Sizing Transformer and Gear

And lets not forget what happens in 10 years when we are now running seven compressors all the time and somone else has added another 100HP of other load. What happens when we start the 8th compressor? Leave your self lots of spare power.

For proper transformer sizing you should know the starting sequence of the drives which are connected to the drive specially the drive which is having highest load capacity.....

because in the transfomer it should be capable enough to take running loads of all the drive which are connected plus starting current of the highest rating drive...

hope it might helps.........

I think able supporting you in your project , simplify Installations & fees decrease I am a specialist of power quality PF.Large Motors Starting up. Harmonics reduction. Call me by email to saadaj@netvision.net.il . You do not need resizing your transformer only using available technologies with bright and successful refferences Regards Joshua

To size a transformer I would take the following in to consideration.Direct or assistant starting of motors? Is load control during start up available? Is sequence starting of motors possible? Diversity of 80% of total load to be considered.Estimated transformer size thus 2 to 2.3 MVA. An oversized transformer will increase losses and fault levels thus adding to the cost of transformer and switchgear.

What is the starting of the Compressors? If you plan for VFD then of course you are going to save the extra capacity requirement by controlling the starting current and that along with other's will be saving a lot, since you are using quite high power.

Along with that put the APFC and you may not really need too much of current/KVA.

Put the capacity (including extra capacity in case future expansion is planned) based on your load on transformer selection. You may not have to spend too much if you slightly oversize it.

The individual ACBs will take care of the - may be around 400A or so for each, if you have APFC and VFD.

Electricalexpert65 explained it fully. Up to you to work the numbers.

I will only add the following: since 6/8 = 0.75, and you should allways have spare 20% (not to load your transformer more than 80% of its load) then consider all the 8 are running. (Not forgetting to check Electricalexpert65's calculations and take the highest value).

Good advice all around. I agree with using VDFs to shave peak start-up load. The easiest way to plan for future capacity increases on the transformers will be to order units sized to fit the need but equipped with forced air cooling options. Thermostats wells and fan & radiator mounts already built in to each transformer. That will allow you to add the cooling equipment later without changing the transformers, increasing the KVA capacity. Size wiring switches and buss bars with the increased capacity in mind.

You have to decide the Diversity factor based on the operating sequence of compressors. If these compressors are for a central plant, I mean all out let pipes are connecting to a common header, then the demand to running the compressor should be based on the required air pressure set point in the compressed air line.Hence all compressors are not required to run always. You can use VFD for starting . In that way , you can limit the starting current in the range of 100% of FLA. Other thing, for air compressors, normally there will be dryers installed. By seeing the capacity of motor, I guess that each dryer will be 30 KW. do u have any dryer in the system?...