The impact of fault blocking converters on HVDC protection

Abstract

Multiterminal High Voltage Direct Current (HVDC) systems are anticipated to enable flexible transmission of renewable energy across continents, however protection strategies for such systems are in their infancy. Fast circuit breakers have been proposed, however their implementation on a network is undecided. The protection requirements are likely to depend on both the AC/DC converter and network topologies.

This thesis examines several aspects of the protection of HVDC systems, considering factors influencing circuit breaker ratings, and examining primary and backup protection philosophies. A comparison is made throughout between fault feeding and fault blocking converters, aiming to investigate the impact of fault blocking converters on HVDC protection.

The ratings of HVDC circuit breakers on meshed networks are evaluated, considering factors such as the current breaking magnitude, operation time, additional inductance and energy dissipation requirements for various network and converter topologies. It is shown that the circuit breaker requirements in network areas with fault blocking converters are reduced compared to when a fault feeding converter is implemented.

HVDC protection is investigated, considering primary and backup methods for several protection philosophies. The influence of the converter, network and circuit breaker topologies are examined, and the impact of the HVDC protection strategy on the connected AC systems is evaluated. It is shown that slower protection strategies using fault blocking converters might be technically feasible from both the HVDC and AC system perspectives, which could result in an effective protection strategy with a reduced requirement for circuit breakers.