6_Koch_Moisture.pdf

Moisture in Transformers Sources, Risks and Measurements

Dr. Maik Koch

1. Risks, Sources, Distribution 2. Measurement Methods and Comparison 3. Case studies

PresenterPresentation NotesIntroduce myselfMaik Kosch, germanholding a PhD in diagnostics of HV equipmentHead of product management with OmicronOmicron: known for testing solutions for protection relaysComplete product range for testing transformers, CT/VT, cables etcToday: Specific problem of oil-paper insulations: Moisture content

Temperature / C50 70 90 110 130

0,1

1

10

100

1000

Life

exp

ecta

nce

/ a Dry1%

2%

3%

4%

Risks of Water in Transformers 1. Dielectric strength decreases

- PD inception voltage - Breakdown voltage

2. Accelerated aging of cellulose Depolymerization by hydrolysis

Short circuit current forces may destroy winding

L. E. Lundgaard, Aging of oil-impregnated paper in power transformers, IEEE Transactions on Power Delivery, Jan. 2004

x B

reak

dow

n vo

ltage

/ kV

0

20

40

60

80

100

0 20 40 60 80 100Moisture saturation / %

HOSOFR3Midel 7131Midel eNNN3000X

HOSOFR3Midel 7131Midel eNNN3000X

PresenterPresentation NotesWhy should we know how wet a transformer is?Water causes three dangerous effects:1. dielectric strength of oil and of paper decreasesDiagram shows how the breakdown voltage in mineral oil decreases with increasing moisture saturation. It also depends on the total acid number TAN.

2. Depolymerization: Cellulose molecules get splitted into smaller parts. Degree of polymerization decreases from 1200 to 200, which is considered to be the end of life criterion. Degree of polymerization gives the number of joined glucose rings per cellulose molecule. The more, the higher the mechanical strength. Water accelerates aging together with temperature by a chemical reaction called hydrolysis. The glucosidic bond between two glucose rings gets broken. Low molecular carboxylic acids (e.g. acetic) from paper and oil aging play the role of a catalyst that degradation process.

Risks of Water: Bubbling

External player

3. Bubble evolution from wet paper PD or breakdown may occur

4. Standards like IEC 60422

PresenterPresentation Notes3. Bubbling comes from evaporation of water inside cellulose and decreases the dielectric strength.

Video shows bubble evolution from wet paper having 4% moisture content into oil. The temperature is that at the conductor surface, below the 10 layers of paper.In case the video won't run, open it in an external player using the embedded link.

Sources of Water

Breathing

Leaky seals Installation, repair

Water from aging

Residual moisture

How Wet Are Transformers?

0

1

2

3

4

5

6

7

0 10 20 30 40 50

Moi

stur

e co

nten

t / %

Age / years

D1.0 M1.5R3.0 P3.0WCO WSO

61 Transformers, some measured several times 6 different measurement techniques Statistical evaluation possible

0 10 20 30 40 50 60 70 80 90 100

5

10

15

20

25Solvent and free water

Increasing pressure and/or temperature

Strongly bound monolayer

Less strongly bound water layers and capillary adsorbed water

Adsorptio

n

Desorptio

n

Relative humidity (%)

Wat

er c

onte

nt(%

)

Page: 6

Water Absorption in Oil and Cellulose

20 30 40 50 60 70 80 0

200

400

600

800

20 30 40 50 60 70 80 0

200

400

600

800

Moi

stur

e Sat

urat

ion [

ppm

]

Oil 1 Oil 1 Oil 4 Oil 4

Oommen Oommen NN 0,49

Silicone Silicone

Temperature [C]

Capillar condensation

Physical adsorption

Chemical adsorption

HH

H H

HO

O

OO

O

HH

H

H

H

HHC

H

H

HO

O

O

H

HH

HH O

O

OH

HH

O

O HH

O

H

Oil: Saturated hydrocarbons Nonpolar molecules very low

water solubility (ppm) Increases with aromatics,

aging products (acids)

Cellulose: Glucose rings with OH-groups Polar and therefore hygroscopic, Water receptivity 2000-fold to oil

Moisture Distribution

OMICRON Seite 7

[Ryzhenko, V. Sokolov, V.: Effect of Moisture on Dielectric Withstand Strength of Winding Insulations in Power Transformers. Electrical Stations (Electric Power Plants) No. 9, 1981]

125/95C

85/65C

Temp.

1,4/2,1%

2,4/2,9%

Moisture

270/420

441/1105

DP

T+ T Oil 16 ppm 1,1 kg H2O

cellulose W = 3 % 210 kg water

Example: 150 MVA, 7 t cellulose, 70 t Mineral oil, Temperature 40C

Important to know how wet the paper/pressboard is, rather than the oil!


Dr. Maik Koch



History of Moisture Estimation Methods

1935 Karl Fischer titration Determination of water in liquids and solids Regular testing of oil samples

Equilibrium Diagrams 1960 Fabre Pichon, based on ppm, often redrawn Various uncertainties 1995+ first on-line RS probes RS instead of ppm

Dielectric Response Analysis 1927 Schering bridge C/DF/PF at 50/60Hz 1991 RVM today not used 1995 PDC 1999 FDS 2007 Combination PDC+FDS

Frequency

Dis

sipa

tion

fact

or

Karl Fischer Titration

Reference for other methods Measures water content Water relative to weight

[g, %, ppm]

Possible errors: Transportation to laboratory Sample preparation Titration system Measurement of bound water depends

on heating temperature and time Scattered results obtained by Round Robin Tests

5,8

16,215,2

8,9

12,2

19,8

7,5

0

5

10

15

20

25

US B C D E F G

Moi

stur

e in

oil

(ppm

)

Sample A Sample B Sample C

4,7 5,8

32,8

6,7

16,2

54,8

11,215,2

44,3

3,5

8,99,512,212,1

19,8

4,87,5

40

0

10

20

30

40

50

60

Moi

stur

e in

oil

/ ppm 340

35,339,8

ABCDE

GF

Dev

iatio

n fro

mav

erag

e/ %

-40

-20

0

20

40

60

80

A B C D E F G

with

out s

ampl

e C

Round Robin Test on Oil Samples

Comparability is dissatisfying! Moisture in paper via equilibrium diagrams?

Calculation of Moisture in Paper: Equilibrium Diagrams

1. Onsite oil sampling, transportation to laboratory 2. Moisture content determination (ppm) 3. Application of an equilibrium diagram

Sampling Uncertainty of KFT Equilibrium conditions Literature sources Absorption capacity Aging

Aging

Improvement: Moisture saturation

Capacitive Probes

20 30 40 50 60 70 80 0

200

400

600

800

20 30 40 50 60 70 80 0

200

400

600

800

Moi

stur

e Sat

urat

ion [

ppm

]

Oil 1 Oil 1 Oil 4 Oil 4

Oommen Oommen NN 0,49

Silicone Silicone

Based on moisture equilibrium Moisture relative to saturation Hygroscopic polymer film Change of capacity Result: 0-100 % or 0-1 aw Possible errors: Diffusion of aging byproducts Corrosion of electrodes Calibration necessary

Cw,S = 122 ppm

Cw,S = 280 ppm

Calculation of ppm (g/g) by oil specific coefficients

Example: Cw,rel = 10%, 40C New Oil: Cw = 12 ppm Aged oil: Cw = 28 ppm Calibration to oil essential

upper porous electrode

bottom electrode , glass substrate

polymer film

diffusion

Equilibrium Based on Moisture Saturation

Aging of oil can be excluded Onsite and on-line application

01.06.2003 05.06.2003 09.06.2003 13.06.2003 17.06.200305

101520253035404550556065

0

2

4

6

8

10

Top

oil t

empe

ratu

re /

C

Time, date

Oil temperature

RS in cellulose

RS in oil

Rel

ativ

e sa

tura

tion

/ %

Moisture relative to saturation / %

0

1

2

3

4

5

0 10 20 30 40

Moi

stur

e in

aged

Kra

ftpa

per/

%

Aged KP 21C

Aged KP 40C

Aged KP 60C

Aged KP 80C

2,2

4,1

Equilibrium conditions: Long time constant Only elevated temperatures Not for factory test

Aging of cellulose

Dielectric Response Analysis

OMICRON Page 16

Tank

Guard

HV-winding

LV-winding

Voltage source

Main insulation

~ Current meter

Frequency/Hz

0.0001 0.01 0.1 1.0 10 0.002

0.010

0.100

1.000

1000 0.001

5.000 DF

0.12

0.0024 50

0.0036

New Moderate Aged

?

Dissipation factor vs. frequency

Interpretation and Analysis

OMICRON Page 17

f/Hz 0.001 0.01 0.1 1.0 10 100

Dis

sipa

tion

fact

or

0.0001

0.001

0.01

0.1

1

10

0.0001

Overall response 1%, 1pS/m, X30, Y15

1000

Oil: carbon, soot, hmw acids

Pressboard: water, lmw

acids

Insulation geometry

Pressboard, connections, guarding

Automatic Moisture Calculation

Automatic Moisture Calculation

Oil conductivity

Water content

Saturation

Assessment

Page: 20 October 13

Combined FDS-PDC Test C

urre

nt [n

A]

Time [s]

Trans- formation

Frequency [Hz]

Dis

sipa

tion

fact

or

0,001 0,001

1

1000

1000 1

100

1 Frequency [Hz]

Dis

sipa

tion

fact

or

1000

1

0,001 0,1

0

2

4

6

8

10

12

14

PDC Combined

Tim

e ne

ed /

h

0,0001

0,001

0,01

0,1

1

10

100

1000

Fre

quen

cy r

ange

/ H

z

FDS

f > 0,1 Hz frequency domain f < 1 Hz time domain 22 min for 1 kHz - 1 mHz 2:50 h for 1 kHz - 0,1 mHz

Page: 21 October 13

Moisture Content and Age

0

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6

7

0 10 20 30 40 50

Moi

stur

e co

nten

t / %

Age / years

D1.0 M1.5R3.0 P3.0WCO WSO

DIRANA MODS

Water content Water saturation

Dielectric Response:

Equilibrium:

Dielectric Response Analysis

Seite 22

Different data bases However good agreement Differences for aged transformers

0

1

2

3

4

5

25 22 25 25 22 32 22 55 78 21 21 16 20 9 25 29 30 55 25 25 21

DIRANA MODS

Wat

er c

onte

nt /

%

Temperature / C

Equilibrium Methods

OMICRON Seite 23

High moisture content using moisture content in oil ppm Reasonable agreement between moisture saturation and

dielectric response analysis

Relative Deviation

Good agreement of dielectric response analysis with paper samples

OMICRON Seite 24

-40%-20%

0%20%40%60%


Dr. Maik Koch



Page: 26 October 31, 2013

New Transformers Very different DF curves

B / A

Same moisture content 0,4 % / 0,4%

Different oil conductivity 0,94 pS/m / 0,06 pS/m

PI would undervalue A

Stop at 1 or 2 mHz would make analysis impossible

0.001 0.01 0.1 1 10 100 1000 Frequency / Hz

Dis

sipa

tion

fact

or

0.0001

0.01

0.03

0.1

0.3

0.7

0.003

A B

PresenterPresentation NotesTwo new transformers, one (orange) filled with new oil, the other (blue) filled with re-used oil. High oil conductivity, but dry transformer. Only the wide frequency range makes discrimination between oil conductivity and moisture possible. Polarisation indes PI would undervalue transformer. Stop at 1or2mHz would not give sufficient information about the insulation condition.


Transformer in Meiningen/Austria

Manufactured in 1967 Rated power 133 MVA 230/115/48 kV Cooling: Oil forced/air forced

Technical data

Drying required?

PresenterPresentation NotesThe customer wanted to investigate the moisture content in order to schedule a drying process if necessary.


Measurement Instruments

Onsite oil samples Capacitive probe Vaisala

HMP 228: RH = 10,1% KF titration CW = 19 ppm

0

1

2

3

4

5

6

0 10 20 30 40Moisture relative to saturation [%]

Moi

stur

e in

Kra

ft pa

per [

%]

21C

40C

60C

80C

Dielectric measurements FDS, PDC Analysis by DIRANA

PresenterPresentation NotesThree measurement approaches:Equilibrium via conventional diagrams (Oommen), equilibrium via new relative saturation probes (see photograph), dielectric response using PDC and FDS, analysed by DIRANA.

Drying History

On-line drying with oil circulation for 1,5 years

0

1

2

3

4

5

2005 2006 2007 2008 2009 2010 2011

Moi

stur

e co

nten

t / %

Year

Dirana CHL Dirana CLT RS equilibrium PPM equilibrium


Heavily Aged Transformer III. Dielektrische Messverfahren: Praxis

0

1

2

3

4

5

6

Moi

stur

e co

nten

t / %

Contradictory results

Oil sampling Moisture in cellulose derived from oil

Dielectric methods Moisture in cellulose from dielectric properties (PDC, FDS, Dirana)

Manufactured in 1950 Oil: Shell K6SX from 1965,

acidity 0,5 mg KOH / g oil, conductivity 1300pS/m @ 21C

DP 593 top / 718 bottom DP from furane analysis: 237

Oil

ppm

Oil

RS

PD

C

FDS

DIR

AN

A

Proved by paper samples Moisture in cellulose by KF titration

KFT

PresenterPresentation NotesAcidity (total acid number) around 0,02 for new oils and increases because of paper and oil deterioration to 0,5 or more.Conductivity around 0,05 pS/m for new oils, around 5pS/m under moderate conditions and up to 1300pS/m if highly aged.Degree of polymerisation (number of joined glucose rings per cellulose molecule) here with 593-718 still rather good; new more than 1000, end of life 200,Various moisture determination methods applied, different results obtained.

Moisture in Transformers - Sources, Risks and Measurements

Maik Koch

1. Measurement Methods 2. Comparison 3. Monitoring of the Factory Drying Process

Drying in the Manufacturing Process

Vacuum ovens costly

Bottleneck in process

Drying time depends on ambient humidity and raw material

Optimizing drying time saves energy and costs!

Progress of Oven Drying without vacuum is the lowest moisture content limited lower values can be reached with vacuum

0

1

2

3

4

5

0 50 100 150 Drying Time [min]

Without vacuum

With vacuum

0.3 0.8

Summary

Utilities approach 1 Regular oil sampling

(ppm, preferably RS) Dielectric response test

after indication

Utilities approach 2 Regular DR analysis along with

other electrical tests Comparison to RS equilibrium

for confirmation

Dry

Moderately wet

Wet

Extremely wet

0

1

2

3

4

5

6

7

0 10 20 30 40 50

Moi

stur

e co

nten

t / %

Age / years

D1.0 M1.5 R3.0 P3.0 WCO WSO

IEC60422

Moisture in Transformers Sources, Risks and MeasurementsRisks of Water in TransformersRisks of Water: BubblingSources of WaterHow Wet Are Transformers?Slide Number 6Moisture DistributionMoisture in Transformers Sources, Risks and MeasurementsHistory of Moisture Estimation MethodsKarl Fischer TitrationRound Robin Test on Oil SamplesCalculation of Moisture in Paper:Equilibrium DiagramsCapacitive ProbesEquilibrium Based on Moisture SaturationDielectric Response AnalysisInterpretation and AnalysisAutomatic Moisture CalculationAutomatic Moisture CalculationCombined FDS-PDC TestMoisture Content and AgeDielectric Response AnalysisEquilibrium MethodsRelative DeviationMoisture in Transformers Sources, Risks and MeasurementsNew TransformersTransformer in Meiningen/AustriaMeasurement InstrumentsDrying HistoryHeavily Aged TransformerMoisture in Transformers - Sources, Risks and MeasurementsDrying in the Manufacturing ProcessSlide Number 34Summary

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6_Koch_Moisture.pdf