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You have not given me nearly enough information. You need to employ a qualified electrician or electrical engineer who is familiar with the regulations in your country to design the system for you.

You need to know at least: the transformer fault level, the cable type, the length, the installation method, the ambient temperatures expected over the full length, the load characteristics (including any starting current).

The general principle here in the UK is:

1. You know how much power you need.
2. You choose a transformer to supply that power.
3. You choose a fuse that will both supply the power and protect the transformer secondary windings. If you can't do that, go back to step 2 with a different (larger?) transformer.
4. Choose cables of the correct size that can be protected by the fuse and carry the current that you have, and having an acceptable voltage drop.

As you've said you have a transformer, you know the maximum current it can supply, and as this is significantly greater than the current you desire, the general idea is to choose the nearest fuse above your load current. Then choose your cable as the next size above the fuse rating, after derating it for the installation method (including any adjacent cables), for ambient temperature and for the type of protection. If the voltage drop at full load exceeds the value allowed, increase the cable size until the drop is acceptable/legal.

Note that you could have quite a high fault level out of your transformer and you need to ensure that the fuses you choose are capable of clearing a bolted short-circuit. If they can't, you'll need a backup fuse to protect the fuse!

As I wrote at the beginning, my best advice is employ a local professional.