This　work　proposes　an　improved　broadband　equivalent　circuit　model　of　the　winding　system　of　an　ultrahigh-voltage　direct　current　(UHVDC)　converter　transformer　and　the　validation　experiment　of　the　model　conducted　on　a　tapped　transformer.　The　matrices　of　the　inductance,　capacitance,　and　resistance　parameters　in　the　improved　model　were　all　obtained　by　the　finite　element　method　according　to　the　winding　system　structure　of　a　UHVDC　transformer.　Then,　the　potential　distributions　along　the　windings　under　impulse　voltages　with　different　waveforms　were　studied　in　detail.　Finally,　the　relationship　between　the　potential　gradient　and　waveforms　was　obtained.　This　work　provides　a　convenient　method　to　acquire　the　broadband　electromagnetic　transient　characteristics　of　the　winding　systems　within　UHVDC　converter　transformers.　©　1965-2012　IEEE.