2004 Annual Report Conference on Electrical Insulation and Dielectric Phenomena
High Voltage Nanosecond Breakdown in Transformer Oil Wang Jue', Shao Taol.2,Yan Ping', Yuan Wei-Qunl, Huang Wen-Li', Zhang Shi-Changl, Sun Guang-Sheng' I Institute of Electrical Engineering Chinese Academy of Science, Beijing, 100080, China. Graduate School of Chinese Academy of Science, Beijing, 100039, China
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experiential formula that fit to pulse width range from 150 to 30011s and relate with electrode area. Dr. J.J. Mankowski got the experiential formula that tit to pulse width less than 5ns under uniform field. The formulae as follows: J.C. Martin: E3n=80xt&l (I) Electrode area is 0.01m2, E is electrical field (MV/cm), L~is the effective time (ns), which is the duration of the pulse between 63% 100% of the peak voltage reached. JJ. Mankowski: E=7.9t4.95 (2) E is electrical field (MV/cm), t is in nanosecond and is the duration of the pulse between IO%-lOO% of the peak voltage reached US air force research laboratory's J.M. Lehr, F.J. Agee had studied on transformer oil breakdown characteristics under high voltage repetitive suhnanosecond pulses[4]. Because these researches was under different conditions and for different purpose, the results have the limited and far from the applied demands. There is few data for putting pulse width from lOns to 5Gns's pulse and ns level repetitive pulses on transformer oil. The breakdown characteristics in transformer oil under single (pulse width 8 to 30ns) and repetitive (from 1Hz to IOOOHz, pulse width 30ns) pulse had been tested in our laboratory.
Abstract: In this paper, Main influence factors and results of others research of nanosecond breakdown in transformer oil have been introduced. The breakdown characteristics of transformer oil under single and repetitive nanosecond pulses ranged from 1Hz to 1000Hz have been investigated. The voltages with single and repetition pulsed are applied and the gap distances are ranged from 0.15mm to lmm. The breakdown waveforms of voltage, current and breakdown time have been measured. The results indicate that ns level high voltages pulse breakdown field is much higher than breakdown in DC and AC. The breakdown field value decreases with the repetitive rate increases. From loHz to IOOHz, the breakdown field falls quickly. When repetitive rate surpasses lOOHz, the field value fall speed is slow. The experiential formula was put forward in this paper which is fit to transformer oil breakdown characteristics under ns high voltage pulse. The experiment results have been discussed.
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Introduction Transformer oil is the general and important insulation material. With the development of pulsed power technology, high voltage pulse's rise time and repetitive rate is faster and faster, the insulation breakdown characteristics in this condition have to be investigated [I]. Pure transformer oil have very high electrical hreakdown field. Impurity is the main factor that reduces the insulating performance of transformer oil. All transformer oil using in engineering are impurity, so our research object is the impurity transformer oil. There were two main concepts had heen proposed for describing the breakdown process in transformer oil (i) a bubble process and (ii) an electronic process, hut both of them were hard to explain transformer oil breakdown characteristics when nanosecond level high voltage pulse was applied. There were a few breakdown experiments of transformer oil in single pulse and several breakdown tests of transformer oil in repetitive pulse had been carried out. Some data and experiential formula responsible for the breakdown process in transformer oil in the nanosecond or sub-nanosecond regime had been obtained [2][3]. J.C. Martin had given the
0-78038584-5/04/$20.00 02004 IEEE
Experimental Setup Single Pulse Breakdown Experiment: The schematic diagram of single pulse breakdown test system is shown in figure 1. The output waveform of this generator is given in figure 2. The output voltage is in the range of 50kV to 300kV. The pulse width is 30 to 4Ons. hf.L Ilrlrtarc
Flgurel: Schematic diagram of single pulse breakdown test system
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The capacitive divider and the self-integrating Rogowski coil are used for measuring breakdown voltage and current waveform respectively [ 5 ] . Agilent 54820B oscillograph is adopted for waveform data sampling. Oil gap distance is from 0.06 to Imm. The positive plate and negative hemispherical electrode system are used to simulate uniform electrical field across the gap. The DC breakdown field of transformer oil in our experiments is ahout 20kVlmm in standard oil cup.
The Max output voltage is 200kV, the pulse width is 20 to 3011s and the pulse rise time is less than Ions. The capacitive divider and the diverter are used for measuring breakdown voltage and current waveforms. Oil gap distance is from 0.3 to 1.5mm. The standard oil cup is used in experiments. The DC breakdown field of transformer oil is about 16kV/mm in standard oil cup. More than five times ‘test were done at the same condition. The duration of the pulse is 100s in IHz, 100s in IO&, 40s in 100Hz, 20s in 500Hz, 20s in
1000Hz.
Experimental Results Single Pulse Breakdown Experimental Results and Discussion: A curve fit the data for oil for pulse width 8-3011s is attempted. In figure 5 is displayed the data for transformer oil on a log-log scale for electrical field versus time to breakdown. J.C.Martin curve and J.J. Mankowski curve also are shown in this figure. The experiential formula is provided as (3). Figure2 The voltage output waveform(5Vldiv. 20nsldiv)
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Repetitive Pulses Breakdown Experiment: The circuitry of repetitive pulses breakdown experimental system is shown in figure 3. The output waveform of the generator[6] is given in figure 4.
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Figure5 Breakdown data for transform oil in single pulse
E = 9.5r4.”
Figure. Circuitry of repetitive pulses breakdown eiperimntal system .
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E is electrical field (MV/cm), t i s in nanosecond and i s the duration of the pulse between 10%-100% of the peak voltage reached.
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The results indicate that ns level high voltages pulse breakdown field was much higher than one in DC and AC. Because of the different condition, our experimental results are higher than the date of J.J. Mankowski and are less than the date of J.C.Martin. It indicates that the effect of increasing breakdown voltage is decreases with the pulse width decreasing. The breakdown field can he improved in thinner gap. The effect of impurity for transformer oil breakdown is less with the pulse width decreased. The reason is that a
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(3)
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F’igure4: The voltage output wavefarm(enve1ope)
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lot of impurities in oil haven't enough time to be polarized, so it hasn't offered help for breakdown.
The experiments show that the breakdown field value decreases with the repetitive rate increases. From IOHz to IOOHz, the breakdown field falls quickly. When repetitive rate exceeds lOOHz, the field value fall speed is slow. This phenomenon can be interpreted by impurities polarization, which has the "accumulation effect" in repetitive high voltage pulses field. Such as water, its time of thermal- polarization is 10'- 10"s [7],which compare with the pulse repetitive rate, so electrical field will continually act on water for polarization. The breakdown characteristics in different repetitive rate correspond with polarization of different impurities.
Repetitive Pulses Breakdown Experimental Results and Discussion: The diagram of breakdown voltage, cument and duration of pulse has been shown in figure 6 and 7 respectively. The largest electrical fields which dose not result in breakdown and the smallest electrical fields which all result in breakdown have been tested. The results of electrical field versus repetitive rate for transformer oil are display in figure 8.
Conclusion The experimental results indicate that ns level high voltages pulse breakdown field was much higher than breakdown field in DC and AC. The effect of increasing breakdown voltage is decreases with the pulse width decreasing. Through the experiment, the breakdown electric field of repetitive pulses is much lower than that of single pulse. The breakdown field value decreases with the repetitive rate increases. From lOHz to lOOHz, the breakdown field falls quickly. When repetitive rate exceeded 100Hz, the field value fall speed was slow. The experiential formula which was fit to transformer oil breakdown characteristics under ns high voltage single pulse was obtained in this paper.
~igure6:Breakdown voltage and current waveform
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.repetitive pulses.
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Acknowledgments The authors wish to thank sixth department of Northwest Institute of Nuclear Technology for providing the some installations and instruments for repetitive pulses breakdown experiment.
References [I1 E. Schamiloglu, K.H. Schcenbach. "Basic research on pulsed power for narrowband high power minowave sou~ces".SPIE Intense microwave pulses IX :2-3, pp. Orlando, Apri1,2002.
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121 1.1. Makowski, 1. Dickens and M. Krisliansen, '"High volrage subnantsecond breakdown,"lEEE Trans. on Plosmn Science, Val. 26. pp. 874-881, June 1998.
Breakdown Area
[31 T.H. Martin. A.H.Guenther and M. Kristiansen, J.C. Martin on Pulsed Power. New York, USA Plenum Press, 1996.
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[41 J.M. Lehr. F.J. Age% R. Copeland and W.D. Rather, "Measurement of the elecoic breakdown strength of transform oil in the sub-nanosecond regime", lEEE Trans. On Dielecnics and Electricnl Insulorion, Vo1.5, pp. 857-861, Dec.1998.
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(51 Wang Jue. Zhang Shi-Chang. Yan Ping and Sun Guang-Sheng, "Self-integrating Rogowski coil for measuring the nanosecond
Figure8 Breakdown dam for transformer ail in repetitive pulse
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current", High power law and panicle beam. vol. 16. pp 399-403, May 2004.
[6] Su Jiancang, Liu Guoahi, Ding Yongzong, Ding Zhejie, Qiu Shi, et al., "Nanosecond sos-based pulsed generator SffiZOO". Proceedings of the third inferntiom1 symposium on pulsed power and p l a s m npplicntions. pp. 258-261. Mianyang, P.R. China. Oct. 2002.
[71 Jin Weifang, Dielecmric Physics. Xi'an, China: Xi'an IioTong University Insulation Group Press. 1992.
Author address: Wang Jue, Institute of Electrical Engineering Chinese Academy of Science, Beijing. looO80,China, 086-010-62542102, Email:
[email protected]
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