Stray voltage

[ptonsparky]

I get to work with an area POCO next week while they use a SVM10 from PMi which looks specifically for voltages under 10 volts.
Any one have some experience with that system?

 

[gar]

220205-1103 EST

ptonsparky:

What is a SVM10 and who is PMi? What do you mean by voltages under 10 V?
What is the problem, and what is to be monitored?
What are the parameters on the measurements to be performed?

I believe you are referring to a company PMI, not little i.

I also believe you are looking at nominal voltages of 120 V or higher, likely 60 Hz sine waves, and want to see small variations. What kind of variations, time periods, peak or minimum, measurement criteria ( peak, full wave rectified, average reading calibrated to RMS, true RMS, averaging time, etc. ).

See my plots P26 and P27 at at https://beta-a2.com/EE-photos.html . The voltage plot is a full wave rectified average measurement caliberated in RMS and averaged over 1 second time periods with a resolution of 0.1 V at the main panel.

.

 

[kwired]

I'm with Gar, more details. Is this looking for stray voltages for a specific client or something else? I know you do some dairy operations and could see such search being pretty high priority in those kind of places.

 

[ptonsparky]

It is a dairy. Power Monitor I(i)
The monitor specifically looks for 'stray voltage' and the limit is 10 volts RMS.

 

[ptonsparky]

View attachment 2559296
Above is From their manual.
Questions arise.
CH 1: Utility primary at the pole before it travels 600' to padmount, or at the padmount?
CH 2: Farm Secondary Neutral of the 480/277 (only neutral load would be a fault condition)
Then again 480 to 120/240 step down neutrals?
CH3: Primary neutral to Secondary neutral? of both transformers? Distance for either is less than 40'
CH4: This presumes the shock is from water lines or is the best indicator. For this place I'm more interested in the milking lines.

 

[kwired]

View attachment 2559296
Above is From their manual.
Questions arise.
CH 1: Utility primary at the pole before it travels 600' to padmount, or at the padmount?
CH 2: Farm Secondary Neutral of the 480/277 (only neutral load would be a fault condition)
Then again 480 to 120/240 step down neutrals?
CH3: Primary neutral to Secondary neutral? of both transformers? Distance for either is less than 40'
CH4: This presumes the shock is from water lines or is the best indicator. For this place I'm more interested in the milking lines.

clicking on attachment brings up message that I don't have permission to access it

 

[gar]

220205-1226 EST

ptonsparky:

What is stray voltage? In my backyard over a 12 ft distance with two screwdrivers as probes pushed in the ground I seldom see over an 0.1 V Fluke 27 reading. Not really different with a Fluke 87.

What is the maximum voltage a standing cow can tolerate between front and rear legs? A cow drinking water from a metal container connected conductive pipe to a water supply with an electric pump powered from some distance away?

The two screwdriver test with a high impedance meter as the measuring instrument is a good tool. If you go to a location well away from the farmer's yard area, but under power lines, then what voltage do you measure below the wires, both perpendicular and lengthwise, and further out in an open field? This may provide some baseline reference.

Then do various tests in the farmyard. Turning off various loads until no load is present may allow you to track down origins of various sources of stray voltage.

.

 

[kwired]

Stray voltage - especially on a diary farm is any voltage present on equipment the cows come in contact with regardless of what the source/cause is.

Utilities using MGN is a common place for this to start though, simple voltage drop on the MGN will cause a voltage on anything bonded to the service neutral (via all your EGC's and other natural bonds). Just a couple volts is enough to effect cows and ultimately milk production also.

Following art 547 requirements is a good start at minimizing issues but won't necessarily eliminate all possibilities.

 

[ptonsparky]

All the connections are neutral to neutral or remote rod.

.5 volt measured across a 500 ohm resistor is excessive for dairy.

 

[dereckbc]

Dairy farms are not my area of expertise, but I do understand the complications of MGN and the stray voltage produced. One of the biggest electrical myths is Ground Rods are at Zero-Volt potential. Nothing could be further from the truth. Under fault conditions, stray voltages turn into step potential.

My understanding the solution is the same used in a substation using counterpoises for the cattle to stand on, a steel deck.

 

[ptonsparky]

Dairy farms are not my area of expertise, but I do understand the complications of MGN and the stray voltage produced. One of the biggest electrical myths is Ground Rods are at Zero-Volt potential. Nothing could be further from the truth. Under fault conditions, stray voltages turn into step potential.

My understanding the solution is the same used in a substation using counterpoises for the cattle to stand on, a steel deck.

For new construction an equipotential plane is a must. Thirty years ago they may have accidentally done it.

I've done work here for close to 20 years and it is the first I've heard a manager mention it.

 

[GoldDigger]

Also included in modern design is a deliberate gradient from the building equipotential plane to local earth at all of the entrances to the building. Otherwise the cattle will experience a step potential at the interface. Making the whole farmyard an equipotential surface is usually not practical and still leaves a chance for step potential at fence gates to pasture, etc.

One way to achieve such a gradient is to increase the depth of a ground mesh from inches to several feet at the outer edge of the transition zone.

 

[don_resqcapt19]

You can get some utilities to install a Neutral Isolator that isolates the connection, under normal conditions between the primary and secondary neutrals to reduce this problem.

 

[kwired]

Dairy farms are not my area of expertise, but I do understand the complications of MGN and the stray voltage produced. One of the biggest electrical myths is Ground Rods are at Zero-Volt potential. Nothing could be further from the truth. Under fault conditions, stray voltages turn into step potential.

My understanding the solution is the same used in a substation using counterpoises for the cattle to stand on, a steel deck.

One must also realize the step potential is different for a cow that has more distance between front and rear feet than it is for humans and is a reason why this is a bigger problem when these animals are involved, they can more easily cross higher gradient zones.

 

[ptonsparky]

My cows aren't 150' long, but it will be interesting to see what the voltages are to that rod. More interested in hoof to piping or stanchions.

 

[kwired]

My cows aren't 150' long, but it will be interesting to see what the voltages are to that rod. More interested in hoof to piping or stanchions.

That is what is important - what potential they can come in contact with not what potential to some remote earth point is.

 

[ptonsparky]

We did a walk through with POCO engineering documenting potential issues that we could see. About an hour into the walk the engineer asked me where to start. All I could do was shrug.

The one that brought my level of patience to breaking was where a 480 disconnect had been submerged in flushed manure at some point. Four to five feet above where any should have been. Still energized AFAIK. Very obvious no one had opened the door.

POCO has indicated they will take no more action on the customers side of padmount.

 

[Hv&Lv]

We did a walk through with POCO engineering documenting potential issues that we could see. About an hour into the walk the engineer asked me where to start. All I could do was shrug.

The one that brought my level of patience to breaking was where a 480 disconnect had been submerged in flushed manure at some point. Four to five feet above where any should have been. Still energized AFAIK. Very obvious no one had opened the door.

POCO has indicated they will take no more action on the customers side of padmount.

Many years ago we lost a lawsuit involving stray voltages on a dairy farm. We didn’t document correctly..
We document everything now, and see many problems on the customer side, yet they don’t want to fix anything, just want the utility to fix the issue. Many fail to see the majority of problems stem from such deep crap as you saw…
(there’s a pun there)

 

[kwired]

We did a walk through with POCO engineering documenting potential issues that we could see. About an hour into the walk the engineer asked me where to start. All I could do was shrug.

The one that brought my level of patience to breaking was where a 480 disconnect had been submerged in flushed manure at some point. Four to five feet above where any should have been. Still energized AFAIK. Very obvious no one had opened the door.

POCO has indicated they will take no more action on the customers side of padmount.

With 480 volt service problems are more likely to be within the facility and not from POCO side. Problems on the MGN is about all they have to contribute. There is likely only 277 volt lighting for neutral loads on the service, though I did wire up some 277 volt radiant heaters in a dairy one time. All the stray voltage from separately derived 120 volt systems is not a POCO issue and what most stray voltages likely will associated with as long as POCO doesn't have any MGN issues.

 

[ptonsparky]

No 277 volt loads.

The manager hadn't documented any occurrences and other than one animal in the hospital area we saw no nervous or fidgety animals.