Research Result Summaries

Latest results from ongoing tasks

HVDC

Over the last two decades, EPRI developed a comprehensive reference book covering many aspects of HVDC technology and it is being updated annually with the latest information. The 2023 edition of the EPRI HVDC Transmission Reference Book consists of the following 30 chapters:

  1. Introduction
  2. Overview of HVDC Transmission
  3. Analysis of Converter Operation
  4. ConfigurationsofHVDCTransmissionSystems
  5. Components of an HVDC Transmission System
  6. Planning and System Design
  7. Control and Protection
  8. Reactive Power
  9. AC¬DC Interactions
  10. Interference Effects from Converter Operation
  11. Insulation Coordination of HVDC Converter Stations
  12. Converter Station Equipment
  13. DC Transmission with Voltage¬Sourced Converters
  14. DC Transmission with Series Capacitor Compensated Converters
  15. Overhead Lines with HVDC Transmission
  16. HVDC Cables
  17. Simulation of HVDC Systems
  18. Reliability and Availability
  19. SystemEfficiency
  20. HVDC Cost Estimates
  21. System Design Studies
  22. Commissioning of HVDC Systems
  23. HVDC Project Implementation
  24. Operation and Maintenance
  25. Life Extension of Existing HVDC Facilities
  26. AC¬to¬DC Power Transmission Line Conversion
  27. HVDC Ground Electrodes
  28. Integrating HVDC into the AC Grid
  29. Design and Operational Challenges of DC Grids
  30. Live Work Practices on HVDC Transmission Lines

FACTS:

With the introduction of renewable power generation, the power flows on the HV systems are changing. As a result, some lines are overloaded whereas the loading on other lines is well below their thermal capability. Building new lines is becoming more and more challenging due to environmental permitting and capital costs. The transmission operators are looking for the application of FACTS (Flexible AC Transmission Systems) controllers to mitigate power flow and other issues like voltage regulation. FACTS controllers have been used for steady state, transient and dynamic stability of power systems and for damping system oscillations all around the world for more than 30 years. Series reactance of long transmission lines limits their power transmission capacity. System operators often need to keep the power flow in long transmission line well below their thermal limits to maintain sufficient transient stability margin. This leads to underutilization of the transmission assets.

Series FACTS controllers are being used to increase power flows in the existing AC systems. Series capacitors, Thyristor Controlled Series Capacitors (TCSCs), and Static Synchronous Series Compensators (SSSCs) could be used as series controllers to maximize the power flow on the existing AC transmission corridors. EPRI studied these options and published the EPRI Technical Update 3002021404 – Technical and Operational Comparison of Thyristor Controlled Series Capacitor (TCSC) and Static Synchronous Series Compensator (SSSC), July 2021.

Shunt compensation is used to improve the voltage profile in the transmission systems by providing necessary reactive power. Though shunt capacitors and shunt reactors can be used for static reactive power compensation, dynamic reactive power compensation is needed to maintain the voltage profiles and optimize the power flow on the transmission systems during different operating conditions including equipment outages. Dynamic reactive power compensation can be provided using power electronics-based compensators such as Static Var Compensators (SVC) and Static Synchronous Compensator (STATCOM) and rotating machine based such as Synchronous Condenser. EPRI studied the comparative advantages and limitations of these technologies and published the EPRI Technical Update 3002024629 – Technical and Operational Comparison of SVC, STATCOM, and Synchronous Condensers, April 2022.

The most sophisticated FACTS controllers include Unified Power Flow Controller (UPFC) and Interline Power Flow Controller (IPFC). UPFC consists of a STATCOM and a SSSC and thus provides both series and shunt compensation to the AC system. IPFC consists of two or more SSSCs, one in each line and thus transfer active power from one line to the other.

EPRI report- 3002027143 published in 2023 describes the operation of STATCOM, SSSC, UPFC and IPFC and focuses on technical and operational comparison of the UPFC and IPFC technologies.

A FACTS Application Guide is being prepared in 2024 comparing all the FACTS controllers along with the synchronous condenser.