Capacitive Current Breaking Issues in Large Res Power Plant Cable Networks

The fast growth of exploitation of renewable energy sources (RES), such as solar photovoltaic (PV) and wind farms (WF), has led to the installations over 100 MW power plants (PPs), connected to the high voltage (HV) transmission grid via dedicated medium voltage (MV) radial cable networks. In Italy, the MV voltage levels of these networks has increased from 20 kV to 30 kV, up to 36 kV introduced for RES - PPs networks up to 100 MW, classifying them within the 36-150 kV HV networks. These cable lines, often spanning tens of kilometers, present challenges due to their capacitive nature. Under normal no-load conditions, capacitive currents must remain within the MV circuit breaker's interruption capability but also in case of single-phase-to-earth faults $(1-\phi$-to-Gr). In these conditions the increase of the capacitive currents in the healthy phases may overcome circuit breaker (CB) ratings. This paper examines a 132/30 kV system to quantify capacitive currents during no-load and $\mathbf{1}-\phi$-to-Gr conditions, referencing IEC standards. It also discusses mitigation countermeasures, such as using higher-rated switchgear or installing shunt reactors (SRs). The analysis focuses on how SRs, especially with grounded neutrals, modify steady-state currents and transient CB recovery voltages (TRVs). While SRs reduce 1- $\phi$-to-Gr-related capacitive component current, they can increase TRVs after fault clearing, requiring careful assessment of switchgear dielectric strength.