Both DC and AC Needed

Feb. 17, 2015

AC and DC are both important in high-voltage and ultra-high-voltage transmission networks.

HVDC has a very important role to play in transmission networks and is an economical viable option at ultra-high voltages (800 kV) in several regions in the USA. These DC links need to operate as hybrid HVAC and HVDC networks for integrating and controlling remote renewable resources, and they are well established to interconnect asynchronous areas. At the relative low capacity factors of wind (40%) and solar PV (20%) power production, HVAC networks are not utilized at an economic level for integrating these intermittent resources to the load centers, especially over long distances or with submarine cables from a relative weak remote AC network. HVDC is clearly the better option, especially the newer voltage source converter technologies. For no or very limited additional cost, two STATCOMs are added on both sides of the HVDC link. These STATCOMs are excellent to interconnect the remote power from relative weak networks to the load centers.

Multi-terminal HVDC networks and hybrid HVDC imbedded into HVAC networks are already commercialized and implemented in Europe and will provide the additional capacity to the transmission network in the USA. Furthermore these hybrid networks will at the same time increase the transmission capacity with reduced right-of-way (ROW) requirements. A HVDC link can transmit three to five times the power in the same ROW when compared to HVAC networks. At the same time, financing these new HVDC links is easier than traditional HVAC lines under merchant line agreements, since full control of the power flows can be guaranteed between remote resource and load center.

It is not a question of AC or DC but both, especially in the high-voltage and ultra-high-voltage transmission networks.

About the Author

Johan Enslin | Director, Energy Production and Infrastructure Center

Johan H. Enslin, PhD, is the director for the Energy Production and Infrastructure Center (EPIC) and Duke Energy Distinguished Chair, Power System Engineering at the University of North Carolina at Charlotte.

Enslin has combined a 33-year career with leadership in industry and universities in the U.S., Europe and South Africa. He served as an executive and consultant for private business operations and as a professor in electrical and electronic engineering. Enslin initiated and managed renewable energy groups, executing multiple complex projects for U.S. and international industry in power system planning, power electronics and the integration of large-scale solar and wind power to the grid. Over the course of his career, Enslin has worked for more than 80 U.S., European, Asian and African utilities, governments and industries.

Enslin came to EPIC in 2011 after serving as chief technology officer for Petra Solar, a smart grid and renewable energy technology company based in New Jersey. In previous roles, Enslin also served as vice president for Quanta Technology, and for Alpha Technologies Group, where he was general manager for the company’s Renewable Energy Division. Enslin was earlier vice president of Power System Planning at KEMA Inc., with lead responsibility for establishing a new medium-voltage smart grid and power electronics research, development and testing laboratory in Arnhem, The Netherlands.

In South Africa, Enslin worked at the utility ESKOM, as well as the Universities of Stellenbosch and Pretoria as department chair and full professor. He is a founding member of the board for E4 Carolinas, a non-profit dedicated to the development of the Charlotte region as a hub of the global energy industry. He is also on the Board of Envision Charlotte and on several advisory boards, including FREEDM at NC State University, VICTER at University of Arkansas.

Enslin has authored or co-authored more than 280 technical journal and conference papers for IEEE and other organizations, and has written several chapters in scientific books. A lifelong leader in IEEE and CIGRÉ working groups and standards committees, Enslin holds more than 21 provisional and final patents. He received the 2014 Charlotte Business Journal Energy Leadership Award. He is a registered professional engineer in South Africa, Fellow of the SAIEE and Fellow of the IEEE.