Power Factor vs. Load Imbalance vs. Cost of Generation 3

[ShuOfAz]

How would someone calculate what the savings in generation costs would be to a utility if the load imbalance on a distribution system was corrected. The thought is this will correct the low power factor to some extent.

 

[dpc]

I don't see much of a relationship between imbalance and power factor. There are good reasons to correct both, but balancing out the phases won't do much to the power factor. The power factor is mainly determined by the characterisitics of the load.

 

[busbar]

You may find some guidance at IEEE Std 739-1995 Recommended Practice for Energy Management in Industrial and Commercial Facilities a/k/a “Bronze Book,” and is available for online purchase, with sample first chapter at:

http://www.ieee.org.

ISBN: 1-5593-7696-1 Description of document at: standards.ieee.org/reading/ieee/std_public/description/colorbooks/739-1995_desc.html

 

[ShuOfAz]

In reply to DPC reply and working with the idea of voltage imbalance causing poor Pf.
Does not voltage imbalance cause lower Pf?
Does not load imbalance cause voltage imbalance?
If these both are true, then correcting load imbalance must correct poor Pf to some extent.
My initial question more focuses on what savings are there in the generation area when you correct the Pf .01% or more.

 

[electricpete]

"Does not voltage imbalance cause lower Pf?"

No. I agree with dpc that voltage imbalance and power factor are two separate issues.

 

[dpc]

I agree that load imbalance causes voltage imbalance, but I don't believe that voltage imbalance has a direct impact on power factor.

Power factor is related to the phase angle between the voltage and current phasors. Changes in the relative phase voltage magnitudes do not impact the phase angle between voltage and current in a particular phase.

 

[ShuOfAz]

Utility owned Three Phase 7200v Power Distribution System heavily loaded on 'A' Phase.

Okay, I agree that load imbalance does not "directly" effect Pf but if load imbalance does cause voltage differences on three phase systems, how is it then that you would not agree that this consequence of the loading imbalance, 'voltage difference' does indirectly cause a lower Pf.

If one has a motor and the voltages are different between the phases and the motor must work harder, less efficient, does not this effect the power factor? Likewise, what if the voltage difference is caused by load imbalance on the feeder? Would you not then agree that poor loading equaled poor voltage which increased the current causing lower Pf.

This seems to make sense to me but I'm struggling to understand why it doesn't work the way it appears.

 

[jwerthman]

I have to agree with DPC and Electricpete - power factor is not related to voltage imbalance or load imbalance, only to the relative phase angle between the voltage and current.

You are correct that voltage imbalance on a motor does cause it to work less efficiently, but that results in additional losses (real power) in the motor. If anything, this would likely increase (improve) the power factor of the motor, rather than decrease it.

The only real savings from the generation side of the equation are the reduction of losses in the system when the power factor is improved. For the very small improvement that you have cited (0.01%), the reduction in generation due to lower system losses would be negligible.

 

[ElectricTman]

I agree with both sides of the discussion yet now I can see to understand how although Pf and Imbalance are separate issues they do seem to indirectly relate to one another assuming your discussion focuses directly on high voltage utility owned distribution systems. One would think by correcting loading imbalances or correctly identifing phase attributes one would eventually help the Pf.Is it not true power produced at generation is unity? Inductive loads causes pf to fluctuate to some degree. Imbalanced pre-existing loading conditions must add to the problem,one would think.

 

[ElectricTman]

In reply to Jwerthman, I apologize for using such a small increment of improvement and do understand that Pf is only a measurement of the relative phase angle between voltage and current but would like to emphasize the measurement of the discussion is the utility's Pf and how correcting their phase loading imbalances may result in a savings at the generator. If A is at 200amps, B is at 240amps and C is at 280amps, would not balancing these phases in the feeder help correct the Pf especially if many of the feeders 75%,are as out of balance. If this is incorrect would anyone be able to explain why this action on the system would not relate to savings on the power plant side. What does a balanced system mean to the utility?

 

[ShuOfAz]

Electrictman, After our discussion last week, somehow I lessened the improvement of Pf you stated and typed it as .01 on the reply today. My mistake.

 

[stevenal]

Power factor is not efficiency. Substitute efficiency in your statements above, and they become valid. Improved pf > increased efficiency > savings. Improve load balance > increased efficiency > savings. Improved balance does not yield improved pf, and improving pf does not mean better balance.

 

[busbar]

Improving either/both can be used to increase system capacity, but should not be considered interchangeable.

Aside: With modern instrumentation applied at the point of common coupling, it is possible to log varying per-phase power factors, but unless extreme, the degree 'power-factor imbalance’ in itself typically represents no significant loss. Improving load balance versus power-factor correction may likely be achieved with less effort to the system of interest.

 

[jbartos]

Suggestion to the original posting: The power factor will be changed marginally by balancing the utility load. However, the utility load on the primary distribution level is essentially balanced three phase load. The imbalance is very small or negligible. The larger imbalances are caused by faults that cause trips. When it comes to single phase loads, e.g. motors, there is some potential change in the voltage unbalance by changing the power factor, i.e. reversed way than indicated in the original posting. If the single phase motor current is reduced by a power factor capacitor compensation, the current from the power source decreases and the voltage at the power source increases in that phase. Also, the single phase VA power being drawn from the source is decreased. Similar reasoning can be applied to the three phase motors, namely, the voltage unbalance causes the motor individual line power factor to be different. The balanced voltage source implies the power factor in each phase to be the same.