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Knowing These 3 Fault-Clearing Strategies Will Make Your HVDC Transmission Reliable

Offshore wind power generation plays a critical role in the energy transition in Europe. High voltage direct current (HVDC) is the maturing way to transmit offshore energy to the land. Yet, it is prone to faults. So, what are fault-clearing strategies known today?

Differing reasons for the application

The usage of HVDC has 4 primary objectives:

· Move more power further.

· Integrate renewables.

· Interconnect grids.

· Improve network performance.

Rapid technical progress in voltage source converter-type HVDC (VSC HVDC) has brought economic justification.

From 2020 to 2025 HVDC market is predicted to expand by 11% compound average growth rate (CAGR), more than three times faster than the predicted growth of global GDP.

 

Cumulative New Capacity of VSC HVDC. Credit: ABB Hitachi.

Cumulative New Capacity of VSC HVDC. Credit: ABB Hitachi.

 

Different nations use this technology for various reasons.

Many countries like the UK, Denmark, Japan, Philippines are the collection of hundreds and thousands of islands. The world is fractured. HVDC solves power supplies challenge among the fractured territories.

China, India, and Brazil use ultrahigh voltage direct current (UVHVDC) at 800 kW to meet increasing load demands. Whereas Europe uses it for interconnections and to integrate renewable energy such as offshore wind.

The need for protection

The opportunities go along with challenges. HVDC carries a set of faults that may cause you a headache.

 

The strategy you adopt to clear and recover from fault will define the impact of the fault on the system.

 

The Western Link HVDC with a length of 387 km brings renewable energy from Scotland to Wales and England. On the 20th of January 2020, the subsea cable went down and remained offline till the 8th of February 2020. The incident resulted in National Grid ESO paying £31 million by Balancing Mechanism payments for wind farm operators to curtail output. Prysmian, the cable supplier, investigated and localized the issue in the Southern land cable section.

Yes, reliability is crucial.

3 main purposes of protecting the HVDC grid:

  1. Ensuring human safety.

  2. Minimize fault impact on the grid.

  3. Minimize stress to components.

And when you don't have a proper protection system in place the 2 critical situations caused by HVDC faults that may cause large blackout:

· Voltage drops sharply.

· Current increases rapidly.

Fault-clearing strategies

The strategy you adopt to clear and recover from fault will define the impact of the fault on the system.

You can consider the following 3 alternative strategies:

· Non-selective strategy: shutting down the entire system once a fault is detected.

· Selective strategy: disconnecting only faulty zones by dividing the system into different protection zones.

· Partially-selective process: the combination of the previous ones.

 

Fault-clearing strategies. Credit: Frontiers in Energy Research.

Fault-clearing strategies. Credit: Frontiers in Energy Research.

Each strategy has distinct features that you need to consider carefully. For example, a non-selective strategy requires the longest fault-clearing time - 60 ms.

P.S.:

The future of bulk long-distance power transmission looks HVDC due to recent technological advancements. Does it mean that Edison has won ultimately the war of the currents against Tesla?

 

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