Characterization of Short and Rapidly Elongating Arcs for Fast Current Commutation in MVDC Circuit Breakers

MVDC grids are part of the future power distribution system and have the potential to collect renewable energy sources more effective and cost-efficient. However, circuit breakers for DC are demanding faster switching because of high fault current rise rates and they are more complex to develop because of the missing zero current crossing in DC systems. Recent concepts are using an ultra-fast mechanical switch in form of a Thomson Coil Actuator (TCA) to commutate the current into a parallel capacitor to break the circuit. The success of the commutation is strongly dependent on the voltage of the arc forming between the contacts of the switch. To understand and optimize the switch and the commutation process, a thorough
understanding and characterization of the arcs that occur is necessary. This includes the dielectric recovery of the switching gap as well.

Experiments are carried out in the high current laboratory in order to characterize short and rapidly elongating arcs by means of different measurements. The research also includes the development of arc models to determine the arc voltage as a function of interruption current. The influence of current, contact material, contact velocity and other influential factors is investigated.

This PhD research is expected to provide new knowledge about the to date little researched rapidly elongating arcs and, thus, enable a more effective and cost-efficient circuit breaker technology for the power market.

The following specific objectives apply to the PhD project:

1. Physical characterization of the arcs and the previous metal vapor discharge
2. Evaluation of the dielectric recovery of the electrode gap after arc extinction
3. Development of models to describe the arcing, the dielectric recovery and the influence on
   the commutation process

• NTNU HVT