The electrical currents induced in the modern technological systems generated by great geomagnetic storms (known as geomagnetically induced currents or GICs) can disrupt or damage the transformers of the high voltage power grids.These harmful effects have been usually observed only at high geomagnetic latitudes (such as in Canada or Scandinavia). Nevertheless, some transformer failures in lower latitudes than that of Spain were reported in South Africa on the occasion of the Halloween storms of 2003.To assess the accuracy of the model developed by the Ebro Observatory, GICs are measured at some transformer neutrals in the grid. The GIC is measured by means of an open loop Hall Effect transducer. The output voltage of the transducer is digitized at 1 kHz using a Real-TimeAcquisition System. This system also measures the temperature of the transducer using a thermocouple in order to take into account the temperature variations of the transducers. Finally the measurements are synchronized by GPS and the data are transmitted using a UMTS modem. This controller allows performing harmonic analyses of the neutral current, in order to detect the possible existence of the sixth harmonic, which is an indicator of the transformer saturation. These measuring devices have been deployed and installed at three different nodes of the grid.