| Abstract |
A renewed interest for dc breakers has evolved owing to the visions of connecting several HVDC links into a HVDC grid. Several breaker concepts have been presented and some also have been implemented and tested. A new approach is proposed in this paper. The fundamental principle is to take advantage of the fast recovery of the voltage withstand capability in a Vacuum Interrupter (VI) when the current is temporarily forced to zero using a low-voltage power electronic converter. The latter excites an oscillating current in a passive resonant circuit during the time interval needed to mechanically separate the contacts in the interrupter. The sum of the line current (to be interrupted) and the oscillating current passes through the vacuum interrupter and experiences zero-crossings when the amplitude of the oscillating current exceeds the line current. The most important benefit of the proposed concept is that a favorable cost can be achieved, because excitation of the oscillating current only requires a low output voltage (compared to the breaking voltage across the VI terminals) from the converter. The total voltage rating of the semiconductors in the latter therefore is only a fraction of that needed in a hybrid HVDC breaker and, additionally, they are not requested to turn off the main current but rather to commutate close to current zero-crossings. Experimental verification of the concept has been performed with current up to 1.6 kA against 1.2 kV. |
