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8/6/2019 Humidity in Transformer Insulation
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Moisture Estimation in
Peter Fong
e ec ron cs orp.
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Content
1. The Effects of Water in Transformer
2. How Does Water Get In?
.
4. What can be Done about it?
OMICRON 9 November 2009 Page 2
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The Effects of Water in Transformer
Generates BubblesPremature Failure
r ggers art a sc arge of Good Transformers
Accelerates the A in of InsulationShorten Life Expectancy
r
ans ormer
OMICRON 9 November 2009 Page 3
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Effect 1: Bubbling200
Effect:Bubbling inception 180perature[C]
Kraft Paper New Oil
TU Paper New Oil
Aged Kraft Aged Oil
decrease with higher
moisture content 140
160Tem
120Risks: Ince tion of Partial Dischar e
80
100
1,0 2,0 3,0 4,0 5,0 6,0
Lower Dielectric Strength Short-Circuit of Windings
OMICRON Page 4
Moisture in paper [%]
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Effect 2: Dielectric Strength
Effect: PD Inception Voltage
=
rea own o age
content Dielectric strength of Oildecreases Tem erature
w ,
Risks:
a ure o rans ormerInsulation
OMICRON Page 5
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Effect 3: Aging
Effect:High temperature and100
1000
ctance/
a
Dry1%
dramatically lower the
mechanical strength of
10Lifee
xp
2%
3%
paper nsu a on
Risks:50 70 90 110 130
0,1
4%
ower t e expecte e otransformer Run transformer at lower rating
Temperature / C
OMICRON Page 6
L. E. Lundgaard, Aging of oil-impregnated paper in power transformers,IEEE Transactions on Power Delivery, Jan. 2004
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Paper Insulation
Network transformersGenerator stepup units
of chains of glucose rings As the paper ages, theserings breaks up and formswater molecules Water also accelerates the
breaking up of these rings
New: ~ 1200 DPEnd of Life: ~ 200 DP
[Neumann, Micafil-Symposium,Stuttgart, 2004] +H2O-H2O
Condensation Hydrolysis+H2O-H2O
Condensation Hydrolysis
OMICRON Page 7
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The Aging Process
When a transformer is manufactured in the factory,the paper insulated windings are subjected to
At this stage, the transformer has a moisture contentof < 0.5% b wei ht in a er and 6 m in oil
As the transformer ages, the moisture content willincrease progressively
In a severely deteriorated system, the moisturecontent could reach > 4%
OMICRON Page 8
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Where Does Water Come From?
OMICRON Page 9
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I. Grundlagen: Feuchtigkeit in l-Papier
u Normal aging of paperproduces water
ea s cou expose
insulation to atmosphericmoisture
Exposure to atmosphericmoisture duringmaintenance
Failure to dry out theinsulation during
Increase of water
0,1-0,2% per year
Water content in the paper/Pressboard: New: 0.4 to 0.8 % Aged: 3 to 5 %
Page: 10 November 09
[Cigr WG12.18 Life Management ofTransformers, 1999]
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ere s e a erMost of the water is contained in the cellulose!->>> ore mpor an o measure e wa er
content in paper than oil
100000 kg
13000 kg
Water content at 60 C:40 ppm
Water content at 60 C:4 %
Mass of the water, desolved in theoil:
Mass of the water contained in thepaper:
OMICRON Page 11
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Insulation?
OMICRON Page 12
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Moisture Estimation
There is no practical direct way of measuringmoisture levels in transformer insulation, therefore awet condition may go unnoticed for a long time
This has led to indirect method of moisture estimation
OMICRON Page 13
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Direct Method
Take paper sample from transformer and test
Limited use since possible only during repair or
tear-down
OMICRON Page 14
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Indirect Methods
Measure properties of the insulation which
1. Moisture-in-Oil Measurements (Chemical
Method)2. Moisture Saturation (Relative Humidity)
3. Dielectric Spectroscopy (Electrical Method)
OMICRON Page 15
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Moisture-In-Oil Method
Karl Fischer Titration on oil sample Use E uilibrium Curves to correlate moisture in oil to
moisture content in paper
Easy to Perform Need to wait for equilibrium (days ~ weeks)
Uncertainty in Estimates
Not accurate for aged oil
-
OMICRON Page 16
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Equilibrium Curves
OMICRON Page 17
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Round Robin Test at Oil Samples
340,5 ppm]
50
60
noil[
ppm]
Uni StuttgartBC
54,8160
180
average[
40Moist
urei
E
GF
44,3
39,8 39,7
35,3120
140
eviation
fro
30
,
19 8
80
100
10
20
5 86,7
16,2
11,2
15,2
8,99,512,212,1
7,5
40
Sample A Sample B Sample C0
,3,5
,
0US B C D E F G
December 2007
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Moisture Saturation Method
instead of ppm as in the lab Moisture probes inside the transformer measures
changes in capacitance of water molecules
Moisture diffused into the probe and changes its,determined
More accurate than oil sampling method since no
handling is involved Instrusive
equ res qu r um
OMICRON Page 19
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Dielectric Spectroscopy
Electrical Method
Method of Choice due to: on- es ruc ve