3. The deterioration of large generators or for
that matter any electrical equipment is
normal, and this process begins as soon as
generator is installed.
If deterioration is not checked, it can cause
electrical failures and malfunctions.
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4. In addition a TEAM of stresses
- Thermal
- Electrical
- Ambient
- Mechanical
further contributes to the
deterioration process.
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6. The purpose of a good maintenance
program shall be
• to discover the potential reasons of
deterioration
• take remedial measures for correction
to avoid catastrophic failures.
failures.
The other important purpose of
maintenance program is to maximize
reliability and availability, improve
operational efficiency and productivity.
productivity.
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8. GAP* is a proactive action and the solution to
ensure availability and reliability of generators as
well as improve operational efficiency and
productivity to ensure smooth and trouble free
running of the plant.
GAP* is an inspection and maintenance process
during the lifetime of a generator and is planned
for during either operation or outage.
GAP* can be linked to the generator planned
outage time thereby ensuring minimum downtime
of the plant and at the same time assessing the
healthiness of the generator.
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10. 1 GAP 2
GAP
GAP*
GAP 4 GAP 3
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11. • During operation of the
generator
• Data collection and on-
line measurement when
the generator is in
GAP 1 operation
• Recommended after
8,000 hours of
operation
• Usually takes 1 day
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12. GAP 1 deliverables
Thermal Life Assessment by Arrhenius Equation
Thermal Life Assessment by N-Y method
Schedule for GAP2, GAP3 and GAP4
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13. • During outage with
power cables removed
from the generator
• Data collection and off-
line electrical
GAP 2 measurements
• Recommended after
16,000 hours of
operation
• Usually takes 2 days
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14. GAP 2 deliverables
Condition Assessment based on Diagnostic Tests
Residual Life Assessment by D-map Method
May include GAP1 deliverables
Schedule for GAP3, GAP4 and GAP1
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15. • During outage on
partially disassembled
generator (end-covers
and inspection windows
removed)
GAP 3 • Inspection and tests to
the extent possible
• Recommended after
32,000 hours of
operation
• Usually takes 3-5 days
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16. GAP 3 deliverables
Visual Examination and inspection
Residual Life based on Stress Analysis
May include GAP1 & GAP2 deliverables
Schedule for GAP4, GAP1 and GAP2
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17. • During outage on fully
disassembled generator
with rotor threaded-out
• Inspection and
appropriate testing
GAP 4 • Recommended after
64,000 hours of
operation
• Usually takes 10-12
days
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18. GAP 4 deliverables
Residual Life based on Stress Analysis
Condition Assessment and Index
Risk Assessment and Index
may include GAP1, GAP2 & GAP3 deliverables
Schedule for GAP1, GAP2 and GAP3
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20. Life Cycle Concept
Value to Customer
through Maintenance
Optimized Maintenance Line
} Continuous
Upgrading/
Replacement
Maintenance
Overhaul
Aging
Repair
Upgrade and Time
Warranty Period Modernization Period Replacement & Recycle Period
Maintenance Period
Customer Project Lifecycle
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22. Strength
Stress
Calculated
calculated
from GAP1
from GAP1
Strength
Calculated
Stress
from GAP2
calculated
from GAP2
Strength
Calculated
from GAP3
Stress
calculated
from GAP3
Strength
Stress Calculated
calculated from GAP4
from GAP4
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23. uncertainty
Strength
Strength/stress
Stress
Time
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25. Failure statistics
Detection during Normal Operation
11%
5% Bearing
3% 37% Winding
6%
Rotor
Shaft/coupling
Brushes/slipring
5%
External devices
Not specified
33%
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26. Failure statistics
Detection during maintenance or test
10%
4%
Bearing
7%
Winding
Rotor
Shaft/coupling
8% Brushes/slipring
2% External devices
8% Not specified
61%
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27. Failure Statistics Conclusion
• Bearings fail frequently
• Windings also share a significant failure rate
• Very few winding failures are detected
in maintenance (8.3%) as against the
total failure of 33% in normal operation
• This indicates poor insulation problems
detection technique
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