AN innovative integrated current/voltage sensor for outdoor fault detectors

To improve the quality of supply, many European and foreign Utilities use motor-driven switches along the MV lines, both simply remote-controlled and able to operate autonomously (for example thanks to protections). Enel, in Italy, installed about 90,000 motor-driven switches in protected boards and nearly 20.000 remote-controlled pole-installed switch disconnectors. About 1/3 of switchboard installed switches are equipped with fault detectors (to be installed on MV underground cables) and, by means of an Remote Terminal Unit signals from fault detectors, it is operated an automatic fault clearing and supply restore. Recently ENEL purchased some thousands of an outdoor fault detector equipped with an innovative integrated current/voltage sensor, suitable both for networks with compensated neutral, isolated neutral or resistor earthed. The current signals are detected by means of non ferromagnetic transducers. The overall performance of this outdoor fault detector is absolutely in line with that of the traditional cable fault detectors, allowing it to be totally coordinated with the MV feeder protections (its sensitivity allows to select phase to earth faults up to 6 kΩ on networks with compensated neutral). These outdoor fault detectors, able to detect overcurrents and cross country faults besides the directional detection of phase to earth faults, are perfectly suitable to equip pole-installed switch disconnectors and reclosers, making possible the automatic selection of faults with low costs.