Test · Stator core
ELCID Test — Electromagnetic Core Imperfection Detection
Diagnosis of stator magnetic cores in synchronous generators and turbogenerators. The ELCID test induces reduced magnetic flux (4% of nominal) and detects anomalous eddy currents with a Chattock sensor — identifying lamination shorts and air-gap degradation before rewind, without energizing the core to full flux.
Electromagnetic Core Imperfection Detection
IEEE 56 (guide)ISO 9001:2015Technical definition
What is the ELCID test
ELCID (Electromagnetic Core Imperfection Detection) is a non-destructive diagnostic technique for the magnetic core of generator stators. Unlike the High-Flux Ring test (which requires energizing the core to nominal flux with hazardous currents), ELCID induces a very low magnetic flux (4% of nominal) and measures the induced eddy currents with a Chattock sensor that traverses every stator slot. It is the modern replacement for legacy full-flux testing on most service applications.
- References: test methodology documented in technical literature (e.g. CIGRE TB 257); IEEE Std 56-2016 (Guide for Insulation Maintenance of Electric Machines) as general reference guide
- Magnetic flux induction at 4% of nominal — safe, no thermal damage
- High-sensitivity Chattock sensor maps eddy currents across all slots
- Full mapping of the air gap and every slot of the stator
- Quantitative detection of anomalous currents (mA) by stator zone
- Graphical report with severity map per section of the stator core
Operational opportunity
When the ELCID test is recommended
ELCID is applied before costly decisions on the magnetic core — rewind, restacking or replacement. The test prevents wrong investments and prioritizes the right scope of intervention.
- Before stator rewind — to validate that the core is recoverable
- After a severe electrical event (phase short-circuit, overtemperature)
- On generators with several decades of service — accumulated degradation evaluation
- As part of major turbogenerator maintenance
- To evaluate the trade-off between rehabilitation and full stator replacement
- Before commissioning a legacy generator relocated to a new site
Client value
What the ELCID test detects
Lamination shorts in the magnetic core (between adjacent laminations)
Insulation degradation between laminations
Surface damage to the air gap from rotor contact or particles
High eddy-current zones that would generate overheating in service
Exact location of the defect (slot, row, approximate depth)
Quantitative severity to prioritize partial restacking vs full rewind
Deliverables
What we deliver at the end of the test
Each test is delivered with a signed documentation package with ISO 9001:2015 traceability and the acceptance criterion agreed in writing. Full traceability by work-order number and signature of the responsible engineer.
- 1Signed protocol with methodology, stator map and the acceptance criterion agreed in writing
- 2Graphical map of eddy currents per zone (air-gap heat map)
- 3Prioritized list of defects by severity (mA measured vs acceptable threshold)
- 4Diagnosis: core recoverable / partial restacking needed / replacement required
- 5Technical recommendation with cost-benefit of rehabilitation vs replacement
- 6ISO 9001:2015 traceability with raw data for independent verification
Illustrative example
Not a published project record.
Pre-rewind evaluation on a hydroelectric generator stator
IEEE 56
Reference guide
Restack + rewind
Option evaluated
Stator replacement
Alternative compared
On a hydroelectric generator with decades of service and an insulation fault, ELCID can be applied before quoting the rewind to evaluate the magnetic core. If it detects mild, localized fault-current zones, the usual recommendation is to compare a partial restack plus rewind against a complete stator replacement; the decision is made with the current map and a visual inspection of the core.
FAQ
Frequently asked questions — ELCID test
Questions we often receive. Can't find yours? Email us at ventas@temisapowergen.mx.
Why ELCID and not the traditional High-Flux Ring test?
High-Flux Ring requires energizing the core at 100% of nominal flux — hazardous, requires a high-current source and can damage marginal laminations. ELCID induces only 4% of nominal flux — it is safe, non-damaging, and maps each stator zone quantitatively. It is the reduced-flux core test, an alternative to the rated-flux loop test.
Does the rotor need to be removed for ELCID?
It depends on the configuration the machine allows. With the rotor removed, the sensor traverses the slots with direct air-gap access and rotor removal is included in the scope. With the rotor installed, the low-flux core test is performed during the outage with a specialist partner's robotic air-gap system: the entry clearance must suit the system (for the system we coordinate, at least 17 mm between retaining ring and core), guards, fan blades or other parts must be removed at both ends, and the unit must be isolated. Feasibility is confirmed with the general arrangement drawing, core and retaining-ring dimensions and the location of probes or obstacles.
How long does an ELCID test take on a large turbogenerator?
It is set per machine: number of slots and core length, full core versus re-measurement of a specific zone, configuration (rotor removed or robotic with rotor installed) and access preparation. The proposal lists set-up, testing and demobilisation separately so it can be planned within the outage window.
Can the ELCID test replace visual inspection of the core?
No. ELCID is complementary. Visual inspection detects macroscopic damage (impacts, thermal staining, bent fingers); ELCID detects electromagnetic degradation invisible to the eye. Combined, they deliver a complete diagnosis.
What happens if ELCID detects severe lamination shorts?
We document severity quantitatively (mA measured vs acceptable threshold). If defects are localized, we recommend partial restacking. If they are extended, we evaluate major restacking or full stator replacement. The decision belongs to the client, with data in hand.
Do you perform ELCID on large turbogenerators or only on smaller machines?
Feasibility depends on access rather than rating: with the rotor removed, disassembly and working space inside the stator; with the rotor installed, an entry clearance and geometry that admit the robotic system. We review it with the drawing and dimensions before quoting.
Related testing
Pair the ELCID diagnosis with the complete electrical testing suite
Contact
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ISO 9001:2015 · IEEE / IEC