Power Factor Correction $ Savings on Motors? 1

[Ray100]

I am an electrical contractor and I have a commercial customer who is interested in installing PF correction capacitors to improve PF on some of his motors.

He, naturally, is interested in how much money such an installation could save him.

An electrical engineer assisted me in surveying his situation and trying to estimate the potential $ savings.

The client’s got 22 motors ranging in HP from 20-60. Voltage 460/230. We measured kw, V, I, KVA, KVAR, and PF on all the motors. We collected hours of op and load information along with nameplate info. Then we looked up the multiplier factor for the KVAR on the web page for GE capacitors and sized the capacitors to bring PF up to (usually) .95. The customers kwh charge is about 0.06.

But the question remains, how much $ savings can we expect? I need this to estimate the payback on the client’s investment. The engineer helping me says that if a utility charges a PF correction penalty, then usually you can expect total savings of 10-15%. Our utility does NOT charge a PF correction penalty, therefore the engineer estimates that savings of 5-10% are achievable.

Of course, after the installation, we’ll measure the amp usage and compare that with the initial measurements and then be able to calculate kwh savings…...but what about now...before the installation? Are these rough estimates the engineer is giving me pretty close to reality or not? I don’t need an exact estimate, but I need it to be in the ball park when its all said and done or I’ll eat this job.

Thanks…
Ray Hutchins

 

[DanDel]

If the utility is charging a low PF penalty, with proper correction, you can expect to recover 100% of the penalty charges.
If the utility does not charge a PF penalty, the only savings you will experience is on a small amount of I^2R losses in cables and equipment due to overall current reduction. (I^2R losses are basically kW heat losses)
In most cases, it does not pay to improve PF if there is no utility penalty, unless your PF is so bad and your system is so overloaded that freeing up some kVA will help extend the life of equipment. Maybe your engineer's 5-10% figure is based on this.

 

[busbar]

Outfits like Aerovox, Commonwealth-Sprague [and GE] typically have PFC-applications literature for independent estimation. Payback is closely related to utility tarriffs. Read their information carefully.

If there's no utility-levied PF penalty, no kVA-/kVAR-demend or averaged monthly kVARh metering, then 5-10% savings seems unlikely.

Be very cautious if there is significant plant load from electronic motor drives or other rectifier-based equipment. Harmonic currents can raise heck with uncompensated or non-detuned capacitors. Directly paralleled/across-the-line capacitor sets make wonderful, self-destructive harmonic-current "sponges."

 

[d23]

Ray:

Are all the starters involved D-O-L?

 

[jwerthman]

If the utility does not charge a power factor penalty, it is very doubtful that the minor reduction in energy savings will justify the cost of the power factor correction. I think the estimate of 5-10% savings is over optimistic. There may be other reasons to do it, however, such as poor voltage regulation, overloaded feeders or transformers, etc.

 

[jbartos]

Suggestion: If the PF correction is implemented close to the motors, there will be some advantages in an increased motor terminal voltage. If the motor terminal voltages are relatively low, e.g. less than 90% of the motor rated terminal voltage (according to NEMA MG-1), the motor will be drawing more current than it is designed for and this will increase the motor temperature and decrease the motor life expectancy.
Therefore, it is a good idea to look into the power factor compensation under all advantageous angles to arrive at the full benefit of the PF compensation.

 

[Marke]

Hello Ray100
The addition of power factor correction will not alter the power consumed by the motors, but it will reduce the current drawn from the supply. This in turn will reduce the I^2 R losses in the supply. If you have significant distribution losses between your metering and the motor, then you may see a reduction in the KWHr consumed. You could also achieve the same result by beefing up the cables supplying the motors. In the interest of reducing energy wastage, and maximizing plant utilization, many supply authorities charge a penalty for poor power factor. This penalty can be a direct penalty based on measured power factor, or commonly and KVA Maximum Demand penalty. Both of these (and other penalty schemes) will yield savings if power factor correction is added. If you are charged on KWHr only, I would not expect a satisfactory payback from the addition of power factor correction.
Best regards, Mark Empson

http://www.lmphotonics.com

 

[infomaniac]

When a penalty is not involved, the minimal I2R savings will not pay for the installed capacitor bank in your lifetime. The capacitor will likely fail and need replacement before savings are ever achieved.