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Grounding of distrubution grids: High impedancegrounding compared to solid grounding with Fault Current Limiter
2017 (English)Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
Abstract [en]

Today cables replace overhead lines in distribution systems and

cause higher system capacitance and higher capacative fault

currents. This fault current, in the fault location, is limited by a

Petersén coil and a resistance in parallel when a fault occurs in so

called “high impedance grounded systems” which are commonly used in

Europe. The high impedance however has the disadvantage that it

needs to be adjusted to the capacitance in the system in order to

optimize the limitation of the fault current.

Another option is to use a solidly grounded system with a so called

“Fault Current Limiter” (FCL) instead, on the outgoing terminals of

the transformer feeding the system. The FCL interrupts the outgoing

current on the load side of the transformer that feeds the system,

in case of a fault, by forcing the current to a zero with a counter

voltage. The FCL in this master thesis triggers on 1.5 times higher

current than nominal current. After fault clearing the FCL is

reclosed. The FCL has the advantage that it does not have to be

adapted to the capacitance in the system. It should be noted that

the current in all of the phases (even the healthy phases) are

interrupted downstream the FCL. It also has the ability to interrupt

the single line-to-ground fault before it develops into a three

phase fault.

This thesis presents a comparison between the high impedance

grounding and the FCL. The characteristics of the two grounding

principles are investigated in a distribution system from

Vattenfall. The assessment is done via simulations in the program

PSCAD with three types of grounding of the transformer; high

impedance grounding, solid grounding (without FCL) and solid

grounding with FCL. The system is simulated with the faults “single

line-to-ground” and “three phase short circuit” respectively, even

if a line-to-line can occur. The results from the simulations show

that the FCL gives a short fault duration time and a possibility to

limit both single line-to-ground faults and three phase faults. The

high impedance grounding on the other hand is able to limit single

line-to-ground faults whereas it is generally known that not able to

limit three phase short circuits.

Place, publisher, year, edition, pages
2017.
Series
UPTEC E, ISSN 1654-7616 ; 17 013
National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:uu:diva-332461OAI: oai:DiVA.org:uu-332461DiVA, id: diva2:1153151
External cooperation
ABB
Educational program
Master Programme in Electrical Engineering
Supervisors
Examiners
Available from: 2017-11-17 Created: 2017-10-27 Last updated: 2017-11-17Bibliographically approved

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CiteExportLink to record
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Citation style
  • apa
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