In　order　to　improve　the　insulating　performance　of　air-insulated　high　voltage　electrical　apparatuses,　solid　barriers　are　always　introduced　in　the　interelectrode　gaps.　The　breakdown　paths　and　conditions　of　air-insulated　rod-plane　gaps　in　the　range　of　2-5　cm　under　alternating　voltages　were　investigated　for　three　different　sizes　of　polyvinyl　chloride　barriers　inserted　at　different　gap　positions.　The　breakdown　processes　were　observed　using　two　cameras　placed　in　orthogonal　directions,　and　two　typical　breakdown　paths　were　captured.　The　statistical　results　showed　that　the　occurrence　probabilities　of　the　two　typical　breakdown　paths　were　related　to　the　barrier　position,　but　that　the　breakdown　voltages　were　very　similar　in　all　breakdown　events.　Further,　formulae　to　predict　the　breakdown　voltage　were　deduced　using　a　linear　regression　method.　The　results　provide　a　reference　for　improving　the　insulation　performance　of　gas-solid　hybrid　insulation　systems　based　on　the　barrier　effect　as　well　as　for　modelling　gas　discharges　in　hybrid　gaps.　(c)　2019　Author(s).　All　article　content,　except　where　otherwise　noted,　is　licensed　under　a　Creative　Commons　Attribution　(CC　BY)　license　(http://creativecommons.org/licenses/by/4.0/).