Sorry, just read your further thread with regards to the VFD suppling Auxillary motors, that are supplid to the machine down a common umbilical.
Check waveforms and AC on the DC bus with the VFD running, and them for test, without, over a coulpe of load and speed ranges.
I take it that the VFD...
I agree with the other threads that spring pressure & vibration could be issues. If you have replaced all the brush holders for new, this removes them from the equation.
Has the neutral plane been interfered with? Where the brush holders positions marked before replacement, or can they only be...