Abstract: An apparatus for sensing and measuring the HV surge arrester current includes two toroidal current transformers arranged coaxially with respect to the earth wire of the surge arrester, elements for sensing the current signals emitted by the transformers and for converting the current signals in digital signals, and elements for transmitting the digital signals to an information network and analog state signals by relay activation. The two toroidal current instrument transformers are associated, respectively, one to elements for sensing the normal leakage current, and the other to elements for sensing the impulsive current, the latter comprising a circuit (TRIGGER) discriminating between “switching” and “lightning” signals, in which the basis for discrimination is a signal duration threshold, of about 35 ?s.