harmonics??
- Thread starter wyatt
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Re: harmonics??
I understand that the neutral current can be 17.3 amps in the worst case, but not sure of the origin of that claim.
You should use a true RMS ammeter though for the non-sinusoidal currents.
jb, You could say that the currents are "bent out of shape" by the non-linear loads.
I understand that the neutral current can be 17.3 amps in the worst case, but not sure of the origin of that claim.
You should use a true RMS ammeter though for the non-sinusoidal currents.
rick hart
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Re: harmonics??
We haven't even gotten into negative sequence harmonics in this discussion.
Be cautious about thinking amps as they apply to 60HZ and amps related to higher magnitude. The values we are used to in 310.16 go out the window because of the higher frequency creates more imepedance and lowers the ability of the conductor to carry the added current. Or so I have been told by some pointy heads.
We haven't even gotten into negative sequence harmonics in this discussion.
Re: harmonics??
Let make sure I got this right. the harmonic wave is still at 60hz. but we use higher hz to mathematically describe the distorted wave. impedance would still be the same. the distorted wave spends more time at its peak. and is not canceled out by an opposing normal phase. and is it right that harmonics can add no more than 200% on 1 phase and 173% on 3 phase
Let make sure I got this right. the harmonic wave is still at 60hz. but we use higher hz to mathematically describe the distorted wave. impedance would still be the same. the distorted wave spends more time at its peak. and is not canceled out by an opposing normal phase. and is it right that harmonics can add no more than 200% on 1 phase and 173% on 3 phase
Re: harmonics??
In one of the facilities where I work, We have an 800amp distribution panel feed from a UPS that feeds 7, 100 amp branch circuit panels.
I have been there several weekends with the electrical engineer who oversees the operations for this room. He is a very smart man, but his english is lacking, so sometimes I dont completely understand him.
We moved alot of loads from one panel to another, and he keep saying that he was balancing the panels.
None of the branch circuits share neutrals, so I am confused about what he means by balancing the panels. And how moving the circuit from one panel to another could help. Why he wanted the load evenly distributed from panel to panel.
Is it possible that he was attempting to balance the harmonics?
[ December 10, 2005, 09:30 AM: Message edited by: jbwhite ]
In one of the facilities where I work, We have an 800amp distribution panel feed from a UPS that feeds 7, 100 amp branch circuit panels.
I have been there several weekends with the electrical engineer who oversees the operations for this room. He is a very smart man, but his english is lacking, so sometimes I dont completely understand him.
We moved alot of loads from one panel to another, and he keep saying that he was balancing the panels.
None of the branch circuits share neutrals, so I am confused about what he means by balancing the panels. And how moving the circuit from one panel to another could help. Why he wanted the load evenly distributed from panel to panel.
Is it possible that he was attempting to balance the harmonics?
[ December 10, 2005, 09:30 AM: Message edited by: jbwhite ]
Re: harmonics??
Along with the others replies, the following article is informative and pretty easy to understand.
Harmonics Made Simple
Roger
Along with the others replies, the following article is informative and pretty easy to understand.
Harmonics Made Simple
Roger
Re: harmonics??
JB, perhaps he is just trying to even out the loads on these seven panels?
Or, perhaps he is trying to balance the neutral currents as you say. That won't cancel the 3rd harmonic currents, but it would even out the voltage drop on the neutrals and would reduce the resistive loss in these neutrals.
For example, imagine In = 100A in one neutral and 0 in another. The power dissipated in the first would be,
P = 10,000xRn + 0xRn = 10,000*Rn
Now balance the neutral current, the power is now,
P = 2,500xRn + 2,500xRn = 5,000xRn
I doubt though that the cost savings would justify a weekend of OT, but there are other considerations.
JB, perhaps he is just trying to even out the loads on these seven panels?
Or, perhaps he is trying to balance the neutral currents as you say. That won't cancel the 3rd harmonic currents, but it would even out the voltage drop on the neutrals and would reduce the resistive loss in these neutrals.
For example, imagine In = 100A in one neutral and 0 in another. The power dissipated in the first would be,
P = 10,000xRn + 0xRn = 10,000*Rn
Now balance the neutral current, the power is now,
P = 2,500xRn + 2,500xRn = 5,000xRn
I doubt though that the cost savings would justify a weekend of OT, but there are other considerations.
Re: harmonics??
rattus, what i was getting at was that he was trying to reduce the harmonics on as many of the neutals as he could.
this is a government facility, the ot is minimal versus the consequences of an unscheduled shutdown due to a neutral over heating. that is a different topic and has something that i dont understand to due with how the systems are networked. if one goes down, a whole area of the country can be affected.
rattus, what i was getting at was that he was trying to reduce the harmonics on as many of the neutals as he could.
this is a government facility, the ot is minimal versus the consequences of an unscheduled shutdown due to a neutral over heating. that is a different topic and has something that i dont understand to due with how the systems are networked. if one goes down, a whole area of the country can be affected.
Re: harmonics??
I hear you JB,
If the neutrals are overheating from the harmonics, then they are not sized to handle the non-linear loads.
Whatever the source of the neutral currents though, it is better to have them evenly distributed--I^2*R loss and I*R drop.
But when you get back to the main panel, they will combine again.
Interesting problem.
I hear you JB,
If the neutrals are overheating from the harmonics, then they are not sized to handle the non-linear loads.
Whatever the source of the neutral currents though, it is better to have them evenly distributed--I^2*R loss and I*R drop.
But when you get back to the main panel, they will combine again.
Interesting problem.
Re: harmonics??
On one of the shutdowns, we re pulled the main feeds and TWO full size neutrals from the distribution panel back to the UPS, and Main panel at the transformer.
This thread is helping me understand why the engineer had us do all that work. It was unclear before, because, as you said. it is alot of overtime and a bear to schedule shutdowns.
[ December 10, 2005, 01:41 PM: Message edited by: jbwhite ]
On one of the shutdowns, we re pulled the main feeds and TWO full size neutrals from the distribution panel back to the UPS, and Main panel at the transformer.
This thread is helping me understand why the engineer had us do all that work. It was unclear before, because, as you said. it is alot of overtime and a bear to schedule shutdowns.
[ December 10, 2005, 01:41 PM: Message edited by: jbwhite ]
rick hart
Senior Member
- Location
- Dallas Texas
Re: harmonics??
The mathematical description helps in identifying the order of the harmonic which can add, subtract or be neutral to the fundamental waveform. Knowing where the harmonic resonates and its magnitude tells us if there is anything to worry about.
No, only fundamental frequency is at 60 HZ, the harmonics are a separate voltage created by the currents which are drawn asymmetrically by the load. The effect is to impress themselves upon the fundamental frequency, thereby distorting the 60HZ waveform for both currents and, in worst case, voltage. The harmonic component is still there in the conductor at the frequency of all harmonics and the fundamental. The RMS meter value will give you a relative to 60HZ current based upon the different frequencies present.
The mathematical description helps in identifying the order of the harmonic which can add, subtract or be neutral to the fundamental waveform. Knowing where the harmonic resonates and its magnitude tells us if there is anything to worry about.
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