6_Koch_Moisture.pdf

(1)

Moisture in Transformers –

Sources, Risks and Measurements

Dr. Maik Koch

1. Risks, Sources, Distribution

2. Measurement Methods and Comparison 3. Case studies

(2)

Temperature / °C 50 70 90 110 130 0,1 1 10 100 1000 Li fe ex p ec ta n c e / a D_ry 1% 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 do w n v ol ta ge / k V 0 20 40 60 80 100 0 20 40 60 80 100 Moisture saturation / % HOSO FR3 Midel 7131 Midel eN NN3000X HOSO FR3 Midel 7131 Midel eN NN3000X

(3)

Risks of Water: Bubbling

 External player

3. Bubble evolution

from wet paper

 PD or breakdown may occur

(4)

Sources of Water

Breathing

Leaky seals

Installation, repair

Water from aging Residual moisture

(5)

How Wet Are Transformers?

0 1 2 3 4 5 6 7 0 10 20 30 40 50

M

o

is

tu

re

c

o

n

te

n

t

/ %

Age / years D1.0 M1.5 R3.0 P3.0 WCO WSO

• 61 Transformers, some measured several times

• 6 different measurement techniques

(6)

0 10 20 30 40 50 60 70 80 90 100 5 10 15 20 25 Solvent and free water Increasing pressure and/or temperature Strongly bound monolayer

Less strongly bound water layers and capillary adsorbed water

Adsorpt ion Desorp tion Relative humidity (%) W at er c on ten t (% ) 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 M oi s tur e S at ur at 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 H H H H H O O O O O H H H H H H H C H H H O O O H H H H H _O O O H H H O O H H 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

(7)

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]

125/95°C 85/65°C 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 40°C

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

(8)

Moisture in Transformers –

Sources, Risks and Measurements

Dr. Maik Koch

2. Measurement Methods and Comparison 3. Case studies

(9)

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 Di s s ip a ti o n f a c to r

(10)

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

 Scattered results obtained by Round Robin Tests

5,8 16,2 15,2 8,9 12,2 19,8 7,5 0 5 10 15 20 25 US B C D E F G M oi s tur e i n oi l ( ppm )

(11)

Sample A Sample B Sample C 4,7 5,8 32,8 6,7 16,2 54,8 11,2 15,2 44,3 3,5 8,9 9,512,1 12,2 19,8 4,8 7,5 40 0 10 20 30 40 50 60 M oi s tur e i n oi l / p pm 340 35,3 39,8 A B C D E G F D ev iat ion f rom av er a ge / % -40 -20 0 20 40 60 80 A B C D E F G w it hout s a m p le C

Round Robin Test on Oil Samples

Comparability is dissatisfying!

(12)

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

(13)

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 M oi s tur e S at ur at 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

C_w,S = 122 ppm

C_w,S = 280 ppm

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

Example: C_w,rel = 10%, 40°C • New Oil:  C_w = 12 ppm • Aged oil:  C_w = 28 ppm

 Calibration to oil essential

upper porous electrode

bottom electrode , glass substrate polymer film

(14)

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 17.06.2003 0 5 10 15 20 25 30 35 40 45 50 55 60 65 0 2 4 6 8 10 T o p o il t e m pe ra tur e / ° C Time, date Oil temperature RS in cellulose RS in oil R el at iv e s at u rat ion / %

Moisture relative to saturation / % 0 1 2 3 4 5 0 10 20 30 40 M o is tu re in ag ed K raf t p ape r / % Aged KP 21°C Aged KP 40°C Aged KP 60°C Aged KP 80°C 2,2 4,1  Equilibrium conditions:

 Long time constant

 Only elevated temperatures

 Not for factory test

(15)

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

?

(16)

Interpretation and Analysis

© OMICRON Page 17 f/Hz 0.001 0.01 0.1 1.0 10 100 D is s ipat ion fac tor 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

(17)

(18)

Automatic Moisture Calculation

Oil conductivity

Water content

Saturation Assessment

(19)

Page: 20 October 13

Combined FDS-PDC Test

C ur rent [ nA ] Time [s] Trans- formation Frequency [Hz] D is s ipat ion f ac tor 0,001 0,001 1 1000 1000 1 100 1 Frequency [Hz] D is s ipat ion f ac tor 1000 1 0,001 0,1 0 2 4 6 8 10 12 14 PDC Combined T im e n eed / h 0,0001 0,001 0,01 0,1 1 10 100 1000 F requ en c y r an ge / 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

(20)

Page: 21 October 13

Moisture Content and Age

0 1 2 3 4 5 6 7 0 10 20 30 40 50

M

o

is

tu

re

c

o

n

te

n

t

/ %

Age / years D1.0 M1.5 R3.0 P3.0 WCO WSO DIRANA MODS

Water content Water saturation

Dielectric Response: Equilibrium:

(21)

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 W at er c ont ent / % Temperature / °C

(22)

Equilibrium Methods

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

(23)

Relative Deviation

• Good agreement of dielectric response analysis with

paper samples

-40%

-20%

0%

20%

40%

60%

(24)

Moisture in Transformers –

Sources, Risks and Measurements

Dr. Maik Koch

2. Measurement Methods and Comparison 3. Case studies

(25)

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 D is s ipat ion f ac tor 0.0001 0.01 0.03 0.1 0.3 0.7 0.003 A B

(26)

Page: 27 October 31, 2013

Transformer in Meiningen/Austria

Manufactured in 1967 Rated power 133 MVA 230/115/48 kV

Cooling: Oil forced/air forced

Technical data

(27)

Page: 28 October 31, 2013

Measurement Instruments

Onsite oil samples

 Capacitive probe Vaisala HMP 228: RH = 10,1%  KF titration C_W = 19 ppm 0 1 2 3 4 5 6 0 10 20 30 40

Moisture relative to saturation [%]

M oi s tur e i n K raf t p ap er [ % ] 21°C 40°C 60°C 80°C Dielectric measurements  FDS, PDC  Analysis by DIRANA

(28)

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 M oi st ur e co nt ent / % Year Dirana CHL Dirana CLT RS equilibrium PPM equilibrium

(29)

Page: 31 October 31, 2013

Heavily Aged Transformer

III. Dielektrische Messverfahren: Praxis

0 1 2 3 4 5 6 M oi s tur e c ont ent / %  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 @ 21°C  DP 593 top / 718 bottom

DP from furane analysis: 237

O il ppm _Oil R S P DC F DS DI RA NA

Proved by paper samples

Moisture in cellulose by KF titration

K

(30)

Moisture in Transformers - Sources,

Risks and Measurements

Maik Koch

1. Measurement Methods

2. Comparison

(31)

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!

(32)

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 vacuum With

0.3 0.8

(33)

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 M oi s tur e c ont ent / % Age / years D1.0 M1.5 R3.0 P3.0 WCO WSO