Corona discharge

from Wikipedia, the free encyclopedia

A corona discharge ( Latin corona , crown, crown, ring) is an electrical discharge in a non-conductive medium, for example in air. It often occurs as a peak discharge . It is often associated with a luminous phenomenon; this explains the name. In nature it is observed as an Elmsfeuer .

A similar phenomenon is the corona , ring-shaped rays from some polar lights .

Corona discharges are usually undesirable in technology. However, they also have utility applications, see for example corona treatment .

Emergence

Corona discharges, recognizable as bright “tufts” in the upper area of ​​the image, in a high-voltage laboratory .

The discharge requires ions as charge carriers. These can either already be present ( plasma ) or they form in the medium as a result of field ionization if the electrical field strength is high enough (typically around 100 kV / m). If the high field strength prevails at the surface of the cathode , field ionization can also contribute to field emission of electrons with subsequent impact ionization .

Under suitable conditions, a corona discharge can “burn” permanently. If the field strength increases even further, it can turn into a voltage breakdown or an electric arc .

Unwanted corona discharges

In high voltage - transmission lines corona discharges provide a smaller part of the transmission losses . Except represents energy loss they cause noise (crackling sound), radio interference and result in charges of the dust particles in the air. To reduce them, corona rings are attached, overhead lines are designed as bundled conductors (often two to four wires of the same phase at a short distance from one another) and with a diameter that is not too small. The occurrence can be monitored with a corona camera .

The discharges are also generally undesirable in high-voltage components such. B. transformers and especially in high voltage applications where no ozone should be generated.

Uses of corona discharges

Demonstration: Corona discharge on a high-voltage Wartenberg

Corona discharge can be used to evenly charge an insulator surface electrically. In photocopiers and laser printers, the surface of a drum, more rarely a belt, passes close to a corona wire stretched across the direction of movement for this purpose, before exposure allows the charge to flow away again in places.

In Van-de-Graaff generators , corona discharges serve to stabilize the high voltage, and in many cases also to charge the strip that transports the charge to the high-voltage electrode.

Further applications are:

literature

  • Andreas Küchler: High voltage technology . 2nd Edition. Springer, ISBN 3-540-21411-9 .

Web links