Extending Their Lifetimes : Keeping HVdc and FACTS Installations in Service Longer

High-Voltage (HV) DC transmission and flexible ac transmission systems (FACTSs) have been in operation for over 50 years, and in many cases these installations have become an indispensable part of many power networks around the world. With a design life of typically 30 years, some of the original installations have already been, or are presently being, partially refurbished or replaced, while others are in the planning stages for some method of life extension. The strategy adopted for extending the life of an HVdc system depends on many factors, both commercial and technical, and ranges from refurbishment through the replacement of a few components, to replacement of the complete link. Individual installations have their own specific issues, such as increasing levels of maintenance, obsolescence of particular components, or increasing failure and outage rates, which all lead to a real or perceived risk to availability in the near future.