We have a bad stator temperature sensor in one of our GE Frame 6B generators. It is built by EGT around 1997. We are taking the rotor out for rotor/stator cleaning and rotor balance to improve the insulation resistance. While we have the rotor out we want to replace the faulty temperature sensor - can anyone advise how difficult this is to do and what is the GE part number?
Most of the RTDs in GE-manufactured generators used for heavy duty gas turbine applications are embedded into the stator when the windings are installed in the slots. They are not really replaceable--at least none of the ones I've ever worked on. Unless you were rewinding the stator I don't believe it's possible to replace the stator RTDs (on a GE-design manufactured generator used for heavy duty gas turbines).
Since EGT packaged the unit, is it a GE-manufactured generator? Many of the packagers used other generators (such as Brush); but it's possible that EGT was using GE generators. The two sites I worked at that had EGT-supplied gas turbines did not have GE-manufactured generators.
Most of the RTDs I've seen in generator stators are dual-element RTDs, meaning that there are two RTDs in a single strip/housing. Have you checked to see if there are one or two RTDs in the location, and have you checked to see if the second RTD (element) is working or not?
Finally, MANY GE-design control systems use three-wire, and sometimes four-wire RTDs in the generator stator, but only use twisted, shielded pairs (two-conductor cables) to get the signals into the control system. THIS IS FINE--it works fine (contrary to popular myth). But, the wiring has to be correct at both ends to work properly. So, this might be worth checking if the control system is a GE system, or possibly even if it's not.
Hope this helps!
The RTD was disconnected in the junction box on the end of the machine but the resistance was ok, about 114 ohms. There were spare RTD's wired from the generator stator to the junction box so we used one of them in case the original one had an intermittent fault. Some of the spare RTD's had their wired linked together - is there a reason for this eg. for generator testing?
The only reason I can think of for wiring RTD leads together is that in days gone by, no unused, low-level analog devices were left "floating" (unconnected to some circuit). So, their leads were wired together to prevent induced voltages from being developed and potentially causing sparks and/or electric shock to unwary individuals. (It's a really good idea for unused RTDs embedded in generator stators.)
This doesn't seem to be a common practice (from the factory) these days, and most field service people aren't aware of the dangers or the practice.