High current on neutral with a balanced load

[oldsparky52]

gar, this is great stuff (I think ), you are over my education level, but I sure love reading this stuff.

How much of what you are seeing could be a result of the electrical distribution system being grounded so often? With all the grounding, there are parallel paths for current all over the place.

 

[gar]

200930-1059 EDT

oldsparky52:

Do you have any sort of scope, and isolated current probe available? If so, then you can start experimenting, if not, then possibly a friend has this equipement.

Now that I have found the sample averaging function on my scope I can see its real value in this application. It greatly stabilizes the plot that I see.

If you are not familiar with a scope, then start playing with simple controlled experiments. A bell transformer can be an isolated safe power source. A 1 ufd mylar capacitor at 60 Hz is about 2650 ohms. A series circuit of 2200 ohms with 1 ufd across the transformer secondary is a good experiment. Connect the scope common to the resistor capacitor junction. Use channel A to measure the resistor voltage, and sync from this channel. Use channel B to measure the capacitor voltage. Both voltages will be about the same with the resistance value being slightly lower. The capacitor voltage will lead the resistance by 90 degrees.

My scope measurements of my water pipe current show very distinct different waveforms that change when something somewhere changes.

I am not on a multi-grounded wye primary power source. My power source at the substation may be wye, but it is delta from a distribution perspective. There is no neutral or ground wire from the substation to any of my poles.

I have not yet shut my whole house down. After that I will get back to jhardy13's problem.

.

 

[gar]

201001-1243 EDT

Generally when I look at my water pipe current it is about 10 to 20 mV or 0.1 to 0,2 A. My home load is not much of it. A 120 V 10 A heater load makes possibly a 10% change. Most of the time the dominate frequency components are 60, 180, and 300 Hz. Turning off the entire house has little effect on the water line current. The current waveform stays consistent for reasonable time periods, then chnges to something different. Also its phase position changes.

Pretty much the water line current is a result of factors external to my home.

.

 

[gar]

201001-1709 EDT

jhardy13:

Looking back at some of your recent posts it appears you are getting neutral current in the 100 mA range with your home shutdown. This is in the area of what I see at my home.

Some comments on measurements:
1. A scope allows seeing approximately instantaneous voltages and currents.
2. An RMS reading (Fluke 87) or full wave rectified reading (Fluke 27 or Simpson 260/270) provides some sort of averaged reading over a number of 60 Hz AC cycles.
3. The instantaneous current in a circuit is the sum of the instantaneous currents feeding said circuit.
4. The RMS or average reading of current in a circuit may not equal the algebraic sum of RMS or average currents feeding said circuit. This is waveform and timing dependent.

The next step in your analysis of your problem is to start from the state of no load in your home. Using your scope and meters measure source voltages, and currents in the various circuit paths. Then add a single substantial 120 V resistive load. At least one 1500 W space heater. Possible add a second one on the same phase. This provides you with some base reference information from components with known charcteristics. Do you get expected results?

Next remove the resistive loads. You should return to your original base state.

Now turn on only one circuit at a time, and look for what causes your abnormal current.

Report back.

.

 

[jhardy13]

201001-1709 EDT

jhardy13:

Looking back at some of your recent posts it appears you are getting neutral current in the 100 mA range with your home shutdown. This is in the area of what I see at my home.

Some comments on measurements:
1. A scope allows seeing approximately instantaneous voltages and currents.
2. An RMS reading (Fluke 87) or full wave rectified reading (Fluke 27 or Simpson 260/270) provides some sort of averaged reading over a number of 60 Hz AC cycles.
3. The instantaneous current in a circuit is the sum of the instantaneous currents feeding said circuit.
4. The RMS or average reading of current in a circuit may not equal the algebraic sum of RMS or average currents feeding said circuit. This is waveform and timing dependent.

The next step in your analysis of your problem is to start from the state of no load in your home. Using your scope and meters measure source voltages, and currents in the various circuit paths. Then add a single substantial 120 V resistive load. At least one 1500 W space heater. Possible add a second one on the same phase. This provides you with some base reference information from components with known charcteristics. Do you get expected results?

Next remove the resistive loads. You should return to your original base state.

Now turn on only one circuit at a time, and look for what causes your abnormal current.

Report back.

.

I'll find some time to do this and I will update.

 

[Electricmo]

Without scrolling through every response I did see one where apparently the neighbor is having the same distorted wave. It maybe a close by solar installation that is causing the issue. By close by I mean within mile. I have no idea where the OP is located but his POCO should have a record of close by solar if it was legally installed. It could be a issue.

 

[jhardy13]

Okay here is a quick update. On Thursday I loaded one phase with a 50amp draw to try and get unbalanced voltages, and the voltages remained even. On Friday POCO was here for about 5 hours. We tested quite a bit. We ran bypasses for both phases and the neutral which confirmed this was not a loose or damaged cable situation. We then completely disconnected our neighbor and the well pump at the transformer to isolate my home and the harmonic distortion was still present. Since that didn't reveal anything we decided to swap the phase cables in our panel to see if the THD% would also switch phases and it didn't. So that didn't help either. We checked all of the connections at the well pump as well. After this, we were out of ideas so we spent a little over an hour with an oscilloscope thoroughly checking every circuit for the source of the high current THD%. This is the second time we have done this. After turning off each circuit one by one and unplugging devices on those circuits, we found that the fridge in our kitchen was the biggest contributor in our home but it was only causing an increase of 4% to the current THD. With nearly every circuit turned off, and the nonlinear devices on the remaining circuits unplugged, we were still seeing a current THD% that was consistently at or above 20%. At that point, even the engineer was puzzled on what could be causing this. These current measurements were taken with a picoscope 2204a. The current probe used was a TA019. The accuracy of these measurements were verified with a Megger PA-9 Plus power quality analyzer which shows the exact same THD%. I don't know what brand of probe it was using, but they were coil probes. So lastly, I showed the engineer the Neutral to Earth Voltage and he thinks it could be related somehow. He said that it might not be on the neutral and might actually be voltage in the earth coming from a ground fault somewhere and getting onto our circuits from our ground rod. Not sure what to think about this.

The main take aways here are we don't have a loose or damaged neutral, our neighbor and the well pump aren't at fault, and we cannot locate a specific circuit that is causing the high current THD%. This really points to this being caused by something external. How, we have no idea.

Gar, I am buying a couple of electric heaters later when I get off work so I can test what you want me to test. From here, I really don't know what to do.

 

[synchro]

... With nearly every circuit turned off, and the nonlinear devices on the remaining circuits unplugged, we were still seeing a current THD% that was consistently at or above 20%.

If the load current is very small, then a 20% THD means that the absolute level of the THD is also small. So I wouldn't be overly concerned about this, especially because I can't really see it damaging appliances in any way.

... So lastly, I showed the engineer the Neutral to Earth Voltage and he thinks it could be related somehow. He said that it might not be on the neutral and might actually be voltage in the earth coming from a ground fault somewhere and getting onto our circuits from our ground rod. Not sure what to think about this.

Do you have a 'scope waveform of the neutral to earth voltage that you could share? Perhaps you already did and I missed it. I assume this means the voltage from the neutral to a separate ground rod placed some distance away from the meter?
Have you measured the currents through the existing grounding electrode conductors, with and without loads present?

By the way, going back to the scope waveforms in your post #157 of this thread (at the links below), your waveform of the neutral current In(t) seems to indicate that there's some phase shift between the Ia(t) and Ib(t) line current waveforms which limits how much the neutral current can be balanced out by changing the loading. The reason I say this is that you can see the clearly identifiable spike of the Ib current from the B phase in the waveform of the neutral current In(t), and the more sinusoidal part of the waveform (likely from current Ia(t) on phase A) appears to be shifted at least 60 degrees from Ib(t). If you could get the line voltage on one scope channel and synch to it, and then put a line current (i.e, Ia or Ib, one at a time) on the other channel then you could see how the load current on each leg is phase shifted relative to the applied voltage. A phase shift would limit how much the neutral current could be balanced out.

https://forums.mikeholt.com/attachments/20200825_121849-jpg.2553363/

https://forums.mikeholt.com/attachments/20200825_121913-jpg.2553362/

https://forums.mikeholt.com/attachments/20200825_121824-jpg.2553364/

 

[oldsparky52]

He said that it might not be on the neutral and might actually be voltage in the earth coming from a ground fault somewhere and getting onto our circuits from our ground rod. Not sure what to think about this.

Well I would think that could have been determined by disconnecting the ground rod connection and checking he scope.

Thanks for the update.

Just one thing though. You wrote

I loaded one phase with a 50amp draw to try and get unbalanced voltages, and the voltages remained even

. I find it difficult to believe the voltage did not drop just a tad, and I would be curious as to what the actual voltage readings were. By saying the remained even you make all the interpretations.

 

[jhardy13]

Well I would think that could have been determined by disconnecting the ground rod connection and checking he scope.

Thanks for the update.

Just one thing though. You wrote . I find it difficult to believe the voltage did not drop just a tad, and I would be curious as to what the actual voltage readings were. By saying the remained even you make all the interpretations.

My apologies, I was quickly getting everything posted. There was a small voltage difference (2 to 3 volts) but not at the level that would point to a bad neutral. POCO eliminated this possibility on Friday anyways.

 

[oldsparky52]

Remind me again, what started you looking at all of this? Have you been able to connect the problem to these issues?

 

[jhardy13]

If the load current is very small, then a 20% THD means that the absolute level of the THD is also small. So I wouldn't be overly concerned about this, especially because I can't really see it damaging appliances in any way.

Do you have a 'scope waveform of the neutral to earth voltage that you could share? Perhaps you already did and I missed it. I assume this means the voltage from the neutral to a separate ground rod placed some distance away from the meter?
Have you measured the currents through the existing grounding electrode conductors, with and without loads present?

By the way, going back to the scope waveforms in your post #157 of this thread (at the links below), your waveform of the neutral current In(t) seems to indicate that there's some phase shift between the Ia(t) and Ib(t) line current waveforms which limits how much the neutral current can be balanced out by changing the loading. The reason I say this is that you can see the clearly identifiable spike of the Ib current from the B phase in the waveform of the neutral current In(t), and the more sinusoidal part of the waveform (likely from current Ia(t) on phase A) appears to be shifted at least 60 degrees from Ib(t). If you could get the line voltage on one scope channel and synch to it, and then put a line current (i.e, Ia or Ib, one at a time) on the other channel then you could see how the load current on each leg is phase shifted relative to the applied voltage. A phase shift would limit how much the neutral current could be balanced out.

https://forums.mikeholt.com/attachments/20200825_121849-jpg.2553363/

https://forums.mikeholt.com/attachments/20200825_121913-jpg.2553362/

https://forums.mikeholt.com/attachments/20200825_121824-jpg.2553364/

I'm attaching a couple photos of the Neutral to Earth voltage referenced from a remote ground rod 10 ft from the bonded ground rod at the meter. The voltage is usually between 1.5v to 3v. Just happened to take this while it was low. The DC offset on this voltage is real. I was sure to zero both channels before testing. The second photo doesnt show the offset because I had it set to alternating coupling in the scope which filters out dc components. This voltage is present with the 200amp breaker turned off.

 

[jhardy13]

Remind me again, what started you looking at all of this? Have you been able to connect the problem to these issues?

Lights throughout our home burning out the same week they are installed even though they are rated for 130v, multiple PSUs acting erratically and needing replaced, and multiple electricians coming out to check all of our wiring and saying everything is up to code. This points to power quality issues. These problem started 4 years ago. I've lived in this home my whole life and this was not a problem before 4 years ago. I also find all of this very interesting and thought this would be a good place to get professional opinions and advice.

 

[oldsparky52]

I'm attaching a couple photos of the Neutral to Earth voltage referenced from a remote ground rod 10 ft from the bonded ground rod at the meter. The voltage is usually between 1.5v to 3v.

A step voltage at 10' of 1.5-3 volts seems like a lot to me. Does the PoCo engineer know about this?

 

[jhardy13]

A step voltage at 10' of 1.5-3 volts seems like a lot to me. Does the PoCo engineer know about this?

I showed him with my scope before he left on Friday. He said it could be related but doesn't know what could cause it. He was a bit dismissive on it.

 

[oldsparky52]

I showed him with my scope before he left on Friday. He said it could be related but doesn't know what could cause it. He was a bit dismissive on it.

That would concern me. If you can drive 2 metal rods (conduit or pipe) 10' apart (a couple of feet deep) and take a voltage measurement and you get those readings, I'd show that to the PoCo rep. Forget the scope, that voltage means something.

 

[jhardy13]

That would concern me. If you can drive 2 metal rods (conduit or pipe) 10' apart (a couple of feet deep) and take a voltage measurement and you get those readings, I'd show that to the PoCo rep. Forget the scope, that voltage means something.

It was measured from remote ground to neutral. Between two remote ground points shows 200mv.

 

[oldsparky52]

It was measured from remote ground to neutral. Between two remote ground points shows 200mv.

Can you get the 3 volts you spoke about?

 

[jhardy13]

Can you get the 3 volts you spoke about?

Some clarification: when I measure between two remote grounds, the highest voltage I have seen is 200mv. When I measure between one remote ground to the mains neutral, I've measured a high of 4.6 volts but on average it stays around 1 to 3 volts. This was with our 200amp breaker turned off. In one of the two photos I posted above, you can see the voltage at the bottom which is 1.6v. Several people have said this voltage is normal and several have said that it should be closer to zero.

 

[jhardy13]

By the way, going back to the scope waveforms in your post #157 of this thread (at the links below), your waveform of the neutral current In(t) seems to indicate that there's some phase shift between the Ia(t) and Ib(t) line current waveforms which limits how much the neutral current can be balanced out by changing the loading. The reason I say this is that you can see the clearly identifiable spike of the Ib current from the B phase in the waveform of the neutral current In(t), and the more sinusoidal part of the waveform (likely from current Ia(t) on phase A) appears to be shifted at least 60 degrees from Ib(t). If you could get the line voltage on one scope channel and synch to it, and then put a line current (i.e, Ia or Ib, one at a time) on the other channel then you could see how the load current on each leg is phase shifted relative to the applied voltage. A phase shift would limit how much the neutral current could be balanced out.

https://forums.mikeholt.com/attachments/20200825_121849-jpg.2553363/

https://forums.mikeholt.com/attachments/20200825_121913-jpg.2553362/

https://forums.mikeholt.com/attachments/20200825_121824-jpg.2553364/

I measured the voltage waveform on phase A in both photos and compared it to each phase current. It is exactly as you said. The current on Ib crosses at zero and the current on Ia does not cross at zero. The waveform on Ia changes frequently depending on the load but it is always shifted a bit to the right.