A DC9-50 IN CRUISE AT FL310 DECLARED AN EMER AND DIVERTED DUE TO ELECTRICAL BURNING ODOR CAUSED BY A R BUS 'B' PHASE INTERNAL FAILURE.

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AT CRUISE AND BEGAN TO SMELL SOMETHING ELECTRICAL. THEN SEVERAL CIRCUIT BREAKERS BEGAN TO POP (FUEL BOOSTPUMPS IN EACH TANK (2) R AC BUS; RIGHT AC SENSING; GALLEY PWR). THIS WAS FOLLOWED BY A LOSS OF SOME GAUGES AND INSTRUMENTS. PRIMARY FLT INSTRUMENTS WERE STILL WORKING. THE AC BUS AND SIDE OF CIRCUIT BREAKER PANEL WAS VERY HOT BUT BEGAN TO COOL DOWN WITHIN 10 MIN OF CIRCUIT BREAKERS POPPING. MADE DECISION TO RETURN TO DTW AS THE WX AT DESTINATION (MSN) WAS 500 1/2 WITH RAIN AND ALL SURROUNDING ARPTS WERE NOT MUCH BETTER. DTW WAS VFR. DECLARED AN EMER WITH ATC AND GOT CLRNC DIRECT TO DTW. DID THIS THINKING OF A POSSIBLE ELECTRICAL FIRE AND NORDO APCH IF CONDITIONS GOT WORSE. GRR AND LAN WERE ALSO OPTIONS ENROUTE TO DTW AND ALTHOUGH THEIR WX WASN'T AS GOOD AS DTW IT WAS BETTER THAN ORD; MKE; ETC. THIS ALSO ALLOWED ME TIME TO ASSESS WHAT EQUIP AND SYSTEMS WERE AFFECTED. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATED THE ELECTRICAL BURNING ODOR HEAT WAS CAUSED BY THE R AC BUS 'B' PHASE CIRCUIT BREAKER INTERNAL FAILURE. THE RPTR SAID THIS RESULTED IN A LOSS OF 'B' PHASE PWR ON THE R AC BUS.