Duration in PowerBi

Hi All

Im struggling to impliment duration in my reports at the moment in a way that can be agregated up. 

AHT and Time is an important metric in my company and at the momment it seems prohibativly difficult to get any time of time aggregation to work. All we would like to do is sum 01:00:00 and 01:00:00 in a table and get 02:00:00.

At the moment this is a very simple process in other products and I would like to understand if im missing somthing in PowerBI as at the moment I cannot get it to work even after reading all the documentation.