Arcane Surge not working?

I have a stormweaver sorceress and 1'180 maximum mana. With Arcane Surge and Force of Will, that should result in having 78% increased cast speed. I don't feel that? When i cast spells i have the same speed that i have when i right click Arcane Surge to remove the effect. The mana regeneration is definitely there. But i don't think the cast speed is working? Or am i completely missunderstanding how cast speed works? Because in my brain, it should make my cast animation faster