Power Distrubution

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Old 08-10-10, 07:45 AM
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Power Distrubution

I'm doing a building design for a class project. I have a 600V 3phase distribution panel that uses a 600/208v transformer to feed a 120/208V panel. I need a 460V 3phase supply for a panel for a motor control center. What would be the best way to provide the 460V? Could I get a 600/460V distribution panel or could I use another transformer? Any advice would be greatly appreciated.
 
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Old 08-10-10, 10:17 AM
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You would need a separate 600/480Y-277 volt transformer.
 
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Old 08-10-10, 11:23 AM
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Is POCO assumed to be supplying a 600v, 3-phase, 3 wire (Delta Configuration) service to your hypothetical building? This is not common although sometimes encountered in the southern region of the U.S., and possibly elsewhere. This type service provides phase voltage of 600v, and line voltage (phase to ground) of around 347v if memory serves me correctly. Because it has no neutral, 120v is not available (I think the Brits have 4 wires w/ a neutral). If the motors in your hypothetical motor control room could run at 600v, then this higher voltage service might be advantageous by drawing less current . . . otherwise, Iím not seeing the advantage for this 600v service (I admit to possibly missing something). Iím not aware of POCOĒs offering 600v/208v service, and it appears youíre installing 2 step down transformers to meet different electrical requirements . . . not sure this is the least cost alternative.

Has the professor locked in the electrical design for this building as youíve posted, or is he allowing flexibility to design it on a least cost basis? If the design is locked in, I think furdís response answers your question. However, in the real world when large industrial motors are involved, the customerís engineers are working w/ POCOís engineers and the motor manufacturer to determine the optional motor wiring configuration and other supplemental equipment which may result in energy savings.
 
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Old 08-10-10, 11:49 AM
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Basically I am designing a car wash. I have complete flexibility and I can change the incoming supply if I want. I need a 120/208V supply for lighting and some equipment and i need to run 10 motors which are rated at the following:
2 - 5 HP 3-phase 208-230/460 VAC 16.5A -14A / 7.5A
2 - 15 HP 3-phase 208-230/460 VAC (45-41/20.3 amps)
1- 7.5 HP 3-phase 208-230/460 VAC (23-19/11 amps)
1- 30 HP 3-phase 208-230/460 VAC (88-80/40 amps)
4- 10 HP 3-phase 208/230/460/575 VAC (28/26/13/9.2 amps)
These motors are supplied through a motor control center,
Which come in 460V/230V/208V/575V.
Could I run all these motors off 208V and only use one panel?
 
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Old 08-10-10, 12:24 PM
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You could, but 208V is the least-optimal choice because at that voltage the motors will draw the most current. This means bigger transformer, bigger wires, bigger conduits, worse voltage drop and an all-around more expensive option.

To me, the clear option is to have the power company provide a 480Y277 service. Your motors and possibly parking lighting will run directly off this service at 480V and possibly building lighting at 277V. If 277V is not needed for lighting you could go for a 480V delta service instead of wye. You can then add a much smaller 480V-208Y120V transformer to run a few small panels for misc lights and general-purpose use. It would also be possible to take two legs of the 480V delta service and throw in a center-tapped 2:1 transformer to get a more residential-style 240/120 for the general-purpose panel(s) if the general load is low.

With the suggestions that other are sure to make, I hope you realize that in this type of situation there are many correct answers and a good design requires evaluation of several options.
 
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Old 08-10-10, 01:37 PM
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Thanks, so the motors will not have any trouble running off the 480V delta? Can you buy a 480V delta distribution panel?
 
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Old 08-10-10, 02:01 PM
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To me, the clear option is to have the power company provide a 480Y277 service.
Based on the flexibility you have, I agree w/ Ben.

I canít speak for all regulated and non-regulated utilities operating in the U.S. but many larger ones are geared to helping their customers. I suggest you request a meeting w/ a commercial service planner from your POCO, and after explaining what youíre trying to do and electrical requirements, ask the planner if an electrical engineer could also be present to answer questions and provide guidance. Sometimes the service planners feel they have adequate engineering knowledge . . . these folks are usually starting out their careers and may not have the depth of knowledge as more senior engineers who have progressed in their careers. Other than making the request and making it known youíll have various technical questions, youíll have to be guided by the decision of the service planner . . . if he/she doesnít know the answers, theyíll go back to get them but that losses time. The more homework youíve done in preparing for this meeting will allow it, and the process, to proceed more smoothly . . . specific motor info and electrical requirements should be available as a handout so the POCO person doing the analysis has it readily available.

Given common electrical requirements for a commercial customer, a threshold question I would have is understanding my options as to whether the customer elects to own the transformer(s) or have them owned by the utility. I see no reason for you to install a 120/240v transformer for basic lighting and stuff as that cost should be built into the commercial rate schedule. While the cost may be higher if the high voltage equipment is owned by POCO, it offers an advantage of having more reliable service to the business. If a transformer fails near a weekend, it may take days to find, buy, and have it installed. A utility should have spare transformers on hand, emergency crews able to install them, and able to restore power to the business to minimize business interruption losses (they too have a vested interest as they make more money when the meter is spinning).

There are a number of electrical pros on this forum having far more knowledge about inside electrical work, and code requirements than I do. So Iím bowing out of this discussion unless you have later questions about your POCO. Good luck.
 
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Old 08-10-10, 03:20 PM
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Originally Posted by JBenson92 View Post
Thanks, so the motors will not have any trouble running off the 480V delta?
The motors wouldn't have any trouble, but there could be an issue with your "motor control center" whatever that actually is. You'd need a lot specs to know for sure, but I assume a lot of that can be left vague as this is just proof-of-concept project.

Can you buy a 480V delta distribution panel?
A 480V panel can be configured for use with a delta service. Do you understand what is meant by a delta and wye when it comes to services and transformers? What is the nature of the class so we can better understand what you're trying to learn with the project? Obviously none of us wants to do the project for you, but would be happy to help with understanding the concepts.
 
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Old 08-10-10, 04:48 PM
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I see some very good ideas presented, but am wondering if all the participants realize you are from Canada. I also have some ideas, but I don't know what the common voltages available in Canada are so I'll keep my suggestions to myself at this point. But, I do have a question. What is the criteria under which your design will be judged? Least expensive to install? Long term cost effectiveness for the customer? Are you being graded on this project?
 
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