Influence of Copper on the By-products and Dielectric Properties of Different Oil-paper Insulations...
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Influence of Copper on the By-products and Dielectric Properties of Different Oil-paper Insulations Jian Hao 1, 2 , Ruijin Liao 1 , George Chen 2 and Chao Ma 3 1 University of Chongqing, Chongqing, China 2 University of Southampton, Southampton, UK 3 Gansu Electic Power Reaserch Institute, China Introduction Conclusions Transformer failure caused by the corrosion of copper material in transformer attracts great attention of researchers and engineers. In this paper, 25# naphthenic mineral oil, 25# paraffinic mineral oil, Kraft paper and copper were used to compose four combinations of oil-paper insulation samples. The ageing by-products and dielectric properties of the four combinations of oil-paper insulation samples were compared after being thermally aged at 130°C for 77 days. The influence of copper on the by-products and dielectric properties of different oil-paper insulations was obtained. [email protected] University of Southampton, Highfield, Southampton, SO17 1BJ, UK Contact details : Copper can accelerate the ageing rate of insulating oils and reduce their AC breakdown voltage. The content of copper substance dissolved in insulating oil increases with ageing time at first and then decreases. Copper has great effect on the moisture content of oil impregnated paper in the ageing process. SEM results show that there is copper product deposited on the insulating paper surface , which will deteriorate the dielectric properties of oil-paper insulation. Figure 7. Color of innermost paper in NK, NKC, PK and PKC (from left to right) (c) tanδ of oil impregnated paper (d) v of oil impregnated paper Experiments K raft p ap er o r p ap er-w rapped co pp er p lates sam ples v acu um d ry in g fo r 4 8 h o u rs(9 0 0 C , 50P a) im m ersio n o il in v acu u m fo r 2 4 h o u rs(4 0 0 C , 50P a) vacuum coo ling oil to 40 0 C bo ttlin g o il an d pap er sam p les w ith ou t co pp er p lates(N K , P K) b o ttling o il an d p ap er-w rap p ed copper p lates sam p les sam ples(N K C , P KC) vacu u m izin g th e b o ttles an d sealing th em w ith nitrog en sam ples ageing at 130 0 C naph th en ic oil o r p araffin ic o il vac uum d ryin g fo r 4 8 h o u rs(9 0 0 C , 5 0Pa) Figure 1. Pretreatment of samples The pretreatment of samples and the flow chart of ageing test are shown in Figure 1. After being pretreated, the moisture content of paper or paper-wrapped copper strip is 0.70%. The oil samples have a moisture content of 9 mg/kg. 400 ml oil and the paper (7.5 g) or paper-wrapped copper strip (paper: 7.5 g, copper strip: 215 cm 2 ) were placed in the same glass vial (500 ml), respectively, as presented in Figure 2. Sample Sample composition NK naphthenic oil ＋ Kraft paper NKC naphthenic oil ＋ Kraft paper ＋ copper PK paraffinic oil ＋ Kraft paper PKC paraffinic oil ＋ Kraft paper ＋ copper Table 1. Samples used for thermal ageing test Experimental Results 0 10 20 30 40 50 60 70 80 0.0 0.2 0.4 0.6 0.8 1.0 1.2 T im e (days) A cid V alue o f O il(m gK O H /g) PK C NKC PK NK Figure 3. Changes of oil acidity during oil-paper insulation samples ageing process Oil Property: Paper Property: 0 10 20 30 40 50 60 70 80 0.5 1.0 1.5 2.0 2.5 3.0 A geing T im e (day) NK NKC PK PK C W ate r C o n ten t o f p ap e r(% ) Figure 6. Water content in paper varying with ageing time Figure 4. Breakdown voltage of oils versus ageing time Figure 3 shows that NKC samples with copper have higher oil acidity than NK samples without copper all the time. However, PKC samples with copper have lower oil acidity than PK samples without copper initially, after aged 29 days the oil acidity of PKC samples becomes higher than that in PK samples. Figure 4 indicates that the existence of copper substance in oil- paper insulation during the ageing process weakens oil AC breakdown property. Naphthenic oil performs better than paraffinic oil under the same ageing condition. (a) tanδ of oil (b) v of oil Figure 9. Dielectric loss and volume conductivity of insulating oil and oil-immersed paper of NK and NKC sample aged for 77 days Figure 2. Photographs of samples 10 -3 10 -2 10 -1 10 0 10 1 10 2 10 3 10 4 10 5 10 6 10 -15 10 -14 10 -13 10 -12 10 -11 10 -10 10 -9 10 -8 10 -7 10 -6 C onductivity (S/c m ) Frequency (H z) NK NKC 10 -3 10 -2 10 -1 10 0 10 1 10 2 10 3 10 4 10 5 10 6 0.0 0.1 0.2 0.3 0.4 0.5 10 0 10 1 10 2 10 3 10 4 10 5 10 6 0.00 0.02 0.04 0.06 NK NKC tan Frequency (H z) 10 -3 10 -2 10 -1 10 0 10 1 10 2 10 3 10 4 10 5 10 6 0.00 0.02 0.04 0.06 0.08 0.10 10 0 10 1 10 2 10 3 10 4 10 5 10 6 0.002 0.004 0.006 0.008 0.010 0.012 F requency (H z) NK NKC tan 10 -3 10 -2 10 -1 10 0 10 1 10 2 10 3 10 4 10 5 10 6 10 -16 10 -15 10 -14 10 -13 10 -12 10 -11 10 -10 10 -9 10 -8 Frequency (H z) NK NKC C onductivity (S/c m) （ a ） NK Figure 8. SEM results of innermost paper in NK and NKC (a) NK (b) NKC 0 10 20 30 40 50 60 70 80 0 1 2 3 4 5 6 7 8 Tim e (days) C opper Products C ontent ofOil(m g/K g) PK C NKC Figure 5. Content of copper substance dissolved in oil The increased oil acidity will increase the corrosion rate of copper. Therefore, the copper corrosion in PKC sample is more serious than that in NKC sample. The content of copper substance dissolved in paraffinic oil is larger than that in naphthenic oil up to ageing 35 days as shown in Figure 5. The increase formation of insoluble sludge will cause more heavy copper- organic compounds sediment in the sludge. Consequently, a decreased content of copper substance dissolved in oil is observed after ageing 35 days, and the content of copper substance dissolved in paraffinic oil is less than that in naphthenic oil. It’s noteworthy that the moisture content of paper aged in PKC is higher than that aged in PK, and the moisture content of paper aged in NKC is higher than that aged in NK. The innermost paper next to the copper plate of NKC samples aged for 77 days were measured by SEM. Figure 8 shows that there is copper element deposited on the surface of paper. Figure 9 shows the dissipation factor (tanδ) and volume conductivity ( v ) plots of oil and oil impregnated paper in NK and NKC sample aged for 77 days, respectively. It can be seen that the oil in NKC sample has higher tanδ and v values than the oil in NK sample. In addition, the oil impregnated paper in NKC sample also has higher tanδ and v values than the oil impregnated paper in NK sample.
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Transcript of Influence of Copper on the By-products and Dielectric Properties of Different Oil-paper Insulations...
Influence of Copper on the By-products and Dielectric Properties of
Different Oil-paper InsulationsJian Hao1, 2, Ruijin Liao1, George Chen2 and Chao Ma3
1University of Chongqing, Chongqing, China 2University of Southampton, Southampton, UK
3Gansu Electic Power Reaserch Institute, China Introduction
Conclusions
Transformer failure caused by the corrosion of copper material in transformer attracts great attention of researchers and engineers. In this paper, 25# naphthenic mineral oil, 25# paraffinic mineral oil, Kraft paper and copper were used to compose four combinations of oil-paper insulation samples. The ageing by-products and dielectric properties of the four combinations of oil-paper insulation samples were compared after being thermally aged at 130°C for 77 days. The influence of copper on the by-products and dielectric properties of different oil-paper insulations was obtained.
University of Southampton, Highfield, Southampton, SO17 1BJ, UKContact details :
Copper can accelerate the ageing rate of insulating oils and reduce their AC breakdown voltage. The content of copper substance dissolved in insulating oil increases with ageing time at first and then decreases.
Copper has great effect on the moisture content of oil impregnated paper in the ageing process. SEM results show that there is copper product deposited on the insulating paper surface , which will deteriorate the dielectric properties of oil-paper insulation.
Figure 7. Color of innermost paper in NK, NKC, PK and PKC (from left to right)
(c) tanδ of oil impregnated paper (d) v of oil impregnated paper
Experiments
Kr af t p ap er o r p ap er - w r ap p edc o p p er p la tes s am p les
v ac u u m d r y in g f o r 4 8h o u r s ( 9 0 0C , 5 0 P a)
im m er s io n o il in v ac u u m f o r2 4 h o u r s ( 4 0 0C , 5 0 P a)
v ac u u m c o o lin go il to 4 0 0 C
b o ttlin g o il an d p ap er s am p les w ith o u tc o p p er p la tes ( N K, P K)
b o tt lin g o il an d p ap er - w r ap p ed c o p p erp la tes s am p les s am p les ( N KC , P KC )
v ac u u m iz in g th e b o tt les an ds ea lin g th em w ith n itr o g en
s a m ple s a ge ing a t 130 0 C
n ap h th en ic o il o rp ar af f in ic o il
v ac u u m d r y in g f o r 4 8h o u r s ( 9 0 0C , 5 0 P a)
Figure 1. Pretreatment of samples
The pretreatment of samples and the flow chart of ageing test are shown in Figure 1. After being pretreated, the moisture content of paper or paper-wrapped copper strip is 0.70%. The oil samples have a moisture content of 9 mg/kg. 400 ml oil and the paper (7.5 g) or paper-wrapped copper strip (paper: 7.5 g, copper strip: 215 cm2) were placed in the same glass vial (500 ml), respectively, as presented in Figure 2.
Sample Sample composition
NK naphthenic oil ＋ Kraft paper
NKCnaphthenic oil ＋ Kraft paper ＋
copper
PK paraffinic oil ＋ Kraft paper
PKC paraffinic oil ＋ Kraft paper ＋ copper
Table 1. Samples used for thermal ageing test
Experimental Results
0 10 20 30 40 50 60 70 80
0.0
0.2
0.4
0.6
0.8
1.0
1.2
Time (days)
Aci
d V
alue
of
Oil
(mgK
OH
/g)
PKC NKC PK NK
Figure 3. Changes of oil acidity during oil-paperinsulation samples ageing process
Oil Property:
Paper Property:
0 10 20 30 40 50 60 70 800.5
1.0
1.5
2.0
2.5
3.0
Ageing Time (day)
NK NKC PK PKC
Wate
r C
on
ten
t o
f p
ap
er(
%)
Figure 6. Water content in paper varying with ageing time
Figure 4. Breakdown voltage of oils versusageing time
Figure 3 shows that NKC samples with copper have higher oil acidity than NK samples without copper all the time. However, PKC samples with copper have lower oil acidity than PK samples without copper initially, after aged 29 days the oil acidity of PKC samples becomes higher than that in PK samples.
Figure 4 indicates that the existence of copper substance in oil-paper insulation during the ageing process weakens oil AC breakdown property. Naphthenic oil performs better than paraffinic oil under the same ageing condition.
(a) tanδ of oil (b) v of oil
Figure 9. Dielectric loss and volume conductivity of insulating oil and oil-immersed paper of NK and NKC sample aged for 77 days
Figure 2. Photographs of samples
10-3 10-2 10-1 100 101 102 103 104 105 10610-15
10-14
10-13
10-12
10-11
10-10
10-9
10-8
10-7
10-6
Co
nd
ucti
vit
y (S/
cm)
Frequency (Hz)
NK NKC
10-3 10-2 10-1 100 101 102 103 104 105 106
0.0
0.1
0.2
0.3
0.4
0.5
100 101 102 103 104 105 1060.00
0.02
0.04
0.06 NK NKC
tan
Frequency (Hz)
10-3 10-2 10-1 100 101 102 103 104 105 106
0.00
0.02
0.04
0.06
0.08
0.10
100 101 102 103 104 105 106
0.002
0.004
0.006
0.008
0.010
0.012
Frequency (Hz)
NK NKC
tan
10-3 10-2 10-1 100 101 102 103 104 105 10610-16
10-15
10-14
10-13
10-12
10-11
10-10
10-9
10-8
Frequency (Hz)
NK NKC
Conducti
vit
y (S
/cm)
（ a ） NK
Figure 8. SEM results of innermost paper in NK and NKC(a) NK (b) NKC
0 10 20 30 40 50 60 70 80
0
1
2
3
4
5
6
7
8
Time (days)
Cop
per P
rodu
cts
Con
tent
of
Oil
(mg/
Kg)
PKC NKC
Figure 5. Content of copper substance dissolved in oil
The increased oil acidity will increase the corrosion rate of copper. Therefore, the copper corrosion in PKC sample is more serious than that in NKC sample. The content of copper substance dissolved in paraffinic oil is larger than that in naphthenic oil up to ageing 35 days as shown in Figure 5.
The increase formation of insoluble sludge will cause more heavy copper-organic compounds sediment in the sludge. Consequently, a decreased content of copper substance dissolved in oil is observed after ageing 35 days, and the content of copper substance dissolved in paraffinic oil is less than that in naphthenic oil.
It’s noteworthy that the moisture content of paper aged in PKC is higher than that aged in PK, and the moisture content of paper aged in NKC is higher than that aged in NK.
The innermost paper next to the copper plate of NKC samples aged for 77 days were measured by SEM. Figure 8 shows that there is copper element deposited on the surface of paper.
Figure 9 shows the dissipation factor (tanδ) and volume conductivity (v) plots of oil and oil impregnated paper in NK and NKC sample aged for 77 days, respectively. It can be seen that the oil in NKC sample has higher tanδ and v values than the oil in NK sample. In addition, the oil impregnated paper in NKC sample also has higher tanδ and v values than the oil impregnated paper in NK sample.
