Cogeneration power plants by gas turbines in industrial installations: connection to the internal electrical system, interface with external grid, protection schemes

Cogeneration power plants, using gas turbines operating in combined cycle, are today spreading in industries, for the production of electrical energy and steam. This trend is due to several reasons, i.e. more efficient use of fuel, the availability of waste fuels as a consequence of production processes, the requirements of a quite reliable source of electrical energy for vital loads and the opportunity of selling excess energy to external Board at profitable prices. The selection of the most convenient connection point of the power plant to the electrical distribution network of the industrial installation requires a detailed analysis of the existing power schemes, in order to ensure maximum reliability and availability to critical loads, flexibility with respect to load management and to keep fault currents within the sizing of existing apparatus. Attention should be paid to the problem of interface with the external grid: the prescriptions of the Electrical Authority Board shall be complied with as well as national or international recommendations or standards, and in the meantime it is mandatory to satisfy all the requirements of the production process. The authors illustrate several problems to be faced in the design of cogeneration power plants inside different industrial installations