voltage drops when lightning strikes nearby, why? - Page 1
Forum section: electronics / beginners

author: mcinque
author_rank: Unknown
timestamp: September 30, 2013, 09:13:41 pm
content: I know, probably this is not a strict-electronics related thread, but someone can explain me why whenin the exact momenta lightning stikes nearby my house (not farther than 400 meters I think, because the thunder comes exactly with the light) I can see a quick voltage drop (home tv's and lights turns of and on again in a hundred of second)?I mean, what's the principle of this behaviour? Of course the lightning didn't hit something of my house, nor some of its energy has discharged into my power line or I (or my tv's!) would not be here...I think the phenomenon should be linked to some kind of discharge lightning safe system on the local power transformer. What do you think? Have you experience in this kind of equipment? I'm really uneducated on this.

author: madires
author_rank: Super Contributor
timestamp: September 30, 2013, 09:29:16 pm
content: I think that the lightning strike changes the potential of the ground/earth around the point of the strike for a very short time. And since neutral is connected to earth at the main distribution panel the voltage between line and neutral changes until earth' potential is back normal.

author: Phaedrus
author_rank: Frequent Contributor
timestamp: September 30, 2013, 09:45:50 pm
content: http://en.wikipedia.org/wiki/Ground_potential_rise

author: MacAttak
author_rank: Unknown
timestamp: October 01, 2013, 04:22:46 am
content: Yeah, not so much that the voltage is dropping in your home as much as the ground potential itself is briefly unstable. It's essentially a massive amount of noise on the AC signal while the ground potential settles back to a stable reference level.

author: IanB
author_rank: Super Contributor
timestamp: October 01, 2013, 08:23:31 am
content: Depending on where exactly the lightning strikes, the dimming could also be caused by a brief short circuit on the power distribution system. Most electrical systems have protection that will divert lightning to ground rather than along the cables. Since plasma is highly conductive the power in the cable will follow the same path to ground that the lightning is taking for the brief period that the arc exists. I think the power distribution equipment will see such a short circuit as a fault condition and will momentarily interrupt the supply to protect itself. Remote consumers will experience a brief "lights out" for half a second or so.

author: johansen
author_rank: Super Contributor
timestamp: October 01, 2013, 08:43:22 am
content: its more or less impossible to determine exactly what you seem to observe, (that which you state in the subject line)without a whole lot of data.first off:lightning is dc.meaning it causes all nearby transformers to saturate and that will cause a RMS DROP due to the RESISTIVE voltage drop due to the SATURATION of the transformer core caused by the DC current flowing through the lightning bolt LEAKING into the AC system...in a sense you are lucky to observe this more than once.. lest the lightning create a potential rise which destroys everything electrical you own.lightning is a 10/300 uS effect typicallymeaning it takes 10uS for the lightning current to rise from 0 to ~20,000 or 100,000 ampsand 300uS to fall to half the peak value.

author: mcinque
author_rank: Unknown
timestamp: October 01, 2013, 11:18:28 am
content: Yes MacAttak and madires, I like this explaination.I like also your reply IanB's, since I live not too far from the power station and I can expect that kind of phenomenon.Quote from: johansen on October 01, 2013, 08:43:22 amOf course, but since this is not the first time I see this behaviour, I think that what you're describing is not my case, or I wouldn't have tv's anymore.

author: jamesb
author_rank: Regular Contributor
timestamp: October 07, 2013, 03:36:31 pm
content: Quote from: johansen on October 01, 2013, 08:43:22 amThis is incorrect, sorry.Karashtin, et al. 2005. High-Frequency Radio Emission of the Lightning Discharge.Radiophysics and Quantum Electronics. 9-2005, Volume 48, Issue 9, pp 711-719Edit: Source

author: johansen
author_rank: Super Contributor
timestamp: October 07, 2013, 10:01:45 pm
content: Quote from: jamesb on October 07, 2013, 03:36:31 pmfrom the title, high frequency radio emission... you are correct, it is ac.but this is not AC,nor is it high frequency.

author: jamesb
author_rank: Regular Contributor
timestamp: October 09, 2013, 06:00:09 pm
content: Really? That is all you have?So you mean to say that just because there happens to be a DC pulse, there is no significant AC component?Nice source btw. LOL. Keep looking kiddo ... maybe you might find something you can manipulate to better serve your misguided opinion.Ground potential rise can and most certainly will have an AC component of varying frequencies.PS:NO NEED TO YELL TO MAKE A POINT

author: hotshoe383
author_rank: Newbie
timestamp: December 02, 2013, 03:27:42 pm
content: Here's what is really happening. You say "home tv's and lights turns off and on again in a hundred of second" In all likely hood the lightning has hit the substation high voltage line supplying your home, or the high voltage supplying the substation that supplies your home. The power system has many different ways of detecting faults (tree on line, lightning, power system equipment shorts. etc.) In this case it would likely be the line "relaying" (fault detecting sensors on the power system) has detected the fault (lightning to power line to ground) It sees the fault, trips (opens) the breaker (shuts the power off) to where the fault is (the one supplying your house or your substation) and "recloses" (a feature of the fault detecting system that very quickly closes the breaker back up) as the vast majority of faults on the power system are transient (very short lived, tree branch burn off, lightning stike over, etc.) The reclosing feature is quite often only set for 1/2 a second. I know this as ran the high voltage power system (550,000 V) for 32 years. I stumbled across your sight looking for a good laymen's explanation of voltage drop from ground zero for a lightning strike for a court case I have with a cable tv system company. I'll check back once or twice in the next month or so in case anyone has questions or comments. If the lights hadn't gone out completely that would be an entirely different scenario with an entirely different explanation.

author: mcinque
author_rank: Unknown
timestamp: December 02, 2013, 10:25:43 pm
content: Very clear and instructive! thank you