Nebraska Power Review Board authorization shall not be required for the following:

(1) Construction of microwave facilities to be completed in a reasonable time where the district has, prior to April 24, 1978, entered into binding contractual obligations with respect to such facilities;

(2) Extensions of fifty miles or less of any single portion of a microwave system if such portion was in existence on or before April 24, 1978; or

(3) The addition of new equipment to modernize or upgrade but not to extend microwave facilities.