Installation of an integrated turbine-generator control system for a pulp mill

A British Columbian pulp mill had experienced the "spiral of death" many times when the turbine-generator controls were unable to survive the loss of utility tie-line connections. The mill has two high efficiency rotary turbine-generator units rated 32.2 MVA each and a heat sink capable of generating 47 MW, approximately 87% of the mill power needs, though only 44 MW was being produced. The mill believed that with a load rejection strategy the mill had the potential to continue operation after the loss of a utility tie. In order to ride through the loss of the utility and to fully utilize the process heat sink, the mill needed to replace the 1960s era turbine-generator control system supplied by the turbine-generator OEM. A triple modular redundant control system for each unit was installed. These systems integrate turbine governor controls and generator excitation control system in a single digital control. The systems are connected in order to jointly coordinate dispatch of real and reactive power demands and achieve load control for the mill. In a staged test, the mill was able to survive the loss of a utility tie-line, and has increased total generation. The new system completely automates the startup, loading and synchronization of both generators.