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 .mu.s.
