Comparison of HVAC and HVDC technologies

Alternating and direct current (AC and DC) solutions are the two main options to upgrade the transmission system. However, in the context of grid reinforcements, one needs to consider more options than more than only AC and DC, but also properties such as overhead or underground, the technology used, and the additional features, both technical and nontechnical. DC transmission is inherently suited to control the power flow through a line. When using voltage source converter (VSC) high-voltage DC (HVDC), the reactive power at both terminals can be controlled dynamically. In the case of AC transmission, power flow control is only possible with usage of FACTS devices and phase-shifting transformers. This chapter gives a cost comparison between HVAC and HVDC transmission solutions. The breakeven length between HVAC and HVDC transmission depends on the transmission system length and the rating of the transmission system.