Direct Lighting Strike on Power Line

[Mbrooke]

Do direct lightning strikes on power lines damage surge arrestors? For example, starting at 0:16, lightning strikes a distribution circuit causing what appears to be a flash over down the line:

https://www.reddit.com/r/Lineman/comments/lzpee6/lightning_hits/

Was the surge to great for the arrestors to clamp the voltage down? Do such lightning strikes damage windings in transformers?

 

[mparenteau]

Recently had an arrestor fail due to a strike near an air switch.

Mike

 

[Mbrooke]

I'd imagine a direct stroke would blast anything apart.

 

[cranky108]

Sometimes lightning arresters are damaged by lightning. The old ones would quickly develop a gas inside, and explode. The newer ones will pop off the bottom cap.

The arresters in the substations normally have bigger blocks than the ones on the lines, and can arrest more of a surge. Normally the arresters and line insulators have a lower withstand that transformer windings do. But it does happen that transformer windings can be damaged. In fact most transformer damage is additive over tens or hundreds of events. Which is why some companies will replace substation transformer every 30 years or so.

 

[Mbrooke]

Arrestors aren't enough to reduce or prevent failure after 30 years? Or is it just misapplication/poor installation? For example I frequently see leads hit the bushing then the arrestors when it should be the other way around.

 

[DTR2011]

We’ve come a long way since these.

 

[bacon4life]

Arrestors can definitely fail from direct strikes. Shielding is the appropriate protection for direct strikes. Arrestors are placed to reduce over voltages due to strikes occurring some distance away from the equipment.

At 15 kV, the routing of conductors is very important since a few feet of incorrectly routed leads can cause a voltage drop exceeding the equipment rating. At transmission voltages, the equipment voltage rating is so much higher that a few feet of additional conductor adds only a small percentage to the overall peak voltage.

The IEEE guide on substation lightning protection explains the economic tradeoffs for various levels of surge protection. In my region with very infrequent lightning, it ends up being overall cheaper to accept occasional transformer failures rather than install tons of surge arrestors/shielding.

 

[jghrist]

Arresters aren't everywhere. Lightning can strike where there are no arresters and flashover insulators before the lightning reaches the nearest arrester. Also, the lightning surge current through the arrester resistance will cause a voltage across the arrester. This voltage can exceed the withstand voltage of the arrester.

 

[RRaghunath]

In 33kV distribution system, the company I worked used to install 5kA rated Surge Arresters.
The specification as changed and all the arresters were replaced with 10kA rated ones, as they faced frequent failures of 5kA arresters.
When it comes to failure of transformer windings, the surge arrester rating is chosen in such a way that it provides at least 25% margin from the lightning impulse withstand voltage (BIL) of the transformer.
If the arrester is
* sized correctly,
* installed within 5m of the transformer bushings and
* arrester earthing is healthy
I suppose the lightning surge should not reach the transformer / cause failure of transformer windings/leads.

 

[cranky108]

Did anyone study wave theory, and see that voltage reflection happens at dead ends, so for that case you want a rounded lead takeoff leading to the arrester.

No not many spark gaps left.

Shielding seems to work better than having an arrester on every third pole, no matter what the experts say.

Besides distribution transformers are cheap in terms of overall distribution cost.

 

[cuky2000]

Although the vast majority of overhead distribution networks do not have shielding protection as the HV line does, the failure rate of distribution surge arresters is fairly low even for those directly exposed to lightning strikes. This makes us believe that the surge arresters are somehow reliable. HV surge arresters are highly reliable. See the publication below for further details.

. .

 

[Mbrooke]

How does wave theory work? At first glance it does not seem to follow the laws of physics.

 

[oldfieldguy]

DTR2011-

I was told that the protruding horn functions were better described as giving a less damaging path once an arc is established by a flashover. Instead of the path being over the surface of the solid insulator, it conveniently slides over to take place between the less-expensive horn(s)

old field guy

 

[Mbrooke]

You need to trip and reclose for arc horns, right?

 

[RRaghunath]

The ZnO arresters have precise operating characteristic.
So, you better remove the arcing horns as these are only a nuisance.

 

[Mbrooke]

What is a ZnO arrestor?

 

[RRaghunath]

ZnO stands for Zinc Oxide. These arresters are also known by names - Metal Oxide arresters as ell as Gapless arresters.

 

[Mbrooke]

Ah, thanks!

 

[DTR2011]

I don’t know much about the arcing horns, other than we remove them and the bus arrestors as part of a station rebuild. New Zno arrestors are installed on the lines. That smell of a new arrestor is almost sweet.

We’re going through an asset renewal phase where OCB’s, disconnect switches and relay panels are being upgraded. I’ve pulled some old SEL-121’s and 221’s out recently.

On our last outage on a straight bus, one of the bus tie breakers failed to trip via SCADA. We were the middle bus of a 3 bus arrangement. I guess that was a “just in time” asset renewal!