Beschreibung
This dissertation introduces a technical overview of the HVDC breaker. Based on the working principle, there are mainly three kinds of HVDC breakers: the all-solid HVDC breaker, the resonance HVDC breaker and the hybrid HVDC breaker. Their topologies, working principle, advantages and disadvantages are presented. A comparison of different HVDC breakers based on their functions is also made, which includes the usage of HVDC breakers in multi-terminal HVDC systems. A new HVDC protection scheme is presented in this dissertation; it combines the principle of HVDC breaker and MMC topology. The original topology uses a double-thyristor-switch MMC sub-module to cut off the energy flow from the AC side to the DC side. The rest energy is consumed in the fault-current loop. However, for some extreme cases, the AC breaker could be opened because of a long-time short-circuit in the AC side. Hence, a one-arrestor version of the new protection scheme is developed to cut off the DC short circuit in a short time, and the DC fault current is reduced in a free-wheeling diodes loop. This scheme also has a disadvantage, which could affect the restart of the HVDC system in extreme cases. For this reason, the two-arrestor version is proposed, which can cut off the DC short circuit and consume rest energy in the DC line in a short time. According to the calculation, the loss power for different protection schemes can be attained and compared. The new protection scheme has less loss power than most schemes, and it also overcomes disadvantages of others.
