For the purpose of ascertaining the reasonableness and justice of the rates and charges of public utilities, or for any other purpose authorized by law, the commission may cause a hearing to be held in the manner prescribed in chapter 28-32 to determine the value of the property of any public utility actually used or useful for the convenience of the public, excluding therefrom the value of any franchise or right to own, operate, or enjoy the same in excess of the amount, exclusive of any tax or annual charge, actually paid to any political subdivision of the state as a consideration of such franchise or right, and exclusive of any value of the right by reason of a monopoly or merger.