water in paper tutorial
TRANSCRIPT
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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
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Part I
Introduction
Presented by
Dr. Jim DukarmPresident
Delta-X Research Inc
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Introduction
Water-in-Paper Activity:a New Concept for
Moisture Assessment in Transformers
Jim DukarmPresident
Delta-X Research Inc
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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
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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%.
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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
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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.
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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
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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.
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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.
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And now for the details . . .
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Part II
Outline of Water-in-Paper Activity
Concept
Presented by
Dr. Oleg RoizmanIntellPower Pty Ltd
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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
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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
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Many Faces of Water
Free, mobile, bound, dissolved, active...
WCP (%) and WCO (ppm)
RS, ERS and RH
Dew point
Water activity and water potential
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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
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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
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Introduction of Water-in-Paper Activity (Awp)
Historical BackgroundDefinitionDeterminationMeasurementsInstrumentationTest procedureComparison to other parameters used for moisture assessment
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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.
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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.
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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!
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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
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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
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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
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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, %
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Indicative Water Activity Isotherm
http://www.lsbu.ac.uk/water/activity.html
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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
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Instrumentation and Methods for AwpMeasurement
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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
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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
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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
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• 20 MVA• 66/22 kV• ONAF/OFAF• 15,000 L• New• Conservator - free breathing • Monitored over 16 hours
Factory Experience
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Position of Moisture Transducer
CoolerConservator
Bottom Drain Valve
Oil-PaperSystem
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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
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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
RS Response to T Rise
Awp=0.04
Awp=0.13
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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
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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
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Diagnostics by Awp
0.2 – 1.0
0.1 – 0.2
0 – 0.1
Quick diagnostic guide
Awp
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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
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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
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Part III
Research Results and Case Studies
Presented by
Dr. Valery [email protected]
Centre for Power Transformer Monitoring, Diagnostics and Life ManagementMonash University, Australia
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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
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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
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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
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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
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Conclusion 1
Sorption curves relating Awp to WCP for new and aged paper are different.
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2. Paper-Oil Physical Complex: Study into Moisture Equilibrium for New Paper and Oil
Winding Disk
1-mm Pressboard
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Test Model: Winding Disk and 1-mm Pressboard Coil
Winding Disk
1-mm Pressboard
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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
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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%
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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
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“Foggy” Oil during Cooling at Awp = 0.32
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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.
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3. Use of Awp for Assessment of Online Dryout of 70+ y.o. 4 MVA Tx
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Awp in 4 MVA TxImmediately Following Dryout
CoolerConservator
Awp ≈ 0.06
Bottom Drain Valve
Oil In
Oil Out
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Distribution of Moisture in Winding Insulation after Dryout
Conductor
Inner Layers (WCPa≈5%)
Outer Layer (WCPa≈2%)
Note: Tx operates at low temperature
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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.
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4. Experience with Vegetable Oil Filled Tx
10/16 MVAONAFOil preservation: non-standard (on customer’s request)Manufactured in 20051 year in operation
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Position of Moisture Probe in Txduring Factory Temperature Rise Test
CoolerConservator
Oil-PaperSystem
Moisture Probe
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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
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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, %
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Assessment of Awp in Vegetable Oil Filled Txafter 1 Year in Service
CoolerConservator
Awp = 0.014
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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.
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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.
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Questions?