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3 phase wye neutral current #130152
02/18/06 05:32 PM
02/18/06 05:32 PM
R
randyagr  Offline OP
Junior Member
Joined: Mar 2004
Posts: 6
Lanark, IL US
Been trying to understand 3 phase wye neutral currents by reading this.http://www.allaboutcircuits.com/vol_2/chpt_10/2.html
Does this mean neutral current is the same for one 120v load and 2 120v loads, but drops to zero for 3 120v loads assuming all loads equal? Have only worked on 3 phase center tapped Delta in this area, so I know the neutrals cancel each other since both 120v legs are from the same phase, but I'm not sure I get this 3 Phase wye. Thanks, Randy

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Re: 3 phase wye neutral current #130153
02/18/06 09:29 PM
02/18/06 09:29 PM
L
Larry Fine  Offline
Member
Joined: Feb 2005
Posts: 693
Richmond, VA
Randy, look at it mathematically: Start with an equal load, say 20 amps, on all three phases. The neutral current is the sum of the three currents, including the phase angles, which equals 0.

Now, remove the load on one phase, as well as its contribution to the neutral sum, -20 amps from each. This results in 20 amps subtracted from the previously-balanced zero neutral current, meaning 20 amps.

So that leaves 20 amps on two phases, and 20 amps on the neutral. Now, let's "check our math" by reversing the process: Each amp drawn by the third phase reduces the neutral current by the same amount, until it's back to zero.


Larry Fine
Fine Electric Co.
fineelectricco.com

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