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Customer Success Story
Rapid City

The 200 MW Rapid City back-to-back HVDC tie in South Dakota is owned by Basin Electric Power Cooperative and interconnects power systems in the eastern and western U.S.

Low short circuit power in the 230 kV networks made Hitachi Energy's Capacitor Commutated Converter (CCC) concept the ideal choice for this back-to-back station.

CCC technology has been selected for a number of similar projects because of its suitability for applications in relatively weak network locations. The modular converter design enables shorter project execution times, while CCC technology allows higher converter ratings relative to system strength at the point of connection, which enhances power transfer capability between power networks with minimal need for new transmission lines.

The Rapid City DC Tie consists of two parallel HVDC CCC power blocks each nominally rated at 100 MW. Together the two power blocks are rated to deliver 200 MW in either direction to the receiving 230 kV network.

The thyristor valves for each 12-pulse bridge are housed in a valve enclosure and transported to the site as factory tested units. The enclosures are placed together at the site and connected to the commutation capacitors on the AC side and to the smoothing reactor on the DC side.

Interconnected power grids using a high-voltage direct current (HVDC) back-to-back systems are able to transfer power from one grid to another during emergencies, or exchange energy between the systems. An HVDC interconnection controls power flow, and enhances both voltage and frequency stability, which significantly increase grid reliability, and helps to prevent blackouts.

Main data
Commissioning year: 2003
Configuration: Back-to-back
Power transmitted: 200 MW
Application: Interconnecting grids