2012 arippa technical symposium steam turbine generator maintenance for optimized availability david...
TRANSCRIPT
2012 ARIPPA Technical Symposium
Steam Turbine Generator Maintenance for Optimized Availability
David Branton, CEO
Turbine Generator Maintenance, Inc.
Steam Turbine Generatorssome statistics and history
80% of all electricity in the world is generated by steam turbines driving electrical generators:
10,632 TWH [terrawatt (1012) hours] – World
3,244 TWH – U.S.
1,485 TWH – China (expected to be 6,560 TWh by 2030)
The first practical steam turbine generator was designed and built by Sir Charles Parsons in 1884 and generated 7.5 MW. Generation principles remain the same.
GE’s first production steam turbine generator was introduced in 1901 and was rated at 500 KW; just two years later a 5000 KW unit went into commercial service for Commonwealth Edison.
Designing a Maintenance Plan
Qualitative Tools
Running Assessments
Periodic Minor Inspections
Objective Based Major Inspections
RequirementsMaximum unit availabilityNo unplanned outagesPredictable maintenance costs
OptionsMaximum efficiencyMaximum power output
The turbine and generator are the largest single investment in a fossil power plant and in many manufacturing and refining facilities. Proper maintenance is required to maintain efficiency (cost of production) and availability (the amount of time the unit is able to operate).
Efficiency issues Steam leakage into the environment Steam path steam leakage Blade/nozzle erosion/deposits
Availability issues Lubrication failures Steam path failures
Control system malfunctions Protective device malfunctions
Maintenance Issues
Maintenance Planning
Maintenance planning considerations
Steam pressure/temperatures
Type of duty cycle
Speed of turbine and generator
Extraction, backpressure, condensing considerations
Over temperature/pressure operation
Environment of facility
Quality of water/steam
Expectations of plant
There is no “one size fits all” maintenance plan.
Maintenance Planning
Maintenance planning considerations Major inspections provide opportunities for availability and efficiency improvements
with minimum outage impact if planned properly.
Major Inspection outages can be better scheduled with qualitative rather than subjective data
Availability of the turbine and generator and reliability of critical auxiliariescan be optimized:
Periodic Running Assessments combined with data trending and analysis Periodic minor (3-5 day) outages to inspect critical areas for issues
A combination of Running Assessments and Focused Minor
Inspections can assure availability and optimize major inspections.
Turbine Generator MaintenanceOutage Cycle
Running AssessmentsCritical parameters
Vibration/Noise Turbine inlet temperature fluctuations Stage performanceSteam chemistryBearing temperaturesPedestal expansion/lubrication/cleanlinessElectrical system groundingMotor loading Gland system integrityAir in-leakageLubrication backup integrity Lubrication cleanlinessOverspeed protectionGenerator partial discharge and rotor flux probe
Data must be monitored, collected, trended, analyzed, and used for outage planning
Running Assessments - Vibration Trending
Running Assessments – Grounding Brushes
Turbine Availability issue
Running Assessments – Oil System Integrity
According to the International Association of Engineering Insurers
• The highest frequency of turbine generator failures in the 10 – 400 mw range has been lube oil incidents
Dirt and/water contamination Loss of oil pressure
Running Assessments – DC Backup
Turbine Availability issue
Running Assessments Generator Rotor Windings
Shorted Turns in Pole A - Coil 5, Pole B - Coils 6 and 7Magnetic Wedges in Coil 1 – note small signal
Minor Inspection Scopes
Bearing Inspections – every two yearsCritical inspections for availability
Standard Scope should include Coupling alignment checksDisassembly and inspection of thrust bearing - including total rotor travel and thrust clearanceDisassembly and inspection of journal bearings - including UT and LPT Oil system including the oil reservoir, pumps/motors, oil coolersMaintenance oil flushBackup oil system integrityTurbine shaft grounding maintenanceCheck and calibrate protective devices including overspeed, bearing temperatures and vibrationGenerator borescope and electrical tests
Minor Inspections – Bearing Inspections
Uneven wear Varnish deposits
Minor Inspection – Electrical Discharge through the Thrust Bearing
Minor Inspection Scopes
Valve inspections – every two yearsCritical inspections for safety, efficiency, and control
Standard Scope should include:
Disassemble, clean, and inspect steam side- Include all stop and control valves- Include all non return valves- Seat integrity and contact- Stem and stem seal integrity
Disassemble, clean and inspect control side Check valve set points and travels Perform protective systems inspections and calibration checks Perform borescope inspections of steam inlet/nozzle Perform generator borescope and maintenance tests
Minor Inspections – Valve Inspections
Minor Inspections – Valve InspectionsMinor Inspections – Valve InspectionsLP Governor valve seat damage
Proper planning can significantly reduce planned outage inspections.
Based on the turbine configuration, a major inspection can be completed in 2 – 6 weeks based on unit size.
The turbine-generator is almost always the critical path, and any generator maintenance/repair must be placed in the same outage window.
Factors critical to achieving minimum outage durations: Planning for the outage should begin after the last major inspection
and developed over a maintenance cycle of Running Assessments and Minor Inspections. Most turbine and generator replacement parts
can be sourced from non-OEM suppliers with less lead time.
Develop contingency repair plans – identify potential scopes of work, identify repair resources, and develop repair schedules.
Contract experienced turbine generator teams that understand the unit and have the skills and tools necessary to handle the anomalies and with minimum impact to the schedule.
Outage Implementation Major Inspections
Major Inspection Findings Averting Forced Outage
HP Turbine Nozzle box movement First stage rotating buckets Nozzle migration Turbine wheel corrosion
LP Turbine• Last row blade migration
Generator• Rotor winding short• Stator core overheating
Major Inspection – Steam PathHeat shield weld failure in stage 4
Major Inspection – Steam PathLocking pin failure in rotating stage 1
Major Inspection – Steam PathMissing seals
Major Inspection – Steam PathNozzle migration downstream
Major – Steam PathLast row blade migration
Downstream side Upstream side
Major Inspection – Steam PathCurtis stage severe damage
Steam Turbine Design Types
Advantages and Disadvantages – Reaction vs. Impulse
Reaction designed turbines start out at a higher efficiency – less leakage Impulse design turbines have fewer stages
Tip Leakage Root Leakage
Fig. C-F. Reinker, J.K., and Mason, P.B., Steam Turbines for Large Power Applications, GER-3646D, GE Power Systems, Schenectady, NY.
Major Inspection – Steam PathStage efficiency improvement
Major Inspection – Steam PathBoiler carryover
Major Inspection – Steam PathBoiler carryover
Major Inspection – Steam PackingExcessive clearances
Major Inspections – GeneratorStator and core
Major Inspection – GeneratorRotor winding
Major Inspection – Implementation
Outage duration for a major inspection can be optimized by:• Effective planning – contingency plan development, safety plan, quality plan• Team implementation – daily reporting and proactive management• Pre-Qualified personnel – professional, resumes, down to working level• Defined and organized tools
Steam turbine generators are rugged and with a comprehensive maintenance program can operate reliably.
Using proper assessment techniques and performing strategic minor inspections, Major Inspection intervals can be optimized and performed predictably and cost efficiently.
Proper operation is imperative to maintain the equipment performance but when anomalies occur, the potential impact must be assessed.
A tailored maintenance program can greatly reduce operating costs by maintaining efficiency, availability, and reliability.
A planned and well organized outage plan/team can assure on-time outage duration.
Conclusions