Facility Design - Transformer Sizing

[glfrank]

Hi all ... I am working on the design of a new facility being built in Asia and I want to check the estimate for the transformer size shown on the design drawings. We have a facility in the US with similar process loads and hours of operation and fortunately we have good energy usage records. From the billing database we have monthly, yearly and peak demand usage for 2005, 2006 and 2007.

Is there a way to use monthly or yearly kWh or the monthly peak demand in kWh to estimate kVA to check the design estimate for a new transformer? The 3 year average for the peak demand is about 1650 kWh.

Thanks in advance for any help you can offer!

 

[jghrist]

Is there a way to use monthly or yearly kWh or the monthly peak demand in kWh to estimate kVA to check the design estimate for a new transformer? The 3 year average for the peak demand is about 1650 kWh.

Demand would be measured in kW, not kWh. If you knew or could estimate the power factor at peak load, you could get peak kVA by dividing peak kW demand by the power factor.

If you have hourly energy data, then use the maximum hourly kWh.

If you only have energy (kWh) usage, then you would need to know the load factor, the average demand divided by the peak demand. Average demand is kWh for a period divided by the hours in the period.

 

[glfrank]

Thanks for your reply, I misspoke before, I should check my notes before I write. Here is the actual data and we do have demand in kW:

2005 Demand kW = 1,187 (June); yearly total kWh = 7,413,982
2006 Demand kW = 1,016 (July); yearly total kWh = 7,206,440
2007 Demand kW = 1,004 (August); yearly total kWh = 7,154,650

Can I use the demand kW to estimate the a transformer size?

Thanks again!

 

[davidbeach]

Looks like a transformer with 1250-1500kVA should be adequate if there is no plan for future load increases. A transformer in the 2000-2500kVA range might be a better choice to allow for all the unknown variations between the two locations. Even better would be to do a load calculation for the entire facility and select the transformer based on calculations rather than speculations.

 

[waross]

You may also want to spend a little time talking to the production people.
Find out if there is a way that the facility may be operated or configured so as to put more than the normal amount of loads on line simulteneously.
Is there a greater chance that such a condition may arise at the new facility and drive the demand above what is now accepted as normal?

Bill
--------------------
"Why not the best?"
Jimmy Carter