Power system stability analysis of cable based HVAC transmission grids with reactive power compensation
Authors
Dall, Laurids Martedal Bergholdt ; Foo, Yi Wern
Term
4. term
Education
Publication year
2016
Submitted on
2016-06-01
Abstract
Specialet undersøger, hvordan lange højspændte vekselstrømskabler (HVAC) påvirker kraftsystemers elektromekaniske adfærd, især under store forstyrrelser. Forbigående stabilitet og spændingsstabilitet ved store hændelser vurderes med RMS-simuleringer i DIgSILENT PowerFactory. Et referencesystem med luftledninger (OHL) sammenlignes med et tilsvarende kabelsystem. Resultaterne viser, at et 100% kompenseret kabelsystem i de fleste tilfælde har længere kritisk udkoblingstid (CCT) end OHL-systemet. En højere grad af SR-kompensation kan yderligere forbedre CCT. Samtidig tyder spændingsstabilitetsanalysen på, at underkompensation øger systemets evne til at bære last, målt via spænding–effekt (V–P) lastbarhed. Kabelsystemet opnår også en højere P_max end OHL-referencesystemet. En styrke ved kabelsystemet er, at det har afbrydelige SR-enheder (kompenseringsudstyr). Ved midlertidigt at reducere deres indstilling (X_SR) under en stor forstyrrelse kan den kapacitive strøm fra kablerne bidrage til at hæve spændingen i netværket. Casestudierne viser, at SR-kobling kan forbedre systemspændingerne, og at en blid spændingsgenopretning opnås ved sekventielt at koble de knudepunkter med de laveste spændinger først. Der er behov for yderligere arbejde for at generalisere og kvantificere effekten af SR-kobling.
This thesis examines how long high‑voltage AC (HVAC) cables influence the electromechanical behavior of power transmission systems, especially during major disturbances. Transient stability and large‑disturbance voltage stability are evaluated using RMS simulations in DIgSILENT PowerFactory. A baseline overhead line (OHL) system is compared with an equivalent cable system. The results show that a 100% compensated cable system has a longer critical clearing time (CCT) than the OHL system in most cases. Increasing the degree of SR compensation can further improve CCT. Voltage stability analysis indicates that undercompensation increases the system’s loadability in terms of the voltage–power (V–P) margin. The cable system also achieves a higher P_max than the OHL baseline. A key advantage of the cable system is the availability of switchable SR units (compensation devices). Temporarily reducing their setting (X_SR) during a large disturbance allows the cable’s capacitive current to support the network voltage. Case studies show that SR switching can improve system voltages, and a smooth recovery is achieved by sequentially switching at the nodes with the lowest voltages first. Further work is needed to generalize and quantify the impact of SR switching.
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