• The Transactions of The Korean Institute of Electrical Engineers
• /
• v.59 no.8
• /
• pp.1416-1422
• /
• 2010

$SF_6$ is the most commonly used insulating gas in electrical systems. But In these days $SF_6$ mixtures and alternative gas has been studied because of global warming. so although many studies have been carried out about binary gas mixtures with $SF_6$, few studies were presented about breakdown characteristics of $SF_6/N_2$ mixtures. At present study the breakdown characteristics of $SF_6/N_2$ mixtures in Non-uniform field was performed. In this paper, The simulation value are compared with experiment values. Streamer breakdown criterion was used for predicting breakdown voltage. For accurate simulation this simulation apply utilization factor using CST(computer simulation technology) EM $studio^{tm}$ program. AC breakdown experiments in non-uniform field was performed to compare with the breakdown simulation values. The pressure range of gas mixtures was 0.4 MPa to 0.7 MPa. The rod-plane was used and mixture ratio is $SF_6$ 20% : $N_2$ 80%. The gap lengths are 10mm to 70mm. As the pressure increase, this simulation value does not correspond to the experiment value. So this simulation need surface roughness factor. As a result of applying surface roughness factor this simulation decrease a relative error (|experiment value - simulation value| /simulation value).

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
• /
• v.29 no.1
• /
• pp.44-49
• /
• 2016

Studies on a $SF_6$-mixture and -alternative gas has been in progress to reduce the use of $SF_6$ gas as an insulation material of GIS (gas insulated switchgears). In this paper, we dealt with PD (partial discharge) characteristics in pure $SF_6$ and $N_2$, and their mixtures on aspects of insulation design and risk assessment for GIS. A POC (protrusion on conductor) and a POE (protrusion on enclosure) as the major defects were fabricated to simulate PD. We analyzed the DIV (discharge inception voltage), DEV (discharge extinction voltage), pulse magnitude, counts and phase distribution of PD pulse in $SF_6-N_2$ mixtures ($SF_6$ 100%, $SF_6$ 80%-$N_2$ 20%, $SF_6$ 50%-$N_2$ 50%, $SF_6$ 20%-$N_2$ 80%, and $N_2$ 100%) according to the IEC60270. The DIV, DEV as well as magnitude of PD pulse decreased on the POC as increase of $N_2$ ratio. For the POE, the DIV and DEV in $N_2$ ratio below 50% were the same voltages as those in $SF_6$ 100%. In this experiment, $SF_6$ 80%-$N_2$ 20% mixture could be considered with the equivalent insulation performance to a GIS.

• The Transactions of the Korean Institute of Electrical Engineers P
• /
• v.59 no.2
• /
• pp.146-150
• /
• 2010

Distribution Function and Drift velocities for electrons in $SF_6$-Ar mixtures gases used by MCS-BEq algorithm has been analysed over the E/N range 30~300[Td] by a two term Boltzmann equation and by a Monte Carlo simulation using a set of electron cross sections determined by other authors, experimentally the electron swarm parameters for 0.2[%] and 0.5[%] $SF_6$-Ar mixtures were measured by time-of-flight method. The results obtained in this work will provide valuable information on the fundamental behaviors of electrons in weakly ionized gases and the role of electron attachment in the choice of better gases and unitary gas dielectrics or electro negative components in dielectric gas mixtures. The results show that the deduced electron drift velocities agree reasonably well with theoretical for a rang of E/N values.

• The Transactions of the Korean Institute of Electrical Engineers C
• /
• v.50 no.6
• /
• pp.288-295
• /
• 2001

Predischarges in nonuniform electric field stressed by lightning impulse voltagesin SF(sub)6-$N_2$mixtures are initiated by streamer coronas. Due to field ehnancement at a protrusion point of electrodes new ionization processes occur and a precursor, which leads to a first leader, is created. The leader proceeds step by step to the opposite electrode and the final jump bridges the test gap. It was found that the predischarge is propagated with a leader mechanism of stepwise expansion from the predischarge current waveforms measured by a shunt. The predischarge current is closely related to the amplitude and polarity of applied voltages, the gas pressure and the gap geometry. The time intervals between step leaders for the positive and negative polarities were inversely proportional to V.P$^2$. When the gas pressure increases in the positive polarity, statistical time lag to statistical time lag to streamer corona inception increase slightly, but the formative time lag to flashover is significantly decreased.

• The Transactions of the Korean Institute of Electrical Engineers P
• /
• v.64 no.3
• /
• pp.125-129
• /
• 2015

Energy distribution function for electrons in SF6-Ar mixtures gas used by MCS-BEq algorithm has been analysed over the E/N range 30~300[Td] by a two term Boltzmann equation and a Monte Carlo Simulation using a set of electron cross sections determined by other authors experimentally the electron swarm parameters for 0.2[%] and 0.5[%] $SF_6-Ar$ mixtures were measured by time-of-flight(TOF) method, The results show that the deduced longitudinal diffusion coefficients and transverse diffusion coefficients agree reasonably well with theoretical for a rang of E/N values. The results obtained from Boltzmann equation method and Monte Carlo simulation have been compared with present and previously obtained data and respective set of electron collision cross sections of the molecules.

• The Transactions of the Korean Institute of Electrical Engineers P
• /
• v.51 no.1
• /
• pp.28-32
• /
• 2002

Energy distribution function for electrons in $SF_6+Ar$ mixtures gas used by MCS-BEq algorithm bas been analysed over the E/N range 30-300[Td] by a two term Boltzmann equation and by a Monte Carlo Simulation using a set of electron cross sections determined by other authors, experimentally the electron swarm parameters for 0.2[%] and 0.5[%] $SF_6+Ar$ mixtures were measured by time-of-flight(TOF) method. The results show that the deduced electron drift velocities, the electron ionization or attachment coefficients, longitudinal and transverse diffusion coefficients and mean energy agree reasonably well with theoretical for a rang of E/N values.

• The Transactions of the Korean Institute of Electrical Engineers P
• /
• v.59 no.2
• /
• pp.197-201
• /
• 2010

$SF_6$ gas would be used in power transformer, GIS (Gas insulated switchgear) and so on because of its electrically superior insulation and chemically stable structure. Recently, the reduction of $SF_6$ is required to avoid global warming and the researches on the dilution of $SF_6$ with other gases have been carried out. $SF_6$ mixture gases with $N_2$ and $C_xF_y$ have drawn attention to the synergy effect. However, in order to understand the mechanism of the synergy effect, it is important to analyze and evaluate properties of mixture gases quantitatively. In this paper, we investigated the mechanism of synergy effect from electron collision processes and electron energy distribution by solving Boltzmann equation with propagator method. Three kinds of gases for dilution of $SF_6$ ($SF_6/N_2$, $SF_6/CF$4 and $SF_6/C_4F_8$) are considered in this simulation. On the properties of $SF_6/N_2$ mixture gas, the variation of reduced electric field was shown highly within 0%~40% mixtures of $SF_6$. And the more low-level electron energy has been distributed, the higher insulation capability has appeared.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
• /
• v.22 no.12
• /
• pp.79-86
• /
• 2008

This paper presents the experimental results of impulse breakdown characteristics in $SF_6/N_2$ gas mixtures under a highly non-uniform electric field with a change in temperature. The test temperature ranges from -25[$^{\circ}C$] to 25[$^{\circ}C$]. The processes of impulse preliminary breakdown developments were analyzed by the measurements of current pulse and luminous signals. As a result, the temperature dependance of breakdown voltage for the negative polarity was much stronger than that for the positive polarity. When increasing the temperature, The leader stepping time for the negative polarity was shown to be longer than that for the positive polarity. The results presented in this paper can be used as a useful information in designing the gas insulation lines with prominent ability for lightning surge.

• The Transactions of The Korean Institute of Electrical Engineers
• /
• v.59 no.10
• /
• pp.1850-1855
• /
• 2010

The application field of the pulse power is very wide. Recently, Pulse power technologies take a large place in several applications. Then, many civil and military applications proceed. Marx generator is widely used in high voltage applications. Marx generator is widely used in high voltage applications, such as eletromagnetic wave and power lasers. This paper, we described about the high voltage pulse generator. A compact size high voltage pulse generator with nanosecnd rise time has been fabricated and investigated experimentally. The marx generator has 2 stages. Each stage was constructed one charging capacitor, two electrodes and one charging resistor. A inductance structure is used in order to improve the switching performances fo the whole generator. The experiments of rise time in pure gas and mixtures of gases were described. We tested the Marx generator at different insulation gas. the results show that the dielectric strength of the $N_2-SF_6$ mixture was significantly increased compared with pure nitrogen gas. The experimental results show that the rise time characteristics of the Marx generator can be controlled through varying insulation gas.

• Journal of Electrical Engineering and Technology
• /
• v.10 no.4
• /
• pp.1734-1737
• /
• 2015

Insulating characteristics of Cl₂-He mixture gases in gas discharges were analysed to evaluate ability of these gases for using in medium voltage and many industries. These are electron transport coefficients, which are the electron drift velocity, density-normalized longitudinal diffusion coefficient, and density-normalized effective ionization coefficient, in Cl₂-He mixtures. A two-term approximation of the Boltzmann equation was used to calculate the electron transport coefficients for the first time over a wide range of E/N (ratio of the electric field E to the neutral number density N). The limiting field strength values of E/N, (E/N)_lim, for these binary gas mixtures were also derived and compared with those of the pure SF₆ gas.