Back Forty


EPRI Journal looks back 40 years at the electricity sector and research

HVDC Emerges as
an “Attractive Complement”
to AC

The June 1978 issue of EPRI Journal reported that “high-voltage direct current (HVDC) transmission is emerging today as an attractive complement to AC [alternating current] power systems,” driven by advances in electronics, falling costs, and improving reliability. The article pointed to HVDC’s potential role as an interconnect to buffer and control power flow between AC systems in adjacent regions and countries.

The authors added that the high cost of converter stations (devices that convert electricity back and forth between DC and AC) was a significant barrier to widespread adoption of HVDC. “Based on present converter station costs, overhead HVDC transmission generally becomes attractive at lengths in excess of 400-500 miles,” the article said.

Today, while high converter costs remain a challenge, HVDC typically becomes cost-effective over 300 miles. In recent years, several factors have increased demand for HVDC. It’s well-suited for the integration of large-scale solar and wind generation, it can help reduce the spread of large-scale blackouts, and the capacity of existing AC lines can be increased by converting to DC.