Generator Condition Assessment Program
GCAP L1 is designed to accommodate combustion inspections of Gas turbines. Same can be applied on Steam Turbine Generators on 2 or 3 yearly shutdowns in which inspection covers are removed.
With just the inspection covers removed, technicians can perform electrical and mechanical testing of the rotor, collector, exciter (brushless), and stator. They also can perform stator core tests, visually check the enclosure, and inspect the bearings.
Tests/inspections include the following:
- Borescope inspection of armature winding, rotor winding and blocking (as accessible), and stator-core step laminations and fingerplates.
- Electrical tests on RTDs, armature winding, and rotor winding.
- Armature winding tests: insulation resistance, polarization index, and winding resistance.
- TGR test: insulation resistance, polarization index, winding resistance, impedance test.
- Exciter (brushless): visual inspection, insulation resistance test.
The tests/inspections above can be completed in about 12 hours and can reveal imminent faults in the winding of the stator and rotor. And, they can detect deterioration of the coils caused by partial discharge or end-winding vibration. The tests also create a baseline for trending.
GCAP L2 is recommended during HGP inspections and any extended shutdown on Steam turbine generators (rotor is not drawn out).
During a hot-gas-path inspection, with the upper end bells removed, additional generator tests can be performed. The rotor windings can be examined and tested, as can the insulation in the stator. A borescope inspection, under the rings, also is suggested.
The specifics:
- Visual and borescope inspection of rotor windings and blocking, plus stator-core laminations and fingerplates (as accessible).
- Insulation tests on RTDs, armature winding, and rotor winding.
- Armature and rotor winding tests: insulation resistance, polarization index, and winding resistance.
- Shorted Turn detection tests on Rotor.
- Core tightness checks (visual indications of looseness).
- Doble Power Factor Tip-up test.
- Corona probe tests, as assessable, to determine areas and severity of any corona activity.
- Step voltage tests (DC step voltage/dielectric absorption or high potential) to determine insulation integrity of armature windings.
- Exciter visual inspection and insulation resistance test.
These tests/inspections take two or three days and provide more in-depth information than those done during the CI inspection; plus they provide information on the integrity of the armature winding insulation. Results offer baseline data to guide future inspections and work required during the next major outage.
GCAP L3 is designed around a GT or ST Major inspection usually at 5 years interval.
Engineers can perform comprehensive testing on the generator during a major outage, when the rotor is removed. A full examination takes five to seven days.
Inspections/tests include these:
- Visual inspection of stator and rotor.
- Borescope inspection of rotor winding and blocking (as accessible).
- Tests on RTDs, armature winding, and rotor winding.
- Armature and rotor winding resistance checks.
- Core tightness verification.
- Corona tests to determine areas and severity of any corona activity.
- Step voltage tests (DC step voltage/dielectric absorption or high potential) to determine insulation integrity of armature windings.
- Core El Cid test.
- Wedge-tightness mapping.
- Doble Power Factor Tip-up test.
- Rotor impedance and pole balance tests.
- Generator rotor retaining-ring NDE inspection (based on OEM requirements).
- Exciter visual inspection and insulation resistance test.
This level of inspection and testing provides a comprehensive picture of a generator’s condition and is the best way to assess potential life and determine what, if any, maintenance is required.
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