By getting inductance-current curve and DC-biased exciting current peak-DC curve of ultra high voltage（UHV） transformer

we put forward a kind of real-time model for DC-biased exciting current calculation

in which

the DC resistance of UHV transformer is ignored.Compared with the time-domain magnetic-circuit coupled method

the real-time calculation is proved to be exact.Through selecting the optimal iterative algorithm and applying a variable step strategy

the efficiency and real-time performance of real-time calculation model can be enhanced.Given any DC data of the value

we can get the corresponding waveform of exciting current with the DC bias in the millisecond time.Results show that real-time model for DC-biased exciting current calculation has great advantages in terms of performance on computing speed and accuracy.The real-time model has widespread application prospect in online assessment on electric parameter perturbation due to the DC-biased problem of UHV transformer

preventing refusing action or incorrect tripping of power system relay protection and other electrical equipment safety operation and so on.