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Compressed air is used in spark gap switches as an insulating gas. Triggered by nanosecond pulsed voltage, the streamer bridges the electrode gap in the switch. During the streamer-arc transition, the spatial distribution of the arc changes drastically. The nitrogen and oxygen in the compressed air will react with each other under high temperatures. Damaging effects in the switch are caused by arc reaction. In this paper, by adjusting the parameters of the high-energy pulse discharge circuit, the arc is produced with different current waveform in the spark gap switch, while the gaseous product is analyzed. The results show that, when current pulse-width remains constant, the amount of transferred charge is approximately linear with the production of nitrogen oxides. The proportion of NO is higher when the current pulse-width is shorter. The concentration of nitrogen oxides is determined by the chemical reaction, which relies on the dynamic change of the impulse arc. During the arcing time, there is the collision dissociation reaction in the local thermodynamic equilibrium (LTE) plasma, leading to the production of gas atoms and excitation molecules. In the boundary of the arc channel, the nitrogen oxides formation reactions mainly occur in the arc quenching period. According to the characteristics of the high-current arc, a simplified analysis of chemical kinetics on the reactions of nitrogen and oxygen is implemented to expound the effect of pulsed arc on the gas composition. [ABSTRACT FROM AUTHOR]

As a rule, the site pollution severity (SPS) is determined by the ESDD and NSDD of cap and pin standard disc insulator (reference insulator) under de-energized conditions. But now standard disc insulators are seldom used on transmission lines. In order to determine the SPS of certain districts, it is essential to figure out the coefficient of conversion from ESDD and NSDD of reference insulators to that of other profiles of insulators. Moreover, pollution condition prediction may require the quantification of insulator pollution characteristics. For the reasons above, a one-year-period natural pollution experiment of de-energized insulators was carried out in Henan, China. For the first time, the Dixon test is introduced to detect the outliers among the natural contamination data, which contributes to unveiling the data's law. The coefficient of conversion is defined as the relative contamination coefficient in the paper, which is based on the ratio of the contamination data of a certain type of insulator to that of the reference insulator. The Shapiro-Wilk test and normal quantile (Q-Q) plot testify the normality of the relative contamination values. Based on the normality of relative contamination values obtained in the experiment, the insulator pollution characteristic is quantified. Via the relative contamination coefficients, it is easy to judge the contamination accumulation difficulty between insulators and predict the pollution condition of most profiles of insulators. Moreover, a determination method of SPS is raised in the paper, which helps to reckon the pollution condition of one type of insulator on the basis of the known pollution condition of insulators of other types. Besides, the pollution discrepancy between the top and bottom surfaces of insulators is analyzed by the relative contamination values. [ABSTRACT FROM AUTHOR]

Fault diagnosis of power transformers is crucial to the healthy operation of transformers. In order to enhance its accuracy and reliability, a new fault diagnosis method based on Set Pair Analysis (SPA) and association rules was proposed in this paper. Via analyzing the relationship of fault symptoms and fault types, the corresponding association rules could be established. Via computing the support degrees and confidence degrees of the association rules, the constant weight coefficient of each symptom and the variable weight coefficient of each type could be obtained. The diagnosis method could avoid the subjective defects effectively. Via introducing the concept of subordinate degree, the connection degrees of each fault type and the whole running state of transformer could be obtained. This method could also improve the accuracy of uncertainty factors of transformer fault diagnosis. Experimental results of the test substation proved this method had a higher accuracy by comparing with both association rules and SPA. [ABSTRACT FROM PUBLISHER]

Air-core Tesla transformer combined with semiconductor devices can generate repetitive high-voltage pulses effectively. Air-core Tesla transformer of spiral type is suitable for repetitive operation since its primary voltage is relatively low. Based on the double resonance circuit of air-core Tesla transformer, the expressions of secondary voltage, primary current, and the maximum rise-rate of primary current are deduced. The effects of tuning characteristic on the output voltage and energy efficiency are simulated, and further verified by experiments. An air-core Tesla transformer prototype of spiral type is developed. To achieve repetitive operation, a resonant charging and discharging circuit based on air-core Tesla transformer is designed. The repetitive system based on this prototype can generate microsecond pulses with an average peak voltage of -140 kV at 300 Hz repetition rate. In repetitive mode, the tuning ratio is recommended to range in 1.0-2.0 to achieve high energy efficiency. The output voltage could be higher by increasing the charging voltage or tuning ratio. [ABSTRACT FROM PUBLISHER]

Condition assessment for power transformer requires not only integrating the known artificial intelligence (AI) technology, but also exploiting the interrelation of the measured data. According to the association rule of information data and the variable weight synthesizing theory of factor spaces, an assessment method of transformer condition was proposed in this paper. Via analyzing the interrelation of the independent status parameters (ISP) and transformer fault types, the set of synthetic status parameters (SSP) can be built up. For avoiding interference from subjective experience, association rule theory was used to calculate the constant weight coefficients (CWC) of the ISPs. Since the true transformer condition may not always be accurately reflected under the condition of CWCs of a few SSPs, the method of variable weight synthesizing was used for computing the variable weight coefficients (VWC) of the SSPs. Then, combining with the existing maintenance procedures, a preferable condition assessing system of power transformer was proposed. Operational example proved the condition assessing system may reflect the real operation condition of power transformer. [ABSTRACT FROM PUBLISHER]

Analysis of breakdown mechanism in gas-insulated trigatron switches is important for the engineering design and function prediction. Based on the gas discharge theory, a physical model was proposed to estimate the breakdown time for gas-insulated trigatron switches. And the model can explain the breakdown in the trigatron switches with two modes of the breakdown mechanism, i.e., fast breakdown mode (FBM) and slow-breakdown mode (SBM). Based on Raether breakdown criterion, this paper discussed the factors affecting on the E-field enhancement. The E-field is composed of the static E-field and the dynamic E-field, which leads to transformation of breakdown mechanism. Some coefficients could be determined by experiment and simulation, which are helpful to get the quantitative solution of breakdown time. [ABSTRACT FROM AUTHOR]

Working characteristics of a three-electrode trigatron spark gap is discussed in this paper. Breakdown probability is proven to fit a Weibull distribution. For an engineering application, the lower limit of undervoltage ratio depends on breakdown probability, and the upper limit of undervoltage ratio depends on self-breakdown probability. Some characteristics have been determined experimentally, such as the influence of the air pressure and the influence of the undervoltage ratio on spark gap operation. Curve fitting and quasi-data mining are good methods for research on triggering characteristic in the paper. Therefore, a maximum operation range curve and a boundary line of expected delay time could be determined by application requirements, theory calculation, experimental data and curve fitting. On this basis, optimization operation range could be obtained, which represents a preferable performance of breakdown with expected delay time. It may provide guidance for engineering application. [ABSTRACT FROM AUTHOR]

In a high-power laser facility with multiplex power modules, the dispersion of self-breakdown voltages of spark gap switches might result in a so-called pre-fire problem. Pre-fire probability of spark gap switches with graphite electrodes must be constrained at extremely low level. In this paper, Pedersen model was used to explain the causes of pre-fire. The microscopic surface roughness of worn graphite electrodes had a major impact on pre-fire. And this paper had deduced the cumulative probability distribution of pre-fire, and given a relevant Weibull distribution equation. Several typical graphite materials were tested too. The experimental results revealed that electrodes should use graphite with higher hardness, smaller particle size and greater flexural strength. This was consistent with the analysis of Pedersen model. More significantly, based on the experiments of typical graphite materials, two Weibull constants of the cumulative probability distribution of pre-fire were obtained by a graphing method. Therefore, it is possible to calculate, reduce or control the occurrence of pre-fire in a facility with many gas switches. Via optimizing the operating under-voltage ratio of multiplex switches, the expectable pre-fire probability can be achieved. [ABSTRACT FROM PUBLISHER]

Electrode replacement is an effective method to extend the useful lifetime of the spark gap switch with graphite electrodes. In order to perform electrode replacement, suppressing temperature rise and preventing static welding/erosion should be considered for the static electrical contact interface between the electrode and the holder. In this paper, a mathematical model of contact temperature rise is proposed based on the Holm model and heat-conduction equations. This mathematical model can quantitatively prove that some material properties of the metal holder and some mechanical characteristics of the spark gap switch are key parameters affecting temperature rise. Material properties of the metal holder include thermal conductivity, specific heat, density, electrical resistivity, elasticity modulus, and the Poisson ratio. Mechanical characteristics of the spark gap switch include contact radius/area, contact pressure, and contact surface roughness. Optimum configuration of these key parameters reduces temperature rise and prevents static welding/erosion. [ABSTRACT FROM AUTHOR]