Research method of identifying transformer inrush current and fault current based on VMD-HHT

To settle the problem that identifying inrush current and fault current of large transformer is difficult, a new identification method which is a combination of variational mode decomposition (VMD) and Hilbert-Huang transform (HHT) is come up with. Firstly, the inrush current and fault current signals are decomposed into multi-band intrinsic mode function (IMF) by using VMD. Secondly, the instantaneous frequencies of each intrinsic mode function (IMF) of inrush current and fault current are calculated respectively by Hilbert-Huang transform, so that the corresponding Hilbert spectrum is obtained. Finally, the Hilbert spectra of inrush current and fault current are filtered by band-pass filter to remove the similar main lobes and some burrs. It is concluded that the Hilbert spectra of inrush current and fault current are significantly different from each other. In order to facilitate engineering application, the energy values of the first 16 sites in the Hilbert spectra of the two are taken to identify the inrush current and fault current, and the protection criteria are obtained.