HRG or NRG Resistance grounding

[kwired]

We connect single phase loads between line and neutral (connected to X0), which are at a considerable distance from a HRG transformer. So even though the phase to neutral voltages at the transformer terminals are the same, they are not the same at the single phase load terminals which are at considerable distance from the supply transformer due to unbalanced ground capacitive coupling as mentioned in my earlier post.

I'm sorry but that makes no sense at all to me. If your conductors are low impedance, and the load is not a really high impedance capacitive coupling is negligible. It only comes to play with high impedance loads, like in the high K ohm or meg ohm ranges.

Unless you are talking about medium voltage HRG, and I am not going to go there, because I don't know a lot about it, I totally disagree. I am talking about under 600 volts systems.

 

[Sahib]

I'm sorry but that makes no sense at all to me. If your conductors are low impedance, and the load is not a really high impedance capacitive coupling is negligible. It only comes to play with high impedance loads, like in the high K ohm or meg ohm ranges.

Unless you are talking about medium voltage HRG, and I am not going to go there, because I don't know a lot about it, I totally disagree. I am talking about under 600 volts systems.

If what you say were true, the Code would have permitted single phase loads between phase and neutral for LV HRG systems.
I tried to explain the reason behind the code restriction.
If you know any other reason, let us know,

 

[iceworm]

How can the voltage at two ends of a resistor be different if current is not flowing through it?

Capacitive effect.

Sahib -
No. What are you talking about? This is basic physics. No current flow - No voltage drop.

The capacitive coupling of each line conductor of a three phase supply system with ground remains balanced when the neutral is solidly grounded so that the phase voltages remain balanced. When the neutral is ungrounded or high resistance grounded, the phase voltages become unbalanced.

No.

This next one make no sense at all.

We connect single phase loads between line and neutral (connected to X0), which are at a considerable distance from a HRG transformer. ....

Connecting a single phase load between line an neutral on an HRG system is dangerous and illegal under the NEC. It doesn't matter if the load is close or far away. I don't know if it is illegal under your code or not - doesn't matter, it is still dangerous.

... So even though the phase to neutral voltages at the transformer terminals are the same, they are not the same at the single phase load terminals which are at considerable distance from the supply transformer due to unbalanced ground capacitive coupling as mentioned in my earlier post.

No. KW's answer is absolutelycorrect. You really need to open a physics book.

ice

 

[ggunn]

Sahib -
No. What are you talking about? This is basic physics. No current flow - No voltage drop.

It's nice to know that everything I know isn't wrong.

 

[GoldDigger]

Capacitive effect.

Playing the Devil's Advocate here (without, of course, characterizing Sahib as a devil ):

There can be a voltage drop across the grounding resistor even though there is no load or fault current across it if there is capacitively coupled parasitic current across it instead.
If the absolute net current is zero, then there will be no voltage drop.

 

[kwired]

If what you say were true, the Code would have permitted single phase loads between phase and neutral for LV HRG systems.
I tried to explain the reason behind the code restriction.
If you know any other reason, let us know,

I did not say code permits such an installation, I merely said you could connect a 277 volt load from say L1 to X0 (not to the grounded conductor on the other side of the resistor) and it would see 277 volts and would operate. I really don't even remember why I mentioned it, but at this point I don't care either. You are grasping for anything you can to say this wouldn't work, yet haven't given any reason that makes sense for it to not work. Even threw in a what if you are in a lighting storm scenario. Bottom line is there is 277 volts between the two points, if there is not, we will have other problems with the rest of the system - particularly the phase in question.

 

[Sahib]

kwired:
I asked you why the Code does not permit single phase loads between phase and neutral in a LV HRG system.
Try to know that.

 

[kwired]

kwired:
I asked you why the Code does not permit single phase loads between phase and neutral in a LV HRG system.
Try to know that.

Where did you ask this, I am not finding it?

You did ask where to connect the EGC back in post 37, but that isn't really the same thing at all.

 

[Sahib]

Where did you ask this, I am not finding it?

Here it is.

I tried to explain the reason behind the code restriction.
If you know any other reason, let us know,

 

[kwired]

Here it is.

I was never talking about the code restriction you brought it into the conversation:?:?

I said it would be possible to run a load from a line to neutral (not ground) and it would operate, did mention that it may not be code compliant, you mentioned it would not work and so far the only thing you have backed it up with is that code doesn't allow it, and a bunch of other things that may be side effects, but no reason why the 277 volt load would not operate as I suggested.

Tell us why it wouldn't work, I don't care for the moment why it isn't code compliant.

If you have a winding with two access points to the winding that operate 277 volts from one another, you can operate a 277 volt single phase load between these points. It will not matter what is grounded, if anything is grounded, or if somewhere on the system has a high impedance ground system inserted into it. Doesn't matter if both points are part of same phase winding or part of different phase windings. If the voltage between the two points is 277 then it will apply 277 volts to anything you connect to it (up until the load is great enough that the source can no longer maintain 277 volts, but that is for a different discussion).

 

[kingpb]

When are you guys going to figure out that it doesn't matter what is said, there is always a response by a certain person that will twist the post by adding content and arguments that keep it going.

 

[Sahib]

kwired:

In the present discussion I stated about the HRG retrofit in a solidly grounded system and the inadmissibility of phase to neutral loads in such a system without an isolating transformer of suitable rating.

One reason I stated for the inadmissibility is the unbalanced load phase voltages.

True, you may operate single phase loads in such a system when it appears to have normal phase voltages and to have normal operation, but it is a matter of luck; a sort of gambling, because of probability of neutral voltage instability in such a system.

 

[Sahib]

When are you guys going to figure out that it doesn't matter what is said, there is always a response by a certain person that will twist the post by adding content and arguments that keep it going.

 

[kwired]

kwired:

In the present discussion I stated about the HRG retrofit in a solidly grounded system and the inadmissibility of phase to neutral loads in such a system without an isolating transformer of suitable rating.

One reason I stated for the inadmissibility is the unbalanced load phase voltages.

True, you may operate single phase loads in such a system when it appears to have normal phase voltages and to have normal operation, but it is a matter of luck; a sort of gambling, because of probability of neutral voltage instability in such a system.

Why is that voltage going to be unstable? The voltage to ground (which is on the other side of the resistor) very well may vary as the load varies, but the voltage across the connected 277 volt load will remain pretty constant if the load is within reasonable tolerance of what the transformer can deliver. Ahead of the grounding resistor is a typical wye connected set of windings, and we connect 277 volt loads to exactly the same thing all the time.

 

[Sahib]

kwired:
You need to understand what neutral voltage instability is.

It is best you set out to do it by yourself instead of asking me to explain it because that would lead to another series of questions.

When you are done, explain it in your own words to us all here. Okay?

 

[kwired]

kwired:
You need to understand what neutral voltage instability is.

It is best you set out to do it by yourself instead of asking me to explain it because that would lead to another series of questions.

When you are done, explain it in your own words to us all here. Okay?

Where is this instability coming from? We have a solidly connected neutral. If we had open neutral connections, instability is going to happen, and really only if we also have load connections to the other phase conductors involved. For a single phase to neutral load, if the neutral is opened it is no different than placing a switch in the circuit and opening it, all it will do is interrupt current flow and the load will not operate.

We may have unstable voltage reference to ground as we change the load on this, but how is that going to change the operation of the load that still sees a steady voltage? The load doesn't care what the voltage to ground is, if ground is not one of the supply conductors to the load.

I think you are the one that needs to go back to basic electricity 101, I have described a simple single load circuit with an input or 277 volts, and it is a two wire source. We can disregard any grounding and the other phases - it is still 277 volts between the two points. Unless you have some serious overloading, unbalancing, or change of input voltage on the other portions of the transformer it will remain near 277 volts.

 

[iwire]

When are you guys going to figure out that it doesn't matter what is said, there is always a response by a certain person that will twist the post by adding content and arguments that keep it going.

:thumbsup:

I think this should be a forum announcement.

 

[Sahib]

kwired:
You are not still taking into account that the discussion here involves HRG retrofit in a solidly grounded system. It means the power system neutral is high resistance grounded on the source side and solidly grounded on the load side, if no isolation transformer is provided. Consequently for line to neutral load, most of the return current flows through the neutral, but some of the return current will flow through the ground to the source neutral, this current increasing with increase in load causing the system neutral to float more and more above the ground.

 

[kingpb]

kwired:
You are not still taking into account that the discussion here involves HRG retrofit in a solidly grounded system. It means the power system neutral is high resistance grounded on the source side and solidly grounded on the load side, if no isolation transformer is provided. Consequently for line to neutral load, most of the return current flows through the neutral, but some of the return current will flow through the ground to the source neutral, this current increasing with increase in load causing the system neutral to float more and more above the ground.

Really? :slaphead: Let it go man, you have burned the subject out.......

 

[GoldDigger]

kwired:
You are not still taking into account that the discussion here involves HRG retrofit in a solidly grounded system. It means the power system neutral is high resistance grounded on the source side and solidly grounded on the load side, if no isolation transformer is provided. Consequently for line to neutral load, most of the return current flows through the neutral, but some of the return current will flow through the ground to the source neutral, this current increasing with increase in load causing the system neutral to float more and more above the ground.

The current through the ground path will indeed cause the system neutral to float above ground, but the difference in potential between the solidly grounds end of the neutral and the resistance grounded end of the neutral will bw exactly the voltage drop in the neutral wire for that current. So nor very large except under fault conditions.