Selecting the excitation system for the additional turbine generator at the Port Wentworth pulp mill

Weyerhaeuser Company owns a market softwood pulp manufacturing facility at Port Wentworth, GA and the company was looking for a way to reduce manufacturing costs. It was determined that if a used steam turbine generator could be installed at the plant, this would be a viable way to reduce manufacturing costs. The unit would displace purchased electrical energy with "in house" generation during times that the plant could produce the energy for less than it would be charged by the electric utility. During these times, the unit would be operated in a mode such that the electrical energy flowing into the plant through the utility intertie would be kept to a minimum (tie line control mode). During other times of the year, providing that it was economical, the plant could sell electrical energy to the utility. Once the unit was purchased and the degree of reconditioning and repairs to the turbine and the generator had been determined, the next major decision was which of the auxiliary systems could be re-used. This paper covers the process involved in evaluating whether or not to reuse the generator\´s original compound excitation system and if replaced, the type of excitation system that should be installed, compound or potential bus fed type. Discussed are the issues encountered during the evaluation process, the expectations desired, the decisions made and the outcome achieved as a result of the final decision to replace the existing compound excitation system with a potential bus fed excitation system.