Magnetically Controlled Reactor - a Novel Component in Smart Grid

Research output: ThesisDoctoral ThesisCollection of Articles


There is currently rapid increase of solar and wind generation in the grid and growing emphasis on the reliability and availability of electrical supply.  These changes have triggered a need to have a more flexible grid, which can adapt instantly to a different load, production and failure situations. First part of this thesis was to investigate ways to create grid elements presenting instantly controllable inductance, which would fulfill many Smart Grid needs such as compensating reactive power, controlling voltage in a distribution grid or compensating earth fault currents. A reactor topology was identified, modeled and validated in laboratory in which inductance could be controlled quickly, linearly and with no moving parts using an optimized virtual air gap. One promising application for this new type of instantly controllable and linear reactor is in compensating earth faults in resonant earthed distribution networks. Typically arc suppression coils (ASC) are not tuned to exact resonance due to practicalities related to current technology whereas the new magnetically controlled reactor developed in this work is fast and thus allows full resonance tuning. In a second part of this thesis earth fault arcs were modeled using black box models and it was established, that tuning ASC to full resonance improves the earth fault extinguishment probability. This result further indicates, that magnetically controlled reactor is a good replacement for current mechanically operated ASC. In a typical earth fault compensation arrangement the substation transformer provides delta connection to the medium voltage side thereby lacking neutral connection. Arc suppression coil is connected between earth and neutral, which means that normally an earthing transformer is needed to provide connection point for arc suppression coil. Third contribution of this thesis was to model and simulate a novel earth fault compensating reactor, in which the earthing transformer and arc suppression coil functions could be integrated into a same space saving structure, while providing instant control in zero sequence impedance using the magnetically controlled reactor developed in this work.
Translated title of the contributionMagneettisesti ohjattu reaktori - älykkään sähköverkon uusi komponentti
Original languageEnglish
QualificationDoctor's degree
Awarding Institution
  • Aalto University
  • Lehtonen, Matti, Supervising Professor
  • Lehtonen, Matti, Thesis Advisor
Print ISBNs978-952-60-7963-9
Electronic ISBNs978-952-60-7964-6
Publication statusPublished - 2018
MoE publication typeG5 Doctoral dissertation (article)


  • Smart Grid
  • magnetically controlled reactor
  • earth fault
  • power distribution

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