The present paper is a wide review on AC surface dielectric barrier discharge (DBD) actuators applied to airflow control. Both electrical and mechanical characteristics of surface DBD are presented and discussed. The first half of the present paper gives the last results concerning typical single plate-to-plate surface DBDs supplied by a sine high voltage. The discharge current, the plasma extension and its morphology are firstly analyzed. Then, time-averaged and time-resolved measurements of the produced electrohydrodynamic force and of the resulting electric wind are commented. The second half of the paper concerns a partial list of approaches having demonstrated a significant modification in the discharge behavior and an increasing of its mechanical performances. Typically, single DBDs can produce mean force and electric wind velocity up to 1 mN/W and 7 m/s, respectively. With multi-DBD designs, velocity up to 11 m/s has been measured and force up to 350 mN/m.

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Electrical and mechanical characteristics of surface AC dielectric barrier discharge plasma actuators applied to airflow control

Gases for electrical insulation are essential for the operation of electric power equipment. This Review gives a brief history of gaseous insulation that involved the emergence of the most potent industrial greenhouse gas known today, namely sulfur hexafluoride. SF6 paved the way to space-saving equipment for the transmission and distribution of electrical energy. Its ever-rising usage in the electrical grid also played a decisive role in the continuous increase of atmospheric SF6 abundance over the last decades. This Review broadly covers the environmental concerns related to SF6 emissions and assesses the latest generation of eco-friendly replacement gases. They offer great potential for reducing greenhouse gas emissions from electrical equipment but at the same time involve technical trade-offs. The rumors of one or the other being superior seem premature, in particular because of the lack of dielectric, environmental, and chemical information for these relatively novel compounds and their dissociation...

Assessment of Eco-friendly Gases for Electrical Insulation to Replace the Most Potent Industrial Greenhouse Gas SF6

Solid-state transformer (SST) is an emerging technology integrating with a transformer power electronics converters and control circuitry. This paper comprehensively reviews the SST topologies suitable for different voltage levels and with varied stages, their control operation, and different trends in applications. The paper discusses various SST configurations with their design and characteristics to convert the input to output under unipolar and bipolar operation. A comparison between the topologies, control operation and applications are included. Different control models and schemes are explained. Potential benefits of SST in many applications in terms of controllability and the synergy of AC and DC systems are highlighted to appreciate the importance of SST technologies. This review highlights many factors including existing issues and challenges and provides recommendations for the improvement of future SST configuration and development.

/pdf/state-of-the-art-of-solid-state-transformers-advanced-4j8kucud9h.pdf

State of the art of solid-state transformers: Advanced topologies, implementation issues, recent progress and improvements

https://iopscience.iop.org/article/10.1088/0963-0252/25/6/063001/pdf

Dynamics of near-surface electric discharges and mechanisms of their interaction with the airflow

Spacers are key components that are used to support high voltage conductors in gas-insulated substations or gas-insulated lines. The analysis of the surface charge patterns on spacers remains a difficult task, which requires a comprehensive understanding of the physical mechanism of the gas-solid interface charging phenomenon. In this letter, we reported a field dependent property of surface charge accumulation patterns on spacers under DC stress. We verified this finding through experiment, and further, we put forward a field-dependent charging model based on dominant charge transport behavior under different electric fields. It was found that the charging characteristics of the spacer are dominated by the Ohmic conduction from the volume below an electric field of 2.5 kV/mm. When the electric field stress is higher than 2.5 kV/mm, the charging property of spacers is dominated by the enhanced gas ionization according to Townsend's law. The correctness of this model was verified by surface charge measurement results in literature studies, and a method for determining the dominant mechanism of charge accumulation under different electric fields was proposed.Spacers are key components that are used to support high voltage conductors in gas-insulated substations or gas-insulated lines. The analysis of the surface charge patterns on spacers remains a difficult task, which requires a comprehensive understanding of the physical mechanism of the gas-solid interface charging phenomenon. In this letter, we reported a field dependent property of surface charge accumulation patterns on spacers under DC stress. We verified this finding through experiment, and further, we put forward a field-dependent charging model based on dominant charge transport behavior under different electric fields. It was found that the charging characteristics of the spacer are dominated by the Ohmic conduction from the volume below an electric field of 2.5 kV/mm. When the electric field stress is higher than 2.5 kV/mm, the charging property of spacers is dominated by the enhanced gas ionization according to Townsend's law. The correctness of this model was verified by surface charge measurem...

Field-dependent charging phenomenon of HVDC spacers based on dominant charge behaviors

The charge density distribution of the downsized GIS disc spacer made of epoxy resin was measured in 0.5-MPa (abs.) SF6 gas. A dc voltage was applied to the spacer, and the charge density on the surface was measured using an electrostatic probe. Voltage application and charge measurement were conducted in a sealed chamber without opening it. After the voltage application of 60 kV, radial charge patterns appeared on the spacer. Tiny metal particles whose size is smaller than 0.1 mm were observed on the spacer after the voltage application. Metal particles on the spacer may cause the radial charge accumulation in this experiment: if a metal particle adheres on the spacer, partial discharge may occur near the metal particles and negative charges may progress along the surface of the spacer.

Influence of tiny metal particles on charge accumulation phenomena of GIS model spacer in high-pressure SF 6 gas

The influence of residual charge on propagation of surface discharge is experimentally investigated using high-speed framing and streak cameras, and an electrostatic probe. When consecutive impulse voltages are applied 25 times with a change in polarity, the propagation length of the surface discharge increases gradually from 79 to 164 mm and hardly converges. Under such a condition, the potential gradient in the surface leader channel decreases with the consecutive number of impulses, while that in the surface streamer remains constant and the value is 0.5–0.6 kV mm−1. With the residual charge of a previous opposite polarity discharge on an insulator, the propagation velocity increases to three to eight times as large as that of the surface discharge on a clear insulator without any residual charge. The peak current of the surface discharge with a residual charge also becomes much higher than that without a residual charge.

https://iopscience.iop.org/article/10.1088/0022-3727/43/49/495203/pdf

The influence of residual charge on surface discharge propagation

Information on the potential and the field profile along a surface discharge is required for quantitatively discussing and clarifying the propagation mechanism. The sensing technique with a Pockels crystal has been developed for directly measuring the potential and electric field distribution on a dielectric material. In this paper, the Pockels sensing system consists of a pulse laser and a CCD camera for measuring the instantaneous two-dimensional potential distribution on a 25.4 mm square area with a 50 µm sampling pitch. The temporal resolution is 3.2 ns which is determined by the pulse width of the laser emission. The transient change in the potential distribution of a positive surface streamer propagating in atmospheric air is measured with this system. The electric field and the charge distributions are also calculated from the measured potential profile. The propagating direction component of the electric field near the tip of the propagating streamer reaches 3 kV mm−1. When the streamer stops, the potential distribution along a streamer forms an almost linear profile with the distance from the electrode, and its gradient is about 0.5 kV mm−1.

https://iopscience.iop.org/article/10.1088/0022-3727/42/7/075204/pdf

Two-dimensional potential and charge distributions of positive surface streamer

Shack–Hartmann type laser wavefront sensors were developed for measuring a two-dimensional electron density distribution over an arc channel in an extinguishing phase by only a single measurement with high temporal and spatial resolutions. The sensors were applied to pulsed arcs in a 3 mm air gap between rod-to-rod tungsten electrodes with a diameter of 1mm. Electron densities in the arc discharges with currents of several tens of amperes were 2 × 1023 m−3 around the gap centre, which were more than twice lower than those near the anode and cathode.

https://iopscience.iop.org/article/10.1088/0022-3727/45/43/435202/pdf

Shack–Hartmann type laser wavefront sensor for measuring two-dimensional electron density distribution over extinguishing arc discharge

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 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

Shigeyasu Matsuoka

Papers

Influence of tiny metal particles on charge accumulation phenomena of GIS model spacer in high-pressure SF 6 gas

The influence of residual charge on surface discharge propagation

Two-dimensional potential and charge distributions of positive surface streamer

Shack–Hartmann type laser wavefront sensor for measuring two-dimensional electron density distribution over extinguishing arc discharge

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