Test operations began in January and are expected to last up to two months.
Tucurui owners, Eletronorte - part of federal power holding company Eletrobras, is due to complete the second phase by August, boosting capacity to 8370MW.
The expansion programme began in 1998 with the first unit commencing operations in March 2003. Construction of the second phase will add 4125MW to the 4245MW installed in phase I.
