As a consequence of the present-day decarbonisation goals, the number of renewable energy sources (RES) connected to the transmission and distribution grids has been continuously growing over the recent years and will continue to grow. This increasing amount of RES, however, places several changes to the design, planning, operation and regulation of the electric grids.

One important aspect to consider with wind and solar PV RES is that these sources are connected to the grid via power electronics inverters, whereas the conventional sources (thermal and hydro) use synchronous generators.

This new situation may cause problems to the protection systems, since the present protection algorithms have been designed, tested and applied in grids with predominance of synchronous generators. Specifically, the lower current contribution to faults and the consequences in the seen apparent impedance are aspects that might jeopardize the performance of the protection functions.

Having this in mind, R&D Nester undertook the Prot4HiRES project, studying the impact of the renewable energy sources on the protection systems for transmission lines. The scope of the research were the overcurrent, distance and line differential protection functions.

To perform this study, a simulation model of a Type IV wind turbine was developed and integrated in a zone of the Portuguese transmission grid with high penetration of RES. The Type IV is a full converter, that is also suitable to model de DC/AC conversion for the solar PV. Then, faults (short-circuits) were simulated in several points of the grid to produce curves of the currents and apparent impedance seen at the ends of the transmission lines.

The post mortem analysis of these curves (renewable sources against synchronous generators) allowed to envisage the behaviour of the studied protection functions. For instance, it was observed that the short-circuit current supplied by the wind and solar generators was about a half of that supplied by a synchronous generator.

It was concluded that the differential and distance functions are not prone to be affected by the penetration of RES, whereas the overcurrent protection shall be reparametrized.

The project results have been published in three papers, presented at conferences:

• "Assessment of potential problems on the behaviour of protection functions due to the massive integration of wind sources in transmission networks" (22nd Wind & Solar Integration Workshop)

• "Methodology for the assessment of the behaviour of protection functions in transmission grids with high penetration of renewable sources" (PEPSC 2023 - Power Electronics and Power System Conference)

• "Behaviour analysis of transmission line protection functions in grids with high penetration of renewable sources' (Developments in Power System Protection conference).

For more information:

Prot4HiRES Project @ R&D Nester website