Neutral load

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ses30708

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Ok so I am having trouble figuring out the formula to solve this question....

A multi-wire, three-wire branch circuit has 14 amps on phase A and 12 amps on phase B. What is the load on the neutral?


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infinity

infinity

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As Don mentioned the system type is needed to answer the question. For 1Ø it's a simple arithmetic problem you can do in your head for 3Ø it get much more complicated.
 
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gar

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On a single phase center tapped transformer I can load it so that the neutral current could approach 26 A for your numbers. But that is not the expected answer.

You should not be looking for an equation, but rather you need to understand the circuit. Draw the circuit and play with waveforms. Note: the sum of two sine waves of exactly the same frequency and of any arbitrary phase relationship is still a sine wave of the same frequency. Look up trig identities. But depending on the phase relationship of the two sine waves the magnitude of the resultant sine wave changes.

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ggunn

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gar said:
Note: the sum of two sine waves of exactly the same frequency and of any arbitrary phase relationship is still a sine wave of the same frequency. Look up trig identities. But depending on the phase relationship of the two sine waves the magnitude of the resultant sine wave changes.
Click to expand...
Yes, and an understanding of that is essential for comprehending three phase power systems. For me it was truly a light bulb moment when it clicked into place.
 
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dionysius

Senior Member
Location
WA
ses30708 said:
Ok so I am having trouble figuring out the formula to solve this question....

A multi-wire, three-wire branch circuit has 14 amps on phase A and 12 amps on phase B. What is the load on the neutral?


Sent from my iPhone using Tapatalk
Click to expand...

Please recast this question giving more info. If 3-phase is C=0??

Go back to your sources and do some homework so I can work the solution.
 
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gar

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EE
161125-0951 EST

Where is the person that started this thread. That person needs to return with questions, and more information.

Suppose you have a center tapped single phase power source. On one side of the center tap is an inexpensive unloaded (no mechanical load, just a spinning disk with one pointer painted on the disk) induction motor. An optical tachometer is available (that is a calibrated strobe, you can make one with an LED and a 555 timer). For power factor correction a correctly sized capacitor is placed on the opposite phase. Does this improve the power factor seen at the transformer primary? What happens to the neutral current when the capacitor is connected?

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Besoeker

Besoeker

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Location
UK
infinity said:
As Don mentioned the system type is needed to answer the question. For 1Ø it's a simple arithmetic problem you can do in your head
Click to expand...
What if the two loads had different power factors or were non-linear - as most electronic equipment is these days?
But you are probably correct - the simple approach is probably what the examiner was looking for.
Never mind what the situation might be in real life.
 
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