Why is it that high voltage transmission lines do not short to earth during torrential rainfall?


I would love to understand why HV lines don’t carry the voltage required to break the resistance to earth in very heavy rain. Is rain water pure water with low conductivity? Or are the air gaps too much for the voltage?

In: 3

In general electricity wants to travel with the lowest resistance possible and thanks to insulation the lowest resistance path is between the copper cables inside it.

Relatively pure water such as rain is actually a rather poor conductor. The space between raindrops and their conductivity means that the voltages that transmission lines carry are unlikely to arc to ground through the rain.

As the others said, between the gaps in the water droplets, the fact that water is actually a bad conductor, really good insulation and proper grounding/systems on each end, the electricity will stay with the path of least resistance which is the aluminum (or copper) inside itself.

Pure water does not conduct, and rainwater is pretty clean. The other half of the equation is the design of the insulators holding the conductors. You’ve probably noticed that they are either belled or finned…in both cases it greatly increases the surface distance over the insulator that the electricity would have to travel, making a flashover much less likely.

Counter-intuitively, a flashover is more likely to occur in a heavy dew or drizzle where the moisture mixes with accumulated dust/dirt on the insulator. Dirty water does conduct. Heavy rains tend to wash the dust off.

The air gap itself (the linear distance from conductor to a grounded surface or other phase), has significantly higher insulation properties and rain doesn’t really compromise it that much, since even in a deluge the drops are relatively far apart.

As other’s have said it even if water were a good conductor it would need to essentially be a solid mass to have good conductivity.

That said, the insulators on the towers are also designed such that the water is shed away from contact with the tower and wire–they look like stacked umbrellas.