I am interested in anyone's experience of arcing over a slipring.

In the last month, we have had serious arc damage between the brush (copper graphite) and ring (copper).

There is a suggestion that a small amount of arcing is normal between the brush and ring, and that this can cause a build up of damage. However, I feel strongly that as long as some part of the brush surface is in contact with the ring, then no arc can be formed.

is there some phenomenon that I am unaware of that can cause this?