Issue 10/12 http://www.siemens.com/FACTS HVDC/FACTS - Highlights http://www.siemens.com/HVDC

Trans Bay Cable Project

Efficient and reliable Power Supply for

In October/November 2010 Siemens Energy successfully tested and commissioned the world’s first HVDC PLUS transmission link between San Francisco’s City Center and a Bulk Power Substation near Pittsburg, California USA. It transmits up to 400 MW, at a DC voltage of +/- 200- kV. The customer Trans Bay Cable LLC confirmed substantial completion and commercial operation in November 2010.

Some years ago, the California Independent System Operator (CAISO), the entity responsible for overseeing the grid in much of the state, determined that the northern needed additional transmission capacity. The new transmission line was supposed to be energy-efficient and cost-effective. It should also reduce the need to build new power plants in the City of San Francisco, relieve transmission grid congestion in the East Bay, improve power supply safety and reliability, and minimize the risk of blackouts. Siemens’ solution was the world’s first application of its high-voltage direct current (HVDC) Power Link Universal System (PLUS) technology.

In September 2005, CAISO selected a project called Trans Bay Cable Project (TBC) to deliver power from a PG&E Bulk Power Substation in Pittsburg (CA) to the Potrero PG&E Substation in San Francisco. Trans Bay Cable LLC is a wholly-owned subsidiary of Steel River Infrastructure. The chosen transmission solution was an 88- kilometer (53-mile) submarine HVDC cable link connecting the two Siemens’ HVDC PLUS converter stations located in Pittsburg and San Francisco.

HVDC PLUS converters, based on Insulated Gate Bipolar Transistor (IGBT) technology, are the heart of the transmission system and perform the AC/DC conversion at the converter stations in Pittsburg and Potrero (San Francisco). The converters are installed and secured in standard industrial (metal) buildings providing electrical and environmental protection. Fig. 1: HVDC PLUS Converter: Trans Bay Cable Project, USA

Issue 10/12 HVDC/FACTS - Highlights

The HVDC system operates on the basis of voltage-sourced converter (VSC) technology, harmonic-free and therefore does not need the otherwise customary designed harmonic filter systems. This enables compact, space-saving overall system design.

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. It is also ideal for the connection of remote offshore platforms and wind farms to the onshore grid as well as for high-density areas such as San Francisco.

The Trans Bay Cable project was implemented by a consortium of Siemens Energy, Inc. and Prysmian Construction Services, Inc. As head of the consortium, Siemens was responsible for delivering the turnkey project based on the new HVDC PLUS technology. The order volume included the delivery of the complete converter stations as well as commissioning of the transmission system. Prysmian supplied and installed the submarine and land cables connecting the two HVDC converter stations and the AC grids via the PG&E substations.

In the heart of San Francisco, from the Pittsburg Converter Station to the Potrero Converter Station, the system transmits up to 400 MW, at a voltage of +/- 200 kilovolts (kV), providing all the desired benefits: meeting future electrical demand, reducing transmission losses and increasing system Fig. 2: Trans Bay Cable AC Transformers security.

Besides the technical merits, the Trans Bay project is an example of Siemens’ success with developer projects, managing to team up with the project developer at a very early stage of the project, saving the time and money for the developer to engage a technical consultant, assisting during project planning and environmental approval process. After a long and often challenging period for TBC, Michael J. Cyrus, CEO of Trans Bay Cable LLC, congratulates the whole team for their professionalism, focus and outright hard work. Especially about the Siemens team members Cyrus says: “…they have been extraordinarily professional and the best organization I have ever worked with.”

Siemens is therefore the clear market leader for such joint project developments globally, offering not only a better technical solution for electrical transmission, but also a superior project development support for the customer.