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Title: Direct current hybrid vacuum breaker
Author: Shan, Yunhai
ISNI:       0000 0004 5362 7309
Awarding Body: University of Strathclyde
Current Institution: University of Strathclyde
Date of Award: 2014
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Hybrid DC circuit breaker switching techniques have been proposed for use in multi-terminal HVDC networks, to create an efficient, reliable and controllable system. There are two DC hybrid switching techniques. The first is arc interruption based on current oscillation. The second is interruption without an arc, like with a voltage commutation approach. The main difference is whether or not the interruption mechanism deals with the arc. Interrupting the arc not only causes erosion of the electrode surface, therefore reducing useful lifetime, but also introduces uncertainty to the process of successful interruption. This thesis therefore focuses on determination of the best switching technique for HVDC applications. To highlight the advantages of interruption without an arc, this thesis uses a vacuum circuit breaker (VCB) as the main breaker to investigate arc effects on interruption performance, when employing a forced current commutation method. The vacuum arc characteristics are detailed, thereby giving the VCB operation understanding needed. The VCB opening time is reduced from approximately 50ms to 13ms by employing a coil DC activation method. This allows the coil counter-EMF to be observed and utilised to optimally trigger the auxiliary commutation circuit. An active commutation test circuit is proposed, and in simulation and experimentally, the VCB interruption properties are investigated in terms of varied interruption current, di/dt, dvVCB/dt, and gap distance. Experimental results elicit that the key parameters determining arc interruption probability is di/dt, where even if dvVCB/dt is low, successful interruption become impossible if di/dt is above a certain level. By analysing the post-arc current based on its electrical behaviour, the reason why di/dt and dvVCB/dt dominate successful interruption probability is explained. A cascaded commutation circuit is proposed, and its validity is confirmed by simulation and experimentally, showing the interruption probability is improved compared to the test circuit, even with small circuit inductance.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available