Streamer Breakdown Criterion Research Articles

Analysis and modeling of the influence of uniform field and nonuniform field on stream discharge under the flow field

Streamer discharge theory does not consider the influence of airflow on discharge. However, it is found experimentally that the airflow causes a great change in the breakdown process, especially in a nonuniform field. In this paper, a physical model of spark discharge in airflow is established considering the combined effect of the decrease in airflow density and the blowing away of positive ions and electrons on the breakdown process. Furthermore, the classic streamer breakdown criteria both in uniform field and nonuniform field are modified. This model extends the classic streamer breakdown criterion for static gases to the airflow environment.

Effect of voltage waveshape and pressure on streamer breakdown criterion for predicting flashover voltage of polymeric insulators

The flashover voltage (FOV) of an outdoor insulator varies with atmospheric conditions and the voltage waveshapes. When altitude increases, the FOV decreases due to various atmospheric factors, mainly the pressure. The FOV of the insulator changes under normal operating conditions and transient over-voltages. As the flashover is dominated by streamer mechanisms, this study addresses the application of the streamer breakdown criterion to predict the FOV under different waveshapes and pressures. The Streamer breakdown criterion requires three parameters: electric field distribution, the relation between electric field and effective ionization co-efficient and the appropriate streamer initiation constant (K). The electric field distribution is computed using a FEM based electrostatic solver and the corresponding effective ionization coefficient is calculated. Though the computational procedures of the first two parameters are well defined, uncertainty exist in the value of K, as K depends on the type of gas, electrode geometry, gap distance, pressure, voltage waveshapes, etc. Though many studies have been carried out on configurations under AC, DC and LI only with different ranges of K, reports on the effect of voltage waveshape on the same configuration at different pressures are lacking. Hence, FOVs of an 11 kV polymeric insulator under DC, AC, LI, SI and the steepest VFTO for various pressures (0.75–1.013 bar) are measured and exact Ks are extracted. The necessity of the voltage waveshape-specific K range is inferred and quantified for accurate prediction of FOVs and also inferring the possibility of prediction of FOV without doing any experiments. The applicability of the K range for different arc lengths is verified using SiR samples.

Influence of discharge polarity on streamer breakdown criterion of ambient air in a non-uniform electric field

Streamer breakdown of atmospheric air with non-uniform dc electric field in a needle-to-plate electrode configuration is studied using a semi-analytic model and experimental measurements. A high voltage (either positive or negative) is applied to a hollow needle with outer diameter and inner diameter separated from a planar ground electrode by a gap distance of 0.1–1.4 cm. Breakdown voltages are recorded for both positive and negative discharge polarities. Empirical relations between the critical avalanche size for streamer breakdown and the gap distance are proposed. Using these empirical relations, a semi-analytic model based on Meek’s criterion for streamer breakdown is developed to accurately predict the measured breakdown voltages. It is found that for (or d 0.5 cm at one atmosphere) streamer breakdown of ambient air occurs at a lower applied voltage for a positively biased needle compared to that with a negatively biased needle, referred as the polarity effect. For breakdown is attained at a lower applied voltage with a negatively biased needle compared to that with a positively biased needle, and breakdown mode transits from the polarity effect to the so called inverted polarity effect.

Modeling of Strong Wind-Sand Dielectric Streamer Discharge

Due to the complex and harsh climate environment in Northwest China, the external insulation of power lines and high-speed train are exposed to strong wind-sand environment all year round, which brings severe challenges to the external insulation design and protection of the electric systems. Based on the theories of streamer discharge, the plate-plate electrode was taken as the analysis object, and a theoretical physical model of the strong wind-sand dielectric discharge is established. In this model, the analytical expressions of electron ionization coefficient and positive ion generation coefficient in a wind-sand environment are deduced considering the combined effects of the airflow velocity, the distortion of the electric field caused by sand particles, and the electrons captured by sand particles in the discharge process; furthermore, the streamer breakdown criterion in wind-sand environment is proposed. Research results can provide an important theoretical basis for the quantitative calculation of the breakdown voltage and the external insulation protection in a strong wind-sand environment.

AC Breakdown Voltage Simulation of SF 6 /N 2 Mixture in Non-Uniform Field and Its Comparison with Experimental Values

is the most commonly used insulating gas in electrical systems. But In these days mixtures and alternative gas has been studied because of global warming. so although many studies have been carried out about binary gas mixtures with , few studies were presented about breakdown characteristics of mixtures. At present study the breakdown characteristics of 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 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 20% : 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).

Onset corona fields and electrical breakdown criteria

Predictions are made of the electric field necessary for the onset of corona in air for spheres and cylinders from the general breakdown criterion, ; α′ is the net ionization coefficient, r is the radius and Q is a constant. It is found that Q = 104 gives a fair fit to experimental results for both wires and points, and for positive and negative corona, for radii varying from 0.01 to 20 cm. By assuming a linear variation of α′ with the difference of the electric field from the critical field where ionization equals attachment, an analytic formula can be derived for the breakdown field for the onset of corona as a function of the radius of the sphere, which is similar to, but different from, Peek's formula for the onset of corona for cylinders or wires. The formulae also give the breakdown field as a function of temperature and pressure. For Townsend and Streamer breakdown mechanisms, values of Q are typically 3 × 104 and 108, respectively. Thus the value of Q derived from experimental values of the onset field for corona for both wires and points is significantly lower than would be expected from either the Townsend breakdown criterion or the Streamer breakdown criterion. It is suggested that the most likely collision process to explain the observed low value of Q is indirect ionization, for example by collisions between excited molecules.

Formulation of the streamer breakdown criterion and its application to strongly electronegative gases and gas mixtures

Following an examination of the definition of the effective coefficient of ionisation $$\bar \alpha$$ , a reformulation of the streamer breakdown criterion is undertaken. The application of this criterion to strongly electronegative gases and gas mixtures is considered, and a figure of merit is introduced to describe dielectric behaviour. By considering both ideal and practical electrode systems, this parameter is shown to be of fundamental importance with respect to the evaluation of the breakdown characteristics of such gases. Its value can be determined from a precision measurement of the linear portion of the Paschen curve.

Streamer Breakdown Criterion for Compressed Gases

The streamer breakdown criterion for computing the uniform field breakdown voltages is examined for gaps filled with Air, N2 and SF6. The critical avalanche size is obtained for these gases for different values of the parameter pd and it is shown that this size depends upon the type of the gas, its pressure, and the gap length. Furthermore, the amount of error introduced in the breakdown voltage calculations is computed by assuming a critical avalanche size of 108 electrons as a condition for the streamer formation. he results are discussed briefly.

Breakdown Voltage in Particle Contaminated Compressed Gases

A method for calculating the breakdown voltage in particle contaminated compressed gases is proposed in this paper. The method is based on the streamer breakdown criterion. It is assumed that at breakdown voltage, the gap between the particle and the bottom electrode breaks down first, which electrically shorts the particle with the bottom electrode, and then a critical avalanche develops at the top of the particle to cause the complete breakdown of the main gap. Calculations are made for spherical particle in parallel plane electrodes containing SF6 and N2 at pressures varying from 1 to 5 atm (0.1 to 0.5 MPa) absolute. The agreement between the calculations and the experiments is reasonable at lower pressures but at higher pressures the experimental values are lower than the calculated values.

A statistical approach to the streamer breakdown criterion in SF6

The electrical breakdown field strength in SF 6 calculated from measurements has been found to deviate considerably from the values predicted by the theoretical models used up to now. The simplest form of the streamer criterion predicts breakdown to take place at field strength - to - pressure ratios close to 8.9 kV/mm atm. The streamer model can be enhanced by introducing surface roughness and electrode curvature factors, thus explaining some of the experimental results obtained. The model is, however, unable to explain the general dependence of the breakdown field strength on parameters as pressure, electrode area and voltage waveform. This paper gives a new theoretical model for impulse breakdown in SF 6 , using a statistical approach to the streamer breakdown criterion. Field emission is assumed to be the source of primary electrons. This model gives correspondence with the experimental results for different electrode configurations covering a wide range of pressure and electrode area.