645 / 2017-05-15 23:29:56

Passive DC neutral breaker for bipolar HVDC schemes

DC,HVDC,2072

DC neutral breakers are used to reconfigure HVDC transmission systems. One example is the Metallic Return Transfer Breaker (MRTB) that commutates the current from the ground to an overhead line or cable reducing time duration with current flowing in the ground path. An MRTB consists of a passive LC-circuit in parallel with an AC breaker that triggers a resonance by its arc voltage characteristics, that eventually gives a current zero crossing where the current is interrupted. Based on the trend with higher current ratings of HVDC systems, the MRTB performance also needs to be increased. In year 2000 the passive MRTB’s could interrupt 2500 A, in 2007 an upgrade was made to 5000 A and now performance has been validated to more than 6500 A. The paper describes how this performance increase has been achieved by careful design of the LC-circuit and validation in a high power lab.