Transformer thermal characteristics & analysis software output validation

[TimDta]

With reference to transformer thermal characteristics, power system analysis software ETAP shows a short line & inrush current point(s) in protection co-ordination graphs. The transformer, built to AS60076, is 1000kVA, Dyn11, oil-immersed, Z=6%, temperature class of insulation=A, Winding temperature rise=65DegC, Top oil temperature rise=60DegC. Additional info such as Cross Sectional Area (sqmm) is not known and if required must be assumed. To validate ETAP (or even PTW, DIgSILENT) outputs, what additional assumptions need to be made & what steps/IEC equations are required to generate the transformer thermal(i.e. current vs. time) curve, inrush current point(s)?
Based on the basic 1000kVA transformer data inputs to ETAP, following are the data points:
Time(Sec) ETAP Current(Amps)
2 291.6
1.5 344.7
1 437.6
0.5 657

 

[dpc]

The damage curves are based on the applicable standard,transformer impedance, and system impedance. The software would be validated by reference to the standards.

The inrush point has nothing to do with the thermal characteristics. The value shown by the software is an approximation based on a lot of empirical data and experience. It is an educated guess and gross simplification since the actual transformer inrush current is a complex waveform that varies each time the transformer is energized.