Sizing Transformers

[EdCampbell]

Hi,
By the way I am writing to you from Mexico.
I do not think they use the NEC code however I would like to keep this instalation in line with it as best I can.

I am new to this forum and quite new to the project I am about to undertake. I am in the process of designing a complete instalation for a factory with a floor area of about 4000m squared. Basically it will have the following equipment etc.

Main building lighting 34 x 1Kw metal halide lamps situated 8 meters above the floor.
3 levels of offices and storage areas illuminated by an assortment of strip lighting not forgeting the power outlets for standard office equipment and a few microwave ovens and a fridge in the canteen. (Total load of about 250 Amps)

At present one Variable speed compressor with a 75 Kw motor.

One production line which will also use about 80 Kw of power.

An Air conditioning system that will maintain the whole building.

Now I need to plan for future expansion as we paln to out in another production line (80kw) and a number of robots (?w). not forgetting a conveyer system.

The factory needs to run on a supply of 220 V and obviously 110 V ac.

What I would like to know is how do I determine the size of the transformer as the one supplying the building at present is only a 30 Kva. From my calculations I am looking at one of about 1000 to 1500 kva. but I may be wrong. I used the following formula :

volts x Amps x 1.73
3 phase Kva= --------------------
1000
Remember I need to plan for future expansion.

Thanks for your help.

Regards,

Ed.

 

[bob]

Re: Sizing Transformers

Ed
I would suggest that you use 277/480 volt service
to your facility. Its about 36000 sq ft in area.
It will save you on wire size for the long runs.
You can use step down transformers to get 120 volts. Most of the lighting can be at 277 volts
as well as the motors, drives and the AC unit.
Table 220.3A has a minimum of 22va per sq meter listed. 22 va x 4000 sq m = 88000 va mimimum for lights. You will need to count the actual lights to see if this figure is adequate. Normally 180 va per general purpose receptacle. Count them or estimate.

So far we have
88 kva lts
75 kva var speed motor
80 kva production line
80 kva future line
? Air cond unit
? GP receptacle
? Misc
What else is missing?

 

[Dnkldorf]

Re: Sizing Transformers

Definatly bring in a 480/277 service, and run everything you can off it.

It will reduce line losses and energy consumption.

The only thing I think you forgot bob are water heaters and how many computers, laser printers/copiers and office supply loads that are going in the place. Oh yeah, any servers and UPS in the place?


And Mexico, are you planning any backup power?


Dnk...

 

[charlie b]

Re: Sizing Transformers

The word processor for this Forum does not work the same way most commercial word processors work. Therefore, your formula did not appear the way you wanted it to appear.

If you are saying that KVA is equal to (volts times amps times 1.732) divided by 1000, then that formula is correct.

But it is not the way you size a transformer. You start by calculating the load, in units of VA or KVA. Then you pick a transformer that can handle that load and that has whatever spare capacity you want. You use that formula (in another form) to calculate the amps on the primary and secondary sides. Then you use the amps to pick the sizes of your conductors.