3. GAP4 is the inspective approach to
assess the residual life of the
generator
.
4. Methodology
The methodology employed is
conducting standard and special
electrical tests and inspection on stator
and rotor windings and accessories
5. Unit Condition
The machine is in dismantled
condition with rotor threaded-out
Inspection & tests Performed
Physical examination
Tests and inspection
6. Benefits
Reveals pending faults in winding
Reveals deterioration of coil insulation by
corona or end winding vibration
Establish a base line for evaluating future
inspection
Accurately assess life and future
maintenance requirements
Record of core tightness
Preventive maintenance plan
Schedule for GAP2, GAP3 and GAP4
7. Final Report
Standard format provided electronically
Photographs of critical areas
Dielectric absorption graph and analysis of
insulation integrity
Results and summary of all test and
measurements taken
Location and levels of corona activity
Plots showing frequency distribution of end
winding basket
Core tightness record
EL CID test record and wedge mapping
Establishes a base-line for evaluating future
inspections and input for instituting planned
major maintenance activities
10. Geometrical data of the stator coils is collected to make a
model by FEM method for stress analysis
Overhangs
Turbine End
Straight side
Exciter End
Overhangs
14. The following indicators are used separately to
evaluate the condition of stator and rotor
• Operation and maintenance history
• Physical inspection
• Insulation test
• Generator Age
15. These condition indicators are initially evaluated using
inspections, tests, and measurements, which are
conducted by utility staff or contractors over the
course of time and as a part of routine maintenance
activities.
Numerical scores are assigned to each stator and
rotor condition indicator, which are then weighted and
summed to determine the Stator and Rotor Condition
Indices.
The lower of the two indices is selected to represent
the overall Generator Condition Index.
16. An additional stand-alone indicator is used to reflect
the quality of the information available for scoring the
generator condition indicators.
In some cases, data may be missing, out-of-date, or
of questionable integrity.
Any of these situations could affect the accuracy of
the associated condition indicator scores as well as
the validity of the overall Condition Index.
Given the potential impact of poor or missing data,
the Data Quality Indicator is used as a means of
evaluating and recording confidence in the final
Generator Condition Index.
17. Additional information regarding generator condition may be
necessary to improve the accuracy and reliability of the
Generator Condition index.
Therefore, in addition to the Tier 1 condition indicators, this
appendix describes a “toolbox” of Tier 2 inspections, tests, and
measurements that may be applied to the Stator and Rotor
Condition Indices, depending on the specific issue or problem
being addressed. Tier 2 tests are considered non-routine.
However, if Tier 2 data is readily available, it may be used to
supplement the Tier 1 assessment. Alternatively, Tier 2 tests
may be deliberately performed to address Tier 1 findings.
Results of the Tier 2 analysis may either increase or decrease
the score of the Generator Condition Index.
The Data Quality Indicator score may also be revised during the
Tier 2 assessment to reflect the availability of additional
information or test data.
20. DC Ramped Voltage Test
Partial Discharge Measurement
Dissipation Factor Measurement
Ozone Monitoring
Black Out Test
High Potential Withstand Test
Stator Core Inspection
Wedge Tightness Evaluation
Core Loop Test
21. ELCID Test
Corona Probe Test
Coupling Resistance Test
Bump test
Capacitance Measurement
Core Bolt Insulation Resistance
Winding Conductor Resistance Measurement
Impedance Measurement
Winding Dissection
