Load Balancing My Facility Why??
- Thread starter zeilzabob
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Two reasons come to mind. Money and capacity.
The unballanced loads create excess heat in transformers. That excess heat is wasted electricity.
And by balancing the loads you gain additional capacity on your distribution system. Say you have a 1000A service with the following phase loads.
A - 650A
B - 455A
C - 487A
If you manage to ballance the loads more to something like this.
A - 545A
B - 533A
C - 514A
Then you've gained about 10% more capacity on your system. This is just an example of a very unballanced system. Don't expect a perfectly balanced system but it's good to keep the phase amps as close as possible.
The unballanced loads create excess heat in transformers. That excess heat is wasted electricity.
And by balancing the loads you gain additional capacity on your distribution system. Say you have a 1000A service with the following phase loads.
A - 650A
B - 455A
C - 487A
If you manage to ballance the loads more to something like this.
A - 545A
B - 533A
C - 514A
Then you've gained about 10% more capacity on your system. This is just an example of a very unballanced system. Don't expect a perfectly balanced system but it's good to keep the phase amps as close as possible.
- Location
- Lockport, IL
- Occupation
- Semi-Retired Electrical Engineer
First of all, it isn?t a question of advantages versus disadvantages. The NEC requires that the load be balanced. But you don?t need to strive for perfection, in the process of balancing your loads. You don?t need to worry that Phase A is loaded 1% higher than Phase B.
The simple answer to your question is that the rating or size of electrical components (e.g., conductors or panels) is determined on the basis of load calculations. The calculation process presumes that a reasonable effort will be made to balance the loads. If you don?t have a reasonable balance, then the amount of current flowing in one phase might be so much higher than the amount flowing in another phase that the selected conductor size might not be big enough to handle the current. Than runs the risk of overheating the conductor, causing damage to the insulation, short circuits, and fires.
The simple answer to your question is that the rating or size of electrical components (e.g., conductors or panels) is determined on the basis of load calculations. The calculation process presumes that a reasonable effort will be made to balance the loads. If you don?t have a reasonable balance, then the amount of current flowing in one phase might be so much higher than the amount flowing in another phase that the selected conductor size might not be big enough to handle the current. Than runs the risk of overheating the conductor, causing damage to the insulation, short circuits, and fires.
- Location
- Massachusetts
charlie b said:
Isn't it more of a suggestion by the NEC?
What section do you have in mind?
That aside the power company can force you to balance the load within their specifications which can generally be found in the 'Green Book' of you serving utility.
ryan_618
Senior Member
- Location
- Salt Lake City, Utah
iwire said:
I think the closest thing in the NEC to what Charlie is saying is 210.11(C), but it doesn't require you to balance anything other than multioutlet circuits when calculated by sqaure footage.
- Location
- Lockport, IL
- Occupation
- Semi-Retired Electrical Engineer
Thanks, Ryan. I typed that statement, then tried to look it up before I posted the reply. I couldn't find it, and I wondered whether anyone would call me on it. Ya's got me Bob. :roll:ryan_618 said:
- Location
- Massachusetts
ryan_618 said:
Same here, 210.11(C) all I found when I went looking.
Kind of strange IMO.
Twodollar
Member
- Location
- San Jose, CA
Heat is created when power is dissipated in a resistance. Wiring wastes power by dissipating heat due to the resistance. The wire contains series resistance and the power dissipated by that series resistance is determined by the current flowing through the resistance according to P=(I^2)R
Since the power dissipated in this resistance increases by the square of the current flowing through it, you can lower the heat dissipated and power wasted in the wiring by the square by moving some of that unbalanced current to another phase.
using the example:
A - 650A
B - 455A
C - 487A
total=1592A
and let's say there is 0.001 Ohm resistance in each phase
total power dissipated as heat= 422.5W + 207.0W + 237.1W = 866.6W
A - 545A
B - 533A
C - 514A
total= 1594A
total power dissipated as heat= 297.0W + 284.1W + 264.2W = 845.3W
866.6W - 845.3W = 23.1W a 2.5% savings of power in the total wiring.
not very impressive but every little bit helps. Now if your load is an electric arc furnace for steel production, 2.5% could hit the bottom line hard.
Since the power dissipated in this resistance increases by the square of the current flowing through it, you can lower the heat dissipated and power wasted in the wiring by the square by moving some of that unbalanced current to another phase.
using the example:
A - 650A
B - 455A
C - 487A
total=1592A
and let's say there is 0.001 Ohm resistance in each phase
total power dissipated as heat= 422.5W + 207.0W + 237.1W = 866.6W
A - 545A
B - 533A
C - 514A
total= 1594A
total power dissipated as heat= 297.0W + 284.1W + 264.2W = 845.3W
866.6W - 845.3W = 23.1W a 2.5% savings of power in the total wiring.
not very impressive but every little bit helps. Now if your load is an electric arc furnace for steel production, 2.5% could hit the bottom line hard.
rcwilson
Senior Member
- Location
- Redmond, WA
bwyllie said:
The heaviest loaded phase in an unbalanced system will limit the amount of balanced three phase load that can be added. Shifting single phase loads to equalize the loading may allow more 3-phase load to be added, in effect adding capacity.
Of course, new single phase loads could be added to the lightly loaded phases also.
robbietan
Senior Member
- Location
- Antipolo City
three phase motors benefit from a balanced electrical system, as they operate more efficiently in a balanced voltage system than in an unbalanced ssytem.
- Location
- Massachusetts
robbietan said:
That is a great point.
With an unbalanced load the voltages may be unequal and motors do not like unequal.
zog
Senior Member
- Location
- Charlotte, NC
And in an ungrounded system, depending on the type of GFP an unbalanced system may can false groud fault trips.
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