An 88-km (53-mile) undersea high voltage direct current (HVDC) transmission link will be constructed by Siemens Power Transmission and Distribution (PTD) between San Francisco ìs City Center electrical power grid and a substation near Pittsburg, CA. The order was placed by Trans Bay Cable LLC, based in San Francisco, and a wholly-owned subsidiary of the project developer Babcock & Brown. Siemens ì share of the total order volume amounts to more than USD 150 million. From March 2010, the HVDC Plus system will transmit up to 400 MW at a DC voltage of +/- 200-kV and is the first order for Siemens using its innovative HVDC Plus technology. The main advantages of the new HVDC Plus link are the increased network security and reliability due to network upgrade and reduced system losses. 

Today, the major electrical supply for the City of San Francisco comes from the south side of the San Francisco peninsula. The city relies mainly on AC grids which run along the lower part of the bay. With the new HVDC Plus interconnection link power will flow directly into the center of San Francisco. In addition to enabling a straight path for energy from the East Bay, the Trans Bay project will decrease the overall transmission grid congestion in that area, increase overall security and reliability of the electrical system.

After commissioning in 2010, the HVDC transmission line will help to meet the City of San Francisco’s future electrical demand and is designed to be an energy-efficient, cost-effective solution addressing San Francisco’s need for additional transmission capacity. Furthermore, it will reduce the need to build additional new power plants in the City of San Francisco, decrease transmission grid congestion in the East Bay and it will increase the overall security and reliability of the electrical system.

The project will be implemented by a consortium of Siemens and Milan-based Prysmian Energy Cables and Systems. As consortium leader, Siemens was awarded a turnkey contract that comprises the converter stations for the HVDC Plus system, including engineering, design, manufacturing, installation and commissioning of the transmission system. The company will deliver all high voltage components including transformers, converter submodules, converter reactors and breakers and is responsible for the control and protection, civil works and building systems.

Furthermore Siemens fulfills all major requirements, which have to be considered for the electrical components as well as for all buildings for a highly seismic zone like San Francisco. The HVDC Plus solution utilizes a minimum amount of space – crucial for converter sites in urban areas – and minimizes environmental impact such as visual implication, audible noise and transport during construction. The consortium partner Prysmian will provide the submarine power cables that will be installed in the San Francisco Bay.