Hi all, i've a question, how many turns/rounds may a Psiker substain a power? Infinite!?

As long as they keep passing the roll to sustain it they keep the power up, unless they wander too close to an untouchable.

Every ten rounds you sustain a power, you roll it again (though without fear of phenomena). As long as you manage to beat the threshold again, you're fine.

Thank you very much!

Hi again, could u tell me please where i can find the rules that u suggest to me?

Manual, FAQ and so on.

Tnx.

How about the paragraph titled Sustaining Psychic Powers on page 164 of the core rules?