What was found
RT AC BUS FAILURE INFLIGHT. FOLLOWED QRH; RESET. ALL BUSES WE RE RESTORED. 30 MINUTES LATER AC BUS FAILED AGAIN. FOLLOWED QRH & ALL BUSES WERE RESTORED AGAIN. 2 MINUTES LATER AC BUS FAILED AGAIN. DID NOT RESET AGAIN. WITH APU RUNNING LT IN SINGLE GENERATOR OPERATIONS FOR REMAINDER OF FLIGHT. BITE BPCU-HAD DP TRIP; MAIN BUS/OVERLAP ZONE, T/S IAW FIM 24-2 0-00-810-802 PARA I. WIRING CHECK GOOD. FOUND RT BUS TIE BRK RELAY SHORTED CLOSED, S/B OPEN. R & R RT BUS TIE BRK IAW AMM 24-2 2-03-424-006.RAN BOTH ENGS & APU. RT BUS TIE OPS NORMAL. LT BUS TIE OPS NORMAL. APU BUS TIE NORMAL. BPCU BITE-NO FAULTS.