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8/21/2019 1 Borsi Life Cycle TR

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Institute of Electric Power Systems Schering Institute

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Introduction and Life Cycle Management ofTransformers

Prof. Dr.- Ing. habil. H. Borsi

Institute of Electric Power Systems, Division of High Voltage

Engineering

- Schering-Inst itut -

Leibniz Universitt Hannover

Germany


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INDEX

Life Cycle in HV Equipment

Quality Assurance

in

High Voltage Equipments


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SOCIALENVIROMENT

Social Influece

Quality

Enviroment

Legislation

TECHNOLOGICALENVIROMENT

Technological evolution

Kind of network

UTILITY FITTINGS

Asset Management Philosophy: Condition based, Risk based,..

AVAILABILITYRELIABILITY

COSTS


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Life Cycle ManagementSTARTS

during manufacturing

PLANIFICATION TECHNICAL SPEC. PROJECT


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Planification, Technical Spec., Project

Design, Manufacturing and

Acceptance Testing

Site Installation

Service Operation


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Acceptance Testing

Site Installation

Service Operation

Planif ication, Technical Spec., Project


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Site InstallationQuality Assurance:

- Design Review

- Manufacturing Inspections

- Factory Testing----------------------------

- On site Testing

Assembly and Commisioning:

- Site preparation- Transportation and assembly

- Commissioning

Service Operation


Acceptance Testing

Planification, Technical Spec.,Project


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- Strict and controled planning of manufacturing and acceptance testing of HV

Equipment.

- Complete Quality Assurance proccess of HV Equipment on a basis of

homogeneity and rigour. Each part of the proccess must maximize global

reliability.

- Integration and coordination of Quality Assurance proccess in the whole life

cycle of HV equipment.

Main Goals


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Design

Review

Manufacturing

InspectionsAcceptance

Testing

Supplier Qualification

Factory

Tests

Special

Tests

Quality Assurance

Comissioning

Tests


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Supplier Qualification

Quality Management:- Quality policy (real degree of implementation)

- Quality control plan (incoming materials and in- production)

- Traceability

Global Assessment of the factory and manufacturing

processes:

- General data, Incoming materials, sub-suppliers- Manufacturing processes, facilities condition, tools

- HV Testing Laboratory


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Design Review

- Internal design analysis(materials, dielectrics,

electrodynamics, thermal)

- Identification of weak points (design and

manufacturing) and design margins.

-Acceptance tests plan(rutine, type, specials)

- Fitting with functional requeriments


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Manufacturing Inspections

Detailed assessment of manufacturing proccesses:

- Check of incoming controls and material traceability.

- Warehouse management, facilities condition

- Manufacturing proccesses and technology assessment

- Check of in-production quality controls.

- Sub-suppliers management and control

- Maintenance and calibration of machinery, tools and sensors.


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Acceptance testing

Factory tests:

- Checks and tests to validate a correct design and

manufacturing

- Compliance with tests plan and standards

- Correct functionality and calibration of instruments

- Laboratory personnel qualification

On-site tests:

- Checks and tests to validate a correct transportation and

assembly

- Comparison with factory testing

- Initial fingerprint for predictive maintenance


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Transformers arekey equipmentfor power transmission and distribution

Power Transformers belong to the

most expensiveequipment of power networks

Power Transformers are

custom madeand not available as stock equipment


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FACTORY TESTS

-Turn ratio

- Windings resistance

- Insulation resistance

- Capacitance and tg delta

- Load losses and Zcc.

- No load losses -> before dielectric tests

- FQ and DGA oil analysis -> before dielectric tests

- OLTC tests

- Switching Impulse for 220kV trafos

- Lighting Impulse (HV, LV, Tertiary and Neutrals)

- Separate Source withstand voltage

- Long Duration Induced voltage with PD meassurement

- Short Duration Induced voltage with PD when Switching Impulse do not apply-No load losses -> after dielectric tests

- FQ and DGA oil analysis -> after dielectric tests

- FRA and FDS test


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- Insulation resistance

- Capacitance and tg delta (trafo and bushings)

- Excitation test

- Turn ratio

- Leakage reactance

- Windings resistance

- Conmutation dynamic resistance

- DGA oil analysis- FRA test

- FDS test

COMISSIONNING TESTS

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Definition of life time

the life time of a transformer is definedas the life time of its rigid insulation

system

The end of life time is defined by the reduction of the

mechanical strength by more than 50%

In general this is the case at DP-values < 200 ( - 75%)acc to IEEE C57.91-1995

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Failure Curve of Technical Equipment

TimeNew End of

Design Life

FailureRa

te Bathtub Curve

Transformers can fail any time in life cycle Most likely early in life or near the end of life

Due to high age and increase in load the risk for failure oftransformers in service is HIGH

The average expected life time for transformers isbetween 25 and 35 years

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Failure rates on Power

Transformers

windings

21%

tank

15%

core

2%

others

8%

tap changer

39%

bushings

15%

Most failures occur suddenly

The outage time often is very long

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Aging of transformer insulation

Thermal

Degradation

Electrical and

Dielectric

Degradation

Mechanical

Degradation

ChemicalDegradation

Resistive and magnetic losses, capacity

of the cooling system

Alterations of the insulating material due

to the electrical field

Vibrations, deposits out of pumps, fans,

gaskets,...

Oxygen out of the atmosphere (forbreathing type transformers) together

with catalysts leads to acidification, water

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Electrical causes

Local overstressing in the insulationcauses aging of the cellulose and the

insulation oil Acid generation and contamination in the oil

Water content increasing

Gas and sludge generation

Acceleration of the cellulose depolymerisation

Partial discharge or breakdown causes strong transient

overstressing

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Electromagnetic causes

High Current (e.g. due to short circuit in

network) generate high forces

Winding deformation

Paper insulation breakage in

particular in the aged places

Be careful for partial discharge and breakdown

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Dielectric causes

Aging of the cellulose causes breaks ofthe glucose chains (Depolymerisation)

Generation of: Water

Gas (CO, CO2)

Aldehyd groups (Alkaline)

Carboxyl groups (Organic acids)

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Thermal causes

Eddy current losses in the core

Ohm's losses in the coil

Variations in load lead to heating up and

cooling

Increasing the water content of insulationdue to breathing

Hot spot temperature (IEC 60354: Loading

Guide) has crucial influence on the li fe Span

of the transformer insulation

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Institute of Electric Power Systems

Schering Institute

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Chemical causes

Due to aging generates organic acids They attack in particular the paper

insulation

Metals such as copper, iron, aluminum and

zinc act additionally as catalysts Accelerated aging

Microstructure of

Paper with

NZ [mg/kg]0.05 (left)

0.1; 0.2;

0.3 (right)

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Aging of Insulation

Thermal aging

Electrical and dielectrical aging

Mechanical aging

Chemical Aging

Generation

of Water

Additional water is coming from outside (free breathing

transformers)

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Due to ageing the glucose ring chains of the

cellulose break (Depolymerisation) The result

Water

Gases (CO, CO2)

Aldehyd Groups (Alkaline)

Carboxyl Groups (organic acids)

Ageing of Paper

C O

C C

CH CH

O

H2COOH

H

OH

H

H

OH

CH CH

C O

H2

COOH

H

C C

OH

H

H

OH

H2O

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Aging Process

Heat and water accelerate the aging process

1

10

100

1000

0 1 2 3 4RelativeDepolymer

isationsgeschwindigkeit

Wassergehalt im Papier

80 C

100 C

120 C

[%]

Water Content in the Paper

RelativeVelocityofDepaolarization

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WATER IN THE TRANSFORMER

A temperature increase of 6 - 8C is doubling the

depolymerisation speed

A moisture increase of 1% is also doubling the

depolymerisation speed

4% moisture at 50C leads to a moisture content in the oil

of 50 ppm. Is the oil quickly cooled down (power failureduring winter), is it possible to have free water already at

20 C

With a too high moisture content, there is the risk of

bubble formation in the insulation at much lower hot spottemperatures as 140C as with dry insulation

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Possible Measurements

Oil Analysis DGA

Oil parameter

Furan analysis

DP Electrical Failures

Resistance test

Insulation resistance test

Ratio test

FRA (Frequency Response Analysis)

PD (Partial Discharge)

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Oil parameter(IEC 60422, VDE 0370-2) Color

Insignificant

General condition

Particle

Water content

Important parameter

Breakdown voltage Important parameter

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Oil parameterTan

Increasing with thermal stress

Interfacial tension

Aging of oil, degradation product Acidity (total acid number)

Acidity decreases the strength of paper

Inhibitor content

Consumption is a measure for aging

Density, Flash Point, Viscosity

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DGA (Dissolved Gas Analysis) Nitrogen N2

Oxygen O2

Carbon Monoxide CO

Carbon Dioxide CO2 Hydrogen H2

Methane CH4

Ethan C2H6

Ethen (Ethylene) C2H4 Ethin (Acetylene) C2H2

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/DGA

DGA

NORMAL PD PD LOW PD HIGH T< 300C

300C

< T>700C T> 700C

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IEC 60599 Method

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Furan analysis 5-Hydroxylmethyl-2-Furfurol (5HMF) 2-Furfurylalkohol (2FOL) 2-Furfurol (2FAL) 2-Acetylfuran (2ACF) 5-Methyl-2-Furfurol (5MEF)

1200

900

2002FAL

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Resistance Measurement

Measuring of DC resistance for all coils at different tap changerposition (typically: US about 20 m, OS about 1 )

Contacts condi tion (Tap changer, bushing) as well as windingshorts and disconnection in the current path

Insulation Resistance Measurement

Insulation evaluation due to measuring the insulation between coiland ground (typical a few 100 M). Determination of Kr-Factors=R60/R15

With Kr>3 moisture in insulation

Ratio Measurement

Ratio measurement in each position of tap changer Maximum deviation 0,5% Determination the short circui t or disconnection in windings

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PD-measurement Sensitive measurement for insulation

condition evaluation

Chemical (DGA)

Optical (e.g. UV camera for corona)

Acoustic (sensors on the tank)

Electric (narrowband or wide-band) UHF (antenna in transformer)

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Possible measurements

Dielectric measurementsRVM (Recovery Voltage Measurement)

PDC (Polarisation Depolarisation Current)

FDS (Frequency Domain Spectroscopy)

The procedures use similar models.

The comparison between model response and

measurement is used to determine the watercontent in pressboard

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Recovery Voltage Measurement (RVM)


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Recovery Voltage Measurement (RVM)

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PDC

SampleElectrometer


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FDS

Frequency (Hz)

Moisture 4%

Moisture 2,5%

Moisture 1%

Moisture 0,2%


43/xTechnologies for transformer drying


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Vacuum, heat

Vacuum, heat

Technologies for transformer drying

Drying potentially endangers the solid insulation asthe winding coil usually is not re-fastened after drying

(>>> stability in case of shorts?)

Cellulose fibers

Water molecules

Insulating liquid

Vacuum, heat

Vacuum, heat

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Continuous transformer insulation drying

Vacuum and heat

Hygroscopic materials

(molecular sieves,

Zeolites)

Use of the water

equilibrium at different

temperatures

Applicable technologies:

Interfering the

Dissolved GasAnalysis

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R li ti


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Realization

Gentle, continuousdesiccation without

influencing the DGA

Upgraded insulating liquid

Cooling circuit

Cooler

Warm, wet oil

Cellulose filter cartridge

Pump

Transformervessel

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