XFMR Temp rise rating

[mikehughes8]

Transformer temperature rise is defined as the average temperature rise of the windings above the ambient (surrounding) temperature, when the transformer is loaded at its nameplate rating.

Can anyone tell me the relationship between core and winding temperature. Does a core temperature that exceeds the temp rise rating of a transfomer give any indication as to the temp of the windings. With an IR camera I can get a core reading but cant obtain an accurate winding temperature. Since the windings are insulted i can only read the temp of the insulation.

***Im dealing with a dry-type XFMR 150 degree celcius rise with insulation rating of 220 degrees.

Any useful insights will be greatly appreciated

 

[Mike01]

temperature

temperature

Xfmr temperature rise information can be found on most manufacturers website to my knowledge every transformer has a 30 degree hot spot to start where the windings meet at the transformer core the lower the temperature class the lower total loses of the transformer when the load is 50% or greater, plus lower temperature xfmrs run cooler thus extending the life of the transformer and less cooling capacity is required from the other trades a xfmr with a 150 degree rise consist of a 30 degree hot spot and it rated to operate at 40 degree (total of 70) then when you add the temperature rise of 150 degrees you get 220 witch is the insulation class of the xfmr. The lower temperature also allows for a little more loading during an emergency situation as the overload capacity will be greater (15% @80degree) like I stated earlier most manufacturers like square d and cutler hammer have some good information on this at their websites.

 

[zog]

The rating is a rise (Or Delta T) limit based on the uneven expansion of the inner and outer part of the windings, uneven expansion will cause the windings to be damaged.