Hi Gunnar,
I can't help you much other than to say we are having the same issue trying to figure out what if anything we should do with the ground grids at our power plants. Much of the grid is buried in concrete so inspection is not an option. Megger and others make 3 and 4 probe test sets...
One our gas turbines had a fault at its terminals which began as a single phase to ground fault and quickly developed into a three phase arcing fault. This was a 71MVA 13.8kV generator, the generator breaker opened in about 3 cycles and cleared the system contribution (~25kA) to the fault but...
Electricpete, I looked a little closer at the fine print and the part reference to >10 is actually from IEEE PC57.104 Draft 11D, a different part of the poster references IEEE C57.104.1991. I guess the >10 ratio got voted down in the 2008 version. I'll have to read the fine print a little...
I've got a poster from Siemens that shows various standards and ratios and it gives the following two references for CO2/CO ratios
IEEE C57.104:
"CO2/CO Ratio of <3 Excessive
CO2/CO Ratio of >7 - <10 Normal
CO2/CO Ratio of >10 Excessive
*These ratios are only valid when levels exceed minimums...
Can you post some more information about your generator? Voltage, air or hydrogen cooled and type of sensor? High PD on a hydrogen cooled machine is worse than high PD on an air cooled machine, because hydrogen under pressure supresses PD. High PD on a low voltage machine is also worse than...
Another option is to try an online dryout system such as this http://www.dryoutsystems.com/trojan/index.htm, the company I work for purchased one awhile back but I haven't heard how its working out yet.
An engineer from Eskom, a utility in South Africa, present a paper at the Iris Rotating Machines Conference in 2011 about how they had successfully used a robotic inspection vehicle to conduct visual inspections, an EL CID test and a wedge tightness test with the rotor in on 200MW turbo...
I would install the flux probe. At the company I work for we have installed flux probes on all of our 2 and 4 pole generators from ~25MVA up to 360MVA, and we continue to install probes on new units. We use the GeneratorTech version as we started installing these before the Iris model was on...
