Resumo:
This dissertation presents a comprehensive analysis of islanding protection strategies implemented
in industrial power systems with on-site generation, focusing on a petroleum
refining unit. The study addresses islanding detection techniques, connection protection
schemes, and load shedding systems, aiming to ensure the continuity and safety of the
power supply.
The research is centered on two pillars that bring substantial benefits to the production
process. The first pillar is islanding. If islanding protection is properly tuned, its operation
can be delayed as much as possible to avoid unnecessary disconnection and the associated
load shedding. The second pillar is load rejection and shedding. In the event of an islanding
situation, if the load rejection and shedding scheme is able to maintain the balance between
loads and generation in the power system, a blackout can be avoided.
A case study, using a real system belonging to a major Brazilian oil refinery, was used
in the development of the research. The models used to represent the refinery’s electrical
system were described and validated through real tests. Records of actual disturbances
in the utility power system were used to support the analyses. Finally, simulations were
performed in ANATEM to estimate the system behavior under typical disturbances and
to verify the adequacy of the islanding protection and load shedding settings implemented
for the plant.
The results show that the implemented islanding protection provides appropriate sensitivity,
ensuring stability and protection of the industrial electrical system under disturbance
scenarios in the grid. The load rejection and shedding system also showed satisfactory
performance by successfully restoring the balance between load and generation after the
islanding process. The study also identified improvement opportunities for these systems.
For the islanding protection, a setting change was identified that allows for maximizing
the delay before islanding occurs, thus avoiding unnecessary disconnections. For the load
shedding system, the installation of a backup scheme was recommended in case the main
scheme fails, thereby increasing system reliability.
