Hi everyone, just found THIS LINK of what has to be the most incredible example of how bad things can get when the power distribution system's protective relay scheme fails to do it's job. The events starting around 3:50 are especially dramatic.

The comments provide some interesting details..now imagine this nightmare going on FOR HOURS in your neighborhood!!

Thankfully, it seems that modern protective relay setups (the video is from 1988) are more reliable.

Even so, this situation made me wonder..even though the relay system had failed, and admittedly it would be very risky, but wasn't there any way a line crew could have manually cut the power using cutters or a thing I've heard of called a "loadbuster'? It would seem to have lessened the overall damage to the homes and distribution system.

Very sobering.

Makes me happy that all the lines are underground in my town!

Boy, that's some burnout. Around 3:55 is that arcing we're seeing on the service drop to the house? Looks like the HV might have shorted across to it.

The sound of that arc buzz always gives me the creeps. No sound like that in the world.

Why would it take the utility so long to shut down that area of the grid? It would seem that they could knock it down, cut the bad lines out and reenergize it.
Seeing that soffit go up does remind us why we want short service conductors that are not wrapping around the house

It seemed to jumping around on AL siding or a gutter looking for return pathes though whatever it could find that was even remotely conductive in the house.

Could've been a step voltage hazard for those fire fighters walking around as well.

Reminds me that I have an 11KV line in my backyard and a nieghbors tree that needs a trim/lopping....

Reminds me of the 7.4KV (or whatever voltage Peco uses in Levittown) line in my backyard, and our huge Oak tree growing right into the pole transformer feeding onhe whole block...

(That of course my parents refuse to have cut since they think "it'll take care of itself.")

Ian A.

Ian, just show this video to your parents and ask them if that is what they have in mind.

I agree..I get nightmares from that sound...here in So Cal, the earthquakes don't bother me, it's the buzzing from all the O/H lines arcing that scares me.

And I 've been too close to too many arc faults in my lifetime to ever not be scared by it.

Paul, I think from the comments on the video site that the service drop burned down because the transformer(s) on that feeder failed from the stress, letting full primary voltage get through to the secondaries.

If you listen closely before and after that spot, you can hear the transformer's(?) buzzing changing pitch during that timeframe.

Increadible video footage.
I'm amazed that the utility crew did not contact the POCO control room via cellphone or RT and told them to drop the feeder concerned, cut away the fault and reliven the healthy section.
It looks definitely a good HV to LV fault burning through the transformer primary and secondary windings and at later stages the HV supply finding a path through the neutral and earth conductors from the houses affected.
It is interesting that the OH cables don't burn themselves clear from the actual fault within the heat of the arc.
At 3:52 somehow the gutters become path of the fault current as well, could be copper downpipes providing additional return path to ground.
The firemen appear vey casual about the overall incident and don't seem to be aware of stepvoltages and stay very close near the smoking house prior to the spouting starting to arc.
This is definitely a faillure of the Earth fault protection relay on the HV supply.
The overcurrent may not always operate because it may be a long line and the resistance within the arc may not enough to trip the relay on OC.

These cases do happen. I posted last year under photo's about 11 kV lines in te atatu.
We had a charger failed in a sub under rebuilt, alarms not working and lines burning holes in a concrete driveway.
I was first on site. told control to drop the feeder concerned, open nearest ABS and reliven the healthy part of the line.

Am I right to understand that this condition was allowed to exist for hours? The risk to life and property caused by allowing this to continue is absolutely unacceptable... I certainly hope the power company was held responsible for all the property damage!

Our local power company (Portland General Electric) has cutouts on the HV at every transformer and junction... Understanding that their response may not be quick enough to save life/property, the fire department supervisors have been provided with hotsticks and the necessary training to open the cutouts if necessary.

noderaser:

Yes indeed, that is correct. According to the comments from the person who posted the video, the situation was allowed to continue unabated for several hours.

I hope that someone who sees the video and was perhaps either there or working for the POCO at the time can offer up some sort of explanation for the length of time this was allowed to continue.

To quote Rodalco's post:

and



But I wonder if here in the US, the POCOs use earth fault relaying?

No matter what, I agree the POCO was unacceptably negligent in this case.

But this thought is kinda scary too:



Wow. Given the possibly long interval between training and having to open a cutout under fault conditions, I wonder how wise that really is....

Generally, they do this when a building fire is being caused by electrical means not easily disconnected from the building, or if a safety hazard would be present by leaving power on to a building. If a condition like the one in the video existed, I'm sure they would go "upstream" of the problem a safe distance and open a cutout. Of course, this is all done only if the power company isn't able to respond in a timely fashion, to minimize the risk to life and property.

These days, I'm sure that solving such a problem would be as easy as calling the distribution office, and having them shut down the neighborhood.

...yeah, when the genie gets out, all you want to do is run like hells door just opened