Life extension issues for HVDC control systems

Digital based HVDC control and protection system are a common place reality. Experience since the initial installations of these digital control systems indicate clearly that at least one control system replacement can be expected in any system prior to the retirement of the entire system. Control systems have typically fifteen to twenty-five (15-25) year life expectancy. Thyristor valves, converter transformers, high voltage circuit breakers, have a life expectancy of thirty to forty years, while the transmission line life expectancy may be seventy-five to one hundred years. A relevant question that can be asked is; "What can be specified and designed into the HVDC protection and control system, at the project conception stages that would facilitate a control system replacement project in the future"? Controls systems for HVDC systems will be replaced. While control systems are estimated at 8-10% of the cost of a green field HVDC system, control replacement costs are significant larger percentages. By understanding the issues associated with control replacement, there is opportunity at the start of an HVdc project to consider control replacement in the future. This discussion paper reviews HVDC control life expectancy issues and proposes steps the user HVDC can take to increase the life of their control system.