Organic　Rankine　Cycle　(ORC)　technology　is　an　effective　technical　path　to　realize　power　generation　from　low　or　medium　grade　energy.　Utilizing　hermetic　expanders　with　internal　generators　has　become　an　important　development　direction　of　ORC　system　because　the　machines　are　easy　to　get　full　tightness.　However,　due　to　the　high　temperature　of　the　gas　in　expander,　it　will　be　very　difficult　to　cool　the　internal　generators　in　hermetic　expanders.　This　paper　introduces　three　schemes　for　cooling　the　internal　gener-ators　in　hermetic　expanders,　and　establishes　corresponding　thermodynamic　models　as　well　as　quanti-tatively　analyzes　the　influences　of　each　cooling　scheme　on　ORC　system.　The　simulation　results　show　that　the　spray　cooling　scheme　has　the　least　influence　on　the　thermodynamic　efficiency　of　the　system　whether　R245fa　or　R123　is　used　as　the　working　fluid,　and　the　maximum　thermodynamic　efficiency　drop　of　0.21%　caused　by　cooling　the　generator　is　much　smaller　than　the　other　two　schemes.　In　medium-high　tem-perature　conditions,　both　spray　cooling　and　exhaust-spray　cooling　schemes　can　effectively　reduce　the　generator　temperature.　However,　the　latter　has　a　much　larger　impact　on　the　thermodynamic　efficiency　of　the　system　than　the　former　one.　The　conclusions　can　provide　a　guide　for　the　design　of　hermetic　expanders.(c)　2022　Elsevier　Ltd.　All　rights　reserved.