Ablation-assisted current interruption in medium voltage switchgear – Development and prospect

Resumé

SF6-gas is widely used in medium and high voltage
switchgear today because of its excellent insulation and
current interruption capabilities. However, due to its
high global warming potential, there is a political
pressure to replace it wherever possible, resulting in a
need for new solutions in the design of compact lowcost
switchgear. An evident response is to review and
further develop the technologies that were promising
before the entry of SF6. One of these was the application
of gas-emitting insulation materials, in a process of
ablation.
This paper reviews the range of commercial breaker
designs that have taken advantage of ablation in the
interruption process from the 1930s until today. The
main designs and developments are outlined and some
important parameters are explained, such as the steady
state ablation-dominated arc, arc quenching and
dielectric recovery in the presence of ablation material.
The ratings of the mentioned products, as well as more
recent experiments, indicate that there is a design limit
for simple ablation-assisted breakers at around 20 kV,
but the reasons for the apparent limit are not thoroughly
studied or explained.
Reviving the knowledge of ablation breakers, and
combining this with new knowledge and new tools
could prove valuable to the development of SF6-free
MV switchgear.