Frame 6 Users Group MeetingJune 14 – 17, 2010San Antonio, TX
National Electric CoilW. Howard Moudy
Director of Service Management
Effectively Planning, Performing and Documenting Electric Generator
Maintenance and Major Overhauls
Slide 2
Usual Owner Primary Concerns
• Reliability • Cost• Time (schedule)• Quality
Slide 3
Today’s Discussion• Audience Participation is encouraged
(and perhaps rewarded)
• Review – Common Air Cooled Generator Concerns
• Review of Generator Maintenance Practices
• Quasi technical / commercial discussion of Planning, Performing and Documenting Generator Outages
Slide 4
Planning, Performing & Documenting Generator Outages– Create a “Bull Pen” – Qualified Vendors– Expand your vendor options – Data Collection– Establish Blanket T&C’s with key vendors– Become knowledgeable about your machine – “Go to
School”– Develop Performance based specifications– Consider improvements in maintenance practices– Effectively plan and execute outages– Be prepared for emergencies– Document and properly trend generator information
Slide 5
Review - Common Air Cooled Generator Concerns • Stator & Rotor
– Contamination– Insulation Deterioration
• Stator– PD / Corona– Slot Wedge Looseness– Core Inter Laminar Insulation Integrity– Dusting / Greasing– End Winding Resonance / Looseness– Key Bar Rattle– Spark Erosion (units without – slot side ripple filler)
• Rotor– Top Turn Elongation– End Winding Blocking Looseness– Insulation Migration / Shorted Turns– Top Turn Cracking – Pole to Pole Cracking– Main Lead Cracking
Slide 6
It is a simple factGenerators Fail
Effective Maintenance is necessary
or Rewinds will also be necessary
Slide 7
Maintenance Review• Standard Equipment Monitoring• Visual Inspection• Stator – Electrical Testing• Stator – Special Testing• Rotor – Electrical Testing• Rotor – Special Testing
Slide 8
Standard Equipment Monitoring
ContinuousThermal sensitivity, loose component, imminent failure
Vibration
Six MonthsContamination, bearing babbit deterioration
Lube Oil Analysis
ContinuousFailure of ground insulation
Ground
ContinuousOver-temperature operation
Temperature
FrequencyPurpose/FindingsMonitoring Activity
Slide 9
Visual Inspection
Before every minor and major outage to
help determine scope
Discoloration from overheating, loose or shifted blocks, arcing
Rotor
Major outage with the rotor out
Damaged iron, loose iron, discoloration,
foreign objects
Stator Core
Before every minor and major outage to
help determine scope
Dusting, greasing, oily, broken ties,
discoloration, foreign object damage
Stator Winding
FrequencyPurpose/FindingsMaintenance Activity
Slide 10
Visual Inspection –Borescope
• Less intrusive • Technology continues to improve
– Probes have been getting smaller to gain greater access in tighter areas
– Improved optics are yielding improved clarity• While it is a very beneficial tool and can provide
valuable insight, there are limitations to what can be adequately seen and evaluated. Data interpretation and conclusions must be done by experienced personnel.
Slide 11
Electrical Tests - Stator
Major OutageDetermines insulation condition / strength
D.C. Ramp
Major OutageProof test to “stress”insulation
Hipot
Minor and Major Outage
Integrity of brazed connections
Winding Resistance
Minor and Major Outage
Determines presence of contamination
Insulation Resistance or “Megger” with PI
FrequencyPurpose/FindingsMaintenance Activity
Slide 12
Specialty Tests
YearlyInsulation deterioration, coil tightness in slot
Partial Discharge
Major outageDetects resonant frequencies
Bump test
Major outageLoose wedgesWedge Tightness
After rewinds or core repair
Shorted laminationsCore Loop
Major outageShorted laminationsELCID – Electro-magnetic Core Imperfection
Detection
FrequencyPurpose/FindingsMaintenance Activity
Slide 13
Electrical Tests - Rotor
Minor and Major Outage
Determines presence of contamination
Insulation Resistance or “Megger” with PI
Minor and Major Outage
Integrity of brazed connections
Winding Resistance
Major OutageRotor shorted turns (stationary)
Pole Balance
YearlyRotor shorted turns (running)
Flux Probe
FrequencyPurpose/FindingsMaintenance Activity
Slide 14
Specialty Tests - Rotor
After major rotor work and Rewinds
Qualify rotor mechanically & electrically and dynamic balance
High Speed Balance
Major Outage and Rewinds
Detect cracks, corrosion and material deterioration
NDE – Retaining rings and other components
Rewind and based on past assessment
Forging Material Integrity
Boresonic Inspection
FrequencyPurpose/FindingsMaintenance Activity
Testing SummaryBE SURE ALL CIRCUITS ARE DE-ENERGIZED)
MAINTENANCE ACTIVITY SHOWS FREQUENCY Dielectric Absorption Winding cleanliness Major Outage Polarization Index (PI) Winding cleanliness/moisture Major and Minor Outage Cycles Power Factor Insulation integrity Major Outage Cycle Partial Discharge (PD) Coil tightness; insulation integrity On-line or Outage Cycle Megger Integrity of Insulation Major and Minor Outage Cycles Blackout Corona suppression integrity Rewind Resistance Integrity of joints and connections Major and Minor Outage Cycles Flux Probe Rotor winding shorts On-line, Rewind Rotor Impedance Rotor winding shorts Rewind Ground Fault Rotor Ground Continuous Split Voltage Location of rotor grounds As Needed Voltage Drop Presence of shorted turns Major Outage Cycle El Cid Integrity of stator core Major Outage Cycle Core Loop Integrity of stator core Major Outage Cycle Bolt Torque Stator core looseness Major Outage Cycle Ultrasonic Cracks, defects in forgings Major Outage Cycle Temperature Monitoring Normal/abnormal operation On-line and Continuous Dye Penetrant Cracks, defects in forgings Major Outage Cycle Eddy Current Cracks, defects in forgings Major Outage Cycle Magnetic Particle Cracks, defects in forgings Major Outage Cycle Wedge Mapping Stator winding tightness Major Outage Cycle Hi-Pot Insulation integrity Major Outage Cycle Vibration Rotor imbalance Monthly and On-line Visual Inspection Normal/Abnormal Performance As Available Oil Chemistry and Count Bearing oil contamination Twice Yearly
Slide 16
Outages• Planning & Performing
– Proactive Efforts – Timing (spring Fall ) – Outage Specific Efforts
• Four Primary Types of Outages• Documentation
– How?– What?– Trending
Slide 17
Planning and Performing• Proactive Efforts
– Creating a qualified “Bull Pen” (vendor selection)» Data Collection» Blanket Terms and Conditions
– “Go to School”– Scope of Work– Specifications– Basic Emergency Information
• Timing (Spring - Fall ?) • Outage Specific Efforts
– Division of Responsibilities– Safety First– User / Vendor Cooperative Environment– Progress Monitoring– Vendor Factory Surveillance– Contingency Planning– Spare Components - Coils
Slide 18
Creating a Qualified Bull Pen
• Baseball teams (users) have Bull Pens for their Pitchers (vendors). Shouldn't we?
• How can you be sure Vendors have the “stuff” and are ready to pitch?
• What are some of the key considerations?
Slide 19
Vendor Selection Criteria• Company Experience &
Relations With Past Customers
• Safety Program & Record• Cost / Value• Engineering Resources• Facility Resources
– High Speed Balance Pit– Machining – Cleanliness– Lifting Capacity– In House Technology
• Capacity Capabilities– Shop Loading / Capacity– Performance to Schedule
• Coil Supply, Repair, and Manufacturing– Experience– Demonstrated Reliability– Representative sample vs.
100% verification– Delivery
• Personnel Resources– Background– Experience– Depth
• QA/QC Programs– Documentation and Archiving– Certification– In Process checks
Slide 20
Accurate Winding Data Is Essential !
Picture
Slide 21
Terms and Conditions• A necessary evil for everyone in business
today• If handled before generator problems
arise, the focus remains on the generator problem and not the T&C issues.
• Companies need Vendors & Vendors need business! Without a prior commercial understanding, they may not get together.
Slide 22
Blanket Terms & Conditions
• The process usually takes an extended period to resolve
• Should emergencies arise, an absence of T&C’s, with qualified vendors, can cause major delays and increased cost
Slide 23
Blanket Terms & Conditions cont.
• Four most common T&C sticking points:
• Indemnification• Limitation of Liability• Warranty• Termination
Slide 24
“Go to School”• Know your machine
and it’s specific issues• Sources of Information
– Past Outage Reports– Trended Information– Other Users – Users Groups– Vendors– Technical Papers– Exhibitions– IEEE– Web Sites
Slide 25
IGTC Forum
Slide 26
Specifications• The purpose of the specification is to clearly
define the expectations and requirements for the project.
• The best time to develop specifications is before you need them!
• Overall Philosophy?• Process vs. Performance Specification• Clearly State Expectations and Requirements
Slide 27
Primary Generator Specifications
• Test & Inspect• Stator Rewind• Stator Coil Manufacturing• Rotor Rewind
Slide 28
Test & Inspect Specification Elements
• Past outage findings & recommendations• Identify specific concerns• Clarify the level of disassembly• Testing
• Methods & Equipment• Levels• General Protocols
• Required Documentation
Slide 29
Rewind Specification Elements
• Stator Core Iron Evaluation• Rotor Retaining Ring Evaluation• Key Elements for Quality Stator Coils• Stator Coil Side Packing • Rotor Specification Elements• Stator Testing Program• Division of Responsibilities• Vendor to Attach Project Technical Proposal
Slide 30
Stator Core Iron Evaluation ELCID Test
• Excite core to only 4% of rated flux density
• Search coil on trolley detects interlaminar circulating currents
• 100 milliamp action threshold
• Uses 110 vac – easy to set up and use
• 3 Tests - Before Stripping, After Stripping, and After Wedges Installed
Slide 31
.
Stator Core Iron Evaluation cont.
20.1°C
28.2°C
22
24
26
28
AR01: 111.3°CAR02: 78.4°C
AR03: 33.0°C
Loop Test
• Test creates near full flux of the core and is viewed with a thermo graphic camera
• Requires high voltage power supply with adequate current
• Normally a one hour test but significant setup is required
Slide 32
Stator Coil Side Packing• Side packing is a critical
component to the corona protection system and to preventing vibration and coil abrasion
• Flat side Filler does not maintain side pressure on the coil
• Even if initially installed tight, insulation shrinkage, can create gaps and increase the potential for slot discharge
• Ripple side packing keeps constant pressure on the coil to minimize vibration and the potential for abrasion.
Slide 33
Stator Testing Program• Should be a coordinated testing program from
coil final test through in process testing to final machine acceptance testing
• Final testing should at least include:– Megger & PI (PI of 2 or greater to HiPot)– AC or DC HiPot (2E + 1,000) for AC
• DC most common, convenient, and easiest to perform• Most common AC level is 2E + 1= AC• For DC level multiply by 1.7
– Per phase Resistance Test (balanced?)
Slide 34
Stator Testing Program Cont.
Bump Testing• Checks for local
and global natural frequencies near the 120 hz double operating frequency
• End winding can be stiffened after test results
Picture
Slide 35
Key Elements for Quality Stator Coils
• Mica Based, Epoxy Resin Impregnated Insulation System
• Class F (thermal rating) Insulation System• Qualified Insulation System
• IEEE 1043 Voltage Endurance Testing
• Design Uprate?• Design that Minimizes Losses
• Strand Losses – optimize strand thickness• Circulating Current Losses – maximize
transposition/roebel
Slide 36
Strand Size/Arrangement
affects Losses• I2R Losses
– inversely proportional to copper area
• Strand/Eddy Current Losses– proportional to strand
thickness• Circulating Current Losses
– voltage potential differences between strands
• Spec should state losses are to be minimized
Key Elements for Quality Stator Coils cont.
Slide 37
Key Elements for Quality Stator Coils Cont.
• Volts Per Mil state the maximum allowable “insulation stress” or VPM
• Maximize Copper
Original Winding New Winding
Same
Size Slot
More
Copper
Less, But Stronger
Insulation
Slide 38
Key Elements for Quality Stator Coils Cont.
• Superior Semi-conductive Slot Treatment and Gradient Treatment in the End Turns
• Process to insure and verify consistent size and shape
• 100% Final Factory Test – AC Hipot [(2E + 1) X 1.3]– Power Factor Tip up
• Set average value• Per coil target [less than 0.6% tip up]
– Verify Slot Corona Treatment Resistivity
Slide 39
Key Elements for Quality Stator Coils Cont.
Winding Fit-up Inspections
• Cross Over Clearance• Coil Drop• Proper lead alignment
is critical to final brazing operations & good wind ability of coils
• End Turn Clearance
Slide 40
Key Elements for Quality Stator Coils Cont.
Coil Surface Resistivity
• Acceptable level ranges from 1,000 to 20,000 ohms/square
Picture
Slide 41
Rotor Specification Elements• Reused Copper
– Hardness Check– Cleaning and Reshaping Protocol
• New Copper – CDA 107 Oxygen-Free Silver-Bearing
Medium Hard 80-85 F – Qualified Brazing program– 100% Braze Inspection– Edge bend or Corner - build consistency
verification
Slide 42
Rotor Retaining Ring Evaluation
• Magnetic 4340 steel retaining ring
• Inspected by dye penetrant
• Cracks due to High Stress from over-speed and corrosion
Slide 43
Rotor Retaining Ring Evaluation
• 18.5 retaining rings (non-magnetic) are susceptible to SCC and should be inspected or replaced
• Inspected by Zyglo - NDT
Slide 44
Rotor Specification Elements Cont.High Speed Balance
• Recommended after a rewind
• Verifies balance and overall “operability” in running condition
• Over-speed verifies mechanical integrity of the rotor
• Running electrical testing verifies the electrical integrity of the rotor through out the speed range.
Slide 45
Division of Responsibilities ListItem Plant VendorCrane XCrane Inspection XCrane Operator XProject Office XPhone Lines (2) XEthernet, H.S. Internet Line XScaffolding X
Shop Air X220V; 50 Amp Electrical Distribution Panel XLoop Test Power; 2300 V 200A XLoop Test Cable to Breaker XPort-o-Johns XWash Room Facilities X
Slide 46
Four Primary Types of Outages
• Minor – General Maintenance / Rotor In• Major – Rotor Out• Life Extension – Rewind / Replace• Forced Outage
Slide 47
Minor Outages(rotor in)
• Establish and follow your maintenance plan
• Review past outage reports, especially findings and recommendations
• Consider extra work contingencies• Division of responsibilities with vendors• Cooperatively interact with vendors
Slide 48
Major Outages(Rotor Out)
• Get started early!• Start reviewing OEM and other vendor
recommendations as well as past outage reports.
• Before finalizing specifications, interact with vendors to be sure all scope options and solution options have been considered.
• Will FME be required? If so, program / process? Who should have access?
Slide 49
Major Outages cont.(Rotor Out)
• Establish hard milestone interaction points with vendor(s) to review findings and limit wasted time in acting upon issues needing immediate intention.
• Review special tools inventory and condition. Offer inspection by vendor.
• Crane condition and certification?• Rotor support and protection based upon
scope? • Rotor Shipping preparation – Permits? Holiday
restrictions?
Slide 50
Major Outages cont.(Rotor Out)
• Vendor site orientation– Safety requirements– Coordination & Cooperation with other vendors and work being done
at the same time– Lay down plan– Site support resources
• Vendor – Plant contact points• Mobilization plan• Other – this is only a partial list, there many things
along this line to consider; as well as unique company, plant, unit, and project specific items.
Slide 51
Replacement / Rewind Considerations
• Replacement– Not as simple as it may seem unless
swapping identical units– Logistical concerns – Transportation & Lifting– Connecting to BOP – Cooling, Lubrication,
Controls & Monitoring– Has the root case of the problem been
addressed by the replacement?
Slide 52
Rewind Considerations Newer vs. Older
Newer Vintage• Rewind Cause – normally
one or a combination of:– Design concern– Material concern– Operational concern
• What is the root cause? – Specific – not a symptom– How can it best be
corrected• How can long-term
reliable life best be achieved?
Older Vintage• Rewind Cause – normally
age deterioration of components. Possibly machine characteristic change to support system needs.
• Were there any major technical deficiencies in the machine?
• Is an Up-Rate desirable?• Incorporation of new
materials and technologies
Slide 53
Other Rewind Outage Planning Considerations
• Safety Expectations• FME?
– Level– Process for access– Who can enter
• Division of Responsibilities is crucial especially:– Utility requirements– Lifting
• Vendor coordination on the generation deck • Lay-down space allotment – Plant Overhead
Drawing
Slide 54
Forced / Emergency Outages• No one plans to have a forced outage, but
they happen.• Total Cost Impact ???
– Expediting– Lost Generation– Replacement Power– Contract Penalties
• Scheduled rewinds can dramatically reduce total costs if properly planned and implemented
Slide 55
Initial Emergency Communication
• Name plate information• Digital pictures• Nature of failure• Location of failure• Plant Contact names,
phone numbers and location
• Machine design data• Expectations
Slide 56
Outage Contingency Planning
• Back up’s to critical equipment – induction heating / brazing, test set’s
• Specialty Tools on hand and in good condition
• Spares – on hand and qualified for use– Extra Consumables – resins, tapes – Emphasis on Long lead items such as
Brushless Exciter Fuses and Diodes– Spare Coils?
Slide 57
Spare Bars
These spare bars may sit here on this shelf for 30 years and never be used. Then again, they may be needed next week.
Picture
Slide 58
Documentation and Trending
• Outage Reports– Should be kept together, organized by date,
so they can be easily referenced – Electronic and paper files– Track recommendations, their completion and
the details of completion (process, date)– Test Results – File by date
• Normalize temperature and humidity
Slide 59
Documentation and Trending cont.
• Trended Data– Electrical Test – normalized for temperature
and humidity– Megger / Polarization Index– Polarization Index– Impedance– Winding Resistance– Hi Pot / DC Ramp Test
– Flux Probe – Other pertinent electrical tests also perhaps
mechanical readings and findings
Slide 60
Documentation and Trending cont.
• Documented information provides insight about where we have been and where we are.
• Trended information provides insight about where we are going.
Slide 61
Planning, Performing & Documenting Generator Outages– Create a “Bull Pen” – Qualified Vendors– Expand your vendor options – Data Collection– Establish Blanket T&C’s with key vendors– Become knowledgeable about your machine – “Go to
School”– Develop Performance based specifications– Consider improvements in maintenance practices– Effectively plan and execute outages– Be prepared for emergencies– Document and properly trend generator information
Top Related