Raptor1963
Member
- Location
- Illinois
Have something really strange happening w/ a medium voltage generator, 12.47kv @ 1690kW 0.8pf., run through a step-down transformer 12.47kV to 480V, we are floating the neutral at the generator, bonded in the transformer, so delta-to-delta, thru a Cutler-Hammer Magnum 3000a breaker, to a Crestchic 3.3MVA resistive/reactive load bank. We started a full load test yesterday and after the first hour we burnt up one of the 7/phase 4/0 DLO type cable connected to the load bank. We assumed it was a bad cable, replaced, and re-started the test. After about 30 minutes we smoked another cable. Now we start looking at the current in the cables, now take into account monitoring the current/voltage at 3 different places, genset control panel, secondary side of the transformer, and load bank PC program, these all read even currents, equal voltages, and even kW/kVAR distribution across all phases. We have one single copper buss connection connection point on each end, the load bank/breaker/transformer, cable all came off the same roll/same lengths. For some odd reason the current chooses to split un-equally through the cables, to the point of overload. One cable in 'C' phase has double the current of the other cables in that phase, 'B' phase is pretty equal, 'A' phase has two cables that are running 1.5x the others in that phase. We tried taking off the reactive part of the load, same results. Thought maybe a load bank problem, so I brought in another loadbank, check current through the cables, same problem. Checked the cables on both sides of the transformer, unbalanced both sides. Any HELP?????