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									Study Committee C4                                              System Technical Performance

                                   Working Group Form

    WG N°: C4.502                  Name of convener: Wojciech Wiechowski / Denmark


Title of working group: Power system technical performance issues related to the
                 application of long HVAC cables
Background
Due to the increasing public resistance against erection of new overhead lines, transmission utilities
have to consider installation of large number of HV/EHV AC cable lines in their networks. Some of
these cable lines are of very long length, even in the range of 100 km. Such long cables most likely
require installation of reactive power compensating stations along the cable line.

Network planners, network operators and equipment suppliers do not have much experience with the
performance of transmission systems with large share of (very long) HV/EHV AC cables. Currently, the
longest EHV AC cable lines (2x 500 kV, 40 km) are operated in Japan. A 100km-long cable is being
installed in Denmark; it is the 150 kV AC connection of offshore wind farm Horns Rev 2.

As a result of an increasing share of AC cable lines in the Danish transmission network Energinet.dk
for some time has been carrying out studies related to issues that can be described as performance of
transmission system with very long HV/EHV AC cable lines. Some of the studies resulted in a number
of questions that require further analyses.

WG B1.05 has studied maximum lightning overvoltages along long cables. Their report recommended
forming a WG that should study switching transients in long AC cables.

JWG 21/33 was evaluating the influence of transient overvoltages on AC cable insulation design. Their
report recommends further studies especially for cables with extruded insulation. Additionally it advises
further studies using numerical simulation techniques for various network configurations in order to
establish guidelines concerning how to perform calculations and how to interpret the results.


Scope of Work
•   Systems of nominal voltage 72.5 kV and higher
•   Recommendations concerning adequate modelling of AC cable lines (both land and submarine)
    and the rest of the system for various types of studies related to the system technical performance.
    Include the effect of other conducting infrastructure (mainly in urban areas) e.g. gas pipelines, rail
    tracks, etc on the cable circuits performance.
•   Methods for gaining confidence in the accuracy of cable line models for the considered types of
    studies
•   Technical performance of systems with large share of AC cable lines and/or with very long AC
    cable lines
•   Guidelines concerning calculation methods and interpretation of simulation results
•   DC cable lines are not included in the scope of this WG, as the scope focuses on studies related
    specifically to AC cables, based on the assumption that the transmission expansion planning
    process has selected an AC cable option


Objectives
•   To gather available knowledge and expertise
•   To define an adequate level of accuracy of modelling various details of AC cable lines (for example
    bonding of cables, transposition, armour of 3-phase cables, etc) for various types of studies related
    to its technical performance
•   To define methods for gaining confidence in the accuracy of cable line models for the considered
    type of studies
•   To develop guidelines concerning methods of analyses and interpretation of simulation results for
    various types of studies
•   To recommend optimal operational strategies and countermeasures intended for ensuring reliable
    performance of transmission grid with long/many AC cable lines
•   To recommend most favourable reactive power compensation schemes for very long AC cable lines
    with respect to the technical performance
•   To verify some of the performed simulation studies by real-life measurements for example on the
    100 km long 150 kV AC cable line to offshore wind farm Horns Rev 2
•   To compare the obtained overvoltage amplitudes and durations with cable tests recommended by
    IEC
    To study the influence of a large number of AC cables on the network impedance, the network
     natural frequency and risks regarding large generators
•   To prepare a technical brochure that will serve as practical guide for performing studies necessary
    for assessing the technical performance of HV/EHV systems with large share of AC cable lines
    and/or with very long AC cable lines
•   To define further studies and developments

Example issues to be addressed: Temporary overvoltage, slow-front overvoltage (like load rejection or
over-voltage due to resonances), zero-miss phenomenon, network harmonic impedance, voltage or
transient stability, reactive power compensation and voltage control.

Deliverables/time schedule
    -   January 2009: Starting of the working group
    -   2010 : Interim Report
    -   2012 : Final Report TB, Summary on Electra + report to Cigre Session 2012/B1 for better
        diffusion of results within cable Industry.
    -   2012 : Tutorial

Other SC concerned by the work:
B1 (One Member from B1.30 and one additional corresponding member)
A3
Approved by TC chairman: Klaus Fröhlich
Date: 17/02/2009

								
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