Comparison of Partial Discharges in SF 6 and Fluoronitrile/CO2 Gas Mixtures Boya ZHANG, Yang CAO University of Connecticut, USA Nenad UZELAC G&W Electric Company, USA 1
Agenda 1. Background 2. Fluoronitrile gas 3. Setup and test procedure 4. Results and analysis 5. Summary 2
1. Background SF6 has been used successfully for decades in the power industry. One big shortcoming has a high global warming potential (23,500) Included in Kyoto Protocol (1997) on the list to be limited. Global annual SF6 emissions from electrical equipment are reported by ECOFYS: 1,600 t to 2,800 t SF 6. That equals to 37,600 kt to 65,800 kt CO 2! 3
1. Background Since 1997, lots of effort to find alternative to SF6 Proved to be hard task due to unique SF6 properties 4 High dielectric strength (2 x air) Nontoxic, nonflammable, noncorrosive Excellent arc extinction Excellent thermal conductivity Chemically stable (good material compatibility) Failures in the switchgear due to long-term PDs.
2. Fluoronitriles One of the promising options is Novec TM 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 5 mixture Molecular structure of the Novec TM 4710
2. Fluoronitriles Dielectric strength of the gas mixture/sf 6 2.4 2.2 2.0 1.8 1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2 6 100kPa (14.5 psi) 140kPa (20.3 psi) 180kPa (26.1 psi) 120kPa (17.4 psi) 160kPa (23.2 psi) 200kPa (29.0 psi) 0 10 20 30 40 50 60 70 80 90 100 Novec TM 4710 mixing ratio (%) Dielectric strength for Novec TM 4710 fluid in mixture with CO 2 compared with SF 6. The E B of pure Novec is more than two times that of SF 6. E B of pure CO 2 is found only 32-37% of SF 6, while it is doubled by adding only 5% of Novec 4710 into CO 2. For 15% Novec 4710 /CO 2 mixture, the E B is equivalent to SF 6.
3. Setup & procedures First vacuumed for 30 min. Then filled with CO 2 to 150 kpa and vacuumed again. Repeated three. Novec and CO 2 were filled to the designed ratio according to their partial pressures. To determine the PDIV, the applied voltage was increased gradually from 0 until the detection of PD. 10 pc was chosen as threshold of PDIV. To obtain PRPD pattern, the PD signal was recorded for 120 s. 0mm To PC H.V. R 25mm δ=2mm r 20μm θ=30 Configuration of PD defect model 7 PD measuring system
4. Results & Analysis PDIV and breakdown voltage Voltage (kv) rms 60 50 40 30 20 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 5% Novec + 95% CO 2 10% Novec + 90% CO 2 15% Novec + 85% CO 2 20% Novec + 80% CO 2 SF 6 breakdown voltage (psi) 10 PD inception voltage δ=2mm d=10mm 0 10 20 30 40 50 60 70 80 90 100 110 120 130 (kpa) Pressure 8 PDIV and breakdown voltage of the Novec TM 4710/CO 2 mixture and SF 6 at different pressures
4. Results & Analysis phase-resolved partial discharge (PRPD) pattern P=100kPa (14.5 psi) 9 PRPD pattern of 20%Novec/80%CO2 mixture and SF6 under different voltages.
4. Results & Analysis P=100kPa (14.5 psi) 10 PRPD pattern of 20%Novec/80%CO2 mixture and SF6 under different voltages.
4. Results & Analysis phase-resolved partial discharge (PRPD) pattern Counts per second 10000 1000 100 10 1 SF6 20% Novec+20%CO2 SF6 20% Novec+20%CO2 30 25 20 15 10 Average charge magnitude (pc) 11 0.1 14 16 18 20 22 24 26 28 Applied voltage (kv) Comparison of the PD number and PD magnitude for the Novec TM 4710/CO 2 mixture and SF 6 under different voltages. 5
4. Results & Analysis A better PD suppression with the increase of mixing ratio, especially in the positive half cycle. PRPD pattern of fluoronitrile/co 2 mixtures with different ratios. (V=22.5 kv) 12
4. Results & Analysis Comparison of PD levels through PRPD statistics the comparison of their PD amplitudes at different phases. Even 15% mixture has a lower PD level in the positive half cycle compared with SF 6. 13
4. Results & Analysis (a) Comparison of PD levels through PRPD statistic 18000 16000 14000 trigger level (b) 4000 3000 5% Novec + 95% CO 2 10% Novec + 90% CO 2 15% Novec + 85% CO 2 Cumulative Count 12000 10000 8000 6000 5% Novec + 95% CO 2 10% Novec + 90% CO 2 Count 2000 1000 20% Novec + 80% CO 2 SF 6 4000 2000 0 0 10 20 30 40 50 60 70 80 90 100 110 PD charge (pc) 15% Novec + 85% CO 2 20% Novec + 80% CO 2 SF 6 0 trigger level 0 10 20 30 40 50 60 70 80 90 100 PD charge (pc) PD number of SF6 is in between 15% mixture and 20% mixture. In SF 6, there are much more PDs with low magnitude compared with the 20% fluoronitrile/co 2 mixture. 14
5. SUMMARY 15% Fluoronitrile/CO 2 mixture shows equivalent dielectric strength compared with SF 6 under uniform field 15% Fluoronitrile/CO 2 mixture and SF 6 have almost the same PDIV under 11.6psi, 14.5 psi and 17.4psi. Both slightly lower than 20% mixture. PD counts in SF 6 are in-between 15% and 20% mixture. SF 6 has much more PDs with low magnitude and the 20% fluoronitrile/co 2 mixture has less PDs but with higher magnitude. 15
Thank you! Questions? nuzelac@gwelec.com 16