Utility Primary Feeder Blowout

Status
Not open for further replies.
D

divemaster5734

Member
Location
Seattle
I'm a 01 Master in Washington State. We got a call that a small condo complex of Air BnB rentals had guests that were getting shocked when entering or exiting the hot tub.
After checking all the basics, make up, terminating, bonding, operational condition of 50A 2P GFCI spa disconnect, etc, and verifying there were no transient voltages present inside any of the residences I then addressed the 8 gang meter section.
The bonding was good, they did not bond the neutral at the meters, making the electrical point of attachment bond at each unit instead.
There was the typical oxidation present on the ground busses, which I removed and observed the machine screw threads were shiny with screws removed, indicating there was still a good electrical connection, and even though the unit had been mounted around mid to late 70's, all AL conductors had generous amount of Deox, but I wire brushed all the paint from the entire buss contact area, and applied deox to all surfaces.
I then stuck one lead from my Fluke T-6 1000 in the acorn of the first ground rod, the other lead into the dirt a foot away, and got a 56 VAC reading.
The meter bank is fed with 2 x 4/0 USE in parallel that is direct buried.
I then used a Greenlee Pulsar PE2000 and located a 19" section of B phase with the insulation blown out.
I replaced that section, retested all phases and both neutrals, getting a perfect reading on the Pulsar meter.
Once all that was done I am still getting a voltage from the ground rod to the earth.
It increases by about 14VAC with each main breaker that is energized.

The utility crew was not very forthcoming about their side of the distribution and it took a little "reading between the lines" to discover a cover-up.
Once I exposed it, they then admitted they had a primary feeder short out, which blew a transformer, and sent a 7200 VAC surge through their secondary, blowing a Comcast box and left a 8" carbon arc across the ground buss inside the cabinet.
They replaced that transformer, which fed the property next door.
On the other side is a park, which also has a city duplex lift station, fed by another transformer, which they also replaced, but claimed it was only replaced because it had a broken latch.
I seriously doubt that was the only issue. It's a 150KVA pad mounted one, and they had to get a new vault cover.
The work was done over a weekend.
I know there is only one vendor for the utility vaults, they are not open on weekends, and if they had to open up on a Saturday or Sunday they make it hurt.
Those vault covers weigh over 4000lbs, I know because I have set several 4' x 8' underground vaults.
I noticed it had a new sticker from the vault company, so it could not have been sitting around in the utility's back yard.
The way that utility works there had to have been at least 20 people from two different divisions, all on double time.
They spent at least $60,000 to replace that transformer instead of spending $500 for an entire latching rod and handle system.
There is another small transformer that feeds my customer between the two they changed out, and they did not touch that one.
I did not take pictures of the ground voltage, but did take some of the blown out wire.
I've seen 6" to 8" blow outs, but never one 19" long.
The utility swears there is nothing wrong with that transformer, but I think it's to avoid liability.
I'm at the end of knowledge area, the ground is dry, and I know funny stuff happens when there's not enough moisture in the earth to help ground paths, but I'm from an area that isn't far from a rain forest, and we haven't experienced dry earth issues like this in the 20 years I've been in this area.
I'm hoping someone in a more arid climate might have some insights.
Thanks in advanceIMG_20210716_133142_50_1_50.jpgUGCABLE_2_50_1_50.jpgIMG_20210716_144947_50_1_50.jpgIMG_20210716_151242_1_50_1_50.jpg
 
divemaster5734 said:
... I replaced that section, retested all phases and both neutrals, getting a perfect reading on the Pulsar meter.
Once all that was done I am still getting a voltage from the ground rod to the earth.
It increases by about 14VAC with each main breaker that is energized.
Click to expand...
Have you checked L1-N and L2-N voltages as you turn on successive main breakers? Perhaps there is a poor connection on the neutral somewhere between the transformer and where the neutral is bonded to the GES.
 
My suspicion is you have a hot grounded somewhere, similar to your “blow out”, but on one of the other local systems. If you take a ground stake from a 3/4 point ground test meter and a 500 foot spool of #14 you can probe and map out and probably just about locate the issue. The utility is unlikely to be much help.

What you are seeing is called GPR, ground potential rise, which you can google for a better explanation. So with enough good contact with the soil another nearby insulation failure is causing power flow and voltage returning back via your ground rod. I’ll bet you can clamp a clamp meter around it any measure current.

The other term, which I hate to use because it gets overused and blamed for all kinds of things, is stray voltage.
 
I think post #3 is the most likely scenario. Given the dry soil conditions, I wouldn't be surprised if other blowout are present on phases out to the other buildings fed from the same transformer.

One other thing: You mention the voltage increases 14-V per main that gets closed-in. Does this account for the entire 56-V once all mains are switched-in? If you have a low impedance volt-meter, I suggest using that for taking your measurements.
 
Last edited:
I'm going back today. First I'm going to change the point of attachment to the meter section. It's a Hail Mary, but since the stray voltage is AC I think there's a chance the SCR feeding the units has enough of a loop to create a choke that increases resistance like an antenna.
Depending on how the cable was installed the 60 HZ could be inducing enough harmonics through direction changes causing a series of resistors and effectively making the ground a separate phase conductor through feedback delay.
That should be easy enough to do, then a new set of tests with the standard megger to see what changes.
Heck, for all I know there's a pile of SCR in a attic or under the floors laying in several coiled piles because some apprentice didn't feel like pulling out the excess.
If needed I'll chart out a grid of the area and then start making periodic GTE measurements to determine if there is a gradient variable.
I don't know if anyone has checked out other buildings either.
Had a long conversation with the utility engineer who expressed frustration dealing with some of the line crews.
He isn't allowed to even use a multimeter, and is forced to rely on field crew testing.
The crews top concern is avoiding responsibility for anything, so getting straight answers is problematic.
In the meantime there's weddings, bday parties, tour groups from the Midwest, and all sorts of other people coming to stay at the complex, and I'm scared to death someone could be hurt or killed just standing on bare dirt and touching something metal that has a high voltage potential stored from inductive capacitance.
 
It turned out the utility transformer was leaking voltage through the neutral, and it was exacerbated by a utility 72,00V underground feed jumper between vaults with physical damage.
The utility vehemently denied any responsibility and refused to take an active roll in locating the issue.
They made it as difficult as possible by charging $2,000 for every disconnect, making us to wait up to four hours each time, refusing to accept my data after I conducted tests using a megger, a pulsar, and certifying the entire bonding system.
It was only after exhausting all known testing procedures, including testing a commercial building next door, and a senior center on the other side, that I finally decided to try a last resort disconnecting all underground feeders to the building and then installed a 4/0 SCR laid on the ground 100' jumper that they finally agreed to replace the transformer.
When the voltage was only mitigated they then ran a high voltage jumper to anther transformer from the vault directly in front of my customers transformer and realized the underground feed was compromised.
While they will be forced to pay for all the damages, the hell they put me through will never be compensated.
Yeah, I'm obviously still upset with the apathy and denial shown by the utility.
I suppose it's just the way things are these days.
The monopolies think they are part of the government, and since our government takes a dump on America, so do they.
Consider this a FYI if you are suddenly in the middle of a similar issue, what was once an ally in making sure electrical distribution was safe, is now adopting the same arrogant posture the inspectors took in 2015, they are only there to serve themselves.
 
divemaster5734 said:
It turned out the utility transformer was leaking voltage through the neutral, and it was exacerbated by a utility 72,00V underground feed jumper between vaults with physical damage.
The utility vehemently denied any responsibility and refused to take an active roll in locating the issue.
They made it as difficult as possible by charging $2,000 for every disconnect, making us to wait up to four hours each time, refusing to accept my data after I conducted tests using a megger, a pulsar, and certifying the entire bonding system.
It was only after exhausting all known testing procedures, including testing a commercial building next door, and a senior center on the other side, that I finally decided to try a last resort disconnecting all underground feeders to the building and then installed a 4/0 SCR laid on the ground 100' jumper that they finally agreed to replace the transformer.
When the voltage was only mitigated they then ran a high voltage jumper to anther transformer from the vault directly in front of my customers transformer and realized the underground feed was compromised.
While they will be forced to pay for all the damages, the hell they put me through will never be compensated.
Yeah, I'm obviously still upset with the apathy and denial shown by the utility.
I suppose it's just the way things are these days.
The monopolies think they are part of the government, and since our government takes a dump on America, so do they.
Consider this a FYI if you are suddenly in the middle of a similar issue, what was once an ally in making sure electrical distribution was safe, is now adopting the same arrogant posture the inspectors took in 2015, they are only there to serve themselves.
Click to expand...

Thanks for the update.


Sent from my iPhone using Tapatalk
 
Thanks for the update. That had to have been a nightmare.

I agree with Dave that the corrosion shown is typical for damaged cable. That said, I don’t have much sympathy for anyone that directly buries cable in that kind of fill. I may give tail light warranties on the DB cables in the soil conditions we have. Maybe.
 
Status
Not open for further replies.
Top