6_Koch_Moisture.pdf

Dr. Maik Koch

Moisture in Transformers – Sources, Risks and Measurements 1. Risks, Sources, Distribution 2. Measurement Methods and Comparison 3. Case studies

2. Accelerated aging of cellulose Depolymerization by hydrolysis  Short circuit current forces may destroy winding

x

100

HOSO FR3 Midel 7131 Midel eN NN3000X

80 60 40 20 0 0

20

40

60 80 100 Moisture saturation / %

1000 Life expectance / a

1. Dielectric strength decreases - PD inception voltage - Breakdown voltage

Breakdown voltage / kV

Risks of Water in Transformers

Dr y 1%

100

10

2% 3%

1

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

4%

0,1 50

70

90

110 130 Temperature / °C

Risks of Water: Bubbling 3. Bubble evolution from wet paper  PD or breakdown may occur

 External player

4. Standards like IEC 60422

Sources of Water Leaky seals Installation, repair

Breathing

Water from aging Residual moisture

Moisture content / %

How Wet Are Transformers? 7 D1.0 R3.0 WCO

6 5

M1.5 P3.0 WSO

4 3 2 1 0 0

10

20

30

40 50 Age / years

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

Oil: Saturated hydrocarbons • •

Nonpolar molecules  very low water solubility (ppm) Increases with aromatics, aging products (acids)

MoistureSaturation[ppm]

Water Absorption in Oil and Cellulose 800 Oil 1 Oil 4 Silicone Oommen NN 0,49

600

400

200

Cellulose: Glucose rings with OH-groups Polar and therefore hygroscopic,

•

Water receptivity 2000-fold to oil H H O H H H O O H O O H O H H H H H H H H O O H O H O O O H C H H H O H H

H

H

H

0 20

Water content (%)

•

30

40

50

60

70 80 Temperature [°C]

25 Strongly bound monolayer

Less strongly bound water layers and capillary adsorbed water

Solvent and free water

20

15

O

o Des

rptio

n

10

n ptio

5

Chemical adsorption Page: 6

Physical adsorption

Capillar condensation

Increasing pressure and/or temperature

or Ads

0

10

20

30

40

50

60

70

80

90

100

Relative humidity (%)

Moisture Distribution Example: 125/95°C

1,4/2,1%

270/420

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

cellulose W = 3 %  210 kg water

85/65°C

2,4/2,9%

441/1105

Temp.

Moisture

DP

[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]

© OMICRON

T+

T–

Oil 16 ppm  1,1 kg H2O

 Important to know how wet the paper/pressboard is, rather than the oil! Seite 7

Dr. Maik Koch

Moisture in Transformers – Sources, Risks and Measurements 1. Risks, Sources, Distribution 2. Measurement Methods and Comparison 3. Case studies

History of Moisture Estimation Methods 1935 Karl Fischer titration • Determination of water in liquids and solids • Regular testing of oil samples 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 Dissipation factor

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

Frequency

Karl Fischer Titration Reference for other methods Measures water content Water relative to weight [µg, %, ppm]

Possible errors: • • • •

Transportation to laboratory Sample preparation Titration system Measurement of bound water depends on heating temperature and time 

Moisture in oil (ppm)

• • •

25 19,8

20 16,2

15,2

15

12,2 8,9

10

7,5 5,8

5

Scattered results obtained by Round Robin Tests

0 US

B

C

D

E

F

G

50 40

54,8

A B C D E F G

32,8

340

44,3 39,8 40 35,3

30 19,8

20

80 60 40 20 0

16,215,2 12,2 11,2 12,1 8,9 7,5 10 6,7 9,5 5,8 4,7 3,5 4,8

without sample C

60

Deviation from average / %

Moisture in oil / ppm

Round Robin Test on Oil Samples

-20 -40

0 Sample A

Sample B

Sample C

Comparability is dissatisfying! Moisture in paper via equilibrium diagrams?

A B C D E F G

Calculation of Moisture in Paper: Equilibrium Diagrams 1. 2. 3.

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

Aging

Improvement: Moisture saturation

     

Sampling Uncertainty of KFT Equilibrium conditions Literature sources Absorption capacity Aging

Capacitive Probes Based on moisture equilibrium  Moisture relative to saturation diffusion

upper porous electrode polymer film

MoistureSaturation[ppm]

Hygroscopic polymer film Change of capacity

•

Result: 0-100 % or 0-1 aw

Possible errors:

bottom electrode, glass substrate

• Diffusion of aging byproducts • Corrosion of electrodes  Calibration necessary

800 Oil 1 Oil 4 Silicone Oommen NN 0,49

600

• •

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

400

Cw,S = 280 ppm

Example: Cw,rel = 10%, 40°C

200

• New Oil:  Cw = 12 ppm • Aged oil:  Cw = 28 ppm

Cw,S = 122 ppm 0 20

30

40

50

60

70

80

 Calibration to oil essential

Time, date

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

10

8

6

4

2

0

Moisture in aged Kraft paper / %

65 60 55 Oil temperature 50 45 40 35 RS in oil 30 25 20 RS in cellulose 15 10 5 0 01.06.2003 05.06.2003 09.06.2003 13.06.2003 17.06.2003

Relative saturation / %

Top oil temperature / °C

Equilibrium Based on Moisture Saturation 5 4

3 2,2 2

Aged KP 21°C Aged KP 40°C

1

Aged KP 60°C 4,1

0 0

Aged KP 80°C

10 20 30 40 Moisture relative to saturation / %

 Equilibrium conditions:  Long time constant  Only elevated temperatures  Not for factory test  Aging of cellulose

Dielectric Response Analysis Voltage source

~

Current meter

Dissipation factor vs. frequency 5.000 HV-winding

LV-winding

DF 1.000

?

Guard

0.100

0.12 Moderate Aged

New

Main insulation Tank

0.010 0.002 0.0001 0.001 0.01

0.0036 0.0024 0.1

1.0

10

50

1000

Frequency/Hz

© OMICRON

Page 16

Interpretation and Analysis

Dissipation factor

Pressboard: water, lmw acids

Insulation geometry

Oil: carbon, soot, hmw acids

10

Pressboard, connections, Overall response guarding

1 0.1

1%, 1pS/m, X30, Y15

0.01 0.001 0.0001 0.0001

© OMICRON

0.001

0.01

0.1

1.0

10

100

1000 f/Hz

Page 17

Automatic Moisture Calculation

Automatic Moisture Calculation

Oil conductivity

Water content

Assessment Saturation

Combined FDS-PDC Test 100 Current [nA]

Dissipation factor

1

1 1

Time [s]

1000

0,001 0,1

• •  

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

1000 Frequency [Hz]

Frequency [Hz]

1000

14

1000

12

100

10

10

8

1

6

0,1

4

0,01

2

0,001

0

0,0001

FDS Page: 20

October 13

PDC Combined

Frequency range / Hz

0,001 0,001

Time need / h

Transformation

Dissipation factor

1

Moisture Content and Age Dielectric Response:

DIRANA

Moisture content / %

Equilibrium:

MODS Water saturation

Water content

7 D1.0 R3.0 WCO

6 5

M1.5 P3.0 WSO

4 3 2 1 0 0

Page: 21

10

20 October 13

30

40 50 Age / years

Dielectric Response Analysis Water content / %

5 DIRANA

MODS

4

3

2

1

0 25 22 25 25 22 32 22 55 78 21 21 16 20 9 25 29 30 55 25 25 21

Temperature / °C

 Different data bases  However good agreement  Differences for aged transformers

Seite 22

Equilibrium Methods

 High moisture content using moisture content in oil ppm  Reasonable agreement between moisture saturation and dielectric response analysis © OMICRON

Seite 23

Relative Deviation 60% 40% 20% 0% -20% -40%

• Good agreement of dielectric response analysis with paper samples © OMICRON

Seite 24

Dr. Maik Koch

Moisture in Transformers – Sources, Risks and Measurements 1. Risks, Sources, Distribution 2. Measurement Methods and Comparison 3. Case studies

Dissipation factor

New Transformers 0.7

• Very different DF curves B /A

0.3 0.1

• Same moisture content 0,4 % / 0,4%

0.03

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

A

B

0.01

• PI would undervalue A • Stop at 1 or 2 mHz would make analysis impossible

0.003 0.0001 0.001

Page: 26

0.01

0.1

1

10 100 1000 Frequency / Hz

October 31, 2013

Transformer in Meiningen/Austria

Technical data Manufactured in 1967 Rated power 133 MVA 230/115/48 kV Cooling: Oil forced/air forced Drying required?

Page: 27

October 31, 2013

Moisture in Kraft paper [%]

Measurement Instruments 6 5 4 3 21°C 2

40°C 60°C

1

80°C 0 0

Onsite oil samples

 Capacitive probe Vaisala HMP 228: RH = 10,1%  KF titration CW = 19 ppm Dielectric measurements

 FDS, PDC  Analysis by DIRANA Page: 28

October 31, 2013

10

20 30 40 Moisture relative to saturation [%]

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

Moisture content / %

5

Dirana CHL Dirana CLT RS equilibrium PPM equilibrium

4 3 2 1 0 2005

2006

2007

2008 Year

2009

2010

2011

Heavily Aged Transformer  



III. Dielektrische Messverfahren: Praxis

Manufactured in 1950 Oil: Shell K6SX from 1965, acidity 0,5 mg KOH / g oil, conductivity 1300pS/m @ 21°C DP 593 top / 718 bottom DP from furane analysis: 237

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

6 5

Oil sampling

4

Moisture in cellulose derived from oil

3

Contradictory results

Page: 31

KFT

0

Oil RS

Moisture in cellulose by KF titration Oil ppm

1 DIRANA

Proved by paper samples

FDS

2

PDC

Moisture content / %

Dielectric methods

October 31, 2013

Maik Koch

Moisture in Transformers - Sources, Risks and Measurements 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 5 Without vacuum

4

With vacuum

3 2 1 0.8 0.3 0 0

50

100

Drying Time [min]

150

Moisture content / %

Summary 7

D1.0 R3.0 WCO

6 5

IEC60422

M1.5 P3.0 WSO

Extremely wet Wet

4

Moderately wet

3 2

Dry

1 0 0

10

20

• Utilities approach 1 – Regular oil sampling (ppm, preferably RS) – Dielectric response test after indication

30

40 50 Age / years

• Utilities approach 2 – Regular DR analysis along with other electrical tests – Comparison to RS equilibrium for confirmation