Abstract
When very fast transient overvoltages (VFTO) enter a transformer, it happens that they excite large interturn voltage in the windings due to resonance phenomenon. We simulated the transient interturn voltage by the method described bellow.
First, the transfer function H(ω), which represents the ratio of intertum voltage to input voltage, of a transformer is obtained by using the multiconductor transmission-line theory. Secondly, VFTO in GIS, vin, (ω), is analyzed by Electro-Magnetic Transients Program (EMTP), and then Vin (ω) in the frequency domain is simulated using Discrete Fourier Transform. Lastly, applying the Inverse Discrete Fourier Transform to Vin(ω)x H(ω), we obtain the response of intertum voltage to the VFTO in the time domain.
We simulated transient intertum voltage in a 500 kV class model transformer for two kinds of VFTO waveforms. Large intertum voltage was generated when the frequency of oscillation in VFTO coincided with the resonant frequency of transformer windings.
