LUSAKA (Reuters) - Zambia plans to start building two power generation plants that will add 550 megawatts (MW) of electricity to its national grid once completed, Finance Minister Felix Mutati said on Friday. Mutati said in a budget speech one investor planned to build a 300 MW thermal power station in southern Zambia and another a 250 MW hydropower project in northern Zambia is starting next year. Zambia and Zimbabwe have started preliminary financing arrangements for the joint 2,400 MW Batoka hydropower project, he added. (Reporting by Chris Mfula; Editing by Ed Stoddard)