Replacement of Control and Protection in Line Commutated Converter (LCC) HVDC Systems

There are over 150 HVDC systems now in operation around the world. Approximately more than 70 of these systems are 20 years and older. Earlier systems were realized with analog control systems. Some of those systems operated for over 30 years. Digital control systems were introduced in HVDC for a number of technical reasons. All systems that were installed in the last 30 years utilize digital controls. Digital controls typically have a much shorter life of 12- 15 years, with a Human Machine Interface (HMI) replacement about every 7 years. As a result, a number of systems are facing the challenge of replacing the digital control and protection systems. The control systems interact with other subsystems such as the valve base electronics (VBE), thyristor Gate Control Units, cooling controls as well as the measuring equipment. It is often challenging to decide which other related subsystems to replace (e.g. control and protection only or VBE and control and protection, or even to go further and include the cooling controls). This paper describes a process that can be followed to assist in making the decision to replace the control and protection systems, preparing the technical specification, bidding process, testing and commissioning. Even though the paper discusses Line Commutated Converters (LCC), the basic principles apply to Voltage Sourced Converters (VSC) as well}.