Brush discharge
A brush discharge is an electrical disruptive discharge similar to a corona discharge that takes place between two electrodes with a high voltage between them, embedded in a nonconducting fluid, usually air. It is characterized by multiple luminous plasma streamers composed of ionized particles, which repeatedly strike out from the electrode, often with a crackling sound.[1][2] The streamers spread out in a fan shape, giving it the appearance of a "brush".
Corona and brush discharges are sometimes called one-electrode discharges because they occur in the vicinity of a single electrode, and don't extend as far as the other electrode, as in an electric arc (a two-electrode discharge).
- Brush discharge - occurs at a curved electrode (radius > 2 - 3 mm) in the vicinity of a flat electrode. It consists of a short ionization channel which breaks up into a fan of multiple moving streamers which strike toward the other electrode. Brush discharges can occur from charged insulating plastics (for example polythene) to a conductor.
- Corona discharge - occurs at sharp points and edges (radius < 1 mm). It is a uniform ionization (glow discharge) visible as a dim stationary blue glow, fading out as it extends from the conductor.
Both brush and corona discharges represent regions next to conductors where the air has ionized and become conductive, allowing current to leak into the air. They occur when the electric field at the conductor exceeds the "disruptive potential gradient", roughly 30 kilovolts per centimeter. At that voltage, electrons in the air are accelerated by the electric field to a high enough velocity that they knock other electrons off gas atoms when they hit them, creating ions and additional electrons, which go on to ionize additional atoms in a chain reaction call Because the electric field decreases as the distance from the conductor increases, it eventually drops below the value needed for ionization, so corona and brush discharges have a limited extent.
The ability of an electrical discharge to cause an explosion in flammable atmospheres is measured by the effective energy of the discharge. The effective energy of brush discharges is 10-20 mJ, much larger than corona discharges 0.1 mJ.
See also
References
- ↑ Kaiser, Kenneth L. (2005). Electrostatic Discharge. CRC Press. pp. 2.73–2.75. ISBN 0849371880.
- ↑ Britton, Laurence G. (2010). Avoiding Static Ignition Hazards in Chemical Operations. John Wiley. pp. 20–24. ISBN 0470935391.