# Re: note on generator transformer sizing

Home Electrical Engineering Forum General Discussion note on generator transformer sizing Re: note on generator transformer sizing

#12147
Spir Georges GHALI
Participant

saraswatapalit said:

Please help by providing a detail note on generator transformer sizing. What are the factors that governs this rating?

best regard

saraswata

Dear ;

For exp. you have a factory for which you should define the sizes of Transforme & Genrator, first, you should know the following :

– The total installed power in this factory

– The loads that are running in normal working ” P “

– The kind of loads ” Single Phase  or  3 Phases ” and how the ditribution will be done for the single phase loads

– The average value of Cos φ for the factory ( we can calculate it if we know the Cos φ for each load )

– After that we should know an idea if there's some extention and the total power of it

Then the needed apparent power is : S1 = P( total ) / Cos φ, and ad the needed apparent power should be less the power of the transformer by ” 15-20% “, we can say that the apparent power of the transformer is : S ( tr ) = S1 / 0.8

So accordingly to the value of calculated ” S ” we can do our choice of the real transformer from the standard rating that are : 25, 50, 100, 160, 200, 250, 315, 400, 500, 630, 800, 1000, 1250, 1600, 2000, 2500, 3200, 4000, 6300 kVA

For the generator, we should know the vital loads that should be always in running, once we know, we do the same procedure to define the power of generator, noting that once the generator runs it should be loaded at teast 45% of his power.

Regards.