transformer what enclose active conductors providing the differential summation of vector currents which enables the detection of leakage currents, trafo, mis ümbritseb aktiivseid juhtmeid, mis tagab vektorvoolude erineva summeerimise, võimaldades lekkevoolu tuvastamist ja mõõtmist, single, or a group of three, current transformer(s) so connected as to transform only the residual current