Uses such as high-voltage transmission lines, towers and substations, sewage pumping stations, wells and sewage treatment plants, but no service or storage yards, may be permitted. The provisions of this section shall not apply to any existing or proposed building, structure or use or extensions thereof used or to be used by public utilities in furnishing service if, upon petition of the public utility, the Public Utility Commission shall, after public hearing, decide that the present or proposed location in question is reasonably necessary for the convenience and welfare of the public.