Crist Power Plant Case Study: Planning for a Maintenance Outage

1
Crist Power Plant Case StudyPlanning for a
Maintenance Outage

• By Inyang Akpan, Nana Ayensu, Kyla Grigg, Kathy
  Miu

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Goal To produce the most return on investment by
making the turbine-generator units work for many
more years Problem The current Turbine
Generator is 32 years old and is vibrating
excessively

• Alternatives to be considered
• New Generator
• Repair or Replace Rotor
• Replace Retaining Rings
• Replace Stator Bars

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Company Values and Priorities

• Cost
• Major Source of Revenue
• 36,000 per day ? 6.6 MILLION PER YEAR
• Surplus Electricity
• Generates 25-50 BILLION PER YEAR
• Increased Competition
• Deregulation
• Pressure on manufacturing companies to generate
  electricity
• Falling Coal Prices
• Increasing competitiveness of Unit 4
• Failure
• Loss of direct revenue
• Loss of competitive edge
• Loss of future revenue
• Loss of jobs

MUCH AT STAKE
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Comparing Alternatives

• DO NOTHING
• Irresponsible
• Could damage itself and other machinery
• Could injure employees
• NEW GENERATOR
• Most expensive option
• No guarantee of compatibility
• Expert Choice Never top choice
• ROTOR
• Problems caused by misalignment and bearing
  looseness.
• Consultant says Repair Rotor
• Expert Choice says New Rotor
• Inconsistency ? Uncertainty
• NEW RETAINING RINGS
• Only address efficiency issues
• Not necessary for the generator to be
  operational.

X
X
X
X
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Stator Bars

• Stator bars consist of copper windings that run
  along its length and are insulated using asphalt
  insulation.
• Windings and coatings have failed in earlier
  testing
• Weak coil was repaired
• Strong concern about the insulations ability to
  last till planned outage
• Risk in waiting to see if the insulation fails at
  the top layers or the bottom, because the latter
  would lead to a low percentage of repair success.
  Not replacing the bars and having this happen
  would be a failure in our judgment.
• Increased hydrogen content to maintain the
  current bars at a constant temperature

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Which Stator Bars should be used?1960s or new?

• Use Spare Stator Bars?
• Manufactured in 1960
• Perfectly compatible with the unit
• Advantage the parts are readily available
• Cost 300,000 less than new custom-made bars
• Use New Custom-Made Bars?
• More reliable, accurate, adequate
• Longer lasting
• More security in long run

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Considering Risk Alone

• Comparing Bars
• Keeping Rotor Repair constant
• Option 1 2
• Keeping Spare Rotor constant
• Option 3 4

• In all cases
• Solution involving New Stator Bars is rated
  higher
• ? the Ideal solution

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Risk and Cost Weighted Equally
? Options 4 2 respectively better than 3 1
Cost Rated Higher than Risk
X
? Options 4 2 respectively better than 3 2
Risk Weighted Higher than Cost
? Options 4 3 respectively better than 2 1
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CONCLUSION

• Replacing Stator Bars is Essential
• Buying New Stator Bars is the best choice