Modular design

Electrical engineering

Geology

Topology (electrical circuits)

Operating system

Engineering

Voltage

Ground

Seismology

Fault (geology)

Electronic engineering

HVDC converter

Computer science

HVDC converter station

Circuit breaker

Transformer

Earthing system

IEEE Transactions on Industrial Electronics

Although the probability of occurrence of station internal ac grounding faults in modular multilevel converter (MMC)-based high-voltage direct-current systems is low, they may lead to severe consequences that should be considered when designing protection systems. This paper analyzes the characteristics of valve-side single-phase-to-ground (SPG) faults in three configurations of MMC systems. Fault responses for symmetrical monopole MMCs are first studied. Upper arm overvoltages and ac-side nonzero-crossing currents arising from SPG faults in asymmetrical and bipolar configurations are then investigated. DC grounding using an LR parallel circuit is employed to create current zero-crossings, which will enable the operation of grid-side ac circuit breakers. The theoretical analysis is verified through simulations performed in PSCAD/EMTDC, with simulation results and the theoretical analysis showing a good agreement. The studies in this paper will be valuable for the design of protection systems for station internal ac grounding faults.

Analysis of Single-Phase-to-Ground Faults at the Valve-Side of HB-MMCs in HVDC Systems