Feature Article: Management
Hours run per season: 1,200 hours
Diesel fuel costs: $2.20/gallon
Engine fuel usage: 40 gallons/hour
17 percent/100 percent x 40 gal/hr x 1,200 hrs x $2.20/gal = $17,950 per year (ROI = 17,950/8,000 = 224 percent/year)
Now, let’s look at the capacitor brands on the market. Some have two-year warranties, but warranty periods vary. The prices increase along with the longer warranty life units. The anticipated life is usually based on how many hours the motors are run. If you calculate the earlier example for five years, it would be 224 percent x 5 or a 1,120-percent return of $89,600 on an $8,000 investment. Most capacitors have a 17-year or longer life expectancy. Some have internal fuses to protect against indirect lightning coming in the power line if it is connected, but still suggest additional protection.
Another consideration related to the warranty is the voltage rating of the capacitor. Do not use lower-cost, 480-volt capacitors on 480-volt motors, particularly if connected to the electrical grid. Their life will be short due to surges. Typically, power companies are within their rights if the voltage surges up to 10 percent. Most capacitor companies have 600-volt rating models that, typically, last three times as long as 480-volt rated capacitors. The best models are 660-volt rated capacitors, which tend to have the 10-year warranties.
Calculating capacitor size
Standard power analyzer equipment works to size motors or electrical panels for capacitors. Some companies have a secret patented system to measure for capacitor sizing so the person measuring has no clue what KVAR setting is needed. The main two items an operation needs are a power factor and a KW reading, but more data improves accuracy (visit http://usenergyadvisor77.vpweb.com to download a data form).
It is ideal to use a power analyzer and leave it on for 5 to 10 minutes or longer to record the low, mid, and high data. Many power analyzer units do up to 3,000 amps. Remember, it is dangerous to take measurements when a lot of amps are involved. Use an electrician or a qualified maintenance person or engineer to collect the electrical data. The motors need to be in operation to get the data. Once it has been collected, gather quotes from multiple dealers and make sure you get the right size of capacitor.
If your operation has soft starts or variable frequency drives or variable speed motors there are some critical wiring details needed to connect them properly. Not all capacitor companies understand this. Don’t let them tell you that your operation can’t wire up these types of motors to capacitors.
If the operation is connected to the electric grid, it may be worthwhile to add surge protection to minimize external voltage surges. Also, consider adding surge protection if the operation has intermittent operation of large motors because this can set up internal voltage surges. Two items needed on the data sheet to be sized for surge protection are the total monthly kilowatt-hours and total amps. Another location for surge protectors or clean power systems is in the control room for your motors’ operation, which can be affected by voltage surges, harmonics, and electrical noise. Any expensive monitoring equipment should be protected. These single-phase units are much cheaper than three-phase clean power systems. They work well on either engine/gen sets or on operations connected to the electrical grid.
The ROI of capacitors in many motor usage systems can be very worthwhile. By investing in some capacitor expertise to collect data on your operation, you may be able to drop your operational costs and improve profits. AM
Dan Meyer, P.E., Ph.D., is president of Modern Ag Systems Design, Inc., in Waukon, Iowa. He has spent 25 years serving on the faculty of three major universities and an additional eight years as a private consultant. He can be contacted at 563-517-7679 or via e-mail at firstname.lastname@example.org. His Web site, including an electrical survey form, is http://www.usenergyadvisor77.vpweb.com.
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