Transformer sizing

[deetz]

When calculating the size of transformer needed for a 3 phase machine, are you required to up the machine amperage by 125% for the KVA?

 

[Padlock01]

Hi Deetz
Sizing a transformer kVA depends on the following;
a)Size of the load ( inductive / Resistive)
b)Power Factor
c)Motor starting VD % Max should be between 15 and 20% depending on the mechanical load.
d)Motor starting (DOL,SS,VSD)
e)Impedance of transformer
f)Starting a large drive when other loads are operating.
G)And of course what will the VD be at the TX secondary Terminals.
H)The norm is stick with 80% TX loading oil and 90% dry type.
I have attached an Excel spreadsheet that may help you.