10-joe tuseck connell wagner

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High Voltage Plant Asset Management

Joe Tusek

Connell Wagner

[email protected]



HV Asset Management Environment

• Disaggregation

• OEM’s

• Aging workforce

• Staff churn

• Production

• 415V -> 3.3kV -> 11kV -> 22-33kV -> -----

• Profit

• OH&S



High voltage equipment is complex



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.



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



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



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.



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?



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.



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.



Plant Life Cycle

Specification

Design

Construction

Factory Testing

Delivery

Installation

Commissioning

Acceptance

Operation

Maintenance

Refurbishment/LifeExtension



Understanding HV System Degradation

Failure of HV systems is initiated through,

• Electrical

• Mechanical• Thermal

• Environmental/Chemical



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.



Partial Discharge

• Is a breakdown of theinsulation that does not

bridge the primary

insulation

• Corona is a partial breakdown in gas.



Typical Partial Discharge Results



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.



Mechanical sources of degradation

• Short circuit currents and vibration

• Age related loss of strength

• Cycling, creep and fatigue

• Bearings

• Lubricating systems

• Vibration or resonance



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



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)



Environmental

• Oxidation• Hydrolysis

• Corrosion

• Contamination

– external• gasses, particles, acidic or basic substances

• lubrication, cooling or process.

– internal

• ageing products, acids and ozone.



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



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.



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



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.



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.



Transformer - Circuit resistance results



Some other transformer tests

• Applied Test

• Induced Test

• Ratio

• Excitation current

• Leakage impedance



• 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



DDF in 3.3kV motors



DDF in 11kV motors



Partial Discharge in 11kV Motor



Dissolved Gas Analysis (DGA)

• Measures gases in oil

• Different gasses and combinations

are indicative.

• Provides historical as well as current

information.• Cheap.



DGA detects

arcing

overheating

moisture ageing

paper or metal involvement in degradation

need for oil reclamation



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.



Thermography

• Simply one of the most cost effective risk control tools

available to industry.



Ring Flux and ELCID



Ultrasonic or Acoustic Emission Detection

• Primarily a locating test

• Can detect

– Corona

– PD’s

– mechanical vibrations

– leaks



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



Equivalent Paper Moisture

DielectricSpectroscopy

PolarisationDepolarisationCurrent

% paper

moisture

Recovery

Voltage Method



Transformer CM Options



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.



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.



Visual Inspection the ugly duckling of CM?



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



Where is help available?

• Specialists service providers

• OEM’s

• Consultants, in-house or external

• Universities

• Standards

• Technical Organisations

10-joe tuseck connell wagner

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