2012 ARIPPA Technical Symposium Steam Turbine Generator Maintenance for Optimized Availability David Branton, CEO Turbine Generator Maintenance, Inc.

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