Hi
I asked to move 3 phase transformer to new pole.
This 3 phase transformer is feeding apartment building from pole to underground service.
Currently this tx 3-50kva ,600/347 V, 4-4/0 Al.
they gave me the peak load on tx is 135 kva.
77 residents in apartment all 120/240. But I don't know the main Ampere going to building.

my new pole is meter or 240ft away from current location.
I don't know the service size (A) ampere in apartment.
So I don't know how to calculate voltage drop based on new distance.
What cable size should I use? And what is actual size Ampere in there?

I know that 135kva/347 = 389 A peak load
which the cable 4- 4/0 Al (already exist there) can't handle 389A
Need you advise thank you

You should discuss this with your foreman/boss/supervisor/engineer/whatever.
This is a home and garden DIY message board. If you have to come here to ask questions about a job such as this maybe the job is over your head?

The appropriate expression is "in over my head".
Find a professional to help you, not a DIY website.

If you are just moving the transformer to a new pole, you don't really need to know the anything, just move the transformer.

You say this is going to feed an apartment building? What happened to the replacement transformer? Did you look at the panelboard to get the size of the MB?

Did you ask the superintendent of the building to get you the input specs?

so many questions....so few answers