impulse generator

Thread Starter

snp2411

Joined Mar 11, 2009
11
i want to design a impulse generator of rating 15kv and 3.65A...plz help me out.....
 

Thread Starter

snp2411

Joined Mar 11, 2009
11
but the current rating is not mentioned..actually this impulse generator is used to measure the jump in the resistance of spark plug..so at 3.65 amps the jump can be known exactly....
 

beenthere

Joined Apr 20, 2004
15,808
That would seem to imply a resistance in the line to the spark plug that would act as the current limiter. When the arc forms across the electrodes, resistance goes from an open circuit to something very low. If you simply place the voltage across the plug, current will exceed 3.65 amps (what an interesting figure) by several orders of magnitude.

It would seem that, once the ionization path forms, the only way to limit current is with a series element.
 

SgtWookie

Joined Jul 17, 2007
22,201
The dielectric strength of air is approximately 3kV/mm or 76.2kV/inch at sea level; 14.7psi absolute.
Its exact value varies with the shape and size of the electrodes, and increases with air pressure.

So, a 1mm (0.0394") gap would require around 3kv to jump the sparkplug gap at normal atmospheric pressure, but much higher voltage is required to ionize the gap when the air pressure is increased during the compression stroke. A typical automotive engine might have 8.5:1 compression ratio; a high-performance engine may have 11.5:1 or even a higher compression ratio.
 
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