# Hark There is an Arc

AC mains power is almost always transmitted at 50 or 60 Hz. Accepted reasoning is that lower frequencies make transformers larger and higher frequencies have greater transmission losses. Also lower frequencies caused noticable flickering in filament lamps.

My question is: what about arcing? Sure, DC is bad, but wouldn't low frequency AC like, say, 16 Hz railways be worse than 60 Hz? because of longer arc duration causing more damage ? What about 400 Hz aircraft? if the frequency is really high the arc might not have enough time to go out ? So, from a switchgear viewpoint, what frequency would be best?

• I can't give you a proper answer to that but it's a bit swings and roundabouts - lower frequencies are likely to have voltage available to maintain an arc for longer, but also have longer periods where there's little voltage available to maintain the arc. The answer is likely to depend on the current flow and the distance the contacts are able to open, but I can't quantify those off the top of my head.
– Frog
May 14 at 9:27
• 16.67 Hz was used on German railways for a long time. Good for long distance transmission and the motors, but the incandescent lamps in the carriages made everybody feel unwell. New Orleans' pumps ran from 25 Hz (good for the motors), which rather made spare parts inaccessible when hit by Katrina! 50/60 Hz was chosen at the time to be a good compromise between motors, long distance transmission and incandescent lighting. Switchgear didn't really come into it, even 30 ms to the next zero cross with 16 Hz was far better than DC. May 14 at 12:47
• It's a pity this question was closed: here's an experiment that showed arcing duration is minimized at ~500 kilohertz or so (in this particular configuration at least. It undoubtedly depends on what contactors you use; I'd guess that this frequency reduces as you scale things up/larger). Below this you don't tend to get reignition and so arc duration is upper-bounded by time-to-zero-crossing (higher freq better); above this you do (lower freq better). See epjap.org/articles/epjap/pdf/2010/04/ap08450.pdf .
– TLW
May 14 at 18:37
• @TLW It probably also depends on atmospheric conditions, like humidity and air pressure. And what gas it is if it's an inert-gas contactor. May 14 at 23:04
• This does not seem "opinion based" to me. I decided to vote to reopen. If you agree and have enough privilege maybe you can do the same. May 14 at 23:33