Minato Sama
Member
- Location
- Phnom Penh, Cambodia
I have problem! The amp of each phase is 25A, 20A, and 22 A. But the current on the N cable is 53.7A. How can I solve this problem? and what is the reason of this problem?
I have problem! The amp of each phase is 25A, 20A, and 22 A. But the current on the N cable is 53.7A. How can I solve this problem? and what is the reason of this problem?
He already has his own thread...Minato Sama, I moved your question into it's own thread.
He already has his own thread...
http://forums.mikeholt.com/showthread.php?t=139525
...and you closed shockingdave's...
http://forums.mikeholt.com/showthread.php?t=136651
Any other questions?
I didn't have any questions to begin with...He originally posted his question in shocking Dave's thread, I moved his question from Dave's thread to here and closed Dave's thread from last May.
Any other questions?
The neutral imbalance from your loads should be about 4.5 amps.
My gut instinct says the underlined statements are contradictory. :slaphead:Since this is apparently a three phase unbalanced system, then it requires analysis using symmetrical components. Where did this 4.5A come from?
Anywho........
Non-linear devices, which includes florescent lighting, can have a substantial third harmonic component. The third harmonic, or triplen, as well as other harmonics divisible by three (i.e. 6th, 9th, 12th) are in-phase on the supply phases. These currents will sum up on the neutral to three times the individual phase currents. So, in this case you could have a neutral current as high as +60 amps.
Switch mode power supplies can result in neutral currents that exceed the current of an individual phase. When operated on a three-phase system, they can also produce neutral currents up to 1.4 times the phase current.
Well the device will make some difference, so let's talk about the one you say will have up to 3 times the neutral current. That being flourescent lighting and other similar non-linear devices. I will still say you cannot have 3 times the neutral current as each of three phases. For the discussion, the fundamental frequency is 60Hz and the power factor of the three phases is identical. I'm sure we will agree that on a balanced system the fundamental frequency currents cancel at the common neutral node.I see your point, maybe too much info was provided.
The two statements relate to two different pieces/types of equipment. One is fluorescent lighting/non-linear devices and the other is specific to switch mode power supplies. Perhaps it was not that clear.:huh:
Perhaps... but I see that as more of a practical limit rather than a theoretical one. For a theoretical example, let's say we connected, on each of the three phases, "perfect" line-to-neutral 180Hz sine-wave current sources with identical loads. The neutral current would be 3 times that of each phase. The challenge is then creating the "perfect" scenario, which is not practical. Yet we can see that a 1.73 max factor would be one of practicality.It was my understanding that neutral current caused by harmonics should not be more than 1.73 x phase current.
The problem of differing power factors and or harmonics are, shall we say, less discussed for single phase... ahhh, correction... split phase panel feeder neutrals. That is not to say the potential does not exist, but with the ungrounded conductors being 180? out-of-phase with respect to the neutral, the the conditions which cause additive neutral current are different and not as likely to occur. This would include single phase panels fed from a typical delta-configured 3? 4W secondary.Say you had this problem on a single phase panel would there be any additional effect from it being fed from a 3 phase panel?