Originally Posted by tkrussell
The issue you mention is not due to power factor. The inrush starting current is high enough to be affecting the Demand Rate of your utility bill.
Typical you will see two rates on your bill, of course along with all the other fees and charges. They are KWH, which measures watts and time, and Demand KW.
Many times I have found the utility is not familiar with what you have for load, or is using the wrong rate. A 7.5 HP motor is not a big deal, unless your rate is the issue.
Typically, DKW is the max amount of power used, and it checked and recorded each 15 minutes. You get billed for the highest amount. (Trade secret,this is how electricians know what size of new service to install, or add load to an existing system)
Check with your utility as exactly how they do theirs, each utility may have subtle differences.
What Kiss mentions, Soft Start or VFD, same thing, may allow your mixer to start at lower currents.
Another buzz word is "load shedding", that can mean the same thing.
Many times plants will have multiple motors start at once, load shedding causes the motors to start individually, to keep the DKW down low.
Another, but less impacting, is using large lighting contactors to bring up sales floor lighting. Assuming you bring the motor load under control, this would be next to look at. Same effect, bringing up the entire store lighting causes a large one shot load to be recorded in a short period of time.
Again using the load shedding method, bring up sections over a half hour period, to keep the DKW low for any 15 min period.
The dough machine makes me remember a taco machine I had to troubleshoot. It was drawing 90 amps at startup, when it should have been much lower. This unit made the round flat pieces of dough going around in a circle for some reason. It used the vacuum of an air compressor to keep the round dough in place as it went around. Come to find out the cylinders of the air compressor was clogged with dough and flour, leaving no room for the pistons to move, and all the air passages were clogged.
My point is that other than because of a manufacturing process that needs a motor to start or run slow, most times VFD are not used on a small motor such as yours. My guess is with a 2900 count of locations, this is a small convenience retail,that makes something on site, donuts, sandwich rolls. etc.
I am not saying not do use the VFD, do it for possibly this and other reasons. but be sure to look into the utility issue. This will be a chore, with so many stores spread out. be sure to understand the billing process, and be sure they now what demand load you do have.
You should have your store design firm look into any and all load shedding and energy savings methods that can be incorporated into new designs, and create specs for retrofitting existing stores. Also, check with each utility and/or state for rebates towards energy savings measures.
Convert lighting from T12 to T8, and other combinations are popular with getting cash back to help defray retrofitting costs.
Changing over any incandescent,and even fluorescent exit signs to LED is a huge savings.
Be sure to have any new ballasts to be high power factor, and low THD, ( this is another issue too lengthy to explain in this forum).
I can go on and on. Perhaps I should be on your design team? I will let you absorb this and stop talking, you have a few utilities to call.
