Investigating overcurrent stresses on 320 kV HVDC cable systems in a VSC-type symmetrical monopolar configuration according to CIGRE guidelines
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Typ
Examensarbete för masterexamen
Program
Publicerad
2019
Författare
Jain, Palash
Modellbyggare
Tidskriftstitel
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Volymtitel
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Sammanfattning
In several recent High Voltage (HV) DC projects, Voltage Source Converters (VSC) have been the preferred choice of technology together with HVDC cable systems. Topologies of VSCs strongly a˙ect performance of system components, including HVDC cable terminations, which are key elements providing connection of cable grids to external devices. Special testing procedures for HVDC cables terminations are not well defined today. Internal arc is such an exemplary special test for HVDC cable termination that simulates an internal termination fault. Di˙erent elements can be connected to the converter terminals such as DC capacitors and arm induc-tors, which can result in di˙erent travelling wave phenomena in the event of fault. In addition to system related stresses, HVDC cable terminations must withstand faults associated with internal arcing.
This report describes the work performed at NKT HV Cables AB in Karlskrona, Sweden, which aimed to investigate di˙erent types of faults in a 320 kV symmetrical monopolar cable system fed by a half bridge Modular Multilevel Converter (MMC) VSC. Overcurrents’ profile (peak value and time duration) caused by di˙erent dis-charging mechanisms and grounding configurations have been analyzed by computer simulations using PSCAD software. Di˙erent types of faults have been simulated, which were permanent in nature and cleared with the help of AC breakers. The re-sults obtained from simulations showed that the overcurrents during the fault were significantly higher at the midpoint of the cable. The peak overcurrent due to the pole-to-ground fault at the DC side of the converter terminals reached theoretical peak of discharge current defined by the ratio of the system voltage over character-istic cable impedance. Significant reflections of the fault currents were also observed during arm-to-ground faults. The performed study provided insight on the transient phenomena in HVDC cable systems during faults.
Beskrivning
Ämne/nyckelord
HVDC , VSC , MMC , overcurrent , CIGRE