We are in the process of expanding our metal working business and are in need of 3 phase power. We currently have a 400 amp single phase service to our shop. Our expansion includes approx 150 hp total in motors. I spoke with American Rotary about a phase converter setup and they said by their calculations at 100% full load there will be a 251 amp load at 120/208 3 phase which will equate to approx 440 amp single phase. I can get three phase power from the utility company but we will most likely out grow our current facility in the next 3-5 years. The cost for each option is pretty close to the same. Main difference is the phase converters can be moved or sold at a later date. Any insight to the better option would be appreciated. FYI - Non CNC equipment, motors ranging from 1.5 - 25 hp.
3 phase rotary converter vs. 3 phase supply
- Thread starter Jwittmuss
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I'd go with three phase from the utility provider. On efficiency grounds if for no better reason.
Ultrafault
Member
IMHO. The three phase service will increase the value of your building by more than you can gain by reselling the phase converters.
ptonsparky
Tom
- Occupation
- EC - retired
Adding roto phase is more parts to maintain times however many you need. Selling them would be like selling used motors. Surley you have better ways to spend you time.
POCO 3 phase service is the way to go.
POCO 3 phase service is the way to go.
peter d
Senior Member
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- New England
Call a professional. :thumbsup:
- Location
- Wisconsin
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- PE (Retired) - Power Systems
Rotary phase converters do not always play well with 'electronic' loads like machining centers with servos. I worked in a shop that ultimately had to switch from a rotary converter to a digital power switching one.
If your maintenance group is not experienced with 480V, then you might want to stick with lower voltages.
If your maintenance group is not experienced with 480V, then you might want to stick with lower voltages.
ptonsparky
Tom
- Occupation
- EC - retired
- Location
- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
In a production environment like what I think you are describing where the machines will run all the time, the efficiency loss (upward of 30%) via the RPCs for that much load will more than eat up the perceived benefit you have of being able to resell the used RPCs later. I'd go for the 3 phase power from the PoCo, but that also depends on what they would charge you for doing it. In some cases if there is no 3 phase near by, they charge you a one time fee to bring it in from the nearest source, and that can be a huge expense. Did you get that far with them yet? If 3 phase is already there on your street with enough capacity for you, they may not be charging you much at all, so that can make a big difference. If there is an expense, I'd approach the landlord with chipping in toward it, because it's true, his property becomes more valuable and easier to rent with a 3 phase source.
But if you do end up having to go with RPCs, consider this: for 3 phase machines that can benefit from using VFDs, you can use the VFDs to convert single phase to 3 phase. at 208V 3HP and under you can do it with most VFDs without de-rating, above 3HP you must buy a VFD that is 2X the size of the motor FLA. But if you can knock off a bunch of the small motors with small VFDs, you can decrease the size and quantity of RPCs you need, decreasing the efficiency loss they represent.
But if you do end up having to go with RPCs, consider this: for 3 phase machines that can benefit from using VFDs, you can use the VFDs to convert single phase to 3 phase. at 208V 3HP and under you can do it with most VFDs without de-rating, above 3HP you must buy a VFD that is 2X the size of the motor FLA. But if you can knock off a bunch of the small motors with small VFDs, you can decrease the size and quantity of RPCs you need, decreasing the efficiency loss they represent.
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