Field diodes blowing on 1000 kW diesel generator 2

[Djim cameron]

We been having a problems with the positive diodes blowing (4 times) of the diode block on a 1000 kW diesel Generator. This generator is one three generators at a non-grid connected DGS station. The incidences that I investigated the generator would be online by itself supply a load of 60%. Generator would quit producing voltage, AVR (decs250) would alarm over excitation, generator would trip on under voltage. any suggestions on what would be causing this? What generator stator, rotor, excitation system tests should be done? THanks

 

[edison123]

Keith, it's a 'high' voltage 'alternator' what did you expect?

Muthu

http://www.edison.co.in

 

[Djim cameron]

This picture is the rotor of a CAT 3512 oil/gas rig that failed catastrophically. It is now a boat anchor. I thinking/hoping the rotor on the C27 is similar, where I can get some leads on the jumpers to perform the pole drop test. thanks JC

 

[catserveng]

The 3512 tail end looks to be older than the C27 info you provided, the C27 tail end will be similar, but depending on vintage you may only have one jumper accessible in the rear instead of two. But a test across half the generator is better than not testing.

I usually scrape the insulation off the barrel of the lug to get a good test point, I don't recommended trying to unbolt the jumper, if you don't get it back on properly you can end up with another problem. Just coat it with some insulating varnish when you're all done.

On some smaller frames the jumpers are soldered to a tab coming out of the rotor pole winding, a bit harder to attach to.

MikeL.