Abstract
The symmetrical monopolar configuration is the prevailing scheme configuration for high voltage direct current (HVDC) interconnectors utilizing the modular multilevel converter (MMC) topology. However, the rigid bipolar configuration is gaining significance, as first projects are currently in planning stage. The purpose of this paper is to analyse both HVDC scheme configurations with regard to cable voltage stresses originating from short-circuit faults. The study focuses on HVDC cables with extruded insulation connected to MMCs equipped with half-bridge (HB) submodules. Basic design aspects in rigid bipolar configuration such as the station grounding concept are discussed. Moreover, various station internal as well as dc faults are examined by means of electromagnetic transient (EMT) simulations. Occurring cable voltage stresses are analyzed with respect to voltage polarity, peak value and wave front-parameters and compared in symmetrical monopolar and rigid bipolar configuration. It is demonstrated that cable overvoltages with same polarity as the dc operating voltage are significantly reduced in schemes operating in rigid bipolar configuration. Voltage reversals caused by the discharge process during a cable fault are nearly independent of the selected scheme configuration. Obtained results are relevant with regard to upcoming projects in rigid bipolar configuration and provide insights to further refine insulation co-ordination aspects related to dc cable systems.
Highlights
D URING the past decade, modular multilevel converter (MMC) technology gained a significant share of the high voltage direct current (HVDC) market due to many technical and economic benefits such as required foot print of converter stations, operational flexibility and independent control of active and reactive power [1]
The introduction of MMC-HVDC boosted the installation of dc cables with extruded insulation, since MMC technology enables reversal of power flow direction without inversion of voltage polarity [2]
To completely unveil the cable voltage stresses in both scheme configurations, various fault types are investigated by means of a parametric study approach and occurring cable voltage stresses are systematically evaluated with respect to voltage polarity, peak values and wave front-parameters
Summary
D URING the past decade, MMC technology gained a significant share of the HVDC market due to many technical and economic benefits such as required foot print of converter stations, operational flexibility and independent control of active and reactive power [1]. Published literature with regard to SMP schemes focuses on high voltage testing of dc cable systems and evaluates how representative overvoltage wave shapes might be generated [18], [19]. To completely unveil the cable voltage stresses in both scheme configurations, various fault types are investigated by means of a parametric study approach and occurring cable voltage stresses are systematically evaluated with respect to voltage polarity, peak values and wave front-parameters. On top of existing literature, this paper highlights essential design aspects related to scheme configuration which gain in significance for schemes operating in RBP configuration, such as the station grounding concept and related impacts on the insulation co-ordination strategy of the cable.
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