Finding the direction of AC current flow

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11bgrunt

11bgrunt

Pragmatist
Location
TEXAS
Occupation
Electric Utility Reliability Coordinator
Stray voltage complaint.
I am using a Fluke 345, 500 ohm shunt resistor and mechanical jumpers of different lengths.
When a neutral to earth voltage is measured on the Fluke 345, a 500 ohm resistor shunt is used to remove the phantom voltage. There have been many N-E voltages in this area over 7 volts.
This is a very rural area with sandy soil and currently in a drought condition. The POCO line is a 7.2kV single phase, solidly bonded wye system. There are many different properties involved with many fences separating the properties.
The Fluke 345 will show distortion factor ranges between 4-8%. The DF does not changes when the resistor is introduced.
The highest N-E voltages are measured from the POCO pole ground wire to the fence wire. There are many metal T fence post in the ground and many miles of fence wire in the affected area. Most fences become common as they overlap on corner post. When a high N-E voltage is measured, a jumper is installed between the pole ground and the closest fence wire. Current can be measured.

Today the leading opinion is the dry earth & the loaded single phase neutral are causing the N-E voltage. The fences have become parallel paths for neutral current to flow. After the next good rain, the N-E voltage will go away.

I have seen other causes other than dry earth.
I would like to prove the current is moving from the landowner's fence to the POCO ground wire or POCO to fence. The sine wave is 60 cycle.
 
11bgrunt said:
Stray voltage complaint.
I am using a Fluke 345, 500 ohm shunt resistor and mechanical jumpers of different lengths.
When a neutral to earth voltage is measured on the Fluke 345, a 500 ohm resistor shunt is used to remove the phantom voltage. There have been many N-E voltages in this area over 7 volts.
This is a very rural area with sandy soil and currently in a drought condition. The POCO line is a 7.2kV single phase, solidly bonded wye system. There are many different properties involved with many fences separating the properties.
The Fluke 345 will show distortion factor ranges between 4-8%. The DF does not changes when the resistor is introduced.
The highest N-E voltages are measured from the POCO pole ground wire to the fence wire. There are many metal T fence post in the ground and many miles of fence wire in the affected area. Most fences become common as they overlap on corner post. When a high N-E voltage is measured, a jumper is installed between the pole ground and the closest fence wire. Current can be measured.

Today the leading opinion is the dry earth & the loaded single phase neutral are causing the N-E voltage. The fences have become parallel paths for neutral current to flow. After the next good rain, the N-E voltage will go away.

I have seen other causes other than dry earth.
I would like to prove the current is moving from the landowner's fence to the POCO ground wire or POCO to fence. The sine wave is 60 cycle.
Click to expand...
You have something that will show a phasor? That would tell you.
 
Thinking a little here..
what size is the wire? I’ve seen this with 6CWC with 8 CWC neutral before.
Didn’t go away until we changed to 1/0.

does the problem go away once you get back to the three phase?

Check all your deadends back to the three phase. Clean and resqueeze them.
 
11bgrunt said:
Stray voltage complaint.
I am using a Fluke 345, 500 ohm shunt resistor and mechanical jumpers of different lengths.
When a neutral to earth voltage is measured on the Fluke 345, a 500 ohm resistor shunt is used to remove the phantom voltage. There have been many N-E voltages in this area over 7 volts.
This is a very rural area with sandy soil and currently in a drought condition. The POCO line is a 7.2kV single phase, solidly bonded wye system. There are many different properties involved with many fences separating the properties.
The Fluke 345 will show distortion factor ranges between 4-8%. The DF does not changes when the resistor is introduced.
The highest N-E voltages are measured from the POCO pole ground wire to the fence wire. There are many metal T fence post in the ground and many miles of fence wire in the affected area. Most fences become common as they overlap on corner post. When a high N-E voltage is measured, a jumper is installed between the pole ground and the closest fence wire. Current can be measured.

Today the leading opinion is the dry earth & the loaded single phase neutral are causing the N-E voltage. The fences have become parallel paths for neutral current to flow. After the next good rain, the N-E voltage will go away.

I have seen other causes other than dry earth.
I would like to prove the current is moving from the landowner's fence to the POCO ground wire or POCO to fence. The sine wave is 60 cycle.
Click to expand...

Think of it this way, there are probably several unbalanced loads (single phase transformers) distributed along the utility express feeder - all of which are loaded at varying levels and have their primary neutrals grounded. These primary multi-neutral connections with unbalanced load are all impressing their neutral voltages on the earth at their respective locations. Local (substation) and remote pole ground voltages will not be equipotential. Nor will voltage be equipotential between the many remote pole grounds. All multi-neutral connections will be contributing to the NEV problem, so it doesn’t make sense to ask if it’s either the utility or the customer. Obviously, it’s radial distribution all coming from the utility (but that doesn’t help). What I believe is most logical is to determine how this effect can be minimized at the premises.


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210410-1033 EDT

11bgrunt:

A minor point. The question should not be "what is the direction of current flow"? Current is flowing both ways each cycle.

Rather I suggest the question is what is the direction of power or energy flow, and I prefer energy flow?

You indicate this is a single phase supply derived from a three phase wye system. So on the power company distribution poles is there just a single wire, or three wires, or four wires?

So assume it is just a single wire and the second current carrying conductor for the primary is the earth with a ground rod from the earth to the low voltage terminal of the transformer primary, and the secondary neutral is also connected to this same point and to a neutral wire to the farm.

Assume that at the farm service entrance point there is a ground rod, and that nothing else within the electrical circuitry of the farm is grounded (earthed).

On the basis that there is nothing but one single phase in the area, then we can get useful phase information from the power system voltage, and use this to determine energy flow information.

Let us assume that the single phase primary starts at a substation and goes out 5 miles to various farms, and that no farm is the source of energy. Therefore, energy flows from the substation out to many distributed loads along the 5 mile path.

Since there are, by assumption, no energy sources other than at the input to the 5 mile system this means that energy flows from that source to the most remote load on that distribution line.

Deep down in the earth the resistance is very low, assumed zero. But there is surface resistance to the deep down area.

When that surface resistance is high, then other paths (such as fences) can become conductors of some of that primary current,

Metal fence posts connect to the metal fence, and in turn all this fencing can become a parallel conductor of current in the earth.

If you know that current is flowing in the fence, then you can put a current sensor around an adequate portion of the fence to get phase information, and correlating this phase information with the supply voltage phase can tell the direction of energy flow.

I have left out some details, but I would need to be more directly involved to clarify these factors.

.
 
7 Volts I would consider to be a normal Volatge drop over the resistance of the neutral conductor, at the current loading. 7 Volts drop over the length indicates the neutral is a solidly connected, current carrying conductor. A higher or much higher neutral Voltage over ground would ndicate bad neutral or bad neutral connection. 7 is drop over the resistance of the wire along the length.

The neutral conductor should be insulated mostly (isolated from unintended contact with people, floating metal ...), Where the neutral does come in regular contact other metal, say the neutral is a bare conductor and rubs on another metal, my preference would be for an intended bolted connection and not a simple rubbing. One point of connection would reference the neutral to the other metal, two would form a parallel path on the other metal for the neutral current (objectionable current imo).

Generally the Earth is not considered a parallel path for neutral current where the neutral is bonded or connected to earth at multiple points, with normal Voltage drop on the neutral. If the neutral is open, that problem would have to be found and fixed.

In practice, current flow through the Earth can be a problem. Given that there could be multiple causes and mitigation strategies for that, I would only advise that additional investigation of the actual cause is indicated, especially before proceeding to just bonding the neutral to unrelated nearby metal, like fences and structures. I would look carefully and consider (the instance details) before proceeding. Just my guessing. I would probably prefer trying to maintain the insulation or isolation of the neutral, rather than adding obvious and inappropriate parallel paths to it.

Absolutely I would consult with others, the POCO especially, before doing that.
 
The fence as a parallel path for neutral current will be a radiator for EMI, RFI (among other possible unintended consequences). That effect should be avoided.
 
When the Utility neutral reaches the customer premises wiring system and you have an additional conductor available to you, the EGC, the EGC is the conductor you would bond to the fence. Not the neutral.
 
__dan said:
7 Volts I would consider to be a normal Volatge drop over the resistance of the neutral conductor, at the current loading. 7 Volts drop over the length indicates the neutral is a solidly connected, current carrying conductor. A higher or much higher neutral Voltage over ground would ndicate bad neutral or bad neutral connection. 7 is drop over the resistance of the wire along the length.

The neutral conductor should be insulated mostly (isolated from unintended contact with people, floating metal ...), Where the neutral does come in regular contact other metal, say the neutral is a bare conductor and rubs on another metal, my preference would be for an intended bolted connection and not a simple rubbing. One point of connection would reference the neutral to the other metal, two would form a parallel path on the other metal for the neutral current (objectionable current imo).

Generally the Earth is not considered a parallel path for neutral current where the neutral is bonded or connected to earth at multiple points, with normal Voltage drop on the neutral. If the neutral is open, that problem would have to be found and fixed.

In practice, current flow through the Earth can be a problem. Given that there could be multiple causes and mitigation strategies for that, I would only advise that additional investigation of the actual cause is indicated, especially before proceeding to just bonding the neutral to unrelated nearby metal, like fences and structures. I would look carefully and consider (the instance details) before proceeding. Just my guessing. I would probably prefer trying to maintain the insulation or isolation of the neutral, rather than adding obvious and inappropriate parallel paths to it.

Absolutely I would consult with others, the POCO especially, before doing that.
Click to expand...
He works for the utility, so his neutral is the bare wire on the pole.
He’s trying to reduce objectionable current for the customer.
 
Hv&Lv said:
He works for the utility, so his neutral is the bare wire on the pole.
He’s trying to reduce objectionable current for the customer.
Click to expand...

On the pole the neutral conductor is insulated and isolated (air insulated, mounted on insulators, or the wood pole itself is an insulator). The local pole to Earth grounding is to mitigate atmosperic effects. A short distance through the Earth, of the pole ground to the fence, say 10 ft to the fence, the 10 ft of Earth has hundreds or thousands of Ohms of resistance, limiting current flow to a less than objectionable value.

The hundreds of Ohms of resistance between the pole ground and the fence, fence serves as the Earth reference Voltage measuring point, is essentially an open circuit so he is able to measures the Voltage drop at that point from the loaded neutral to the unloaded Earth reference Voltage. And 7 is not a bad reading. When it rains, the connection from the pole ground to the reference point fence is no longer open, the Earth is shunting, and the measurable voltage difference between the fence and the pole ground drops.

The open circuit Voltage difference between the pole ground and fence is not objectionable in this scenario. The cause is conventional. If there is an additional factor that makes this measurable voltage difference objectional, it is not included in the original problem statement.

The fence bonding is not being connected to the pole ground, it is being connected to the Utility neutral, which also happens to be connected to the pole ground. The multiple points, repeated instances of connecting the utility neutral to the fence along the fence run, creates the objectionable scenario of the fence being used as a parallel path for the Utility neutral current. Why this would be preferred is not part of the OP but should be.

He would be causing the objectionable current rather that mitigating it, as the problem has been stated so far. He measures a Votage difference, it is not stray. It is normal and expected according to the information contained in the OP.

If the Utility neutral were open or have a bad connection raising the system neutral Voltage further above the Earth reference, bonding to the fence would not fix that.

11bgrunt said:
Stray voltage complaint.

I would like to prove the current is moving from the landowner's fence to the POCO ground wire or POCO to fence. The sine wave is 60 cycle.
Click to expand...
 
__dan said:
On the pole the neutral conductor is insulated and isolated (air insulated, mounted on insulators, or the wood pole itself is an insulator). The local pole to Earth grounding is to mitigate atmosperic effects. A short distance through the Earth, of the pole ground to the fence, say 10 ft to the fence, the 10 ft of Earth has hundreds or thousands of Ohms of resistance, limiting current flow to a less than objectionable value.

The hundreds of Ohms of resistance between the pole ground and the fence, fence serves as the Earth reference Voltage measuring point, is essentially an open circuit so he is able to measures the Voltage drop at that point from the loaded neutral to the unloaded Earth reference Voltage. And 7 is not a bad reading. When it rains, the connection from the pole ground to the reference point fence is no longer open, the Earth is shunting, and the measurable voltage difference between the fence and the pole ground drops.

The open circuit Voltage difference between the pole ground and fence is not objectionable in this scenario. The cause is conventional. If there is an additional factor that makes this measurable voltage difference objectional, it is not included in the original problem statement.

The fence bonding is not being connected to the pole ground, it is being connected to the Utility neutral, which also happens to be connected to the pole ground. The multiple points, repeated instances of connecting the utility neutral to the fence along the fence run, creates the objectionable scenario of the fence being used as a parallel path for the Utility neutral current. Why this would be preferred is not part of the OP but should be.

He would be causing the objectionable current rather that mitigating it, as the problem has been stated so far. He measures a Votage difference, it is not stray. It is normal and expected according to the information contained in the OP.

If the Utility neutral were open or have a bad connection raising the system neutral Voltage further above the Earth reference, bonding to the fence would not fix that.
Click to expand...

Fences are not to be bonded nor attached to utility pole grounds.
 
Hv&Lv said:
Fences are not to be bonded nor attached to utility pole grounds.
Click to expand...

Yes, Thank You.

11bgrunt said:
There are many metal T fence post in the ground and many miles of fence wire in the affected area. Most fences become common as they overlap on corner post. When a high N-E voltage is measured, a jumper is installed between the pole ground and the closest fence wire. Current can be measured.
Click to expand...
 
210410-1648 EDT

_Dan:

Earth is a good conductor, and very good. Once you are down into the earth it is a very good conductor. As early as back in the beginnings of the telegraph industry this was realized, and used as one conductor to reduce wire costs. Note, telegraph voltages were not real high. It took a lot of 1 or 2 V battery cells to get to 100 V.

There is resistance from a grounding rod to its soil contact, and out to remote earth. Typically for a short ground rods from around 10 to 25 ohms, and higher, sometimes much higher. In appropriate soil conditions, and a long rod you can get to 1 ohm and lower.

At 100,000 V an ohm or so is not of much concern. Even 25 ohms would not be a big deal.

Wye distribution systems have a good deal of the neutral current flow in the earth as a parallel path. Power system people can give you a good estimate.

.
 
Hv&Lv said:
He works for the utility, so his neutral is the bare wire on the pole.
He’s trying to reduce objectionable current for the customer.
Click to expand...
Fences are not being bonded to the POCO neutral. Any connection to a fence is for testing and the fence is doing a great job as an earth reference.
The quality of the earth reference has affected every voltage and current test.
This area is served by a single phase overhead line with a primary wire, neutral wire and each pole has a connection from the neutral wire to the earth by way of a bare solid pole ground wire. The tap connection to the three phase, four wire POCO mainline is miles away from this area.
Fences are bonded to grounding electrodes intentionally when near HV transmission lines to reduce the induced voltage on the fence. That is not what I am writing about here.
I have seen bad LV secondary neutral connections and 120V faults that did not get cleared, contribute to high neutral to earth voltage.
In testing, the voltage and current are present. The main breaker is turned off, meter is pulled or transformer disconnected looking for a change in voltage or current.
 
11bgrunt said:
Fences are not being bonded to the POCO neutral. Any connection to a fence is for testing and the fence is doing a great job as an earth reference.
The quality of the earth reference has affected every voltage and current test.
This area is served by a single phase overhead line with a primary wire, neutral wire and each pole has a connection from the neutral wire to the earth by way of a bare solid pole ground wire. The tap connection to the three phase, four wire POCO mainline is miles away from this area.
Fences are bonded to grounding electrodes intentionally when near HV transmission lines to reduce the induced voltage on the fence. That is not what I am writing about here.
I have seen bad LV secondary neutral connections and 120V faults that did not get cleared, contribute to high neutral to earth voltage.

In testing, the voltage and current are present. The main breaker is turned off, meter is pulled or transformer disconnected looking for a change in voltage or current.
Click to expand...
I understand what your going through. As a utility we fight it also, which is why I suggested checking the connections at the dead ends back to the three phase and asked about the wire size. It may be miles back to the three phase but you shouldn’t have that many double dead ends to check. Maybe two or three per mile?
This is where the potential for bad or loose connections can cause a broken primary neutral.
Also you mentioned the butt grounds. I’m going to assume a rod at every pole with a transformer or any other apparatus installed such as arrestors or capacitors.
I’ve been on systems where there is a rod at every pole and an extra rod at every pole with apparatus on it.

as far as which way current (energy) flows, use a test kit with a CT and phasor for energy flow direction.

But as suggested earlier, it all comes from the utility and has to flow back to the utility.
Xptpcrewx had a good post about it.
 
mbrooke said:
Yes, your top dollar.
Click to expand...
Whoops, sorry. Shouldn’t have said that.
open ended bet with no winner.. ever.
Neither one of us will have great great grandchildren that will remember what the bet was for anyway...
 
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