1 MVA Service Drop/Substation Help 1

[RogerJZ]

Hi,

I would like to do a conceptual design for a plant that would be used to charge batteries used in electric vehicles.
I estimate that they would take 24 hrs for a full charge. So that batteries are removed and replaced with a fully charged battery, rather than charged in the vehicles.

I estimate it would need 1 MVA continuous service to this plant.

I am new to the Power Engineering, but have 22 years in Electronic Hardware and Software design. I have experience in developing SCADA and ICAC equipment for substations.

Could someone assist me on the steps to take to come up with a conceptual design for a 1MVA plant in North America. Assume this is in a city so has access to typcial voltages there, I think 12.2kV feeders would be common.

I am not sure if this would be considered a Service Drop or a Substation, and where the line is drawn between the two.

Any suggestion would be appreciated

Thanks
Roger

 

[dpc]

1000 kVA is equivalent to a large office building or small industrial installation. This can be done easily with the three-phase 480 V service from the serving utility. They would typically provide a pad-mounted transformer with a 480 V secondary. This is abou 1202 A at 480 V.

But don't forget about other electrical loads in the facility, such as cooling equipment to get rid of all the heat generated by the batteries and other building services.

Removing the batteries to charge them seems like a dead-on-arrival idea for a number of reasons, unless the batteries come with their own fork lift.

 

[RogerJZ]

Thanks for you comments dpc,

The batteries would be near dead when they are returned. There would be a mechanical system to assist changing them out with pre-charged batteries.

You are right that I'd need to add extra power to remove the heat, and to cool the building, and the blower motor to heat it in winter, and basic building lights, etc.

Is there a standard next size up current rating, of around 1300 A at 480 V?

Thanks again

Roger

 

[jimgineer]

Roger from the nature of your questions I think you probably have a good idea of the overall load or current draw that would be as a result of your battery charging system that you have in mind. However, to what extent you are trying to do this design would dictate whether or not I would recommend really getting in touch with a power/consulting engineer. If you're just trying to get a general estimate of cost for your overall electrical service, this really depends on your system and loads.

Make a list of large loads that you anticipate, that will be one of your first steps.

A standard current rating would generally be dictated by your overcurrent protection on your main service. Some standard sizes (although you can often change this dramatically) for a trip unit would be 1000, 1200, and 1600A.

 

[RogerJZ]

Hi Jim,

This is a "conceptual" design only. So it needs to suggest approaches that would indicate solutions for the major issues.

This is for a company that is putting in a proposal for the Automotive X Prize. Which is to propose a practical, manufacturable solution to get 100 MPG from a vehicle. A local company proposed fully electric, so I am offering them a possible solution for the charging station side of it.

It doesn't need to be exact, but it should be thought out enough to prove that the concept would work. If it came to an actual project, then yes a professional would need to be consulted for the project. For now it is purely conceptual.

So I understand now that a pad-mounted 480 V service is the start. Next would be another transfer to get down to single phase 120V and 3 phase 240 V. Where would that likely be located? Right inside the building, or on the pad-mount also?

Thanks,

Roger

 

[dpc]

The 480 V to 120 V conversion would be done by smaller transformers inside the building.

Pad-mounted transformers with 480 V secondary are fairly common up through about 2500 kVA. Above that, you might start thinking about two smaller transformers.