Is it possible to expand the saggital length of the upper palatein a 17 year old by applying light forces like damon braces etc.?

Expansion: If you are asking if expansion of the palate is possible with braces only, daemon or not, then the answer is no, you will need an expander device. Also 17 is typically too late for expansion with out surgery. All movement is of the the teeth in the bone and you don't what to move them to far out off the ridge. See an orthodontist for your options, surgery may be one of them.

It is possible: This is possible, but more information is needed. What type of malocclusion do you have? What type of jaw discrepancy is present? How to your teeth line up currently? A full examination with xrays will be needed to provide advice. Please discuss your question with your orthodontist/oral surgeon.

Mixed metaphor: Palatal expansion in a late teen/adult us close to impossible. Expansion must be surgically assisted. Expanders widen the palate, don't make much front-to-back (sagittal) change. Damon braces are merely handles on the teeth. The kind of brace is so much less important than the skill, training, and experience of the operator. See a qualified orthodontic specialist, and perhaps seek 2nd opinion.

Yes, it is possible: even at age 17. Moreover, the Damon braces system has significant advantages over other traditional metal braces. Advantages are: reduced treatment time, need fewer adjustments and they do not require rubber bands.