This paper deals with the analysis of spherical conducting particle motion as well as particle initiated breakdown in electric fields between diverging conducting plates with dc voltage in atmospheric air. Motion of spherical particle was estimated by solving the motion equation numerically, and the results agreed well with the experimental ones. It was found that when the particle is placed on the horizontal electrode surface where the electric field is nearly equal to the lifting field, the particle progresses towards a higher electric field region by the effect of Coulomb force and electrical gradient force. This is true for a nonspherical conducting particle. The obtained results for particle motion suggest that much attention should be paid in the design of GIS particle traps to forces acting on the particle directly towards the higher electric field region. Moreover, the particle-initiated breakdown is discussed on the basis of the experimental and theoretical results. It was found that one of the reasons for reduction of the breakdown voltage is the effect of microdischarge between the particle and an oppositely charged electrode.

Conducting particle motion and particle-initiated breakdown in dc electric field between diverging conducting plates in atmospheric air

In the past ten years there have been significant advances in the theoretical and experimental analysis of high-voltage gas breakdown and surface flashover of insulators in compressed gases. This has probably been fostered by the recent growth in the design and application of gas-insulated high-voltage equipment. The review describes the characteristics of compressed-gas breakdown, including the effects of failure of Paschen's law; conditioning; electrode area; material and surface; breakdown-voltage distribution; particle contamination; voltage waveform; temperature; and gas mixtures. The insulator-flashover characteristics are then described, including the effects of insulator-electrode interface; insulator material; insulator shape; voltage waveform; charge generation; particle contamination; surface contamination; conditioning; flashover distribution; and dependence on type of gas. The various mechanisms proposed for gas breakdown and insulator flashover are reviewed and discussed in relation to the experimental characteristics. Future theoretical and experimental work is suggested to clarify the gas-breakdown and insulator-flashover mechanisms, and which would also help bring about the design of improved high-voltage gas-insulated systems.

Review of high-voltage gas breakdown and insulators in compressed gas

The lifting field of a free conducting particle (FCP) situated on a dielectric coated electrode in compressed SF6 gas is calculated based on two different particle charging mechanisms-partial discharges occurring in the gas surrounding the particle and charge conduction through the dielectric coating. Calculated values are compared with experimental results obtained for different thicknesses of anodized (Al203) coatings and at different gas pressures. It is suggested that at lower pressures a partial discharge mechanism is predominant whereas at higher pressures a charge conduction mechanism is predominant.

Lifting Field of Free Conducting Particles in Compressed SF6 with Dielectric Coated Electrodes

Many researchers have suggested that the space charge field of the primary electron avalanche should not be neglected in calculating the corona onset voltage based on the streamer criterion. Some researchers consider only the space charge field of the positive ions created during the avalanche growth, while others consider only the space charge field of the electrons at the head of the avalanche. The authors suggest that both space charge fields should be considered in calculating the corona onset voltage. Computer programs are written to calculate the breakdown voltage (for uniform field: parallel-plane geometry) and corona onset voltage (for non-uniform field: point-to-plane geometry). The space charge fields of both the positive ions and the electrons are considered in the calculations. Results are obtained for air and SF6 for a wide range of geometrical parameters and gas pressures. The results indicate that the effect of space charge fields is to reduce the corona onset voltage (or breakdown voltage in uniform field geometry) by less than 5%.

Effect of Avalanche Space Charge Field on the Calculation of Corona Onset Voltage

When a spherical conducting particle exists in an electrode system where electrical gradient force acts along the electrode surface, the particle tends to move towards the high field region. The possibility of appearance of this phenomenon is experimentally investigated with wire particles, which can easily produce the corona discharge on their ends resulting the action of a reactive force on the particle by a corona wind. The results show that a hovering particle travels deeper into the high electric field regions regardless of the corona discharge. Moreover, it is found that wire particle with corona discharge hovers near the negative electrode under DC voltage in atmospheric air due to different characteristics of corona discharge by the polarity. But under the AC voltage, the particle hovers near the bottom electrode only and invades in the high field region deeper than under the DC voltage.

Experimental studies of free conducting wire particle behavior between nonparallel plane electrodes with AC voltages in air

Conducting particle charging and detachment into a compressed SF6 coaxial electrode gap energized with high direct voltage have been investigated using the charge simulation technique and dimensional analysis.

C. Masetti

Papers

Particle-Initiated Breakdown in SF6 Insulated Systems Under High Direct Voltage