Power factor corrections.

[william talbot]

Most utilities impose power factor penalties on customers when exceeding the utility limitations. In our area P.F. below .85
is the point at which the utility imposes the penalty. We install a lot of capacitors which are sized to raise the P.F. above
.85, generally to about .89 keep the cost reasonable.

However, we see more and more loads that create harmonic distortion in addition to low P.F. which affect the operation of
capacitors this problem must be solved by tuning with filters at additional expense. And harmonics are becoming a problem with neutrals being overloaded too; the 'bandaid' solution that the code suggests is to double the size of the neutrals!

I think it is time that the NEC address these problems more seriously. Building owners or tenants should be able to buy
electrical equipment that do not create P.F. nor harmonic effects on utility bills. This would require manufacturers to add
capacitors and if necessary tuned capacitors to avoid customer penalties or, as stated above, increase neutral sizing. Or at
least make it a rule that the enhancement be a manufacturer option for the buyer to choose to pay for.

Years ago the NEC required manufacturers of enclosed incandescent down-lights to install non- resettable thermal cut-outs in their luminaires to prevent overheating. That solved the problem of people using higher wattage lamps to increase
lighting levels which must have resulted in fires in some cases. I see this as an example for the P.F. and harmonic problems which are growing daily; as I see it, like a disease in our industry.

 

[mivey]

Perhaps dealing with amps is how the NEC sort of deals with it.

I doubt the NEC is going to do much about the loads themselves. As the costs associated with pf and harmonics become large enough, the utilities and others will start to pass those costs along.

Most utilities already have rules in place but usually only focus on loads with significant individual contribution. Enforcing that for smaller loads can be like spending a dollar to chase a dime so we just generalize the costs. If an individual load, even if small, is suspected of exceeding the limits we have the means to enforce the limits or at least pass along the costs. Someone would really have to exceed the average for that to happen.

 

[ron]

I'm not sure the manufacturers of VFD for example, can predict the intensity of harmonic creations on each individual system since it is dependent on the "stiffness" of the system. They wouldn't be able to accurately correct what they don't know.

The NEC is not a design standard, just a minimum safety standard. Low PF and presence of harmonics is generally not a safety issue.

Systems that you describe should be designed by a qualified person, so it can be mitigated as needed.

 

[kwired]

Power factor and harmonics are not safety issues and limitations of such items do not belong in the NEC.

If they are to be mandated it would by by energy regulatory organizations, just like the requirements driving away the use of incandescent lamps, and other energy saving methods that have been put into laws.

Power companies have given enough incentive to reduce power factor to the largest offenders by penalizing them if they don't correct it. Seems to be much more effective and less cost than if there were laws requiring the same thing, and if you don't want to comply, then you simply pay higher bills, and let the POCO handle correction on their end.

 

[robbietan]

in my neck of the woods (Philippines), the laws passed limit voltage THD at the point of common coupling (5% VTHD) as well as 5% for total demand distortion. however, these laws are for the grid operators, not contained in our Code. one rationale is for the grid operator to have some semblance of control over the loads being operated by the big users on the grid. so as the load of one user would not affect the loads of his neighbor