Winding Temperature Measurement

1. For the stator, on larger machines, Resistance Temperature Detectors (RTD), usually 3 per phase. But these do not give winding temperature, because they are only in "spot" locations and must be insulated from actual conductors. But they can be measured and compared with the recorded factory test result.
2. For Rotor, if brushed, applied voltage (less brush voltage drop) divided by field current, gives rotor resistance, which can be compared with cold resistance and resistance/temperature chart for copper to give (mean) temperature.
3. Some machines have special temperature transmitters which use radio or inductive coupling to pass measurements from brushless rotors.
4. But these measurements do not tell you much, except that you are overloading a machine - which you know already from output volts/amps and excitation current or power factor.
   

Dear , I can't get your answer .. Could u please elaborate and send it to my email id furhrervarun@gmail.com it will be very helpful if u send some photographs Thanks in advance

Elaborating will not help, if you do not understand the short answer. I do not have photographs to hand. But I guess you may not know some things about electrical usage - consider following.

1. A winding on a big electrical machine is large. It is not all at the same temperature.
2. When "winding temperature" is quoted, this usually means the average temperature of the whole winding. A "100 ohm" resistance ( at 0 Celsius) winding of electrical copper increases its resistance to 134.5 ohms at 100 Celsius etc. This makes it quite easy to measure the average temperature of a winding electrically (When it is stationary, and all voltage is removed!).
3. But it is the "hot-spot" temperatures which are critical, because insulation will deteriorate most quickly here. It is not easy to know where! Machine makers go to much trouble to know where. Sometimes they get it wrong!
4. Knowing a relation between "hot spot" temperature and "winding temperature by resistance" the maker can specify the maximum continuous winding temperature for a good life. Because standards, like IEC34, specify maximum insulation temperatures, these are normally met and quoted.
5. It is the rotor which is under most stress in a generator. It is also the most difficult part to cool and measure temperatures.

It is possible you have an instrument called a "Winding Temperature Indicator (WTI)" on your Alternator control panel. They are much more common on transformers. Their purpose is to help indicate limits when an overload occurs. It is practical to overload a machine for a limited time, if it was not at full load and temperature before the overload. But WTI are not measuring the actual temperature, they are "indicators" fed from the output current (and maybe voltage too) of the machine which have a "thermal model" of the machine inside, so that the indicated temperature follows that of the machine - assuming the cooling system of the machine is working as it should!

Thank u very much for ur answer ...:)