Limitation of Spark gap as lightning arrester

The common use of spark gap for as a surge arrester is seen by us mostly in transformers.It is relatively cheap and easily maintainable hence popularly used. But it has some great limitation like failure in case of high rise speed traveling wave.

Spark gap arrangement has two piece of conductor. One is connected to the live cable and another is connected to the earthing. There is some specific gap between this two conductor. This is called spark gap.

The concept is spark gap is to provide conductor gap arrangement, so that under normal voltage there is high insulation gap, thus open circuit for normal current. But in case of traveling wave with high voltage , the gap is surpassed with high voltage thus it acts like a short circuit.

Spark Gap lightning arrester
Spark Gap lightning arrester

Limitation of spark gap for high rise up traveling wave

The peak value for a limited wave depends on the rise speed of the voltage wave. This behavior, due to the air’s ionisation mode, is very different from that of an SF6 or of a solid insulation device that is often used in switchgear.

The drawing below shows the time/voltage data for a spark gap in the air, with a much higher voltage surge possibility than the necessary level of protection.

A switchgear can be destroyed through internal flashover, if the wave from the lightning impulse has a rapid current rise front, even if the protective gap is in good condition.

spark gap as surge arrester
Limitation of Spark Gap as surge arrester.

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