Transient Overvoltages in Onshore HVDC Cable Joints
Surge Reflections and the Influence of Grounding Configurations
T.R. Karmokar (TU Delft - Intelligent Electrical Power Grids, TenneT TSO GmbH)
R.D. Zhang (TenneT TSO GmbH)
M. Ghaffarian Niasar (TU Delft - High Voltage Technology Group)
M. Popov (TU Delft - Intelligent Electrical Power Grids)
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Abstract
This study examines transient overvoltage phenomena in 525 kV high-voltage direct current (HVDC) onshore cable systems, with particular emphasis on the influence of grounding configurations in two joint types: straight-through and screen-separated. Transient overvoltages arising from wave propagation and reflections are analysed, highlighting the impact of joint types, bonding cable configurations (coaxial vs. noncoaxial) and bonding cable length on the resulting overvoltage magnitudes. The necessity of modelling screen-to-earth representations of sectionalised cables at grounded joint locations in the vicinity of faults is emphasised, whereas simplified representations of ungrounded and grounded straight-through joints are identified as sufficient for system-level simulations. To address the computational challenges of detailed electromagnetic transient simulations, a stand-alone simplified circuit is proposed to analyse grounded joint transients and to mitigate errors caused by insufficient time-step resolution. The results provide practical insights for insulation coordination, supporting the reliable integration of HVDC technology into long-distance cable-based transmission networks while enhancing system resilience.
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