In the event that the City and County of San Francisco shall elect at any time to take over and operate as a public utility the business of supplying gas or electricity for heating, lighting, power and other purposes to its inhabitants, and should acquire by condemnation proceedings, or otherwise, the plant and distributing system of any grantee hereunder, no value whatever shall be attached, in said proceedings, to the rights and privileges conferred by this Article, nor shall any value be attached thereto at any time for rate fixing purposes.