Algorithm of Automatic Tuning for Ground-Fault Neutralizer in Distributing Mains

In some countries of the EU middle load power lines operate with a balanced neutral. In this mode a ground-fault neutralizer is usually shunted with a resistor. Line-to-ground short circuit is the most common fault in this kind of power lines. The article presents an adaptation mechanism for a ground-fault neutralizer with mathematical apparatus of descrete wavelet transform, which gives data both in amplitude-frequency and frequency-time range. Wavelet transform has several advantages comparing with short-time Fourier transform (STFT), especialy in nonsteady modes. The suggested algorithm allows excluding high-frequency interference and distortions from the voltage signal in zero-phaze sequence circuit. After WPT of the voltage signal, approximating and detalizing coefficients smaller than the investigated voltage signal operate in the algorithm. Welch's t-test, applied to determine free frequency performs well in non-stationary mode. This algorithm can be applied in control units for ground-fault neutralizers to compensate capacity earth-fault currents.