10-joe tuseck connell wagner
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High Voltage Plant Asset Management
Joe Tusek
Connell Wagner
tusekj@conwag.com
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HV Asset Management Environment
• Disaggregation
• OEM’s
• Aging workforce
• Staff churn
• Production
• 415V -> 3.3kV -> 11kV -> 22-33kV -> -----
• Profit
• OH&S
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High voltage equipment is complex
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What is special about HV Assets?
• New knowledge - not inferable from LV.
• New service providers.
• Special considerations in contracts.
• Wide variation in understanding, ability and degree of self
interest amongst practitioners.
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Results of Poor Asset Management
• Premature or late equipment refurbishment or replacement.
• Under-testing or inappropriate testing -> No useful CM data.
• Over-testing - > damage.
• Unquantified risk (bounded by Worst Case Scenario).
• Unsafe plant.
• Damaged plant.
• Misapplication of capital
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CIGRE - General aging and failure model
Age
Normal aging curve Aging curve withaccelerated aging or fault
Failure
Strength
Stress
New OldAge
Normal aging curve Aging curve withaccelerated aging or fault
Failure
Strength
Stress
New Old
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Characteristics of HV plant failure
Motors
• Apart from infant mortality, most electrical degradation tends to
evolve slowly unless damage occurs -> years.
Transformers
• Most classes of failure can be picked up by DGA taken onceevery quarter for critical plant.
Cables
• Very dependant on failure mechanism but typically within days or
weeks.
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HV Failures
• There are a number of failure mechanisms that can lead to
sudden unexpected failure.
• Cost of preventing all failures is very high.
• A good CM system will limit the likelihood of failure but will
not guarantee freedom from failure.
• On-line systems are good but many stories of after the fact
identification of problems.
• What can help?
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Standards – are a minimum
• Committee system - representatives from OEM’s,
academics and recognised specialists.
• Minimum agreed test levels and pass criteria.
• Agreed compromise on quality, Standards only contain
what OEM’s can deliverable. • Adherence to Standards is a risk management tool.
Not perfect but substantially better than just using opinion.
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Why Are Standards Not Followed
• Ignorance
• Bad advice
• Expediency
• Fear
• Self interest
• Good times can bring about practices that have a
significant negative impact on the bottom line
when times are tough.
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Plant Life Cycle
Specification
Design
Construction
Factory Testing
Delivery
Installation
Commissioning
Acceptance
Operation
Maintenance
Refurbishment/LifeExtension
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Understanding HV System Degradation
Failure of HV systems is initiated through,
• Electrical
• Mechanical• Thermal
• Environmental/Chemical
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Electrical Degradation and Failure
Overstressing of insulating system by external stressesor failure of voltage grading systems.
Partial discharge due to insulating system being
overstressing or contaminated.
Partial discharge due to delamination of compositeinsulating systems.
Tracking – conducting paths often carbonised.
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Partial Discharge
• Is a breakdown of theinsulation that does not
bridge the primary
insulation
• Corona is a partial breakdown in gas.
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Typical Partial Discharge Results
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Electrical Degradation and Failure
Thermal instability of the dielectric in the insulating
system.
Tracking across dielectric surfaces.
Short circuits between windings and winding
components. Damage to bearings from currents.
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Mechanical sources of degradation
• Short circuit currents and vibration
• Age related loss of strength
• Cycling, creep and fatigue
• Bearings
• Lubricating systems
• Vibration or resonance
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Tank
HV
windingLV
windingCore
Radial movement/translation
Tank
HV
windingLV
windingCore
Axial Movement
Tank
HV
windingLV
windingCore
Skewing of the winding
Tank
HV
windingLV
windingCore
Partial Radial Movement (Buckling)
Tank
HV
windingLV
windingCore
Collapsed winding
Top View - (Hoop) buckling
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Thermal
• Overheating of contacts/ connections/ joint
• Thermal ageing of components
• Failure of cooling systems
• Ineffective maintenance of cooling system efficiencies
• Ineffective maintenance of cooling medium condition (eg
insulating oil in transformers)
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Environmental
• Oxidation• Hydrolysis
• Corrosion
• Contamination
– external• gasses, particles, acidic or basic substances
• lubrication, cooling or process.
– internal
• ageing products, acids and ozone.
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Insulation Resistance (IR)/ Polarisation Index (PI)
• Measure the DC resistance of insulation
• Very temperature and humidity dependant.
• Will show up contamination and moisture
ingress.
• Polarisation Index is the ratio of the 10
minute to the 1 minute IR, 2.0
• Often is translated to fixed temperature, but
what is the starting temperature?
I
V
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Insulation Resistance (IR)/ Polarisation Index (PI)
• DC tests generally result is stress distribution that isdifferent from AC operation.
– Depending on the voltage levels to be used, this mayimpact on interpreting or determine how and to what
level the test is performed.• Generally discouraged and misinterpreted for XLPEcables, voltages of <0.3Un for CM are not a problem.
• VLF cable test relies on stress be representative at 0.1Hz.
• VLF test is intended to fail defective cables.
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Insulation Resistance
• Typical IR Results at 10 minutes & 20°C
• HV Transformer = >500 M
• HV Motor = >1000 M
• HV Paper Lead Cable = >100 M
• HV XLPE Cable = >10,000 M
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DC Ramp Test
• Voltage is raised slowly and current is plotted against voltage,i.e. resistance trajectory.
• Generally applied to stators and indicates presence of
damaged or weak ground wall insulation.
• Less informative than PD test although much cheaper toperform and uses portable equipment.
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Winding Resistance / Circuit Resistance
• Measures complete circuit resistance
• Applied to motors, switchgear, cables and transformers.
• Generally 4 - terminal measurement.
• Temperature correction required for comparison to
measurements taken on other occasions.
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Transformer - Circuit resistance results
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Some other transformer tests
• Applied Test
• Induced Test
• Ratio
• Excitation current
• Leakage impedance
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• DDF tests is sometimes referred to as Doble Tests.
Dielectric Dissipation Factor
Measure of the losses in the insulation,
• electronic and ionic conductivity
• dipole orientation
• space charge and interfacial polarisation
• partial discharge
• corona
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DDF in 3.3kV motors
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DDF in 11kV motors
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Partial Discharge in 11kV Motor
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Dissolved Gas Analysis (DGA)
• Measures gases in oil
• Different gasses and combinations
are indicative.
• Provides historical as well as current
information.• Cheap.
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DGA detects
arcing
overheating
moisture ageing
paper or metal involvement in degradation
need for oil reclamation
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Furan Analysis / Degree of Polymerisation (DP)
• DP is the average length of the molecular chain that makes upthe paper
• new ~1200, end of life ~ 200
• Furans DP
• Furan test is non-invasive, relatively cheap, but less accurate.
» Typical large transformer can have over a fewtons of paper and over 200kg of water trappedin the paper and pressboard insulation.
» The insulating oil contains only a small fractionof the water in the insulating system.
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Thermography
• Simply one of the most cost effective risk control tools
available to industry.
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Ring Flux and ELCID
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Ultrasonic or Acoustic Emission Detection
• Primarily a locating test
• Can detect
– Corona
– PD’s
– mechanical vibrations
– leaks
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Frequency Response Analysis
• A transfer function or impedance function that
represents the geometric
and physical parameters of
a transformer winding and
its insulation.
• Sensitive to winding
deformation
102
103
104
105
-85
-80
-75
-70
-65
-60
-55
-50
-45
-40
-35
Ref
Modified
104
105
-85
-80
-75
-70
-65
-60
-55
-50
-45
-40
Ref
Modified
104.87
104. 88
104. 89
-69. 5
-6 9
-68. 5
-6 8
-67. 5
-6 7
-66. 5
-6 6
-65. 5
-6 5
Ref
Mo difie d
104. 58
104.59
104. 6
-45
-44
-43
-42
-41
-40
-39
Re f
Modifie d
10
4. 21
10
4. 22
10
4. 23
10
4. 24
10
4. 25
10
4. 26
10
4. 27
10
4. 28
-66
-65
-64
-63
-62
-61
Re f
Modifie d
103.74
103. 75
103. 76
103.77
-67 .5
-67
-66 .5
-66
-65 .5
-65
-64 .5
-64
-63 .5
Ref
Modi f i ed
104.86
1 04.87
-89
-88. 5
-88
-87. 5
-87
-86. 5
-86
-85. 5
Re f
Modi f i ed
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Equivalent Paper Moisture
DielectricSpectroscopy
PolarisationDepolarisationCurrent
% paper
moisture
Recovery
Voltage Method
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Transformer CM Options
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On- line systems
• Not as good as off-line tests in most cases.• Are good for managing the time towards final failure or end
of economic life.
• Best suited to critical plant items or those with known
advanced active degradation.
• May need expertise in interpretation.
• Generally far less reliable than the plant being measured.
• Relatively expensive as often need to installed in many
locations.
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Database Solutions
Pro’s – Very attractive
– Benefit of large population
– No requirement for internal expertise
Con’s – Significant uniqueness in plant with components made globally.
– Statistical notion of population is not helpful when you only a
few plant items.
– Suspend own judgement.
Decision making can be based on rest of the population and not on
your plant or conditions.
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Visual Inspection the ugly duckling of CM?
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Minimum Electrical CM
HV Motor • Thermography + HV Tests
• MCSA and online measurements
Transformer • DGA + Thermography
• HV Test
Switchgear • Thermography + insulation and circuit resistance + HV
tests
• Timing checks
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Where is help available?
• Specialists service providers
• OEM’s
• Consultants, in-house or external
• Universities
• Standards
• Technical Organisations
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