Life Extension of HVDC Systems

CIGRE Working Group WG B4.54 produces Technical Brochure 649 on “Guidelines for Life Extension of Existing HVDC Systems”.

Toward the end of an HVDC system’s design life, a decision needs to be made as to whether to refurbish or undertake a complete replacement of the HVDC system. Australian and New Zealand members, Malcolm Eccles, Les Brand and Predrag Milosevic have all contributed to a new CIGRE Technical Brochure 649, “Guidelines for Life Extension of Existing HVDC Systems”.

While New Zealand has older systems  and the work will be directly relevant, Australia is a relative newcomer in the application of HVDC technology, with the oldest system having been commissioned in 1999. Nevertheless, the work should also be useful for partial replacement or refurbishment programs, for example, the replacement of control and protection systems that are noted in the technical brochure as having a useful life of 12-15 years.

The brochure also provides an excellent reference for many key aspects of HVDC operation, maintenance and performance that should be useful to those involved in the development of operation and maintenance programs and strategies for HVDC and FACTs devices.

At least five years prior to the end of the HVDC system’s design life an assessment should be made to determine whether to undertake a life extension project or a complete replacement, which would include:

• A review of the past performance of the major HVDC equipment, systems and subsystems.
• Identification of future performance issues associated with the ageing of special components of the HVDC systems.
• Determination of the economic life of various components in the converter station. 

The review of past performance will include a review of operation and maintenance records and identification of operating problems, modifications performed, equipment failures and replacements, original quality and design issues, availability of spare or replacement parts, current state of spare parts inventory, technical skills of operations staff and the normal life of each item of equipment.

The high impact of the downtime required to perform a refurbishment project needs to be considered as a part of the overall project cost and in some cases this can lead to a complete replacement option, where a new converter station can be built with only a short switch over time, being preferred.

The increase in usable life of the HVDC system following a life extension project is likely to be (on average) within the range of 15 to 20 years whereas for a complete replacement project, this is likely to be 35 to 40 years.

Once the above assessment has been completed, criteria, weightings and a methodology should be developed for the technical and financial comparison of performing a life extension project versus a complete replacement project.

The key issues and drivers for the refurbishment or replacement of major items of equipment or sub-systems within a HVDC converter station are detailed in the technical brochure.

The development of the scope of the life extension project essentially requires the identification of those components that will be expected to fail or be uneconomical to operate for the period of life extension and target these for refurbishment or replacement.

The TOR for WG B4.54  can be downloaded here