A2.30 Moisture TutorialID55VER20 [PDF]

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Moisture Equilibrium and Moisture Migration Within Transformer Insulation System Tutorial of CIGRÉ WG A2.30 Conveners: Victor Sokolov, Ukraine Maik Koch, Germany 1

Outline • Introduction: background and definitions • Main sources of water contamination • Water in oil and in cellulose materials • Moisture distribution, equilibrium and migration • Mechanism and criteria for bubble evolution • Methods for moisture determination

MOISTURE EQUILIBRIUM AND MOISTURE MIGRATION WITHIN TRANSFORMER INSULATION SYSTEMS – Tutorial of CIGRÉ WG A2.30

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History Initiator and convener: Victor Sokolov 2001 Presentation on the CIGRE A2 website 2005 Attempt to restart work 2006 Maik Koch took over organization of WG 2007 Final version finished 2008-01-06 Victor Sokolov, convenor, passed away suddenly 2008-06 Brochure 349 available at www.e-cigre.org

MOISTURE EQUILIBRIUM AND MOISTURE MIGRATION WITHIN TRANSFORMER INSULATION SYSTEMS – Tutorial of CIGRÉ WG A2.30

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Moisture - Frequently Discussed • •

Large population operates under aged conditions Hazardous effects: 1. Decreases the dielectric withstand strength 2. Accelerates cellulose decomposition 3. Causes the emission of bubbles at high temperatures

•

Uncertainty of traditional measurement methods New methods available: – Capacitive sensors – Dielectric response methods

1000 Life expectance / a

•

Dr y 1%

100

10

2% 3%

1

4%

0,1 50

70

90

110 130 Temperature / °C

MOISTURE EQUILIBRIUM AND MOISTURE MIGRATION WITHIN TRANSFORMER INSULATION SYSTEMS – Tutorial of CIGRÉ WG A2.30

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Many Measures of Water • • • • • •

Water content (absolute water content) W Water saturation RS Relative humidity RH Water activity aW Water vapor pressure p Dew point

MOISTURE EQUILIBRIUM AND MOISTURE MIGRATION WITHIN TRANSFORMER INSULATION SYSTEMS – Tutorial of CIGRÉ WG A2.30

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Measures of Moisture Water content (absolute water content) W Moisture in Kraft paper / %

• Water mass related to dry mass or mass as sampled 6 • Measure: (0,5 – 5) % for cellulose 5 or (1-~80) ppm (mg/kg) for oil

Water saturation RS (relative humidity RH) • Water vapour pressure p RS = ⋅100 % relative to saturation pS Measure 0 - 100 % • Information about water availability / activity • Important for damaging effects, migration, equilibrium, drying potential • Water activity = RH under equilibrium / 100%

Moisture isotherms

4 3

21°C

2

40°C 60°C

1

80°C

0

10

40 20 30 Moisture saturation / %

MOISTURE EQUILIBRIUM AND MOISTURE MIGRATION WITHIN TRANSFORMER INSULATION SYSTEMS – Tutorial of CIGRÉ WG A2.30

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Outline • Introduction: background and definitions

• Main sources of water contamination • Water in oil and in cellulose materials • Moisture distribution in transformers • Moisture equilibrium and migration • Mechanism and criteria for bubble evolution • Methods for moisture determination

MOISTURE EQUILIBRIUM AND MOISTURE MIGRATION WITHIN TRANSFORMER INSULATION SYSTEMS – Tutorial of CIGRÉ WG A2.30

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Sources of Water Leaky seals Installation, repair

Breathing

Water from aging Residual moisture

MOISTURE EQUILIBRIUM AND MOISTURE MIGRATION WITHIN TRANSFORMER INSULATION SYSTEMS – Tutorial of CIGRÉ WG A2.30

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Sources of Water: Atmosphere •

Main mechanism through poor seals – Typical leaks: top seal of draw-lead bushings, the seals in explosion vents, and leaks in forced-oil circulation systems between the main tank and the coolers – Rainwater can be sucked in when there is a rapid drop of pressure

• •

Free breathing: significant, but limited up to 0.2 % per year Leaky seals Membrane-sealed: about 0.03 to 0.06 % water RHbreather=1% RHair=50%

Installation, repair

Water from aging RSoil=RScellulose= 3%

MOISTURE EQUILIBRIUM AND MOISTURE MIGRATION WITHIN TRANSFORMER INSULATION SYSTEMS – Tutorial of CIGRÉ WG A2.30

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Ingress due to Breathing 1. Grid transformer GT

2. Grid w. heat recovery HE

3. GSU

Rated power (MVA)

600

150

850

Oil volume @ 20C

101 m³

45 m³

100 m³

No. of conservators and breathers

2/2

1/1

2/2

Moisture sensors

1 per conservator and 1 per breather

1 per bre.

RH

RH

MOISTURE EQUILIBRIUM AND MOISTURE MIGRATION WITHIN TRANSFORMER INSULATION SYSTEMS – Tutorial of CIGRÉ WG A2.30

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Air Volume 104

2,4

Oil volume [m³]

103

1,8

Air volume

102

1,2

101

0,6

Air volume [m³]

100 04.1.

Penetrating air volume [m³]

Oil volume

• Change of oil volume and penetrating air volume for GT • GT: typ 0,05 m³/h, max 0,8 m³/h • HE: typ: 0,15 m³/h, max. 4,2 m³/h • GSU: 0,005 m³/h, max. 0,1 m³/h

0 04.3.

04.5.

04.7.

04.9.

04.11. Time [day.month]

10 9

ƒ Volume of air entering the transformers ƒ 2 weeks in February and in May Æ most air enters HE, volume only 45% of that of other transformers

8 7 6 5 4 3 2 1 0 GT

GT

HE Feb HE May

GSU

GSU

MOISTUREFeb EQUILIBRIUM May AND MOISTURE MIGRATION Feb WITHIN May TRANSFORMER INSULATION SYSTEMS – Tutorial of CIGRÉ WG A2.30

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Water mass [g]

Moisture Contamination 600 500 400

Moisture ingress in a period of two weeks

300 200 100 0 GT Feb

GT May

HE Feb

HE May

GSU Feb

180

18

Water mass [kg/10a]

Water mass [kg/a]

20 16

16 14 12 10 8

2 0

163

160 140 120

Extrapolated for 1 resp. 10 years

100 80 60

6 4

GSU May

40 1,5 0

20 0

15,1 0

MOISTURE EQUILIBRIUM MIGRATION WITHIN TRANSFORMER GT AND MOISTURE HE GSU GT HE INSULATION GSU SYSTEMS – Tutorial of CIGRÉ WG A2.30

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Exposure to the Atmosphere

Water mainly in the outer insulation components, depth 0.3-0.35 mm

25 Weight increase (%)

Moisture adsorption of 3 mm high-density pressboard at 23 and 40°C at various humidity’s of the ambient air

23 °C, 97 % rh

20 15

23 °C, 75 % rh

10

23 °C, 50 % rh

5

40 °C, 25 % rh

0 0

7

14

21

28

Time (days)

Leaky seals Installation, repair

RHbreather=1% Water from aging

RHair=50%

RSoil=RScellulose= 3% MOISTURE EQUILIBRIUM AND MOISTURE MIGRATION WITHIN TRANSFORMER INSULATION SYSTEMS – Tutorial of CIGRÉ WG A2.30

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Cellulose Decomposition • Degree of polymerisation new: 1200 end of life: 200

8

W ater [%]

• Aging causes molecular chain scission and formation of by-products 4 Moser Dahinden including water and 3,5 Fabre Pichon furanic compounds Fallou 3 • 4 scissions ~ 1 % 2,5 2 1,5 1 0,5 0 0

2

4

6

8 Chain scissions 14

MOISTURE EQUILIBRIUM AND MOISTURE MIGRATION WITHIN TRANSFORMER INSULATION SYSTEMS – Tutorial of CIGRÉ WG A2.30

Moisture Concentration over Age 5

18

4,5 4

13

3,5 3

8

2,5 2

3

1,5 1

1

Moisture saturation @ 25°C / %

Moisture content in cellulose/ %

of 77 Transformers in DE, PL, SE, REDIATOOL research project

0,5 0

0 0

10

20

30

40

50 60 Age / years

MOISTURE EQUILIBRIUM AND MOISTURE MIGRATION WITHIN TRANSFORMER INSULATION SYSTEMS – Tutorial of CIGRÉ WG A2.30

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Preservation Systems • • • • •

Free breathing Self-drying breather Breathing via a desiccant Flexible diaphragm or “rubber bag” Nitrogen cushion either at atmospheric or high pressure • Refrigerated drier • Hermetical seal Thermo-electric modules • Molecular sieve Breather

Dehydrating breather for free breathing system Air Oil

Drain tube

Refrigerated drier

Main oil pipe connection to tank

Temporary connection to bottom of tank

MOISTURE EQUILIBRIUM AND MOISTURE MIGRATION WITHIN TRANSFORMER INSULATION SYSTEMS – Tutorial of CIGRÉ WG A2.30

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Outline • Introduction: background and definitions • Main sources of water contamination

• Water in oil and in cellulose materials • Moisture distribution in transformers • Moisture equilibrium and migration • Mechanism and criteria for bubble evolution • Methods for moisture determination

MOISTURE EQUILIBRIUM AND MOISTURE MIGRATION WITHIN TRANSFORMER INSULATION SYSTEMS – Tutorial of CIGRÉ WG A2.30

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• Nonpolar molecules Æ Very low solubility • Increases with aromatics, aging products (acids)

W S = WOil ⋅ e − B / T

Moisture Saturation [ppm]

Solubility of Water in Oil 800 Oil 1 Oil 4 Silicone Oommen Aged

600

400

200

0 20

30

40

50

B – oil specific constant

60

70 80 Temperature [°C]

• Free water droplets if saturation level exceeded • Ester liquids dissolve 20 to 40 times more water MOISTURE EQUILIBRIUM AND MOISTURE MIGRATION WITHIN TRANSFORMER INSULATION SYSTEMS – Tutorial of CIGRÉ WG A2.30

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• Moisture Solubility in Four Service Aged Oils Compared to a NonAged Laboratory Used Oil. • Neutralisation value = value for all acids / value for water soluble acids [mgKOH/g]

Saturation humidity [ppm weight]

Solubility due to Acids 450 Non-acidic lab-used Nytro 10X, NV=0.005 Service aged, NV=0.11/0.001 Service aged, NV=0.22/0.003 Service aged, NV=0.34/0.06 Service aged, NV=0.42/0.04

400 350 300 250 200 150 100 50 0

20

30

40

50

60

70 80 Temperature [°C]

MOISTURE EQUILIBRIUM AND MOISTURE MIGRATION WITHIN TRANSFORMER INSULATION SYSTEMS – Tutorial of CIGRÉ WG A2.30

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Adsorption to Cellulose • Polar and therefore hygroscopic • Attraction to OH-groups • Water solubility ~ 2000-fold higher than oil

H

H H O H H H H 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

O

OH

OH

H

O

OH

OH

OH OH

OH

OH

OH

monolayer adsorption

polylayer adsorption

capillary condensation

MOISTURE EQUILIBRIUM AND MOISTURE MIGRATION WITHIN TRANSFORMER INSULATION SYSTEMS – Tutorial of CIGRÉ WG A2.30

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Water content (%)

Moisture Isotherms 25 Strongly bound monolayer 20

Less strongly bound water layers and capillary adsorbed water

Solvent and free water

15 o Des

rptio

• General moisture isotherm for cellulose material

n

10

5

Ads

0

10

Increasing pressure and/or temperature

tio n o rp

20

30

40

50

60

70

80

90

100

Relative humidity (%)

MOISTURE EQUILIBRIUM AND MOISTURE MIGRATION WITHIN TRANSFORMER INSULATION SYSTEMS – Tutorial of CIGRÉ WG A2.30

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Water content [%]

Moisture Isotherms 25 2

20

15

1

0

0,5

1

0

10 Piper Fessler In vacuum In air

5

0 0

5

10 15 20 Water vapor pressure [mm Hg]

• Water-Paper Isotherms (23°C) Experimental and Based on the Formulas of Piper and the Measurements of Fessler

MOISTURE EQUILIBRIUM AND MOISTURE MIGRATION WITHIN TRANSFORMER INSULATION SYSTEMS – Tutorial of CIGRÉ WG A2.30

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Outline • Introduction: background and definitions • Main sources of water contamination • Water in oil and in cellulose materials

• Moisture distribution, equilibrium and migration • Mechanism and criteria for bubble evolution • Methods for moisture determination

MOISTURE EQUILIBRIUM AND MOISTURE MIGRATION WITHIN TRANSFORMER INSULATION SYSTEMS – Tutorial of CIGRÉ WG A2.30

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Moisture Distribution in the Solid Insulation 1. “Thick structures”: supporting components, – about 50 % of insulation mass, diminutive contribution to moisture migration due to a few years time constants

2. “Thin cold structures” pressboard barriers, end caps, etc – 20 – 30 % of insulation mass, at bulk oil temperatures, large amount of the water

3. “Thin hot structures” paper wrapped on conductors – close to conductor temperature, relatively dry Clamping Plate Spacer Block Angle Ring Cylinder

Paper Wrap around Copper Wire

MOISTURE EQUILIBRIUM AND MOISTURE MIGRATION WITHIN TRANSFORMER INSULATION SYSTEMS – Tutorial of CIGRÉ WG A2.30

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Mass and Surface Area of Insulation Structures Thin Hot

Thick

Thick Thin Hot

3

Mass

35

43

38 59

Area

22 Thin Cold

Insulation Structures Classified by Mass and Area for a 400 MVA GSU Transformer 18/347 kV

MOISTURE EQUILIBRIUM AND MOISTURE MIGRATION WITHIN TRANSFORMER INSULATION SYSTEMS – Tutorial of CIGRÉ WG A2.30

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Moisture Distribution Distribution example: 125/95°C

1,4/2,1%

270/420

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

cellulose Cw = 3 % Æ 210 kg water

T+ 85/65°C

2,4/2,9%

441/1105

Temp.

Moisture

DP

T–

Oil 16 ppm Æ 1,1 kg H2O

Æ Important to know how wet the paper/pressboard is, not the oil!

MOISTURE EQUILIBRIUM AND MOISTURE MIGRATION WITHIN TRANSFORMER INSULATION SYSTEMS – Tutorial of CIGRÉ WG A2.30

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Moisture Migration Diffusion time

Oil free pressboard

Impregnated pressboard

Temperature

20°C

70°C

20°C

70°C

Time constant

1,7 h

0,03 h

333 h

6h

Conditions: water content in pressboard 0,5 %, pressboard thickness 1 mm

3,5 3 2,5

W=2,0% ∆T=20oC

W,%

2

W=1,8% ∆T=40oC

1,5 W=1,2% ∆T=20oC

1

Effect of Temperature on Moisture Distribution in Turn Insulation

0,5 0 0,1 0,2 0,3 0,4 0,5 0,6 0,7 0,8 0,9

1

x/d

27

MOISTURE EQUILIBRIUM AND MOISTURE MIGRATION WITHIN TRANSFORMER INSULATION SYSTEMS – Tutorial of CIGRÉ WG A2.30

Moisture Equilibrium • •

Water potential the same everywhere in the system Moisture diffusion depends on differences in moisture saturation / water vapour pressure / water activity (same temperatures, same pressure assumed )

Ψ = Ψ0 + RS =

RT ⎛ p ln⎜ M W ⎜⎝ pS

⎞ ⎟⎟ ⎠

p ⋅100 % pS

RS Pb = RS Oil = RH Air pCellulose = pOil = p Air aW , Cellulose = aW , Oil = aW , Air

RSBreather= 1 %

RHAir= 50% RSOil= RSCel= 3 % MOISTURE EQUILIBRIUM AND MOISTURE MIGRATION WITHIN TRANSFORMER INSULATION SYSTEMS – Tutorial of CIGRÉ WG A2.30

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Traditional Equilibrium Diagrams Used for determination of moisture in paper: • Onsite oil sampling, transportation to laboratory • Moisture content determination (ppm) • Application of an equilibrium diagram

MOISTURE EQUILIBRIUM AND MOISTURE MIGRATION WITHIN TRANSFORMER INSULATION SYSTEMS – Tutorial of CIGRÉ WG A2.30

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Moisture by weight in cellulose [%]

Errors 6

Conditions: 1. Equilibrium exists 40° C New paper 60° C New paper 2. Temperature- and 80° C New paper moisture distribution 60°C Aged oil + PB 3. Sampling, moisture 60°C New pressboard 60°C Aged oil + paper measurement Æ ± 13 % error 4. Results vary for different authors 5. Absorption capacity of oil 6. Absorption capacity of 60 80 100 Moisture by weight in oil [ppm] cellulose Æ 100 % error 21°C New paper

5 4 3,6 % 3,2 % 3 2,9 2,8 % % 2,3 % 2 1,7 % 1 0

0

20 40 20 ppm ± 5 ppm

Diagrams not applicable! Unless adapted to the cellulose and oil MOISTURE EQUILIBRIUM AND MOISTURE MIGRATION WITHIN TRANSFORMER INSULATION SYSTEMS – Tutorial of CIGRÉ WG A2.30

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Moisture in paper [%]

Based on Water Saturation 6

Conditions:

5

1.

Equilibrium exists

2.

Temperature- and moisture distribution

3.

Sampling, moisture measurement Æ ± 13 % error

4.

Steep gradient in low moisture region

5.

Absorption capacity of oil

6.

Absorption capacity of cellulose

4 3

21°C%P

2

40°C%P 60°C%P

1

80°C%P 0 0

10

20

30

40

Moisture relative to saturation [%]

Æ Onsite and online application

MOISTURE EQUILIBRIUM AND MOISTURE MIGRATION WITHIN TRANSFORMER INSULATION SYSTEMS – Tutorial of CIGRÉ WG A2.30

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Application for Online Monitoring

65

10

60 55 50

Oil temperature

8

45 40 35 30

6

RS in oil 4

25 20

Relative saturation / %

Top oil temperature / °C

• Moisture in oil is identical to moisture in cellulose if equilibrium exists • Equilibrium through long time mean value • Type and aging of oil have no influence

RS in cellulose

15

2

10 5 0 01.06.2003 05.06.2003 09.06.2003 13.06.2003 17.06.2003

Time, date

0

MOISTURE EQUILIBRIUM AND MOISTURE MIGRATION WITHIN TRANSFORMER INSULATION SYSTEMS – Tutorial of CIGRÉ WG A2.30

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Outline • Introduction: background and definitions • Main sources of water contamination • Water in oil and in cellulose materials • Moisture distribution, equilibrium and migration

• Mechanism and criteria for bubble evolution • Methods for moisture determination

MOISTURE EQUILIBRIUM AND MOISTURE MIGRATION WITHIN TRANSFORMER INSULATION SYSTEMS – Tutorial of CIGRÉ WG A2.30

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Bubble Evolution • • • •

10 layers Kraft paper 3,9% moisture content Inception at 120°C Temperature measured at conductor surface, below paper

Æ External player

MOISTURE EQUILIBRIUM AND MOISTURE MIGRATION WITHIN TRANSFORMER INSULATION SYSTEMS – Tutorial of CIGRÉ WG A2.30

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Bubble Evolution • • • •

10 layers Kraft paper 3,9% moisture content Inception at 120°C Temperature measured at conductor surface, below paper

MOISTURE EQUILIBRIUM AND MOISTURE MIGRATION WITHIN TRANSFORMER INSULATION SYSTEMS – Tutorial of CIGRÉ WG A2.30

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Bubble Evolution pin = pexternal + pσ • Formation of vapour-filled cavities (bubbles) Æ decrease of the dielectric strength, • De-impregnation of the turn insulation • Begins at gaseous residues in paper R =∝ pe

R >> r pe

R=r pe

R >r pe

pe

2r R =∝

pi = pe

pi = pe + ∆p

pi = pe + ∆pmax.

pi = pe + ∆p

pi = pe

MOISTURE EQUILIBRIUM AND MOISTURE MIGRATION WITHIN TRANSFORMER INSULATION SYSTEMS – Tutorial of CIGRÉ WG A2.30

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Experimental Results Amount of evapourable water in paper Microstructure of paper, depends on aging Gaseous residues in paper Surface tension of oil, depends on polar impurities (aging) and temperature Temperature [°C]

• • • •

200

200

New KP new oil TUP new oil Aged KP new oil

180

New KP aged oil Aged KP aged oil Oommen

180

160

160

140

140

120

120

100

100

80

80 0

1

2

3 4 5 6 Moisture in paper [%]

0

1

2

6 3 4 5 Moisture in paper [%]

MOISTURE EQUILIBRIUM AND MOISTURE MIGRATION WITHIN TRANSFORMER INSULATION SYSTEMS – Tutorial of CIGRÉ WG A2.30

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Risk Estimation

• Steep temperature rise supports formation • Danger limited to areas with high field strength

Inception temperature [°C]

• “Hot Spot” is rather dry, has less gaseous remnants 140

120

100

80 0

10

20

30 40 50 Temperature gradient [K/min]

• Large bubbles might be torn by the electric field. "As a conclusion, the risk of a dielectric breakdown due to bubble evolution is considered to be low." MOISTURE EQUILIBRIUM AND MOISTURE MIGRATION WITHIN TRANSFORMER INSULATION SYSTEMS – Tutorial of CIGRÉ WG A2.30

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Outline • Introduction: background and definitions • Main sources of water contamination • Water in oil and in cellulose materials • Moisture distribution, equilibrium and migration • Mechanism and criteria for bubble evolution

• Practical experiences • Methods for moisture determination

MOISTURE EQUILIBRIUM AND MOISTURE MIGRATION WITHIN TRANSFORMER INSULATION SYSTEMS – Tutorial of CIGRÉ WG A2.30

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Dielectric Strength of Oil Breakdown Voltage [kV]

Breakdown voltage in oil depends on • Relative humidity 100 • Particles 80 • Contaminations 60 (soot, acids …) • Temperature 40 Æ Consider sampling Particles 50g/t 20 temperature! 0 0

20

Particles 20g/t

100 60 80 40 Relative Humidity in Oil [%]

MOISTURE EQUILIBRIUM AND MOISTURE MIGRATION WITHIN TRANSFORMER INSULATION SYSTEMS – Tutorial of CIGRÉ WG A2.30

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Operation at Cold Temperatures • Dissolved water (high relative saturation) • Failures after energizing wet transformers in winter time • Ingress of free water – 400 MVA, 220 kV: breakdown of the oil space between the bushing and the tank – Rainfall Æ low pressure inside Æ sucked in about 500 g of water through a broken seal in the draw-lead bushing

• Rapid cooling of a wet transformer after high loading may result in super-saturation of oil in the cooler and formation of free water

41

MOISTURE EQUILIBRIUM AND MOISTURE MIGRATION WITHIN TRANSFORMER INSULATION SYSTEMS – Tutorial of CIGRÉ WG A2.30

Classification Based on Relative Saturation CIGRÈ WG A2.30

IEC 60422

CLASS I: “good”: RS below 5%@20°C, mc below 1.0 % CLASS II: “fair”: RS below 8%@20°C, mc below 2.0 % RS of oil < 50% at lowest T CLASS III: “probably wet”: RS of oil ~ 50% at lowest temperatures CLASS IV: “wet”: RS of oil up to 100% at lowest temperatures

Dry

Moderately wet

6-22 / 2,2-3,7

Wet

22-30 / 3,7 – 5

Extremely wet

> 30 / > 5

Moisture content [%]

! m – levels p p r e g n Æ No lo

Saturation / content < 6 / < 2,2

5 4 3 2 1

n ure tio ist ina M o tam n co Moderately wet

21°C 80°C

Wet, > 30 % extremely wet

Dry 0

10

20

30

MOISTURE EQUILIBRIUM AND MOISTURE MIGRATION WITHIN TRANSFORMER INSULATION SYSTEMS –Moisture Tutorial of CIGRÉ WG A2.30 saturation [%]

42

Outline • Introduction: background and definitions • Main sources of water contamination • Water in oil and in cellulose materials • Moisture distribution, equilibrium and migration • Mechanism and criteria for bubble evolution • Practical experiences

• Methods for moisture determination

MOISTURE EQUILIBRIUM AND MOISTURE MIGRATION WITHIN TRANSFORMER INSULATION SYSTEMS – Tutorial of CIGRÉ WG A2.30

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Karl Fischer Titration • • •

Reference for other methods 2 H2O + SO2 + I2 Æ H2SO4 + 2 HI Measures water content Water relative to weight [µg, %, ppm] Sample injection

Possible errors: • • • •

Water Vapour Electrolysis electrodes

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

Detection electrode

Sample Heating

Æ Scattering results obtained by Round Robin Tests MOISTURE EQUILIBRIUM AND MOISTURE MIGRATION WITHIN TRANSFORMER INSULATION SYSTEMS – Tutorial of CIGRÉ WG A2.30

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

upper porous electrode polymer film

Moisture Saturation[ppm]

•

Result: 0-100 % or 0-1 aw

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

800

600

Hygroscopic polymer film Change of capacity

Possible errors:

bottom electrode, glass substrate

Oil 1 Oil 4 Silicone Oommen NN 0,49

• •

Ions

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

Water

400

Example: Cw,rel = 10%, 40°C

Cw,S = 280 ppm 200

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

Cw,S = 122 ppm 0 20

30

40

50

60

70

80

Æ Calibration to oil essential

MOISTURE EQUILIBRIUM AND MOISTURE MIGRATION WITHIN TRANSFORMER INSULATION SYSTEMS – Tutorial of CIGRÉ WG A2.30

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Time, date

10

8

6

4

2

0

Relative saturation / %

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

Moisture in aged Kraft paper / %

Top oil temperature / °C

On-Line Application 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 / %

• Long time average for „mathmatical“ equilibrium • RS in oil and RS in paper • Water content in cellulose by moisture isotherms MOISTURE EQUILIBRIUM AND MOISTURE MIGRATION WITHIN TRANSFORMER INSULATION SYSTEMS – Tutorial of CIGRÉ WG A2.30

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Chilled Mirror Dew Point Instruments • Dew point of water vapour in gases • sample equilibrated within sealed chamber • thermoelectric cooler chills the mirror until condensation • detected by an optical reflectance sensor • relative saturation calculated from sample temperature and dew point temperature

Mirror

Optical Sensor Sample Gas

Sample

47

MOISTURE EQUILIBRIUM AND MOISTURE MIGRATION WITHIN TRANSFORMER INSULATION SYSTEMS – Tutorial of CIGRÉ WG A2.30

Dielectric Response Methods 1927+ •

Dissipation factor at power frequency

•

Polarisation index, tip up test

U

U(t) Ur,max

tc

t

t d t peak

At that time: No reliable method for onsite moisture diagnostics 1991 RVM for water determination •

U, I

TC

KTH Stockholm

2007 Combination of PDC and FDS •

idep (t)

t

Dissipation factor

ETH Zurich, Switzerland

1999+ Frequency Domain Spectroscopy •

Uc (t)

Soon questioned by users (Kachler 1996)

1999+ Polarisation Depolarisation Currents •

ipol (t)

Frequency

Universities of Hannover and Stuttgart

MOISTURE EQUILIBRIUM AND MOISTURE MIGRATION WITHIN TRANSFORMER INSULATION SYSTEMS – Tutorial of CIGRÉ WG A2.30

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Measurement • Main insulation between HV and LV winding will be measured • Voltage to shorted HV, current from shorted LV • Guard to tank

Voltage source

~

Current meter HV-winding LV-winding

Measurement of: • Time domain voltage after charging Æ RV method • Time domain current during charging and discharging Æ PDC • Frequency domain current and dissipation factor Æ FDS • Combination of TD and FD

Guard

Main insulation Tank

MOISTURE EQUILIBRIUM AND MOISTURE MIGRATION WITHIN TRANSFORMER INSULATION SYSTEMS – Tutorial of CIGRÉ WG A2.30

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1000 100

moisture of cellulose and aging

high

10 1

Dissipation factor

0,1 1

insulation geometry

low

oil conductivity

Current(nA) (

Interpretation Ipol

Idep

10

100

high low

moisture of cellulose, aging high

high

low 0,1

insulation geometry

low

moisture of cellulose and aging

0,01

0,001 0,0001 0,001 0,01

high

oil conductivity 0,1

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Fast measurement

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No information for t