Project

Space charges in XLPE cables and Accessories - Evaluation of risks for the Danish Transmission Grid including Case studies

Publisher

Companies / Organizations

Location

Greater Copenhagen area

Master project (+ initial special course)

 

Background:

Energinet has many partners around the world with which experiences, procedures and novelties are shared. From some of these partners the question has been raised whether the present system setup at the ends of Extra High Voltage (EHV) cables is a potential risk for the cable integrity.

It is well known that XLPE cable systems exposed to DC voltage experience a build-up of space charges inside the cables and accessories, which is why DC voltage tests are no longer performed on AC XLPE cables in Denmark. However on EHV cable systems it is typical to use capacitive voltage transformers which do not allow leakage current to ground after disconnecting the cables from the grid. Cables may therefore be exposed to a residual DC voltage between disconnection of the cables from the grid and grounding of the cables, which may lead to space charge build up inside the cables and accessories. This can lead to critical field strength enhancements in the cable under re-energization.

 

Project description

This purpose of the master project is to:

  • Describe state-of-the-art knowledge on space charges in XLPE cables and accessories

  • Perform evaluation of criticality of using capacitive voltage transformers versus inductive voltage transformers with respect to residual DC voltages.

  • Analyse specific cases from the real Danish transmission grid where this may be problematic and give recommendations to choice of solutions based on input from Energinet

    The project must come with a general analysis describing if DC voltages in general are harmful to the cable systems in the present setup or if that system design can be allowed in the future.

    The project is broad, allowing the student a large flexibility in analysing the problem in different directions of his/her interest. The project may involve simulations in PSCAD, Comsol Multiphysics and Matlab, which are to clarify the system condition under switching out and in and the temporal development of electrical field strength inside critical components under these events.

    If possible, laboratory studies of space charges in samples, cables and accessories can be performed to support the understanding of space charge behaviour.

The following aspects should be covered:

  • Review space charge theory

  • FEM modeling of space charge development in cables

  • Possible laboratory studies of space charges

  • Review of leakage currents on Siphon systems (combined overhead lines and cables)

  • System modelling of switching events and residual DC voltage over time

  • Calculation of the development of internal field conditions in critical components

  • Risk assessment for switching events under the occurrence of space charges

  • Report writing

     

    Remarks:

    The student will mainly work at DTU, but with close contact to the company supervisors with the possibility to work at Energinet, for example one day a week.

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Contact

Company / Organization

Energinet

Name

Rasmus Aabye Olsen

Position

Team Lead and Senior Cable Specialist

Mail

rao@energinet.dk

Phone

61244380

Suggestion to

Study programme

Technical University of Denmark

For almost two centuries DTU, Technical University of Denmark, has been dedicated to fulfilling the vision of H.C. Ørsted – the father of electromagnetism – who founded the university in 1829 to develop and create value using the natural sciences and the technical sciences to benefit society.


Today, DTU is ranked as one of the foremost technical universities in Europe, continues to set new records in the number of publications, and persistently increases and develops our partnerships with industry, and assignments accomplished by DTU’s public sector consultancy.

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Denmark



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