line conductor. History The first phase of the scheme, completed in May 1970, used only mercury-arc valves in the converters. The valves were series connected in three six-pulse valve bridges for each pole. The blocking voltage of the valves was 133 kV with a maximum current of 1,800 amperes, for a transmission rating of 1,440 MW with a symmetrical voltage of 400 kV with respect to earth. Each converter station housed six mercury arc valves groups, consisting each of seven valves, for a total of 42 valves in each converter. The valves had a width of , a height of and a length of and weighed . Each valve contained mercury, with a weight of . 1972: After the Sylmar earthquake, the Sylmar Converter Station had to be reconstructed due to extensive damage. 1982: The power rating of the mercury arc valve rectifiers was raised by various improvements to 1,600 MW. 1984: The transmission voltage was pushed to 500 kV and the transmission power was increased to 2,000 MW by adding one six-pulse thyristor valve group rated at 100 kV to each pole. 1989: A further increase of the transmission power to 3,100 MW took place by installing a 1,100 MW parallel connected thyristor converter in Celilo and Sylmar. This upgrade was called the Pacific Intertie Expansion. 1993: One pole of the Pacific Intertie Expansion converter station at Sylmar was completely destroyed by fire. The converter was replaced in 1994-1995 by Siemens. 1994: After the Northridge earthquake, the Sylmar Converter Station had to be reconstructed due to extensive damage. 2004: The Sylmar East station situated at was upgraded from 1,100 MW to 3,100 MW. The controls and older converters, including the mercury arc valves, were completely replaced by a single pair of 3,100 MW 12-pulse converters built by ABB. In parallel with this project, the six-pulse mercury arc valves at the Celilo Converter Station were replaced with Siemens light-triggered thyristors in compliance with their Modified Age Replacement Policy (MARP). 2005: The Sylmar East station was rededicated as the Sylmar Converter Station. 2014-2015: The Celilo converter substation was upgraded in a similar manner to the Sylmar East upgrade. The North converter was upgraded from 1,100 MW to 3,100 MW. The new converter was built by the ABB. The new converter connects at 500kV AC instead of the previous 230kV AC connection. After completion, all of the equipment for the south converter