Protection of a 400 kV Parallel Overhead Line System with Series Compensation: Protection in the Transmission Network
Translated title
Protection of a 400 kV Parallel Overhead Line System with Series Compensation
Author
Laustsen, Rasmus
Term
4. term
Education
Publication year
2025
Abstract
This thesis examines how Energinet’s standard protection scheme—differential and distance relays—detects and clears faults in a meshed 400 kV transmission corridor where a series air-core reactor is integrated on the parallel Endrup–Revsing line. A series reactor increases line reactance and, together with mutual coupling between parallel lines and weak infeed at Endrup (due to the COBRA HVDC link and offshore wind), can challenge distance protection. The thesis proposes two sets of impedance settings for the distance relay, selected according to the reactor’s operating state. The approach is assessed in PSCAD using electromagnetic-transients simulations based on a model that includes the Endrup–Revsing connection, a limited upstream network, and reference models for HVDC and offshore wind, with fault cases spanning different resistances. Results indicate that differential protection operates correctly provided accurate CT measurements. The distance relay locates phase-to-phase and three-phase faults accurately but overestimates single-line-to-ground fault distance by about 8–13 percent, attributed to PSCAD’s treatment of zero-sequence and mutual coupling. Post-processing the simulated voltages and currents using a method akin to that in industry relays estimates fault location within 1 percent of the true distance. Within the scope of this study, this validates the adaptive two-setting concept and highlights sensitivity to higher fault resistances (above about 5 ohm).
Dette speciale undersøger, hvordan Energinets standardbeskyttelse (differential- og afstandsrelæer) detekterer og frakobler fejl i et masket 400 kV transmissionsnet, hvor en luftkerne-seriereaktor er integreret i den parallelle Endrup–Revsing-forbindelse. En seriereaktor øger linjereaktansen og kan sammen med gensidig kobling mellem parallelle ledninger og svag indfødning ved Endrup (på grund af COBRA-HVDC-forbindelsen og offshore vind) udfordre afstandsbeskyttelsen. Specialet foreslår to sæt impedansindstillinger for afstandsrelæet, der skifter afhængigt af reaktorens driftstilstand. Løsningen vurderes i PSCAD gennem elektromagnetiske transient-simulationer baseret på en model, der omfatter Endrup–Revsing, et begrænset opstrømsnet samt referencemodeller for HVDC og offshore vind, med fejlscenarier med varierende fejlmodstand. Resultaterne viser, at differentialbeskyttelsen fungerer forudsat nøjagtige CT-målinger. Afstandsrelæet lokaliserer fase-til-fase- og trefasefejl korrekt, men overvurderer 1-fase-til-jord-fejl med cirka 8–13 procent, hvilket tilskrives PSCADs håndtering af nulsekvens og gensidig kobling. En efterberegning af fejlafstand ud fra simulerede spændings- og strømkurver – efter en metode beslægtet med industrirelæer – rammer inden for 1 procent af den faktiske afstand. Inden for specialets rammer validerer dette den adaptive strategi med to indstillinger og fremhæver følsomheden over for højere fejlmodstande (over ca. 5 ohm).
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Keywords