M
AVTMMTO3xx Rev 3 Sept 2013
40
Temperature Entry
If the transformer has winding temperature meters, use theses readings. Most
transformers will have a meter for each winding. Most meters are reading about
the same value for a static transformer. Use the average of the three readings and
place this number in the Winding Temp field of the Transformer nameplate
section of the form. A secondary method is to use the oil temperature. Use this
value in the winding temp field and oil temp field of the form.
Other information
The transformer has been out of service for at least 3 hours
The temperature of the insulating liquid has stabilized, and the difference
between the top and bottom temperature does not exceed 5ºC.
If the transformer is measured without oil, the winding temperature is normally
assumed to be the same temperature as the surrounding air.
Once the information and results are in the form, the results can be switched
from measured resistance to corrected resistance using the checkmark in the
transformer nameplate section.
Conversion of Resistance Measurements
Winding resistance measurements are normally converted to a standard reference
temperature.
The conversions are accomplished by the following formula:
Rs = Rm ( Ts + Tk )/( Tm + Tk )
where
Rs = resistance at desired temperature Ts
Rm = measured resistance
Ts = desired reference temperature
Tm = temperature at which resistance was measured
Tk = 234.5 (copper)
Tk = 225 (aluminum)
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