Anyone familar with DC generators ? Years ago I worked for a Mill that had a Rolling Mill. The Mill had two reel motors at 250 HP and a main mill motor at 500 Hp. In the motor room was all the drives.
Set up on bearing stands from left-to-right were the generators in this order-250kw-250kw-1000hp syn, mot- 500kw-, respectively the 250kw generators were for the reel motors the 500 kw for the main-mill motor, the prime-mover was the 1000 Hp syn, motor, 2300volt @ 250 V DC synch. the synch speed was 1800 RPM.
The question is this, in all there were 5 bearing stands to support the MG set, when disassembled we had found that the bearing stands were insulsted from ground except one. Since then I have talked to Reliance Electric and GE who use to be big in Mill MG sets much bigger than these and nobody has a clue why only one bearing stand was grounded,the only thing I can come up with is stray currents, hysteresis losses etc, I am still not sure why.
Has anyone else seen a situation like this and why the bearing stands are set up like this.
-Mark-