comparison of partial discharges in sf6 and … properties • high dielectric strength (2 x air)...
TRANSCRIPT
Comparison of Partial Discharges in SF6 and Fluoronitrile/CO2 Gas
Mixtures
Boya ZHANG, Yang CAOUniversity of Connecticut, USA
Nenad UZELACG&W Electric Company, USA
1
Agenda
1. Background2. Fluoronitrile gas3. Setup and test procedure4. Results and analysis5. Summary
2
1. Background
3
• SF6 has been used successfullyfor decades in the power industry.
• One big shortcoming – has ahigh global warming potential(23,500)
• Included in Kyoto Protocol (1997)on the list to be limited.
Global annual SF6 emissions from electrical equipmentare reported by ECOFYS: 1,600 t to 2,800 t SF6. Thatequals to 37,600 kt to 65,800 kt CO2!
1. Background
4
Failures in the switchgear due to long-term PDs.
• Since 1997, lots of effort to find alternative to SF6
• Proved to be hard task due to unique SF6 properties
• High dielectric strength (2 x air)
• Nontoxic, nonflammable, noncorrosive
• Excellent arc extinction
• Excellent thermal conductivity
• Chemically stable (good material compatibility)
2. Fluoronitriles
5
Molecular structure of the NovecTM 4710
• One of the promising options is NovecTM 4710 fluid.
• 2x better dielectric than SF6• High boiling temp. (-4.7C)
need to be diluted into buffer gas
• CO2 selected over N2 and air due to reported better arc quenching capability
• In this paper we’ve compared the PD between SF6 and fluoronitrile/CO2 mixture
2. Fluoronitriles
6
0 10 20 30 40 50 60 70 80 90 1000.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
2.2
2.4
100kPa (14.5 psi) 120kPa (17.4 psi) 140kPa (20.3 psi) 160kPa (23.2 psi) 180kPa (26.1 psi) 200kPa (29.0 psi)D
iele
ctric
stre
ngth
of t
he g
as m
ixtu
re/S
F 6
NovecTM 4710 mixing ratio (%)
• The EB of pure Novecis more than twotimes that of SF6.
• EB of pure CO2 isfound only 32-37% ofSF6, while it isdoubled by addingonly 5% of Novec4710 into CO2.
• For 15% Novec 4710/CO2 mixture, the EBis equivalent to SF6.
Dielectric strength for NovecTM 4710 fluid in mixture with CO2 compared with SF6.
3. Setup & procedures
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R 25mmH.V.
δ=2mm0mm
r 20μmθ=30̊
ToPC
Configuration of PD defect model
PD measuring system
First vacuumed for 30 min.
Then filled with CO2 to 150 kPa andvacuumed again. Repeated three .
Novec and CO2 were filled to thedesigned ratio according to theirpartial pressures.
To determine the PDIV, the appliedvoltage was increased graduallyfrom 0 until the detection of PD.
10 pC was chosen as threshold ofPDIV.
To obtain PRPD pattern, the PDsignal was recorded for 120 s.
4. Results & Analysis
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10 20 30 40 50 60 70 80 90 100 110 120 130
1.5 2.9 4.3 5.8 7.2 8.7 10.1 11.6 13.0 14.5 15.9 17.4 18.8
0
10
20
30
40
50
60
PD inception voltage
5% Novec + 95% CO2
10% Novec + 90% CO2
15% Novec + 85% CO2
20% Novec + 80% CO2
SF6
Volta
ge (k
V)rm
s
Pressure
d=10mmδ=2mm
breakdown voltage
(psi)
(kPa)
PDIV and breakdown voltage
PDIV and breakdown voltage of the NovecTM 4710/CO2 mixture and SF6 at different pressures
4. Results & Analysis
9
phase-resolved partial discharge (PRPD) pattern
PRPD pattern of 20%Novec/80%CO2 mixture and SF6 under different voltages.
P=100kPa (14.5 psi)
4. Results & Analysis
10PRPD pattern of 20%Novec/80%CO2 mixture and SF6 under different voltages.
P=100kPa (14.5 psi)
4. Results & Analysis
11
phase-resolved partial discharge (PRPD) pattern
14 16 18 20 22 24 26 280.1
1
10
100
1000
10000 SF6 20% Novec+20%CO2 SF6 20% Novec+20%CO2
Applied voltage (kV)
Cou
nts
per s
econ
d
5
10
15
20
25
30
Ave
rage
cha
rge
mag
nitu
de (p
C)
Comparison of the PD number and PD magnitude for the NovecTM 4710/CO2 mixture and SF6 under different voltages.
4. Results & Analysis
12
PRPD pattern of fluoronitrile/CO2 mixtures with different ratios. (V=22.5 kV)
• A better PD suppressionwith the increase ofmixing ratio, especiallyin the positive half cycle.
4. Results & Analysis
13
Comparison of PD levels through PRPD statistics
Even 15% mixture has a lowerPD level in the positive halfcycle compared with SF6.
the comparison of their PD amplitudes at different phases.
4. Results & Analysis
14
Comparison of PD levels through PRPD statistic
0 10 20 30 40 50 60 70 80 90 100 1100
2000
4000
6000
8000
10000
12000
14000
16000
18000
Cum
ulat
ive
Cou
nt
PD charge (pC)
5% Novec + 95% CO2 10% Novec + 90% CO2
15% Novec + 85% CO2 20% Novec + 80% CO2 SF6
(a)
trigg
er le
vel
0 10 20 30 40 50 60 70 80 90 100
0
1000
2000
3000
4000
trigg
er le
vel
5% Novec + 95% CO2 10% Novec + 90% CO2
15% Novec + 85% CO2 20% Novec + 80% CO2 SF6
(b)
Cou
ntPD charge (pC)
• PD number of SF6 is in between 15% mixture and 20% mixture.• In SF6, there are much more PDs with low magnitude compared
with the 20% fluoronitrile/CO2 mixture.
5. SUMMARY
15
• 15% Fluoronitrile/CO2 mixture shows equivalent dielectric strength compared with SF6 under uniform field
• 15% Fluoronitrile/CO2 mixture and SF6 have almost the same PDIV under 11.6psi, 14.5 psi and 17.4psi. Both slightly lower than 20% mixture.
• PD counts in SF6 are in-between 15% and 20% mixture.
• SF6 has much more PDs with low magnitude and the 20% fluoronitrile/CO2 mixture has less PDs but with higher magnitude.
