A impingement cooling system for heavy duty turbines that includes a manifold affixed to a casing of the heavy-duty turbine, wherein the manifold includes a plurality of impingement holes in the surface of the manifold and a blower that provides air flow across the plurality of impingement holes of the manifold to cool the casing of the heavy-duty turbine to control the clearance between a tip of a turbine blade and a shroud of the heavy-duty turbine.