Whenever any city, or the inhabitants thereof within, or contiguous to, the territory served by an electric transmission line operated by a public utility subject to the jurisdiction of the commission shall desire to obtain the service furnished by such public utility, the proper authorities of such city, or fifteen percent of the inhabitants thereof, may petition the commission for the extension of such transmission line and service to, into, or through such municipality. The commission thereupon shall enter into an investigation concerning the practicability and reasonableness of such proposed extension and service and the public convenience and necessity to be subserved thereby, and if, after notice and hearing, the commission finds that such extension of line and service is practicable and can be made reasonably, taking into consideration the amount of revenue likely to be derived therefrom and the prospect for a reasonable return to the utility upon the value of such extension, and further finds that public convenience and necessity will be subserved thereby, and that the city or territory contiguous thereto is not already receiving electric service from another public utility or electric cooperative corporation, the commission, by its order, shall require the extension of such line and service by such public utility for the purpose of serving such municipality and the inhabitants thereof upon condition that a franchise for such operation be granted to such public utility by the proper authorities of such municipality, and upon such other terms and conditions as may be just and reasonable. A certified copy of such order, when filed with the auditor of such municipality, shall have the same force and effect as an application by the utility for a franchise. The commission shall fix just and reasonable rates for such service and such reasonable rules and regulations as may be necessary pertaining thereto.