Transformer sizing in kVA 1

[confused99]

We are currently having an discussion between engineers (mechanical) about how you calculate a transformer size in kVA from the W/m2 loading figures.

i beleive that the kVA load required is a factor of total floor area, W/m2 and divided by the power factor.

a colleague of mine states that i need to divide this figure by sq rt of 3 to take account of 3 phase vector diagrams.

another colleague states that i need to divide by 3 as there will be 3 phase currents of all equal value to line current.

i beleive that power delievered/required is not dependant on the no of phase and that 3 phase system only reduce conductor size and improve the efficiency of power delivered by not delivering zero power twice in a cycle.

Clarification please?

 

[DanDel]

Since kVA = kW/PF, your belief is the most correct. Don't forget that code requirements usually specify this equipment to be sized at 125% of the calculated load, plus many other factors that an electrical engineer should be called upon to review for your design.
However, your colleagues' recommendation for divisions are correct to get the phase currents from kVA. Divide by sq rt of 3 for the phase currents using the phase-to-phase voltages, and divide by 3 for the phase currents using phase-to-neutral voltages.

 

[rbulsara]

Basic formulas are as follows:

total area m^2 * w/m^2 = totla W, watts.

kW = W/1000
kvA = kW/power factor ( assume p.f.=0.8)

This is the size of your transformer, in kVA.

For line current ( in each phase)=kvA/{(sqrt(3)*V*1000)

Where V is line to line voltage.

Hope this will help for planning purposes.

As always seek help of a qulalified EE for actual desingn.

 

[edison123]

Transformer (or generator or motor) KVA = 3 * Phase Voltage * Phase current. Thus, all three phases contribute equally to the output.

 

[jbartos]

Suggestion: Visit

http://www.control.com/1026178348/index_html

for calculation formulae