This　paper　presents　a　novel　relay　for　power　transmission　line　systems,　which　is　based　on　a　combination　of　positional　and　boundary　protection　principle.　The　relay　installed　at　a　substation　is　responsible　for　the　protection　of　the　transmission　lines　associated　with　the　substation.　The　relay　is　able　to　offer　fast　trip　for　any　fault　on　its　protected　line　sections　without　the　need　for　communication　link.　The　paper　presents　a　detailed　description　to　the　basic　principle,　algorithm　and　design　of　the　combined　positional　and　boundary　protection　relay.　©　2009　IEEE.