Commissioning VSC HVDC schemes

WG B4.63 “Commissioning of VSC HVDC Schemes”, convened by Les Brand from Australia.

Voltage Source Converter (VSC) technology has emerged as a commercially viable alternative to Line Commutated Converter (LCC) technology for certain applications of HVDC power transmission. With the first commercial VSC projects commissioned in the late 1990s, there is over a decade and a half of project and operational experience with this technology. VSC has become the preferred choice of technology for specific applications, including low power transfer applications, the connection of weak networks, offshore wind farm connections and d.c. grid developments.

Commissioning is the final stage of an HVDC project. It allows the HVDC supplier to verify and demonstrate the suitability of the installed equipment, the functional completeness of the system and compliance with the requirements of the relevant contracts and specifications. Commissioning also allows adjustments and optimization to the HVDC system to be made and allows the owners, developers and/or end-user of the HVDC system to witness and be satisfied that the project and operational requirements have been demonstrated.

The figure below describes the overall commissioning process.

• Factory tests - the verification of internal connections within the control cabinets and of the software performed in the factory.
• Pre-commissioning – the equipment tests which are the electrical and mechanical tests and simple functional tests performed on equipment or plant.
• Subsystem tests – the proving of interconnection and functioning of all individual items of equipment within a functional group (or “subsystem”) and verification that these items operate and interact correctly.
• System tests - the start-up and testing of the complete HVDC System in operation starting with the initial energisation of the equipment and ending with the total system in operation and at full active and reactive power transfer.
• Trial operation - a period of trial operation to take place following the completion of the system tests.

Subsystem testing will typically comprise the testing of cabling systems, a.c. protections and interlocking, main circuit equipment, VSC valves, control and protection systems and other auxiliary systems (including valve cooling, auxiliary power, fire systems, air handling systems and ground electrode systems).

System testing is typically comprised of the following key testing activities:

• High voltage energization.
• Terminal tests - also referred to as STATCOM tests, these tests are performed on the converter terminal, disconnected from the d.c. cable/line.
• Transmission system tests - the verification of active power control in conjunction with the reactive power capability of each converter terminal.
• Operation and integration tests.
• Power quality and interference tests.
• A.c. network and remote generation interaction tests.

Some key challenges associated with the commissioning of VSC HVDC systems in today’s environment include selecting a subset of the factory testing program to be repeated on site, commissioning in a market environment and limitations to active and reactive power levels during commissioning. Certain applications often associated with VSC transmission will also have their own challenges, including off-shore wind power projects, multi-terminal systems, offshore platform loads and d.c. lines with parallel a.c. power lines.

The full technical brochure providing guidelines on the testing and commissioning of VSC HVDC schemes, is expected to be published before mid-2017.