A high gain, low distortion and high noise immunity high frequency current transformer, (HFCT) partial discharge sensor device allows obtaining a high measurement accuracy, with a self-check system for fixed monitoring of high voltage equipment and installations. The device includes a ferrite core; a first measurement coil wound to the ferrite core; and a first coaxial cable welded to the first measurement coil. The sensor device further includes a second auxiliary check coil wound to the ferrite core; an electrical resistance in series with the auxiliary check coil; a second coaxial cable welded to the electrical resistance; and an outer coating of resin.