Project: Southern Transmission System (STS) or Intermountain Power Project

Service: Condition Assessment

Client: Los Angeles Department of Water and Power (LADWP)

Country: USA

Year: 2015


Southern Transmission System (STS) comprises of HVdc converter stations at Intermountain and Adelanto and a ±500 kV 490 mile HVdc line. The original 1600 MW STS system was commissioned in 1986 and was later uprated to 1920 MW in 1989. The converter station is currently rated at 2,400 MW after an upgrade that took place in the Fall of 2010, which included the addition, replacement and modification of various ac/dc equipment, as well as replacement of the original control, protection, and monitoring system. The converter stations are based on the line commutated converter technology (LCC).

TGS Condition Assessment services:

  • Determine the remaining life expectancy and provide the study methodology to analyze all the major and related equipment at Intermountain and Adelanto Converter Stations
  • Analyze and propose a plan to replace major components of STS with new components with a life expectancy of at least 40 years, as an alternative to complete system replacement.  Provide life expectancy for the major pieces of equipment.
  • Analyze and propose a plan for replacement of STS, if needed, with new system with life expectancy of at least 40 years.
  • Provide cost estimate and schedule for STS related work to be done, in conjunction with IPP coal replacement project (to be completed by 2025)
  • Provide detailed analyses and description of the best technology available today and under development with an expected commercial release no later than 2020.
  • Evaluate Operating, Maintenance and Reliability improvement methods for Intermountain and Adelanto Converter Stations.


The purpose of this work was to identify the most cost effective way to ensure the function and reliability of the Southern Transmission System for 40 years starting in 2025. This would be accomplished by determining the remaining life expectancy of the major equipment starting from the year 2025, and recommending either a complete system replacement or replacement of specific parts of the Southern Transmission System.