Unbalanced Current

[EEC]

If there is 40 amps of unbalanced current on the neutral. Can you read that current with clamp over amprobe. If so, back at transformer, where does the 40 amps go on Delta/pri-Wye grounded secondary?

 

[roger]

If there is 40 amps of unbalanced current on the neutral. Can you read that current with clamp over amprobe.

Yes

If so, back at transformer, where does the 40 amps go on Delta/pri-Wye grounded secondary?

For simplicity it goes back into the source being the windings/ transformer.

For example, (using single phase) to have any unbalanced current on the neutral the neutral conductor has to be common to more than one ungrounded (hot) conductor on opposing ends of the winding, see the following illustrations.

Unbalanced neutral

True Neutral

Kirschoffs current law says in effect that, current leaving the source must be equal to current returning to the source

Roger

 

[gar]

080529-1900 EST

EEC:

Yes if 40 A is flowing in the Y neutral, then you can read it with a clamp-on current transformer or meter. The neutral being grounded has nothing to do with the question unless you have some other source of energy connected to the neutral besides the three Y secondaries.

So consider no grounding of the neutral. To get a neutral current there must be an unbalance of the current in the hot legs.

Also delta primary has nothing to do with the question that I believe you are asking.

.

 

[weressl]

If there is 40 amps of unbalanced current on the neutral. Can you read that current with clamp over amprobe.

Of course.

If so, back at transformer, where does the 40 amps go on Delta/pri-Wye grounded secondary?

It is called unballance(d) load when there are uneven loads between the phases. Ballanced currents flow between the phases and the unballance returns from the phase via the neutral.

 

[charlie b]

. . . where does the 40 amps go on Delta/pri-Wye grounded secondary?

Some of it flows into the Phase A secondary winding, and some into the Phase B, and the rest into the Phase C. And moment by moment, throughout the "60 times per second cycle," how much goes which way will change. But the simple truth is that with four wires (and no other stray paths) leaving the transformer, any current that leaves on one must necessarily return on one or more of the others. At all moments, the sum of the currents on the four wires must equal zero amps.

 

[Lcdrwalker]

Some of it flows into the Phase A secondary winding, and some into the Phase B, and the rest into the Phase C. And moment by moment, throughout the "60 times per second cycle," how much goes which way will change. But the simple truth is that with four wires (and no other stray paths) leaving the transformer, any current that leaves on one must necessarily return on one or more of the others. At all moments, the sum of the currents on the four wires must equal zero amps.

This is also true, through the windings to the primary side.

 

[Smart $]

...At all moments, the sum of the [instantaneous] currents on the four wires must equal zero amps.

Hmm... more accurate and perhaps better understood as modified?

Sidenote: When using RMS current values, one must account for phase relationships to make the sums equal zero.

 

[weressl]

Hmm... more accurate and perhaps better understood as modified?

Sidenote: When using RMS current values, one must account for phase relationships to make the sums equal zero.

Hmm...... could you explain to me what is the difference between 'all moments' and 'instantaneous'?

 

[Smart $]

Hmm...... could you explain to me what is the difference between 'all moments' and 'instantaneous'?

Hmm...

'At all moments' includes 'all' points in time, and as originally stated, the values do not have to be time correlated with one another. For example, the amount of current on Line A at 6 secs and Line B at 6.1 secs meets the criteria of 'at all moments'. Whereas 'the sum of instantaneous currents' restricts the values used to that of the same moment.

A couple ways to state it without inserting 'instantaneous' would be 'at each moment' or 'at any moment'.

 

[Ranch]

triplens?

triplens?

to have any unbalanced current on the neutral the neutral conductor has to be common to more than one ungrounded (hot) conductor on opposing ends of the winding

Roger - might you want to consider triplens?

 

[Smart $]

Roger - might you want to consider triplens?

If I were to answer in his behalf, I'd say his statement stands as made.

 

[roger]

Thank you Smart, and you are correct, my answer does stand.

Ranch, there can be no additive current on one conductor of a two wire circuit, the current (including any distortion) would be the same through out (on both conductors) the circuit.

Roger

 

[Ranch]

To Smart and Roger,

I need to slow down, I surfed right by the fact this was a two wire circuit and I promise to read more carefully next time ....