Insulation coordination for a fault-ride-through test setup's 66 kV air-core reactor: Root-cause analysis and discharge mitigation
Author
Götting, Olaf Lennard
Term
4. term
Education
Publication year
2022
Submitted on
2022-05-30
Pages
99
Abstract
I en 66 kV fault ride-through (FRT) testopstilling for vindmøller er en luftkernet autotransformer tilbøjelig til elektriske udladninger (gnister). Analysen peger på, at årsagen er koblingsoverspændinger, som opstår når strømmen afbrydes brat – et fænomen kendt som strømhakning. Spolen modelleres med en ækvivalentkreds baseret på analytisk beregnede parametre, og tidsdomænesimuleringer viser store, kortvarige overspændinger på op til 11 p.u. (11 gange mærkespændingen). En gennemgang af mulige modforanstaltninger peger på en snubberkreds – et RC-netværk (modstand og kondensator), der dæmper spændingsspidser – som en praktisk løsning til at begrænse udladningerne. Den resulterende overspænding bestemmes af snubberens RC-værdier og størrelsen af strømhakningen. I simuleringerne reduceres overspændingen til under 2 p.u., når snubberkredsen indgår. Som næste skridt foreslås en målekampagne for at bestemme den faktiske strømhakning.
In a 66 kV fault ride-through (FRT) test setup for wind turbines, an air-core autotransformer is prone to electrical discharges (sparks). Our analysis identifies the cause as switching overvoltages produced when current is interrupted abruptly, a phenomenon known as current chopping. The coil is represented by an equivalent circuit with analytically calculated parameters, and time-domain simulations show large transient overvoltages up to 11 per unit (p.u., 11 times the rated voltage). A review of countermeasures points to a snubber circuit—an RC (resistor–capacitor) network that absorbs voltage spikes—as a practical way to mitigate the discharges. The resulting overvoltage is set by the snubber’s RC values and by the magnitude of the chopped current. With the snubber included, simulated overvoltages fall to below 2 p.u. As future work, we propose a measurement campaign to determine the actual chopping current.
[This summary has been rewritten with the help of AI based on the project's original abstract]
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