High Voltage Plant Asset Management

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High Voltage Plant Asset Management

• Joe Tusek
• Connell Wagner
• tusekj_at_conwag.com

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HV Asset Management Environment

• Disaggregation
• OEMs
• Aging workforce
• Staff churn
• Production
• 415V -gt 3.3kV -gt 11kV -gt 22-33kV -gt -----
• Profit
• OHS

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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 -gt No
  useful CM data.
• Over-testing - gt 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
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Characteristics of HV plant failure

• Motors
• Apart from infant mortality, most electrical
  degradation tends to evolve slowly unless damage
  occurs -gt years.
• Transformers
• Most classes of failure can be picked up by DGA
  taken once every 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 OEMs,
  academics and recognised specialists.
• Minimum agreed test levels and pass criteria.
• Agreed compromise on quality, Standards only
  contain what OEMs 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/Life Extension

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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
  stresses or failure of voltage grading systems.
• Partial discharge due to insulating system
  being overstressing or contaminated.
• Partial discharge due to delamination of
  composite insulating systems.
• Tracking conducting paths often carbonised.

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Partial Discharge

• Is a breakdown of the insulation that does not
  bridge the primary insulation
• Corona is a partial break down 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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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?

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Insulation Resistance (IR)/ Polarisation Index
(PI)

• DC tests generally result is stress distribution
  that is different from AC operation.
• Depending on the voltage levels to be used, this
  may impact on interpreting or determine how and
  to what level the test is performed.
• Generally discouraged and misinterpreted for XLPE
  cables, voltages of lt0.3Un 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 20C
• HV Transformer gt500 M ?
• HV Motor gt1000 M?
• HV Paper Lead Cable gt100 M?
• HV XLPE Cable gt10,000 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 to perform 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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Dielectric Dissipation Factor

• DDF tests is sometimes referred to as Doble
  Tests.

• 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 up the 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 few
  tons of paper and over 200kg of water trapped in
  the paper and pressboard insulation.
• The insulating oil contains only a small fraction
  of 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
• PDs
• 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

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Equivalent Paper Moisture
Dielectric Spectroscopy
paper moisture
Polarisation Depolarisation Current
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

• Pros
• Very attractive
• Benefit of large population
• No requirement for internal expertise
• Cons
• 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
• OEMs
• Consultants, in-house or external
• Universities
• Standards
• Technical Organisations