C5-PFK　has　attracted　much　attention　as　one　of　the　most　promising　SF6　substitutes　for　medium　voltage　(MV)　power　equipment　because　of　its　high　insulation　strength　and　low　global　warming　potential　(GWP).　In　this　paper,　the　dielectric　properties　of　C5-PFK-Air　and　C5-PFK-CO2　mixtures　are　experimentally　investigated,　to　explore　the　most　effective　solution　for　C5-PFK　mixtures　for　application　in　MV　power　equipment.　The　basic　physical　properties　of　C5-PFK　and　its　mixtures　are　calculated　and　compared　with　those　of　C4-PFN　based　gases　and　SF6-N-2　mixtures.　The　GWP　and　saturated　vapor　pressure　for　gas　mixtures　are　calculated,　and　a　relative　value　R-GWP　is　defined　to　evaluate　the　greenhouse　effect　at　specific　pressure.　The　50%　breakdown　voltages　of　C5-PFK-Air　and　C5-PFK-CO2　mixtures　under　lightning　impulse　voltage　are　determined　experimentally.　The　mixture　ratio　and　filling　pressure　are　determined　taking　into　account　of　the　ambient　temperature　and　pressure　for　MV　apparatus.　The　possibility　of　practical　applications　for　these　mixtures　are　analyzed　by　combining　the　saturated　vapor　pressure　characteristics　and　the　breakdown　electric　field　strength.　The　synergy　effects　of　the　C5-PFK-CO2　and　SF6-N-2　mixtures　are　greater　than　those　of　the　C5-PFK-Air　and　C4-PFN-CO2　mixtures.　The　C5-PFK-Air　and　C5-PFK-CO2　mixtures　have　higher　dielectric　strength　than　SF6　at　0.1　MPa　when　the　C5-PFK　is　about　28%　under　the　temperature　limitation　of　-5　degrees　C.　The　pressure　increments　of　0.014　and　0.066　MPa　are　required　for　C5-PFK-CO2　and　C5-PFK-Air　mixtures,　respectively　to　reach　the　dielectric　strength　of　pure　SF6　at　0.1　MPa　under　the　temperature　limitation　of　-25　degrees　C.