Any municipal corporation having a population of not more than two hundred thousand or less than seventy-five thousand and which has issued or which may issue bonds secured by a mortgage on the lands, buildings, machinery and equipment of any revenue-producing public utility, and by a pledge of the income and revenues of such public utility, or secured by either such mortgage or such pledge, for the purpose of refunding or refinancing any of such bonds so issued and outstanding, may, without submitting the matter to a vote of the electors of the municipal corporation, issue refunding bonds of the municipality secured exclusively, principal and interest, by a mortgage on the lands, buildings, machinery and equipment of such public utility and by a pledge of the income and revenues of such public utility, or secured either by such mortgage or by such pledge of said revenues, as the governing authority of the municipality may determine.