B777 FLT CREW IS DISPATCHED WITH APU INOPERATIVE AND ENGINE DRIVEN GENERATOR FAILS AS ACFT IS ENTERING OCEANIC AIRSPACE. FLT CREW ELECTS TO RETURN TO DEPARTURE ARPT.

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ABOUT 2 1/2 HRS INTO FLT; THE L ENG GENERATOR FAILED. ACFT HAD BEEN DISPATCHED WITH AN INOP APU; SO WE WERE LEFT WITH 1 GENERATOR. FORTUNATELY WE WERE JUST APCHING OCEANIC AIRSPACE AND WERE STILL IN CONTACT WITH DOMESTIC ATC. ALL APPLICABLE CHKLISTS WERE RUN AND A CONFERENCE CALL WAS SET UP WITH BOTH MAINT AND DISPATCH TO WEIGH ALL OPTIONS. ULTIMATELY; I MADE THE DECISION (WITH ACQUIESCENCE FROM MAINT AND DISPATCH TO RETURN CONSIDERING THE FOLLOWING: THE WX WAS GOOD BEHIND US ALL THE WAY TO AND INCLUDING ZZZ; ALL OTHER SYS WERE RUNNING NORMALLY. WE WERE STILL CLOSE TO MULTIPLE; GOOD DIVERT FIELDS AND WOULD BE ALL ALONG THE COAST IF WE TURNED AROUND. FLYING FURTHER WITH ONLY 1 ARPT BTWN US AND THE OPPOSITE COAST OVER OPEN WATER WITH 1 GENERATOR WAS NOT AN OPTION I DEEMED PRUDENT AND OPERATIONALLY IT MADE MORE SENSE TO ME TO GET THE AIRPLANE BACK TO A BASE WHERE WE HAD BOTH MAJOR STATION MAINT AND FLT SVC PERSONNEL. WE ACTUALLY ENTERED OCEANIC AIRSPACE AND WERE HANDED OVER TO OCEANIC ATC AS OUR ANALYSIS AND FINAL DECISIONS WERE BEING MADE. WE THEN INFORMED ATC WE WERE DECLARING AN EMER AND INITIATED THE RETURN PROC AND WERE CLRED BACK TO ZZZ. THE REST OF THE FLT WAS UNEVENTFUL.