RAgrawal,
Does your rotor have slip ring connections?
If you can monitor V & A imput to your main field winding, you can derive R in ohms
From there, and with the aid of your manufacturers cold resistance figures and ambient temperature taken at that time, you can use:
temp(Deg k)=[(R hot-R Cold/ R cold)x(234.5 + ambient)]+/- ambient difference (between hot and cold ambient)if the hot ambient is larger than the cold ambient, subtract the difference, if small, add the difference.
This should give you a figure accurate to say + / - 1 degree for average temperature, but will not give you information on 'hot spot' temperatures, or differences between trailing & leading edge temperatures and outhangs.
For that you need embedded PT100 RTD's or similar.
There is a long writeup on the subject in EPRI 5036 V6 page 127-130.
More feasiable for large machines. You likely want to select a location representative of the hottest spot which is inside the copper rotor bar. Thermocouple can be inserted into a hole drilled in the rotor bar. For very large machines may be able to fit an rtd. Get the signal outside the machine using one of two concepts they call
1- "Rotating Transformer Circuit; and 2 - FM telemetry circuit.
They give no mention of which vendors offer this. I'm guessing mabye Adwell?
You may be able to install a viewing port of suitable infrared transparent material which may have line-of-sight access to the end ring temperatures.
If you're going to use this approach then you need to coat the end-ring with black paint so emissivity is precisely known.
The downfall is that the endring is not the hottest spot... the rotor bars are. There will obviously not be any way to get a line of sight path to the rotor bars.
Electricpete,
where can I find this EPRI doccument please?
Also, in my experience, the hottest spot is two or three laminations ( turns) away from the steel corner of the core pack, as this is the area least cooled and suffers most from the restrictions in heat dissipation due to transfer of heat through insulating materials, such as a nomex slot liner, conductor wrapping, etc.
How do you get to that point via drilling without causing potential failures through shorted turns on the rest of the conductors above it?
Don't get me wrong, I am very open to alternative suggestions and it may be that my scale of generator provides greater restrictions than does yours. It's an area of great interest to me & I look forward to your comments.
Unfortunately, the Electric Power Research Institute (EPRI) documents are usually only available to the utility community that pays fees to EPRI to sponsor the research.
I apologize for referring to a document that is not available to the other members of the board... it was the only material I had on the subject.
With regard to the hottest point on the rotor, the author of the document I read believed that the hottest spot on induction motor rotor was the rotor bars. The method used here was to drill a hole axially into the rotor bar through the end ring and several inches into the rotor bar. There was no direct mention of syncronous generator in EPRI5036 V6.
One other lower-tech way to monitor surface rotor temperature was also mentioned... there are thermal-sensitive paints and adhesives which will change color as a function of the highest temperature they are exposed to.
