Whey protein powder actually has a better protein value than soy, so if you're just adding it to foods and drinks, go for it. If you use the soy powder for something like baking, though, I don't believe that protein powder can be substituted.
I believe you are asking if protein powder can be substituted for baking powder and, as Jrahien said, protein powder can't be substituted for baking powder.
Whey protein powder actually has a better protein value than soy, so if you're just adding it to foods and drinks, go for it. If you use the soy powder for something like baking, though, I don't believe that protein powder can be substituted.