Transient Over-voltage Studies of ±800kV, 6000 MW LCC HVDC connected with RE source of Solar and Wind

(RE) sources such as solar and wind, driven by environmental concerns and decarbonization targets. This transition has led to a significant rise in Inverter-Based Resources (IBRs), which, unlike conventional synchronous generators, contribute limited inertia and fault current to the grid. The resulting challenges in system stability, power quality, and grid reliability call for robust transmission solutions.

Though, VSC HVDC Systems have become more popular to evacuate the power from RE sources, still, LCC HVDC are proven and economic solution for bulk power transfer of the order of 6000 MW or more. In country like India with larger geographical area, Line

Commutated Converter (LCC) based High Voltage Direct Current (HVDC) systems-especially at ultra-high voltage levels such as ±800 kV and capacities up to 6000 MW-offer a technically and economically viable means to evacuate large-scale RE power over long distances.

With the inclusion of ultra-high capacity LCC HVDC systems to transmit bulk renewable energy, the study of transient overvoltages becomes critical. In ±800 kV, 6000 MW LCCHVDC links fed from large wind/solar farms, transient overvoltages can result from many switching and fault events: for example, switching or reclosing of converter transformers

(where remanent flux can drive core saturation and heavy inrush), of AC filters or shunt capacitor/reactor banks, and of AC/DC lines (exciting resonant oscillations); AC- or DC-side faults and control/equipment anomalies (e.g. commutation failures from grid disturbances, valve misfires or Valve hall faults causing DC-link oscillations); and limited arrester or damping action – all occurring in the context of a weak, low-inertia AC network under high renewable (wind/solar) penetration. This paper presents a detailed study of transient overvoltages under various critical operating scenarios in a ±800 kV, 6000 MW LCC HVDC system integrated with renewable energy sources. It explores multiple system configurations-including Bipole, Monopole with

PMR/DMR, and Hybrid (Bipole + Monopole)-and examines the effects with severe preconditions. Special focus is given to fault cases on both the AC and DC sides, particularly under weak-grid conditions with high renewable penetration. The study evaluates the impact of these disturbances on overvoltage levels and provides insights into the dimensioning and coordination of surge arresters on both DC & AC side. The findings aim to support robust insulation coordination and system protection design in future HVDC-RE integrated networks.