A franchise which is not revocable at the will of the Council shall not be granted or become operative until it has been referred to and approved by three-fifths of the electors in an election. All irrevocable public utility franchises and all renewals, extensions and amendments thereof shall be granted only by ordinance. The Council shall not refer such an ordinance to the electorate until the application has been on file for 30 days and until a public hearing on it has been held. The ordinance shall not be submitted to an election to be held less than 30 days after the grantee named therein has filed with the Clerk-Treasurer an unconditional acceptance of all the terms of the franchise and unless the expense of holding the election has been paid to the Clerk-Treasurer by the grantee. The City shall not grant an exclusive franchise or a franchise for a term longer than 30 years.