Análise dos impactos da alta inserção de geração distribuída fotovoltaica na proteção de sobrecorrente temporizada

Abstract

Historically the world’s electric energy generation model is based on large power plants connected to the grid. A few years ago new ideas for the power generation model have emerged as the concept of generating energy near to consumers, called distributed generation (DG). It was noted that using renewable sources such as DG could bring advantages beyond environmental ones. Photovoltaic distributed generation (PVDG) readily pleased consumers worldwide due to its quiet technology, the abundance of the source and ease of installation. The photovoltaic technology represents more than 99% of the consumer units with DG installed in Brazil. Despite the advantages, it is known that the insertion of new generating sources into a grid that is designed to operate unilaterally, can modify the power flow.Thus, knowing that the number of DG in the power system is a rising fact, it is fundamental to study the quantitative and qualitative impacts that these can cause in the grid, especially in the already installed and parametrized protection devices (PD). Very common in distribution, the time-delay overcurrent PDs (function 51) are used to electrically protect the feeders against faults and overload, isolating the faulty branch. For correct adjustment of this function, it is necessary to know the rated current at the point where the PD is located. Since high DG penetration can modify operational current values, the protection that was correctly set for a non-DG scenario may not conform to the new system parameters, with the PVDG. Improperly adjusted overcurrent protection may not work for a short-circuit or overloads.This work evaluates, therefore, different scenarios of a feeder under steady-state operation, through simulations, with high penetration of PVDG. The variability of the current at the points where exists PVDG was analyzed focusing only on the values of the operating current, reaching, in extreme cases, a reduction of more than 80% of its load value. The results indicate that changes in time-delay overcurrent protection towards a massive insertion of GD can be fundamental to guarantee the sensitivity of the devices and a correct performance for overload.