asked questions — Magnetic core repair
Questions we often receive. Can't find yours? Email us at ventas@temisapowergen.mx.
When is magnetic core repair necessary?
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.
How do you decide between repairing the core and replacing it?
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.
Do you repair magnetic cores on-site or only in the workshop?
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. The choice is locked at scope definition after the initial diagnostic.
Do you serve cores in large turbogenerators?
Yes. We repair magnetic cores of synchronous generators and turbogenerators. For large-section cores we size the toroide loop test to induce flux close to nominal with high-resolution thermal imaging. The same documented methodology is applied regardless of machine size.
Which standards govern your magnetic core repair work?
Test methods are documented (ELCID per the CIGRE TB 257 literature, loop test), IEEE 56 serves as a general reference guide and acceptance criteria are agreed in writing with the client. The quality management system is certified with document traceability.
Contact
Need service for your industrial generator or turbogenerator?
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Quote requests
ventas@temisapowergen.mxDirect line
+52 33 3614 2460Shop hours
Monday to Friday 8:30–17:30 and Saturday 8:30–13:30 (closed Sunday)
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· IEEE / IEC