Generator Embedded Thermocouples

[Rodmcm]

I am refurbishing a 50year old generator which has embedded type K thermocouples in the stator. We attached thermocouple/4-20mA transducers direct onto thermocouples at stator junction box. We find that the temperature reading on all 6 is fine when there is no generation, but raises by some 30 deg once the generator is on line and generating.Certainly not a heat effect as it rises as fast as we raise current (MW or MVAR). Tried earthing one side of thermocouple with no effect. Have tested and verified no pickup in the transducer or 4-20mA leads when generating. Only conclusion is pickup in thermocouple leads in stator. Any suggestions?

 

[ScottyUK]

BTH? So they're at least 50 years old. I bet they are beautifully built. Must be hydro machines at that speed. Where are you (roughly)?



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Sometimes I only open my mouth to swap feet...

 

[Rodmcm]

As they say, big, thick and heavy but still spinning beatifully. They are in Australia but we are Kiwi engineers doing the refurb

 

[bartb102]

Hi, I'm new to this forum, just browsing and found your problem. We had similar issue with generator stator RTD's feeding a PLC RTD module. One RTD failed during startup, we left it connected, showing minimum temperature. When generator exciter was turned on, other RTD's on the module jumped about 12deg.C. Finally disconnected failed RTD, remaining ones now show correct temperatures. Seems the failed RTD was injecting ground current into the module.