In addition to the powers conferred upon a city elsewhere in this chapter, any city operating a city electric utility on January 1, 2003, may enter into agreements with and acquire equity interests in independent transmission companies or similar independent transmission entities in which they are participating that are approved by the federal energy regulatory commission. The purpose of such equity investments shall be to mitigate expenses incurred by the city electric utility due to its procurement of electric transmission service or to otherwise facilitate investment in transmission facilities and shall not be for general city or city utility investment purposes.