The evacuation of bulk electrical power over long distances can be done mainly by high voltage alternating current (HVAC) transmission systems. However, where there are large water bodies and long distance between the generation source and demand centres like most islands in European countries, high voltage direct current (HVDC) power transmission is gaining more traction and is proving to be a sustainable solution. Regarding the distance between HVDC and HVAC, the break-even threshold in terms of cost is approximately 600 - 800 km for overhead line systems (OHLs) and 40 - 70 km for systems with cables. The global thirsty to harness the renewable energy sources is diverting the attention towards efficiency and flexibility of power transmission. Traditional HVAC systems are being quickly replaced with HVDC systems in various parts of the world. This report highlights the significance of modern HVDC power transmission networks, topologies, converter varieties, contrasts, and main equipment associated with HVDC systems. Through the use of HVDC converters, renewable energy sources (RES), such as offshore, onshore, coastal wind farms and photovoltaic power plant can be linked to the current existing AC grids. Although the difficulties associated with the upcoming DC grids are also highlighted, the views on multi-terminal HVDC systems and DC grids are also outlined.
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