Minn. Stat. § 452.13

Nothing in sections 452.08 to 452.13 contained shall be construed to authorize any city of the first class to make any grants or to lease any public utility for a period exceeding 20 years from the making of the grant or lease; provided, that when a right to maintain and operate a public utility for a period not exceeding 20 years is contained in a mortgage or deed of trust to secure any of the certificates (and no such right shall be implied), the period shall commence as provided in section 452.09 .