1.IntroductionWiththeincreasingofturbo-generator(TG)capacity,thelimi-tationontheabnormalfrequencyoperationisgrowingmorerestric-tive.InordertoensurethesafetyoperationofcertainTGunit,splitingdevicewhichisolatesthegeneratingunitfromthesystemisem-ployedwhenthesystemfrequencyisdeclinedtoacertainextent.However,duringthedegradationoffrequency,toisolatethelarge-sizedTGunitfromthepowersystemwillcausethesystemfre-quencytofurtherdecline.Hence,howtousethelowfrequencysplit-tingprotectionproperlyandhowtocoordinatetheoperationofunderfrequencyloadshedding(UFLS)withunderfrequencygeneratorsplitting(UFGS)aresignificantforsecuringthesafetyoperationof