AN ATR42 CAPT RPTED A TOTAL ELECTRICAL FAILURE IN THE VICINITY OF COY; CAUSING HIM TO RETURN TO SJU; PR.

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SHORTLY AFTER REACHING FL210; WE LOST THE #2 DC GENERATOR ALONG WITH A DC BUS #2; INVERTER #2; BUS TIE CONTACTOR; AND DC SVC/UTILITY BUS. SINCE THIS IS BASICALLY AN 'ELECTRIC' AIRPLANE; ALONG WITH THE ABOVE STATED FAILURES; WE EVENTUALLY LOST BOTH AIR DATA COMPUTERS AND THE EFIS ON THE FO'S SIDE. AN EMER WAS THEN DECLARED AND WE RETURNED TO SJU. AFTER COMPLETING ALL THE CHKLISTS; AN UNEVENTFUL LNDG FROM A VISUAL APCH TO RWY 8 WAS EXECUTED; WITHOUT ANY FURTHER COMPLICATIONS. I BELIEVE THE PROB STARTED WITH THE FAILURE OF THE #2 DC GENERATOR AND QUICKLY DETERIORATED WITH THE BUS TIE CONTACTOR FAILURE THEREBY FAULTING ALL THE OTHER #2 SYS. IF THE BUS TIE CONTACTOR WOULD HAVE WORKED CORRECTLY; ALL THE #2 SYS COULD HAVE AUTOMATICALLY 'TIED UP' TO THE #1 GENERATOR (DC) AND RECEIVED THEIR PWR FROM IT. HOWEVER; THE FAILURE OF THE #2 DC GENERATOR IS CONSIDERED A SERIOUS PROB ON THE ATR42 SERIES ACFT. THE CHKLIST 'DC GENERATOR FAULT' ACTUALLY REQUIRES YOU TO 'LAND AT THE NEAREST SUITABLE ARPT' AND AVOID IMC CONDITIONS. A THOROUGH AMOUNT OF TEAMWORK WAS REQUIRED TO RETURN THE ACFT BACK TO SJU. AS A CREW; I BELIEVE WE DID AN EXCELLENT JOB; SO DID ATC IN GUIDING US BACK TO SJU.