What Causes Sparks During High Voltage Short Circuits?

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Discussion Overview

The discussion revolves around the causes of sparks during high voltage short circuits, exploring the underlying mechanisms and conditions that lead to sparking when connecting wires with differing potentials. The scope includes theoretical explanations and practical observations related to electrical phenomena.

Discussion Character

  • Technical explanation
  • Exploratory

Main Points Raised

  • One participant suggests that sparks may serve as the reason for a short circuit, proposing that a spark can jump between inadequately insulated conductors, creating an unintended current path.
  • Another participant clarifies that sparks occur when connecting wires with positive and negative potentials, inquiring about the source of these sparks.
  • A response outlines several scenarios for sparking:
    • In low voltage high current situations, a high current flowing through a small area can heat the metal, leading to the formation of a hot plasma and visible sparks.
    • In high voltage low current cases, dry air can ionize and spark if the electric field exceeds a certain threshold, with sparks varying in length and color.
    • In low voltage DC circuits with inductance, interrupting the current can cause a voltage spike that produces a persistent spark as the switch opens.

Areas of Agreement / Disagreement

Participants present multiple explanations for the occurrence of sparks, indicating that there is no consensus on a single cause. Various conditions and scenarios are discussed without resolution on which explanation is definitive.

Contextual Notes

The discussion includes assumptions about the conditions under which sparks occur, such as the type of current (AC vs. DC), the presence of inductance, and environmental factors like air ionization. These factors may influence the observed phenomena but remain unresolved in the conversation.

omri3012
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hallo,

what is the reason for sparks once i have a high voltage short circuit?

Thanks,

Omri
 
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Not sure I understand your question fully. However, it seems likely that the sparks are actually the reason for the short circuit. If you have two conductors that are close to each other and not adequately insulated, then a spark can jump across them. This spark serves as a path for the current; a path other than the intended path, which is basically what a short circuit is.
 
i ment that if i have to wires with + and - and in a certain moment i connect them, i will

sparks. my question is what is the source of the sparks?
 
There are several reasons for sparks, depending on the voltage and current:

Low voltage high current (e.g., shorting an automotive battery)
If two conductors capable of carrying a high current touch, there is a high current flowing in a very small cross section (area) of wire, which heats the metal (usually copper) in the vicinity of where the short occurred. A hot plasma can form. The spark is very bright and often has very small and hot specks of copper that shoot away from the point of contact. Examination of the point of contact will show that some copper has melted.

High voltage, low current
Dry air will ionize and spark if the electric field between conductors is greater than about 3 million volts per meter, or 3,000 volts per mm. This is the breakdown potential of air as an insulating dielectric. The sparks are usually thin and range from yellow to blue in color. They can be very long; a spark from an automobile spark plug ignition coil can be over 2 cm long. Sparks from Tesla coils can exceed 10 or 20 cm.

Low voltage DC current with inductance
If there is a current flowing in a dc circuit that has a series inductance L, as soon as the current is interrupted, the voltage across the opening switch will suddenly increase (V = L dI/dt), producing a spark that will persist as the switch opens.
 

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