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Measuring current inside a delta connectioin

Measuring current inside a delta connectioin

Measuring current inside a delta connectioin

(OP)

When measuring current inside a Delta connection what would you expect to read if you put a clamp on meter around two legs of the delta connection.  I know each leg would have 58% of the line current just at different phase angles.  Would a clamp on meter account for this phase angle differene and show the two individual legs adding up to the same as the line current?

For instance lets say on one phase coming into a delta connection we have 100A on the line.  Now if we go inside the delta and measure the combined current where this line splits off into the two dela legs will we see this same 100A while meausing both legs simultaneously with a clamp on?  Or will the phase angles not seen by the meter lead to an error?

RE: Measuring current inside a delta connectioin

Clamp on meter only measures the magnitude of the current. 58% is the magnitude, assuming balanced 3 phase current.

Rafiq Bulsara
http://www.srengineersct.com

RE: Measuring current inside a delta connectioin

You have one wire splitting into 2. If the current clamp on the single wire shows 100A then you would still read 100A if you clamped around both wires just after the split. Seriously, this isn't rocket science...

 

RE: Measuring current inside a delta connectioin

(OP)
I know that each leg inside the delta will be 58% of line current (assuming balanced) and therefore if you measure the two delta legs individually and add them you will arrive at 116% of the line current which will be incorrect.

However if you clamp around both legs after the line splits although the meter only reads magnitude would the 120deg offset of the delta current fields cancel to some degree to leave you with the same magnitude as the line current shown on the meter? Maybe this is what LionelHutz is implying?

I guess maybe I was getting confused due to the fact due to the fact there was contributions from other phases inside the delta and the current simply wasn't splitting off a single phase feeder.

RE: Measuring current inside a delta connectioin

What LionelHutz said.  Kirchhoff's law still applies.

If you encompass multiple conductors, the clamp on meter or a CT would read the magnitude of the Net current after the vectorial addition.

Just as if you pass back the same conductor through the CT (canceling each other) it will read zero current or if you place double turns of the same conductor through a donut CT you will read twice the magnitude.

Rafiq Bulsara
http://www.srengineersct.com

RE: Measuring current inside a delta connectioin

From your example, the sum of the currents in both wires is 100A so the meter will read 100A. It doesn't matter if you are clamped around 2 seperate conductors or a single conductor - if the sum of the currents in the conductors is 100A then the meter will read 100A.

For AC circuits, you always have to sum vectorally.

Yes, if the currents in 2 wires sums to 100A then the magnetic fields produced by those wires would sum to the equivalent of a 100A field when side by side and inside the current clamp.
 

RE: Measuring current inside a delta connectioin

You would measure the line current.  

RE: Measuring current inside a delta connectioin

(OP)
Thanks guys!  This is what I suspected but just wanted to clarify the slight bit of unsureness that I had.

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