55703882 Water in Paper Tutorial

Water-in-Paper Activity: A New Concept for Moisture Assessment in Transformers

Oleg RoizmanValery Davydov

Jim Dukarm

IEEE/PES Transformers Committee Meeting Montreal, Quebec, CanadaOctober 23, 2006

Part I

Introduction

Presented by

Dr. Jim DukarmPresident

Delta-X Research Inc

Introduction

Water-in-Paper Activity:a New Concept for

Moisture Assessment in Transformers

Jim DukarmPresident

Delta-X Research Inc

Subject of the presentation

The presentation shows how the concept of water-in-paper activity is useful for

Understanding the relationship between water in cellulose and water in oil in transformers, and

Assessing and controlling the water content of cellulose insulation

Water in cellulose

Water in transformer cellulose starts out low (below 1% by dry weight) and accumulates as a chemical byproduct of cellulose aging and also as a result of leaks in tank gaskets and cooling system components.

Depending on the type and voltage class of the transformer, it is considered desirable to keep the water content of cellulose below 2% or 3%.

Minimizing water in cellulose

Water in cellulose must be minimized because it can cause or contribute to various problems:

Depolymerization of cellulose (weakens the winding insulation)

Bubble formation (resulting PD causes damage to the paper)

Reduction of dielectric strength of winding insulation

Assessing moisture in cellulose

Partitioning of water between cellulose and oil

Typically over 90% of total water is in cellulose

Thin paper may be 15% of total cellulose

Water solubility in oil increases with temperature

Under typical varying load and ambient temperature, equilibrium between water in cellulose and water in oil is not reached.

Assessing moisture in cellulose

There is a complicated relationship between %RS in oil and water in cellulose.

"Active water content" of paper drives %RS on short time scale

Total water content of bulk cellulose dominates on long time scale

Water-in-paper activity (Awp)

Water-in-paper activity (Awp) is the %RS which the paper is "trying" to force the oil to.

Awp is a good indicator of the quantity of water available for exchange between the paper and the oil on a short time scale.

Awp does not depend much on temperature.

Evaluation of Awp is based on %RS and temperature measurements.

Usefulness of Awp

Awp is directly related to bubble formation tendency and to moisture-related changes in insulation dielectric strength.

Awp is very useful for characterizing moisture in paper and for guiding transformer dry-out.

The water content of the bulk cellulose slowly drives Awp, which has important implications for dry-out.

And now for the details . . .

Part II

Outline of Water-in-Paper Activity

Concept

Presented by

Dr. Oleg RoizmanIntellPower Pty Ltd

[email protected]

Learning Objectives

Methods available today to estimate moisture content of solid insulationIntroduction of the Water-in-Paper Activity (Awp) conceptInstrumentation and methods for the Awpmeasurement and determinationWays of standardization of the AwpNew research results and their application to practical assessment of moisture in transformer insulationHands-on experience with moisture assessment in transformers; case studies

Detrimental Effects of Water

Accelerated paper aging

Vapor bubbles evolution

Corrosion of core and tank

Decrease of PD inception level

Progressive consumption of oil additives

Decrease of insulation dielectric strength

Reduction of transformer life

Many Faces of Water

Free, mobile, bound, dissolved, active...

WCP (%) and WCO (ppm)

RS, ERS and RH

Dew point

Water activity and water potential

Unclear Issues

No consideration for water in Loading Guide, life extension, aging, test codes, standard terminologyNo common view on oil acceptance guide from water perspectiveNo agreed method to assess moisture and judge final drynessNo clear understanding of water effects on dielectric stress, breakdown voltage, vapor bubble formation and aging

Methods for Moisture Assessment

Karl Fischer titration method

Dielectric Loss factor (Tan delta)

Polarization and depolarization currents

Return (recovery) voltage method (RVM)

Dielectric spectroscopy

Water Heat Run Test

Use of equilibrium charts

Introduction of Water-in-Paper Activity (Awp)

Historical BackgroundDefinitionDeterminationMeasurementsInstrumentationTest procedureComparison to other parameters used for moisture assessment

Thermodynamic Activity

1906:The concept of thermodynamic activity was introduced by G. N. Lewis (100 years ago!) J. Am. Chem. Socµ(sys)= µ(w) + RT ln(aw)Used in food, pharmaceutical, pulp and paper industries1999 V.G. Davydov, O. Roizman and W.J. Bonwick, “Moisture Evaluation in Oil and Paper for Sealed Transformer Insulation System”, EPRI Substation Equipment Diagnostics Conference VII.2005 O.Roizman, V. Davydov and B. Ward, “Water – in–Paper Activity: A New Approach for Moisture Management In Transformers”, EPRI Substation Equipment Diagnostics Conference XIII.

Example:

If a dry pressboard (0.5%) and a wet pressboard (4.6%) were placed into a hot oil (80 o C) of 20% of RS, we would expect that over time the wet pressboard will lose some water and the dry pressboard will gain some water.

However, the water content of each will not become equal.

Dry and Wet PressboardT

WCAB=3.25 %

Steady state

WCABi=1.8 %

WCA=0.5%, MA=745gWCB=4.6%, MB=346g

A

B

T

MA’=170g, not 745 g!

Definition of Awp

Water-in-Paper Activity (Awp) of a oil-paper insulation system is a measure of free water available in cellulose for exchange with surrounding oil

Awp = %ERS/100 = p/po;0 < Awp < 1

Types of Cellulose InsulationMax. Sat. Moisture

ApplicationPhotoBrand name

7%support structures, core and coil blocking

ELECTRICAL GRADE MAPLE

10%spacers in multiple barrier configurations

HI-LAM KRAFT TRANSFORMERBOARD

5%washers, filler blocks, stacking blocks, static ring cores and support beams

LAMINATED KRAFT TRANSFORMERBOARD

3%clamping and support blocks

LAMINATED PRECOMPRESSED PRESSBOARD

Water Activity of Multicomponent System

Awp

pw= pw

Awo

Awp

pw = pw = pw

Awo

pw = pw

oil

Aw=%ERH/100

pw = pw

Awp

air

paper

Sorption Isotherm at 80 ºC

Sorption Isotherm for 1mm pressboard at 80 C

0

1

2

3

4

5

6

7

8

9

10

0 0.2 0.4 0.6 0.8 1

Awp

WCP

a, %

Indicative Water Activity Isotherm

http://www.lsbu.ac.uk/water/activity.html

Properties of Sorption Isotherms

Sorption isotherms are valid only for a single material (e.g. one type of cellulose)Sorption isotherms are affected by any variation in material ( e.g. aging)Sorption isotherms show a difference between absorption and desorption curves (sorption hysteresis)Sorption isotherms are experimentally determined

Instrumentation and Methods for AwpMeasurement

Moisture Metersfor determining Awp

Very compact in size and extremely versatileProvides measurement of the relative saturation of water and temperature of oil The sensor operates directly in the oil so it can be installed directly into the transformer or processing equipment Can be used to estimate the water content of paper insulation

Awp Measurement (idealized case)

0 10 20 30 40 50 60 70 80 90 10020

40

60

80

100

T, C

0 10 20 30 40 50 60 70 80 90 1000

20

40

60

80

%rs

hours

Awp=0.18

Determination of Awp for Operating Tx

Moisture Sensor

Moisture Sensor

Temperature Sensors

Temperature Sensors

FuzzyLogic

InferenceEngine

LoadProfileLoad

Profile Water-in-

Paper Activity

Awp

Water-in-

Paper Activity

Awp

• 20 MVA• 66/22 kV• ONAF/OFAF• 15,000 L• New• Conservator - free breathing • Monitored over 16 hours

Factory Experience

Position of Moisture Transducer

CoolerConservator

Bottom Drain Valve

Oil-PaperSystem

Factory Temperature Rise Test

0

10

20

30

40

50

60

70

80

16:0

4:37

16:2

7:37

16:5

0:37

17:1

3:37

17:3

6:37

17:5

9:37

18:2

2:37

18:4

5:37

19:0

8:37

19:3

1:37

19:5

4:37

20:1

7:37

20:4

0:37

21:0

3:37

21:2

6:37

21:5

0:37

22:1

3:37

22:3

6:37

22:5

9:37

23:2

2:37

23:4

5:37

0:08

:37

0:31

:37

0:54

:37

1:17

:37

1:40

:37

2:03

:37

2:26

:37

2:49

:37

3:12

:37

3:35

:37

3:58

:37

4:21

:37

4:44

:37

5:07

:37

5:30

:37

5:53

:37

6:16

:37

6:39

:37

7:02

:37

T, d

eg C

0

1

2

3

4

5

6

7

8

9

10

RS,

%

T RS

T oil

%RS

0

10

20

30

40

50

60

70

80

90

100

0 10 20 30 40 50 60 70

hours

T, d

eg C

0

10

20

30

40

50

60

70

80

90

100

RS,

%

T

[email protected]%

[email protected]

RS Response to T Rise

Awp=0.04

Awp=0.13

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 10

100

200

300

400

500

600

700

800

900

Awp

wco

, ppm

T= 0

20

40

60

100

Awp

wco

, ppm

Awp vs WCO

Awp vs RS

RS is measure of moisture in oil only

Awp indicates moisture in oil-paper interface

RS from 0 to 100%Awp from 0 to 1

%RS highly temperature dependent and can vary within full scale from 0 to 100%

Awp depends on T at equilibrium and varies within narrow range.

RS, %Awp

Diagnostics by Awp

0.2 – 1.0

0.1 – 0.2

0 – 0.1

Quick diagnostic guide

Awp

Awp and Drying Process

Drying transformer insulation is a process of reducing AwpKeeping oil dry at all times by on-line dehydration is one way to maintain safety and dryness of transformer insulationAwp is the most critical parameter to control drying process

Conclusions

Concept of water activity is useful for transformer moisture managementAwp reflects harmful effects of water on dielectric strength and risk of bubblingAwp can be benchmarked by recording RS during factory temperature rise test Awp can be standardized and used as a monitoring parameter for normal operation and dryout

Part III

Research Results and Case Studies

Presented by

Dr. Valery [email protected]

Centre for Power Transformer Monitoring, Diagnostics and Life ManagementMonash University, Australia

1. Sorption Curves(Valid for New Paper-Air and New Paper-Oil Physical Complexes)

0

1

2

3

4

5

6

0 0.1 0.2 0.3 0.4 0.5Awp

WC

Pa, %

0C 20C 40C 60C

80C

100C

Note: WCPa – Active Water Content of Paper

Awp – Water-in-Paper Activity

Study into Moisture Equilibriumfor New and Aged Paper

Salt Solution (Humidity Generator)

T & RH Probe

Air

1 New & 1 Aged Paper Samples (KTU, 127 127 µµmm)

Metal Mesh

Sealed Glass Vessel

T & RH Test Data for Paper-Air Complex Over Salt Solution 1 and Salt Solution 2

(a)ERH1=11.3%(Awp1=0.113)

(b)ERH2=43.2%(Awp2=0.432)

0

10

20

30

0 1 2 3 4 5 6 7

T, d

eg. C

0

20

40

60

0 1 2 3 4 5 6 7Time, days

RH

, %

Measure WCP at ERH1Measure WCP at ERH2

Results of WCP Balance Measurements for Aged and New Paper at Awp1 and Awp2

Awp1=0.113 Awp2=0.432

2

3

4

5

6

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5

Aw

WC

P, %

KTU aged (DP=292)

KTU new (DP=1148)

Awp

Conclusion 1

Sorption curves relating Awp to WCP for new and aged paper are different.

2. Paper-Oil Physical Complex: Study into Moisture Equilibrium for New Paper and Oil

Winding Disk

1-mm Pressboard

Test Model: Winding Disk and 1-mm Pressboard Coil

Winding Disk

1-mm Pressboard

Awp Measurement

0 10 20 30 40 50 60 70 80 90 10020

40

60

80

100

T, C

0 10 20 30 40 50 60 70 80 90 1000

20

40

60

80

RS

, %

hours

Awp=0.18

Note: RS – Relative Saturation

Evaluation of WCPa for:(a) Awp = 0.18; (b) Awp = 0.32

0

1

2

3

4

5

6

0 0.1 0.2 0.3 0.4 0.5Awp

WC

Pa, %

0C 20C 40C 60C

80C

100C

2.7%

4%

Test at Awp = 0.32 (WCPa = 4%)

0

40

80

T, d

eg C T oil

0

50

100

150

WC

O, p

pmWCO (WCPa=4.0%)

0

25

50

75

100

0 6 12 18 24 30 36 42 48

Time, hrs

RS,

%

RS (WCPa=4.0%)

Awp = 0.32

“Foggy” Oil during Cooling at Awp = 0.32

Conclusion 2

Transformer paper-oil systems with the Water-in-Paper Activity approaching and exceeding 0.2 (or with WCPa > 2.7%) are critical in terms of moisture and require immediate attention.

3. Use of Awp for Assessment of Online Dryout of 70+ y.o. 4 MVA Tx

Awp in 4 MVA TxImmediately Following Dryout

CoolerConservator

Awp ≈ 0.06

Bottom Drain Valve

Oil In

Oil Out

Distribution of Moisture in Winding Insulation after Dryout

Conductor

Inner Layers (WCPa≈5%)

Outer Layer (WCPa≈2%)

Note: Tx operates at low temperature

Conclusion 3

During on-line dryout of transformers moisture is removed from surfaces of insulation, reducing the Water-in-Paper Activity to an acceptable level. This in turn guarantees that the WCO will remain at a safe level for several months.

4. Experience with Vegetable Oil Filled Tx

10/16 MVAONAFOil preservation: non-standard (on customer’s request)Manufactured in 20051 year in operation

Position of Moisture Probe in Txduring Factory Temperature Rise Test

CoolerConservator

Oil-PaperSystem

Moisture Probe

Factory Temperature Rise Test @ 1.75 p.u.

0

20

40

60

80

100

8:02 8:16 8:31 8:45 9:00 9:14 9:28 9:43 9:57

Time of Day

T de

g C

& W

CO

ppm

0

2

4

6

8

10

RS,

%

T oil

RS

WCO

0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.20

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

Aw

wcp

, %0

100

80

60

20

40

New Dry Tx with Mineral or Vegetable Oil

Awp

WC

Pa, %

Assessment of Awp in Vegetable Oil Filled Txafter 1 Year in Service

CoolerConservator

Awp = 0.014

Conclusion 4

Limited data available to date indicates that the Awp for vegetable oil filled transformers can be assessed in the same way as for mineral oil filled transformers, and the critical values for Awp are expected to be the same. Further research is in progress.

SummarySorption curves relating Awp to WCP for new and aged paper are different.Transformer paper-oil systems with the Awp approaching and exceeding 0.2 (or with WCPa > 2.7%) are critical in terms of moisture and require immediate attention.During on-line dryout of transformers moisture is removed from surfaces of insulation, reducing the Water-in-Paper Activity to an acceptable level. This in turn guarantees that the WCO will remain at a safe level for several months.Limited data available to date indicates that the Awp for vegetable oil filled transformers can be assessed in the same way as for mineral oil filled transformers, and the critical values for Awp are expected to be the same. Further research is in progress.

Questions?