In this paper the design and construction of an online non-invasive noninvasive partial discharges (PD) localization system is presented; it is integrated by four equal discone antennas with a wideband of 30 MHz to 1.2 GHz and a central frequency of 615 MHz connected to a four-channel high-resolution digital oscilloscope. The obtained electromagnetic signals are processed in a personal computer using Wavelet Transform and Fast Fourier Transform (FFT) to reduce electromagnetic noise and identify the source of the PD respectively. Additionally, a spherical algorithm for spatial localization in R3 is used. High-voltage laboratory and in situ measurements are reported.