moisture in insulation - ieeeewh.ieee.org/soc/pes/saintlouis/2010 12...
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1 /GE /
April 2, 2008
Assessing Water Content in solid transformer insulationfrom dynamic measurement
of moisture in oil
Brian Sparling, SMIEEEGE Energy, Canada
IEEE PES SeminarVancouver BCApril 3rd 2008
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2 /GE /
April 2, 2008
Moisture in insulation
Residual moisture from manufacturing process: Good drying process should result in less than 0.5% moisture in paper
Residual moisture from manufacturing process: Good drying process should result in less than 0.5% moisture in paper
Insufficient maintenance: To be effective, Silica gel system needs constant maintenance, any lapse could result in large amount of moisture into the transformer
Insufficient maintenance: To be effective, Silica gel system needs constant maintenance, any lapse could result in large amount of moisture into the transformer
In transformer, there is several sources of moisture:
In transformer, there is several sources of moisture:
Leaks: Gasket and/or joints could leakLeaks: Gasket and/or joints could leak
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3 /GE /
April 2, 2008
Moisture in insulation
Paper degradation: The thermal degradation of paper does generate water
Paper degradation: The thermal degradation of paper does generate water
Moisture is strongly absorbed by paper, once inside the transformer, it is difficult to remove.
Moisture is strongly absorbed by paper, once inside the transformer, it is difficult to remove.
In transformer, there is several sources of moisture:
In transformer, there is several sources of moisture:
This water will generate yet more paper degradation
This water will generate yet more paper degradation
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4 /GE /
April 2, 2008
Moisture in insulation
Moisture in winding paper is critical • Reduces dielectric strength• Increased risk of bubbling at high load• Accelerates the rate of insulation aging
Moisture in winding paper is critical • Reduces dielectric strength• Increased risk of bubbling at high load• Accelerates the rate of insulation aging
Only moisture in oil can be measuredOnly moisture in oil can be measured
Moisture in oil• Can lead to water condensationMoisture in oil• Can lead to water condensation
Moisture in pressboard barrier is critical • Reduces dielectric strengthMoisture in pressboard barrier is critical • Reduces dielectric strength
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5 /GE /
April 2, 2008
Paper is found in many forms in winding insulation
Clamping plate Tube Cylinder Angle ring Moulded lead exit
Clamping plate Snout Spacer block Cap Metalized stress ring Paper wrap around
copper wire
Cylinder
Cross-sectional view of a 400 kV transformer end insulation (220 kV-side)
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6 /GE /
April 2, 2008
Deterioration of oil and cellulose
AGED Cigre Brochure 323, Oct 2007
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7 /GE /
April 2, 2008
Paper consist of fibers
Paper structure Paper fibre
Cigre Brochure 323, Oct 2007
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8 /GE /
April 2, 2008
Fibers are built from micro fibers -which consist of cellulose molecules
Micro and submicrofibers Cellulose molecule
DP – ValueAverage number of rings in the cellulose molecule chain
Cigre Brochure 323, Oct 2007
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Where does water come from?
CH2OH
O
OH
OHO
CH2OH
OH
OHO
O
CH2OH
OH
OHO
Glucose
C
CC
C
C
C
CC
CC
C
CC
C
C
H
H
H
HH H
H
H
H
H
H
H
H
HH
- - - - - - - Cellulose - - - - - - -COMPOSITION OF PAPER
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CH2OH
O
H
HH
OH
OHO
H
H O
Where does water come from?
Glucose
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OHH
HOH
80 °C - 300 °C
CH2OH
O
H
HHOH
H
OHH
O
H
O
Where does water come from?
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OHH
O
HOH
HOH
O
80 °C - 300 °C
+
CH2OH
OHO
H
H HH
OHH
Where does water come from?
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O
HOH
HOH
80 °C - 300 °C
+
CH2OH
OH
OHO
HH
H HH
HOH
O
+
O
Where does water come from?
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OHOH
HOH
CO
80 °C - 300 °C
+
+
CH2OH
OH
OHO
HH
H HH
O
HOH
+
OC
Where does water come from?
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O CHO
H
H
H
HOH
HOH
CO
80 °C - 300 °C
+
+
+
CH2OH
OH
OHO
O
HH
H HH
O
HOH
+
C
Where does water come from?
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O CHO
H
H
H
HOH
HOH
CO
80 °C - 300 °C
+
+
+
CH2OH
OH
OHO
O
HH
H HH
O
HOH
+
C
Where does water go?
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17 /GE /
April 2, 2008
CH2OH
O
OH
OHO
CH2OH
OH
OHO
O
CH2OH
OH
OH
O
HOH (water)
Acids
CH2OH
O
OH
OHO
H
CH2OH
OH
OHO
O
CH2OH
OH
OH
O
OH
The water will also degrade the paper
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18 /GE /
April 2, 2008
Over saturation of oil when WCO > saturation
Impact of moisture in oil
V. Davydov, EPRI Moisture Management in Transformer Workshop, Nov.2002, Edison, New Jersey
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19 /GE /
April 2, 2008
0
200
400
600
800
0 20 40 60 80 100
Temperature (°C)
Wat
er c
onte
nt (p
pm)
Water-in-oilsaturation curve
75°C
5%
75°
Condensation temperature (°C)
10°C
10
20 5%
Impact of moisture in oil
Sensor Relative Humidity (RH%)
Sensor Temperature(°C)
SensorsAbsolute water
content in oil (ppm)
20ppm
Output
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20 /GE /
April 2, 2008
Rectifier Transformer B21 MVA OFWF
0
10
20
30
40
50
Jan-04 Jan-05 Jan-06 Jan-07
Tem
pera
ture
(oC
)
0
3
6
9
12
15
Wat
er in
Oil
(ppm
)
Change in water-in-oil concentration
Water content in oil varies with Temperature
Top Oil Temp.
Water in Oil
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21 /GE /
April 2, 2008
Most of the water is stored in the solid insulation
Oil90%
Thick5%
Thin2% Winding
3%
Insulation Weight Distribution
Thick55%Thin
22%
Winding22%
Oil1%
Water Distribution
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22 /GE /
April 2, 2008
Example of water distribution in a 25 MVA transformer with 3% moisture in paper
40°C
Oil (25 000litre) 10 ppm 0.25 kg
Paper (2500 kg) 3 % 75 kg
Total 75.25 kg
80°C
80 ppm 2.0kg
2.93% 73.25 kg
75.25 kg
•Most of the water is in the solid insulation•Change in water content of oil does not entail a similar change in the water content of paper
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Paper Aging•Definition, End of life criteria
•Contributing factors
Insulation aging is irreversible
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24 /GE /
April 2, 2008
Moisture content in transformer insulation is a persistent concern
Aging transformers tend to build-up moisture
IEEE Std 62 – 1995:–Dry 0-2%–Wet 2-4%–Very Wet 4.5% +
Only moisture in oil can actually be measured
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25 /GE /
April 2, 2008
The amount of moisture in paper is a very important parameter to know, as it directly affects the following:
Aging rate of the winding insulationBubbling temperature (limits the amount of overloading of a transformer)Dielectric strength of the barriers at the bottom of the winding
Impact of moisture in paper
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26 /GE /
April 2, 2008
Water accelerates ageing of Kraft paper
Cig
re p
ublic
atio
n 32
3 O
ct. 2
007
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27 /GE /
April 2, 2008
•Presence of oxygen has, in laboratory experiments shown an ageing acceleration by a factor 2-3
•Above 2000 ppm O2 showed concentration independent ageing rates
•Oxygen saturated 30 000 ppm O2
•Oxygen free 300 ppm O2
Age
ing
rate
Oxygen concentration
Lampe’s suggestion
Degassing equipment
salesperson
Cigre Brochure 323, October 2007
Oxygen accelerates ageing of paper
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28 /GE /
April 2, 2008
Example of Winding Paper Degradation
Example of treeing in a wet pressboard barrier V.Davydov, EPRI moisture Seminar Nov. 2002
Example excessive paper aging
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29 /GE /
April 2, 2008
Evolution of fault at weak points
The weak points are candidates for a possible failure
V. Sokolov Cigre Colloquium 1997
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30 /GE /
April 2, 2008
Residual water in winding insulation can release water vapor bubbles at high temperature
T.V. Oommen et al, Atlanta, 2001
Impact of moisture in winding insulation
• Increased risk of releasing bubbles at high load• Increased risk of releasing bubbles at high load
50
70
90
110
130
150
170
190
0 2 4 6 8 10
WCP % w/w
Tem
pera
ture
Kobayashi rapid heatingKobayashi slow heating
Davydov
Oommen gas free
Oommen gas saturated
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31 /GE /
April 2, 2008
Example of Overheating
Bubble Emission
Trapped Bubbles
V. Davydov EPRI Moisture Seminar 2002
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32 /GE /
April 2, 2008
Pressboard barrier
EquipotentialHVLV
Moisture reduces dielectric strength of pressboard barriers
Electric field
Tangential field
Perpendicularfield
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33 /GE /
April 2, 2008
Surface discharges are more likely on angle rings
0
20
40
60
80
100
0 1 2 3 4
Moisture in paper (%)
Dis
char
ge in
cept
ion
volta
ge (%
)
HVLV
Alstom T&D, Merida, 2003
Moisture can promote tracking discharges on pressboard barriers
Wet Barriers = Strong Discharges
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34 /GE /
April 2, 2008
Assessing Water Content in Transformer Solid insulation
Fabre & Pichon1960
Moisture in Oil (ppm)
Moi
stur
e in
pap
er %Oommen 1983Two problems :
• Oil saturation curve need to be known
• Transformer must be under thermal stability condition
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35 /GE /
April 2, 2008
The problem:
Should we use absolute water content in oil (ppm) or Relative Saturation (RS)?
Is water content uniform through the transformer solid insulation?
How do we handle the diffusion time between paper and oil?
Determination of water in solid insulation from water in oil
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36 /GE /
April 2, 2008
Oil saturation characteristics
Water content in oil can be expressed in ppm
This value must be related to oil saturation characteristics
But saturation characteristic vary with type of oil and oil condition
Therefore it is more convenient to consider Relative Saturation (RS)
0
200
400
600
0 20 40 60 80 100
Temperature
Wat
er c
onte
nt a
t sat
urat
ion
(ppm
)
New oil
Old oil Oxidize
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37 /GE /
April 2, 2008
Relative Saturation (RS)
Relative saturation is the moisture content relative to the saturation value at a given temperature
At equilibrium, RS in oil = RS in paper
It varies within the transformer
Example:Sensor: 40°C, RS =50%Hot spot: 85°C, RS =10%
0
200
400
600
800
0 20 40 60 80 100
Temperature (°C)
Wat
er c
onte
nt a
t sat
urat
ion
(ppm
)100 ppm
500 ppm
50 ppm
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38 /GE /
April 2, 2008
Moisture Migration Summary
Equilibrium curve exist to relate moisture in paper to relative saturation in oil.These curves assume Equilibrium exists (the moisture has stopped moving between the oil and paper)
But this is never the case.Many people make errors in using these charts, ‘blindly’ without considering equilibrium conditions which must exist, and their mistakes can be costly
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39 /GE /
April 2, 2008
0
1
2
3
4
5
6
7
8
0 10 20 30 40 50 60
Moisture relative saturation (%)
Moi
stur
e in
pap
er (%
)
Jeffries 30°C
Jeffries 90°C
0
1
2
3
4
5
6
7
8
0 10 20 30 40 50 60
Moisture relative saturation (%)
Moi
stur
e in
pap
er (%
)
Jeffries 30°C
Jeffries 90°C
Oommen 30°C
Oommen 90°C
0
1
2
3
4
5
6
7
8
0 10 20 30 40 50 60
Moisture relative saturation (%)
Moi
stur
e in
pap
er (%
)Jeffries 30°C
Jeffries 90°C
Oommen 30°C
Oommen 90°C
Fessler 30°C
Fessler 90°C
Assessing Water Content in Transformer Solid insulation
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40 /GE /
April 2, 2008
Moisture in paper
0 °C
40 °C20 °C
60°C80°C100°C
16
14
12
10
8
6
4
2
020 40 60 80 1000
Relative Humidity (%RH)
Abs
olut
e H
umid
ity(%
)
0 °C
40 °C20 °C
60°C80°C100°C
16
14
12
10
8
6
4
2
020 40 60 80 1000
Relative Humidity (%RH)
Abs
olut
e H
umid
ity(%
)
Equilibrium curves are now available to convert moisture in oil into moisture in paper without considering oil saturation characteristicsBut we still need: • Temperature of oil-paper interface• Diffusion time constant• Facility for integrating results over long period of
time
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41 /GE /
April 2, 2008
Paper at different temperatures inside the transformer will will have different moisture levels
Different areas of the insulation system have different thickness (winding insulation versus barrier insulation)The Equilibrium condition therefore will take much longer for barrier insulation versus winding insulation
Moisture Migration Summary
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42 /GE /
April 2, 2008
Temperature 1mm 2mm 4mm
80 °C 0.9 3.6 14
60 °C 4.2 17 67
40 °C 20 79 317
20 °C 93 373 1493
Insulation Thickness
Typical diffusion time constant (in days)
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43 /GE /
April 2, 2008
Moisture in paper varies within the transformer
Win
ding
44 6456 76
Temperature (oC)
Oil
3.32.21.71.2
Moisture content (%) at equilibrium condition
Winding insulation
Thin barriers
Area of Interest for moisture in paper
Guided convection flowthrough disk windings
1.2% 3.3%
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44 /GE /
April 2, 2008
Migration of moisture in transformers
• Moisture content in solid insulation, is not a single value
• It appears impractical to assess the moisture content of the thick insulation
• Lowest part of pressboard barriers is the most critical location and should determine needs for dying
• Sensitivity analysis indicates that the value assigned to diffusion time constant is not critical
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45 /GE /
April 2, 2008
• There is a correlation between the amount of water in the oil and in the paper
• However, this correlation is dynamic and is changing as a function of transformer loading
• The dynamics of the distribution of water in the transformer is quite complex and changing
Migration of moisture in transformers
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46 /GE /
April 2, 2008
0
10
20
30
40
50
60
70
80
90
100
Time (days)
Tem
pera
ture
oC
, R
H%
0
1
2
3
4
5
6
7
8
9
10
Load
(MV
A)
Sensor Temperature Sensor RH%
Hot spot temp. Hot spot RH%
Load (MVA)
0 5 10 2015
Moisture inside the transformer moves back and forth between the oil and paper by diffusion as a function of temperature
84 ppm
32 ppm
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47 /GE /
April 2, 2008
What to do?
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48 /GE /
April 2, 2008
Advanced Gas and Moisture monitor
H2 and CO
Moisture in oil
Trending
4 analog inputs
Data Logging
Networking
Integrated Modem/TCP-IP
Hydran M2
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49 /GE /
April 2, 2008
Typical HYDRAN M2 Installation
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50 /GE /
April 2, 2008
Hydran M2
With
Models
The Hydran M2 as Advanced Transformer Monitor
Top Oil Temperature
Cooling Fan/Pumps Status
OLTC Temperature
Load Current
Alarms
• Incipient Fault • Moisture in Oil, in Windings and in Barriers
• Apparent Power • Cooling Status and tracking
• Winding Hot Spot • Aging Rate
• OLTC Fault • Bubbling Margin
• Cooling Efficiency • Cumulative aging
Dissolved Moisture
Dissolved Gases
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51 /GE /
April 2, 2008GE Company - Proprietary & Confidential
Temperature and Load
Top oil
OLTC
MagneticallyMountedTemperaturesensor
Clip-On load sensor
Ambient TemperatureSensor
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52 /GE /
April 2, 2008
Field experience with on-line moisture monitoring
US Western Utility
50MVA, Core type,230 / 13.8 kV 55°C rise
Hydran M2 mounted on spare cooler outlet
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53 /GE /
April 2, 2008
Field data recording for moisture assessment - 50 MVA transformer
0
10
20
30
40
50
Sep-03 Oct-03 Nov-03 Dec-03 Jan-04 Feb-04 Mar-04
Tem
pera
ture
, RH
%
0.2
0.4
0.6
0.8
1.0
1.2
Load
Fac
tor.
Top-oil Temp.
Sensor Temp.
RH% at Sensor
Load
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54 /GE /
April 2, 2008
Moisture content in winding insulation - 50 MVA transformer
-20
-10
0
10
20
30
40
50
60
Sep-03 Oct-03 Nov-03 Dec-03 Jan-04 Feb-04 Mar-04
Tem
pera
ture
(oC
), D
iffus
ion
Tim
e C
onst
ant (
days
)
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
Moi
stur
e in
Pap
er (%
)
Averaged Moisture Content
Hot-Spot Temperature
Diffusion Time Constant
Ultimate Moisture Content
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55 /GE /
April 2, 2008
Moisture content in pressboard barrier - 50 MVA transformer
-40
-20
0
20
40
60
80
100
Sep-03 Oct-03 Nov-03 Dec-03 Jan-04 Feb-04 Mar-04
Tem
pera
ture
(oC
), D
iffus
ion
Tim
e C
onst
ant (
days
)
2.0
2.5
3.0
3.5
4.0
4.5
5.0
5.5
Moi
stur
e in
Bar
rier (
%)
Diffusion Time Constant
Averaged moisture in barrier
Bottom oil temperature
Ultimate Moisture in barrier
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56 /GE /
April 2, 2008
Analog Set-up ScreensAnalog Set-up Screens
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57 /GE /
April 2, 2008
Moisture and Bubbling Model
Water condensation temperature
Absolute water content in oil
Winding bubbling temperature
Bubbling temperature margin,alarm point
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58 /GE /
April 2, 2008
Moisture and Bubbling Model
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59 /GE /
April 2, 2008
HYDRAN M2– Communications, real time survey
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60 /GE /
April 2, 2008
Winding Hot SpotCooling Efficiency
Aging
Cooling Status
Gas LevelWater LevelMoisture in PaperLoad
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61 /GE /
April 2, 2008
How degraded is my insulation?
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62 /GE /
April 2, 2008
Detection of paper degradationCO2 / CO
• CO2/CO ratios < 3 indicate fault involving paper degradation
• CO2 can also come from atmosphere in open breathing transformers
• CO can come from oil oxidation, paint, varnishes and phenolic resins
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63 /GE /
April 2, 2008
Several furanic compounds are generated during paper decomposition
2FAL is the most stable and most abundant compound
Detection of paper degradationfrom furanic compounds
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64 /GE /
April 2, 2008
Increasing furanic compound content correlate with falling DP
Detection of paper degradationfrom furanic compounds
Cigre Brochure 323, October 2007
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65 /GE /
April 2, 2008
Reduction of DP with time
0
200
400
600
800
1000
0 2000 4000 6000 8000
Time (hours)
DP-
valu
e
Example of DP reduction with time for
• Kraft paper• 3% water content• 110°C
Note that rate of DP reduction reduces with time; aging is not a linear function
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66 /GE /
April 2, 2008
Mechanical strength is reduces with DP
1250 1000 750 500 250 0DP-value
0
40
80
120
Tens
ile in
dex
[Nm
/g]
Mechanical strength is a function of length of cellulose chains in fibresDegree of polymerisation
(DP) in cellulose fibres describes ageing condition
DP of 200 correspond to remaining strength of about 30%
Cigre Publication 323, Oct. 2007
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DEGRADATION OF PAPERCORRELATION BETWEEN 2-FAL and DPV
DEGREE OF POLYMERISATION
2-FU
RA
LDEH
YDE
(ppb
,m
icro
g/L)
200 300 400 500 600 700 800 900 1000 1100 1200
10000
1000
100
10
0% 25% 50% 75% 100% Residual Life
VIT ST2
PAL T3ALK 1-2BALK 7-8A
ALK 5-6B
KLY 2RX2
KLY SP5RXPAL T2
ALK 3-4B
ASH T-1
RYL SPT1
RLY SPT3
MCA TX
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68 /GE /
April 2, 2008
As temperature and load change, so does the movement of water inside the transformer, between the paper and the oil
In Practice, the perfect equilibrium needed to use the published curves almost never exist in a transformer
Only a dynamic model, computed online in real time, can make a good evaluation of the amount of moisture in the paper, in the areas of interest
In Conclusion
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69 /GE /
April 2, 2008
Trademarks
• © 2008 General Electric Canada. All rights reserved.
• All brand and product names mentioned in this document are trademarks or registered trademarks of their respective companies.
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70 /GE /
April 2, 2008
Thank you