Tutorials and Technical Visits:

The following tutorials will be proposed on Monday, November 20^th 15:00 - 18:30 (break from 16:30 to 17:00)
 

• T1: Updated characteristics of materials for HVDC cables and new materials
  by Petru NOTHINGER, IES Montpellier, France and Gilbert TEYSSEDRE, Laplace CNRS Toulouse, France
   
  The demand and challenges for materials to be used in HVDC cable development are mainly focused on synthetic insulation. Polyethylene materials have been successful in replacing other cable technologies for HVAC undersea or underground cables, and the challenge is presently to adapt materials and find new solutions for HVDC cable insulations.
  In this tutorial, the constrains driven by the DC cable conditions and construction on the materials constituting cables, being insulation as well as field grading materials, will be given, with consideration of cable junctions and the differences with AC stress. Despite a generally higher dielectric strength under AC than DC stress, issues related to resistive field grading and to space charge phenomena under DC stress mark the real challenges for the reliability of HVDC links. The behaviour under polarity reversal is a further challenge.
  As background, we will revisit dielectric physics, highlighting the nature of charge carriers involved in transport processes (conductivity), and the nature of sites providing charge stabilization and trapping in materials. The approaches for understanding and evaluation of materials behaviour ranging from molecular scale approaches to experimental characterization in flat specimen and to cable scale testing will be addressed. Current strategies for materials ranging from crosslinked materials to nanocomposites and to thermoplastics will be reviewed.
   
  
• T2: Converters operation and consequences on cable system in case of fault
  by Hani SAAD and Samuel NGUEFEU, RTE, France
   
  The inclusion of High Voltage Direct Current (HVDC) transmission link in AC grids is expanding rapidly worldwide. The use of voltage source converters (VSCs) based on Modular Multilevel Converter (MMC) topology is becoming more attractive mainly due to their higher performances, absence of commutation failures, ability of independently controlling the active and reactive power, etc. VSC technology does not require the inversion of the voltage polarity when reversing the direction of power flow. This has made the use of extruded insulation cables easier for DC applications. Since then, the number of extruded insulation cables, used in combination with VSCs, has increased for HVDC power transmission applications. Even if VSC does not require the inversion of the voltage polarity, several events can generate transients on cables that are not well covered by standard tests and may stress the cable.
  The presentation will illustrate the typical events that lead to voltage fluctuation on cables connected to VSC converters. DC faults or internal converters faults can result in significant overvoltages at the DC cables which persist even after the system has been disconnected from the AC networks. These transients will be described, analyzed and compared against the standard tests for lightning and switching impulses. Technical solutions to limit stresses on cables will be also proposed and discussed.
   
  
• T3: CIGRE recommendations for electrical and mechanical testing of HVDC cable systems
  by Marc JEROENSE, NKT HV Cables AB, Sweden
   
  HVDC cable systems have been in service for a long time, already since 1954. Now, more than 60 years later thousands of kilometers of HVDC underground and submarine cables have been put in service and are being contracted. The suitability of technologies and technical solutions of these cable systems have been proven by performing internationally agreed tests covering development, qualification, manufacturing and installation.
  Mass impregnated and oil-filled cable systems have for many years been the only types of HVDC cables systems. The last 20 years, though, we have witnessed a dramatic catching-up of extruded cables systems for HVDC applications.
  During the course of development of all these cable systems CIGRE has published recommendations that cover tests that address the stresses that a cable system is exposed to during its life cycle. These stresses are thermal, electrical and mechanical.
  The electrical and thermal tests cover both extruded and lapped cable systems and are described in two different Technical Brochures published by CIGRE, Electra 189 and TB 496.
  Mechanical stresses that these cable system are experiencing during installation, operation and recovery are very different for underground and submarine cable systems. For that reason the recommendations describing mechanical tests for underground and submarine cable systems are different. The use of submarine cable systems has increased dramatically the last decades and the future promises rather an increase than a decrease in these cable systems. Installation conditions also become increasingly challenging. These facts have resulted in the newest recommendations covering mechanical tests for submarine cable systems: TB 623.
  During the tutorial a historical view on the development of the tests related to the birth of new technologies and applications will be presented. The content of the relevant recommendations will be given and explained. Thoughts about future need of new or updated recommendations will be shared based on the observation and fact of an increased pace in project complexity and technology development.
  

Two technical visits will be organized on Wednesday, November 22^nd afternoon:

• V1: The IFA 2000 HVDC interconnector
  Wednesday, November 22, 2017 - 13:30 - 18:30
  Limited number of participants.
   
  IFA2000 (also called HVDC Cross-Channel) is a 2000 MW interconnector between France and Britain in operation since 1986, operated by RTE and National Grid plc.
  The energy conversion is done by two LCC type bipoles (semiconductor thyristor valves) operating under +/- 270 kV DC voltage and the power transmits through 8 x 75 km-long DC cables, including 45 km of submarine cables.
  The technical visit will take place at the converter station near Calais (France) and will include:
  
  • A description of the IFA 2000 converter station: history, energy conversion equipment
  • A visit of the converter station
  • A description of the HVDC cables with a special focus on the refurbishment of land oil filled cables by XLPE cables (a world premiere together with LCC converters at 270 kV)
  • A visit of the connection between submarine cables and land cables.
• V2: The Channel Tunnel and the project Eleclink
  Wednesday, November 22, 2017 - 14:00 - 18:00
  Limited number of participants.
   
  The ElecLink project, which will enable the installation of a 1000 MW Interconnector between the French and the British electricity markets via the Channel Tunnel, has just been launched at the beginning of the year (2017) with an estimated commissioning date for January 2020.
  This Interconnector will be built on the Eurotunnel Concession site in France, in United Kingdom and in one of the Railway Tunnel.
  This Interconnector will a be 69 km long connection with 52 km inside The Channel Tunnel.
  Eurotunnel is the fastest, most reliable, easiest and the most environmentally friendly transport system to cross the Pas-de-Calais / Dover strait. It is also the most widely used in the world combining freight and tourists traffic with more than 350 trains a day,7 days a week and 365 days per year. This single landline has become a vital link between the continent and the United Kingdom.
  The visit will be a combination between 2 presentations: the Eurotunnel system and the ElecLink interconnector.