Transformer Test Report Missing data for PTLoad Heatruns

[williamhung]

I'm currently doing heatruns using EPRI's PTLoad to find the maximum overload a transformer can take.
Under old standards the temperature rise was 55 degree celsius but now it is 65 degrees.
The transformers I'm doing the heatruns to are very old (mfg. before 1970), and therefore have test reports with 55 degree rise data.
I need to find a way to use the data of this old test reports to do heatruns and obtain results according to the the 65 degree temp. rise.

 

[racobb]

I am not familiar with the PTLoad software, but it would seem that you need to do the loading calcs for the temp level of insulation you have. I am pretty sure that for 65 deg loading you need upgraded insulation.

I'm sure we will get some more input.

Alan

Democracy is two wolves and a sheep deciding what to have for dinner. Liberty is a well armed sheep!
Ben Franklin

 

[ichrist]

In my old job, we used software based on ANSI/IEEE c57.92-1981 (Guide for loading oil-immersed power transformers). The guide contains the necessary algorithms to write your own software.
I can't recall if it addresses the older temp rise standards, but there might be enough of what you need to create your own s/w.
Alternatively, the earlier standards , such as the 1962 version of ANSI C57.92 and NEMA TR98-64 have tables that guide you for loading capability. I am assuming your tx/s are designed to those older specs, of course.
Hope this helps,

 

[xfmrexpert]

If it is a transformer with thermally upgraded insulation, but the heat run was done at 55C, just check "55C rise insulation" for the insulation system. Enter the heat run data on the next "Cooling" tab for the 55C rating. Be sure to enter the 55C rating for "Test Load". Also, don't use the calc button to calculate the hot spot rise. Manually add 10C to the average winding rise from the test report and subtract the top oil rise to get the hot spot rise over top oil.

 

[prc]

If the transformer is old, made and tested for 55 C temp ris,it cannot be loaded for 65 C rise.When in US, 65 C was adopted, conductor insulation was changed to thermally upgraded paper.It is a good practice to avoid overloading on old units as normally they will be wet and wet transformers are more suspectable for accelerated ageing or bubble formation with temperature.

 

[Ratron]

For those who cannot afford PTLoad, Here is a link to an affordable Transformer Rating Software called Ratron based on C57.91-1995 IEEE Standard.

http://www.synchrogrid.com/Products.aspx