Unbalanced three phase loads

[mivey]

I am still at a loss to understand this, I see it like Cold F sees it.

A common example in my world is the use of a two pole GFCI circuit breaker and no matter how unbalanced the loading is the breaker will not trip as all circuit conductors are being measured.

In that case you have included the neutral. You can still have ground leakage current, but I would not expect at a value that would be a problem. For multi-grounded neutrals, the ground current can be significant.

A residual ground does not use the neutral. It is like clamping an ammeter around the phases and tripping when the net current gets above a set threshold.

Good thing I came in late that day -If I had heard that, I'd have dropped to the floor and crawled back out - probably whimpering in defeat.

What a strange reaction. Maybe you can catch a ride with iwire. Note to self: Must remember to arrive in separate vehicles.

I didn't think the OP or zog was talking about transmission lines. Even your post was about mis-connected SDS.
cf

The same principles apply, except we wouldn't normally have a multi-grounded neutral inside the plant. You know good and well basic transmission line theory is not restricted to HV lines.

 

[iwire]

In that case you have included the neutral. You can still have ground leakage current, but I would not expect at a value that would be a problem. For multi-grounded neutrals, the ground current can be significant.

Where did the OP say anything about MGNs?

 

[mivey]

Where did the OP say anything about MGNs?

He gave a 120/208 example but never excluded a MGN. A MGN was just an example where it might not matter if you included the neutral.

You could still have a residual ground without a neutral with a SGN.

 

[iwire]

I am sorry your going to have to explain it better for me to understand.

He gave a 120/208 example but never excluded a MGN. A MGN was just an example where it might not matter if you included the neutral.

You could still have a residual ground without a neutral with a SGN.

He did not exclude SWER systems either ........ :roll: But he did give a specific example that he was curios about.


When I see GFP breakers for 600 volt and below distribution they measure current on all circuit conductors and no amount of unbalance is going to trip it.

I think zog dragged this simple question about a 208 volt feeder into a substation, medium / high voltage question that is where he mind is 99% of the time.

 

[mivey]

I think zog dragged this simple question about a 208 volt feeder into a substation, medium / high voltage question that is where he mind is 99% of the time.

I can't argue that we may have gotten side-tracked...just a little.:smile:

 

[Cold Fusion]

---You could still have a residual ground without a neutral with a SGN.

Mivey -
If the system is 5W, the residual ground detection has 4 current sensors. I know that, you know that, I know you know that.

If the neutral stops at the first disconnect, the downstream switch boards have no line to neutral loads. The residual ground needs only three current sensors. And yes, I knew you knew that as well.

You're dithering* (delivered with unseen body language font that says I'm poking at you, not beating you - the body language font is really little)

cf
*('dithering' is a euphenism)

 

[mivey]

Mivey -
If the system is 5W, the residual ground detection has 4 current sensors. I know that, you know that, I know you know that.

If the neutral stops at the first disconnect, the downstream switch boards have no line to neutral loads. The residual ground needs only three current sensors. And yes, I knew you knew that as well.

You're dithering* (delivered with unseen body language font that says I'm poking at you, not beating you - the body language font is really little)

cf
*('dithering' is a euphenism)

cf,

If you don't want to consider cases where zero-sequence currents can flow in non-fault conditions because of different detection schemes or different system conditions, and might cause problems, it's OK with me. Really.

 

[mivey]

Ignoring some potential problems with specific system conditions, detection schemes, and switching arrangements, and limiting the scope to the OP's specific example: #4 answers the OP's question and addresses the biggest concern:

Unbalanced currents can lead to unbalanced voltages and poor voltage regulation.