Switching overvoltages and polarity reversal in presence of HVDC circuit breakers

The recent development of High Voltage Direct Current circuit breakers (HVDC CBs) prototypes may introduce many potential advantages for HVDC links in terms of flexibility and possible meshing. However, introduction of circuit breaker in HVDC links also prompts the need for a detailed assessment of switching overvoltages and polarity reversal, which were not typically of concern for modern voltage source converters-based links, using half bridge modules. The paper deals with the evaluation of switching overvoltages and polarity reversal stresses on overhead and submarine cable HVDC links equipped with dc circuit breakers; the consideration are obviously extendable to all the equipment on the DC side. A simplified theoretical approach is presented, and a comparison is made with transient simulations on the foreseen 500 kV HVDC Italian 'Hypergrid'. Results evidence that switching overvoltages and polarity reversals become a significant design factor with the introduction of dc circuit breaker in HVDC links.