Spark (discharge)

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High voltage discharge (flashover) across several rod insulators
Spark of a spark plug
Slow motion of a spark on a spark gap

As a spark that will light radiating plasma of short-term gas discharge referred at atmospheric pressure. It runs along a thin channel and goes out by itself after charge equalization.

Sparks arise from electrical voltages between two electrical conductors or electrodes through impact ionization when the striking distance is not reached.

In dry air under standard conditions (atmospheric pressure), depending on the prevailing gas, about 1 kV is required per millimeter between the conductors until a spark occurs. However, this value varies greatly depending on the type of gas or gas mixture as well as its humidity and air pressure .


The striking distance, i.e. the distance between two conductors below which a flashover (spark discharge) occurs between them at a given voltage, depends on:

  • the shape of the conductor - pointed ends of the conductor promote flashover (see also field emission )
  • the humidity and the type of gas - moisture tends to lead to flashovers, sulfur hexafluoride can prevent flashovers
  • ionizing radiation , for example ultraviolet , x-ray and gamma rays , charged particles, promote flashover
  • as the air pressure falls, the range increases; This is important for electrical systems at great heights (mountains, airplanes, rockets): high-altitude electrical systems require greater air and creepage distances
  • high gas pressure reduces the throw (importance e.g. for the function of ignition systems on gasoline engines )

If enough current is supplied in a spark discharge, an arc discharge or an electric arc results , see also switching arc : While the electrodes remain essentially cold in a spark discharge, parts of the conductors or electrodes evaporate in an arc discharge and a metal vapor plasma is created. If a spark gap has to ignite very frequently, there is a risk of local overheating and melting of the material. This can be prevented by a column of subdivided extinguishing spark gaps. The discharges take place at alternating points along the circumference of the disks, which are burned off by spark erosion . The heat capacity of the brass plates cools the sparks so that they are quickly extinguished if the current falls below a minimum. With very high outputs, the plates are water-cooled.

Also, flashes of lightning are spark discharges.

When electrical switches are opened and closed , switching or tear-off sparks or switching arcs occur . They lead to contact erosion and can be suppressed or avoided by using additional electrical components ( protective diode , Boucherot element ).

Spark discharges due to electrostatic charge can destroy electronic components ( ESD ).

A spark creates an electrical connection between two electrodes by impact ionization within a very short time (µs down to a few 10 ns) , very high currents occur (with electrostatic discharges several hundred amperes, with lightning up to 100 kA).

In addition to ultraviolet and light radiation , spark discharges also always emit radio wave pulses. They represent strong sources of interference (see electromagnetic compatibility , EMC for short) up to the GHz range. The first radio wave transmitters worked with spark gaps and gave radio technology its name. Ignition systems of gasoline engines are therefore suppressed by u. a. the rate of current rise is reduced with a resistor in the spark plug connector or in the spark plug . The brush fire on DC motors is also a spark discharge.

Spark gaps are used to generate strong electrical impulses (e.g. nitrogen laser , Tesla transformer ), for ionization, for igniting chemical reactions (piezo lighter , spark plug ), for igniting arcs during TIG welding , for overvoltage protection in electronic devices and in energy transmission used.

Another application is the spark chamber to detect the path of ionizing particles.

Individual evidence

  1. Axel Rossmann: Structure formation and simulation of technical systems Volume 1: The static basics of simulation . Springer-Verlag, 2016, ISBN 978-3-662-46766-4 , pp. 285 ( limited preview in Google Book Search [accessed December 14, 2016]).
  2. Joachim Heintze: Textbook on Experimental Physics Volume 3: Electricity and Magnetism . Springer-Verlag, 2016, ISBN 978-3-662-48451-7 , p. 119 ( limited preview in Google Book Search [accessed December 14, 2016]).