Sparkover Voltage Research Articles

Short Time Region Sparkover Characteristics of Compressed N2 and CO2 using Square Impulse and their Quantitative Estimation Method

SF6 is used as a main insulation gas for gas-insulated switchgears (GIS), but it has recently become a gas to be restricted because of its greenhouse effect. Up to now, we have studied the insulation characteristics of compressed N2 and CO2 as a possible SF6-alternative gas. As GIS are subjected to very fast transient voltage due to incoming lightning surges or at disconnector switching operation, it is necessary to clarify the sparkover voltage-time (V-t) characteristics in the short time region. In this report, we describe the V-t curves ranging from 30ns to 10μs for high pressure (0.6 and 1.0MPa) N2 and CO2 obtained by applying square impulse voltage. We next studied the V-t curves for standard lightning and oscillating impulses for the same experimental conditions. Based on these results, we investigated the possibility of quantitatively estimating of the V-t curves for these waveforms by applying the “equal-area criterion”. The minimum sparkover voltage estimated by the criterion very well agreed with the measured characteristic in all conditions studied, and thus it has become clear that the quantitative estimation of the sparkover characteristics is possible for high pressure N2 and CO2.

Discharge characteristics to insulated material

AbstractLightning strikes not only metallic objects such as transmission towers and lightning rods but also insulated material such as blades of wind turbines. The discharge characteristics of insulated material are, however, not clarified till now. In this paper, discharge characterisitics of insulated material have been investigated experimentally using a 12‐MV impulse generator. The effects of polarities of the applied voltages and surface conditions of the insulation material are also studied and it is found that pollution on the surface decreases the sparkover voltage drastically. Copyright © 2007 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

초크코일을 이용한 SPD 조합회로의 잔류전압 저감기법

Gas Discharge Tubes (GDTs) are widely used as surge protectors for communication applications due to their small internal capacitance. In these days, however, they are mostly used in combined configurations, because the sparkover voltage required to initiate the discharge process in the GDTs and the time taken for arc formation process can be large enough to damage to sensitive circuits. For GDTs with a considerably high initial residual voltage, we should limit the peak voltage using a TVS or filter. We made a hybrid SPD circuits of common-mode type and differential-mode type with the filter using common-mode choke. Also, we applied lightning impulse voltage and ring wave voltage which frequency bandwidth are different each other and verified the characteristics of hybrid SPD circuits according to waveshapes. We describe how the applied SPDs operate in protection process steps with the actual data obtained from the residual voltage measurement at each step. The experiment results show that the surge voltage reduction with the choke coil is more effective in differential-mode circuit than in common-mode circuit.

Dielectric properties of a water molecule pinned on the surface of a solid body

A model of the polarization of a water molecule pinned on the surface of a solid body by oxygen and hydrogen ions is studied. As the dielectric constant increases, the spark-over voltage of solid dielectrics decreases. The character of the contaminated surface (alkaline or acid) at the operating locations must be taken into account when designing insulators.

Quantitative evaluation of lightning surge range voltage–time characteristics in high‐pressure SF6 gas

AbstractGas‐insulated switchgear (GIS) is subjected to very fast transient overvoltages such as lightning surges or disconnector switching surges. Therefore, the sparkover voltage and time (V−t) characteristics of SF6 in a very short time range of less than $1\ \mu \hbox{s}$ are of great interest from the viewpoint of insulation design and coordination for a GIS. This paper describes the V−t characteristics of SF6 at a gas pressure of 0.5 MPa using a steep‐front square impulse voltage under a quasi‐uniform field gap and presents a quantitative evaluation of the V−t characteristics for a nonstandard lightning impulse voltage. In the case of a square impulse, the V−t characteristics of positive polarity were observed to be almost flat over a long time range from 80 ns to $10\ \mu \hbox{s}$, and rose steeply over a short time range from 80 ns down to 20 ns. For negative polarity, the V−t characteristics exhibit a gentle rise from 200 ns down to 40 ns. In the estimation of V−t characteristics, the equal‐area criterion parameters were quantitatively estimated using the square impulse. For a nonstandard lighting impulse, we found that application of the equal‐area criterion with these parameters for the nonoscillating impulse and oscillating impulse of up to 5.3 MHz as a model of lightning surge and disconnector switching surge is possible. © 2007 Wiley Periodicals, Inc. Electr Eng Jpn, 159(4): 8– 17, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20309

Measurement of sparkover voltage and time lag characteristics in CF3I–N2 and CF3I– air gas mixtures by using steep‐front square voltage

AbstractA square pulse voltage is useful for studying electrical discharge physics or very fast transient overvoltage issues. This paper describes sparkover voltages and time lag (V– t) characteristics of CF3I gas, which has very low environmental effects and high dielectric strength, and its mixtures with nitrogen gas or air in a very short time range below a microsecond. They are measured by using a steep‐front square voltage with a rise time of 16 ns and a peak value of 200 kV. Pure CF3I gas has 20% higher dielectric strength than SF6 gas. The V– t characteristics of CF3I–N2 or CF3I– air gas mixtures, which contain 60% CF3I gas, are equivalent to those of pure SF6 gas at the same total pressure. A quantitative evaluation of V– t characteristics by the equal‐area criterion is also performed. The equal‐area parameter which is obtained by applying a voltage high enough to make the formative time lag dominant should be chosen. © 2006 Wiley Periodicals, Inc. Electr Eng Jpn, 157(2): 1–7, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20325

Impulse sparkover characteristics of sphere-rod gaps

The sparkover behaviour of sphere-rod gaps under standard impulse voltages is investigated by assessing the influence of gap spacing, impulse voltage waveshape and polarity, and atmospheric conditions on the distribution of the sparkover voltage. At sparkover the growth of streamers of both polarities can be estimated since a value of 2 MV/m is found to be characteristic for the average negative streamer gradient. The IEC atmospheric conditions correction is discussed and compared with a new optimised correction procedure. The feasibility of using the sphere-rod gap as substandard for measuring impulse voltages, replacing the conventional more expensive sphere gap, is examined.

Surface Spark-Over Voltage on Solid Insulator in Sub-Cooled Liquid Nitrogen

Surface spark-over voltages on solid insulators in boiling and sub-cooled liquid nitrogen are studied under ac, dc and impulse voltage. The insulator structure used is a model of a power cable end. In the structure, static capacitance is formed between outer surface and inner conductor of the insulator. The spark-over voltages for several insulators were measured at gap length 60 mm or less under each voltage waveform. The spark-over voltages increase slightly with increasing gap length in boiling and sub-cooled liquid. In range of shorter gap length spark-over voltages in sub-cooled liquid are higher than those in boiling liquid nitrogen. The differences between spark-over voltages in both liquids are caused by bubbles generated due to discharge at low voltage. The spark-over voltage for the insulator with the larger static capacitance is lower than that for one with the small capacitance.

急峻方形波高電圧を用いた SF<sub>6</sub>-N<sub>2</sub>混合 ガス中<i>V-t</i>特性の測定

A square pulse voltage is useful for studying electrical discharge physics and/or very fast transient overvoltage issues. This paper describes sparkover voltages and time lag (V-t) characteristics of SF6-N2 gas mixtures in a very short time range below a microsecond, which are measured by using a steep-front square voltage with a rise time of 16 nanoseconds and a peak value of 200 kilovolts. SF6-N2 gas mixture, which contains nitrogen gas at a ratio of 60 % or less, has equivalent dielectric strength to pure SF6 gas even in the short time range around 10 nanoseconds. Sparkover voltage and time lag characteristics are evaluated by using the equal area criterion even in the short time range below a microsecond.

高気圧SF<sub>6</sub>の雷サージ領域V—t特性の定量的評価

Since gas-insulated switchgear (GIS) is subjected to very fast transient overvoltages such as lightning surges or disconnector switching surges. Therefore the sparkover voltage and time (V-t) characteristics of SF6 in a very short time range of less than 1μs are of great interest from the viewpoint of insulation design and coordination for a GIS. This paper describes the V-t characteristics of SF6 at a gas pressure of 0.5MPa using a steep-front square impulse voltage under a quasi-uniform field gap and presents a quantitative evaluation of the V-t characteristics for a nonstandard lightning impulse voltage. In the case of a square impulse, the V-t characteristics of positive polarity were observed to be almost flat over a long time range from 80ns to 10μs, and rose steeply over a short time range from 80ns down to 20ns. For negative polarity, the V-t characteristics exhibit a gentle rise from 200ns down to 40ns. In the estimation of V-t characteristics, the equal-area criterion parameters were quantitatively estimated using the square impulse. For a nonstandard lightning impulse, we found that the application of equal area criterion with these parameters for the non-oscillating impulse and oscillating impulse of up to 5.3MHz as a model of lightning surge and disconnector switching surge is possible.

急峻方形波高電圧を用いたCF<sub>3</sub>I-N<sub>2</sub>, CF<sub>3</sub>I-Air混合ガス中 <i>V-t</i> 特性の測定

A square pulse voltage is useful for studying electrical discharge physics or very fast transient overvoltage issues. This paper describes sparkover voltages and time lag (V-t) characteristics of CF3I gas, which has very low environmental effects and high dielectric strength, and its mixtures with nitrogen gas or air in a very short time range below a microsecond. They are measured by using a steep-front square voltage with a rise time of 16 nanoseconds and a peak value of 200 kilovolts. Pure CF3I gas has 20 % higher dielectric strength than SF6 gas. V-t characteristics of CF3I-N2 or CF3I-air gas mixtures, which contain 60% CF3I gas, are equivalent to those of pure SF6 gas at the same total pressure. A quantitative evaluation of V-t characteristics by the equal area criterion is also performed. The equal area parameter which is obtained by applying a voltage enough high to make the formative time lag dominant should be chosen.

Nanosecond Electrical Discharge Development in SF6-N2 Gas Mixtures

Both an experimental observation and a numerical modeling of streamer development in SF6-N2 gas mixtures are performed and the results are compared with each other. By using a steep-front square high voltage in the measurements, it is possible to keep the constant condition of the electric field during the streamer development. Minimum sparkover voltage and streamer velocities obtained from the numerical modeling show good agreement with those from the experimental observation, and the change in the streamer velocity against the gas mixture ratio shows a similar tendency.

Voltage-time Characteristics and Observation of Discharge Development in SF6 Using Steep-front Square Impulse and Fast Oscillating Impulse Voltages under Quasi-uniform Field Gap

We describe the sparkover voltage and time (V-t) characteristics and the discharge development process in SF6 at 0.1MPa for quasi-uniform field gaps with steep-front square impulse and fast-oscillating impulse voltages. A square impulse voltage has a very short rise time of 20ns and a fast oscillating impulse voltage has a frequency of approximately 30MHz and rise time of 20ns. Both impulse voltages can be generated up to 10µs. Optical observation in the test gap clarifies the discharge development process. We discuss the difference in discharge development for the square and oscillating impulse voltages.

The role of negative ions in the propagation of discharges across insulating surfaces

The relative importance of atmospheric negative ions in corona formation and breakdown in a radial electric field has been investigated, with special reference to effects occurring at an insulating surface of a cycloaliphatic polyurethane with dolomite filler. The inception times, corona charge, light emission (by UV photography) and sparkover voltages under lightning impulses have been recorded under natural atmospheric conditions and under the influence of negative ions introduced from an auxiliary corona. The presence of excess negative ions on the surface is shown to increase both the charge injected and the mean radius of the corona, attributable to an augmentation of streamer discharges. In similar experiments in air, the excess ions cause a transition to a `glow' discharge. Effects of negative ions on sparkover are not significant on the insulator surface, but they cause a small increase in air. Comparisons between the two cases lead to the conclusion that the most important effect of the ions on the surface is to provide `seed' electrons for streamer propagation, following ion detachment in the field of advancing streamer tips.

Characteristics of surface spark-over voltage for several waveforms on solid insulators in cryogenic coolants

The surface spark-over voltages on solid insulators in liquid nitrogen and helium are studied under alternating current voltage of 50 Hz, direct current voltage and impulse voltage. The insulator structure used in experimental studies is a model of a power cable end. In the structure, static capacitance is formed between outer surface and inner conductor of insulator. The spark-over voltages for several insulators were measured versus gap length, below 6 cm, under different voltage waveforms. The spark-over voltages increase slightly with increase of gap length. The spark-over voltage for the insulator with the larger static capacitance is lower than that with the smaller capacitance. The relation between the surface spark-over voltage and the capacitance can be expressed by an experimental equation for each of the applied voltage waveforms.

電離指数計算による標準球ギャップの火花電圧変動に関する検討

電離指数計算による標準球ギャップの火花電圧変動に関する検討

Phase-to-Ground and Phase-to-Phase Sparkover Characteristics of External Insulation at the Entrance of an UHV Substation

For rational insulation design of a UHV substation, full-scale switching impulse tests of phase-to-ground (shielding ring-to-tower) and phase-to-phase (shielding ring-to-shielding ring) insulating clearance have been carried out in dry and wet conditions. In the tests, shielding rings that will be installed on bushings at actual UHV substations were used. The sparkover voltages depend on not only gap configurations but also the waveform of applied switching impulses; in other words, they show what we refer to as U-characteristics. Critical sparkover voltages are higher than those of rod-rod gaps by 20%-25% in dry conditions and by 7%-10% in wet conditions.

The relationship among AC surface spark-over voltage, specific capacitance of solid insulator and bubbles in LN/sub 2/ and LHe

The characteristics of AC surface electrical discharge on solid insulators in liquid nitrogen (LN/sub 2/) or liquid helium (LHe) are studied. The insulation structure used is a model of a power cable end. Bubbles are generated due to discharge at a lower voltage than that of spark-over. However, it was experimentally and computationally confirmed that the bubbles do not influence the spark-over voltage. In the structure, static capacitance is formed on the insulator surface. The surface spark-over voltage depends on the static capacitance. The relation between surface spark-over voltage and the static capacitance is experimentally considered for several insulators. The results show that the spark-over voltage is lower for larger static capacitance. The relation between the spark-over voltage and the capacitance can be expressed by an equation V=A/spl middot/C/sub sp//sup -B/.

Electrical characterisations of new microgap surge absorber fabricated by using conventional semiconductor technology

The structure of the microgap and the manufacturing processes for a new type of microgap surge absorber, fabricated by semiconductor technology, are described. A very stable spark-over voltage with a narrow distribution was obtained by coating the metallic films in the microgap. As well as the desirable characteristics of common microgap surge absorbers, this new type of microgap surge absorber has other advantages such as small size, low cost and suitability for mass production.

Tests on the breakdown of air at elevated temperatures in non-uniform electric fields

Sparkover voltage characteristics have been obtained using a 20 cm rod–plane gap at temperatures between 294 and 770K. Lightning and slow-front impulse and alternating voltages have been applied; pre-breakdown corona has also been investigated under impulse voltages. The nature of the sparkover characteristics depends strongly on the type and polarity of the applied voltage. These are discussed in terms of the changes in relative air density with temperature and the relationship to the recommendations of IEC 60-1 for the adjustment of sparkover measurements to changes in atmospheric conditions.