Lightning is alternating current...

[joestue]

I found some interesting claims on facebook about this. The discussion can be found in the comments here, look for bob brovey

https://m.facebook.com/story.php?story_fbid=pfbid02BRViBwJ8ZpaFFjE16arD1egBxoYqKTLHYCXsA7ddyU6TCCFuYwW6FAHEQzirQ77rl&id=100044730201835&mibextid=Nif5oz

Seems nonsense to me, i have never heard of this. Of course, multiple restrikes in a tenth of a second is 10 to 100hz.. ac.. but still a net negative (or positive) dc current.

[SparWeb]

Um, sounds ironic, but, don't believe everything you read on the internet, Joe.  Especially on a forum!


So if I had to give it a name it would be "transient" current, not DC or AC because both of those two terms assume some sort of stability.

[Mary B]

It is considered to be an AC source of 100'f of khz to a few mhz frequency... why all my lightning protection systems are designed with AC shunts and not DC only.

[joestue]

It is considered to be an AC source of 100'f of khz to a few mhz frequency... why all my lightning protection systems are designed with AC shunts and not DC only.

well yes, even a square wave is a series of harmonics..

lightening has such a fast rise time you can induce MHZ frequencies in everything around it.

[OperaHouse]

All current is AC.  DC is just slow AC.

[Rob Beckers]

All current is AC.  DC is just slow AC.

I like that one! Actually a good way to view it! To get back to the other message about a square wave and its harmonics: If that square wave goes from 0V to 10V and back to 0V (and repeat) it's "DC", in that current only flows one way (for a resistive load). But, it of course behaves just like AC and will pass through a capacitor, and have lots of harmonics, up to and including the MHz range.

Lightning is like that: Current flows in one direction, but it's fast, it changes intensity rapidly, and his has energy in the 100's of KHz (and Mhz) spectrum. I once tried to tease out its inner works and a long time ago wrote a series of articles, mostly about how to prevent damage from it (it started in trying to do just that for customers with wind turbines). It has some background about lightning too: https://www.solacity.com/lightning-protection/

FWIW..

-Rob-

[tanner0441]

Hi

Surely lightning is static electricity so technically neither AC or DC as we know them, and though it is measured in volts it is EMF not PD volts.

Brian

[OperaHouse]

It is static until it moves.