Abstract: A shell-core current transformer comprising a tubular main insulator, a measuring core arranged at least substantially coaxially with the main insulator and comprising a primary winding and a secondary winding, and a protecting core, likewise arranged at least substantially coaxially with the main insulator and comprising a primary winding and a secondary winding. The measuring core and the protecting core have a common primary winding, arranged outside the main insulator, and a common outer core part functioning as magnetic return circuit. The inner part of the measuring core, with the exception of the inner yoke portions, and the secondary winding of the measuring core are within the main insulator placed inside the inner part of the protecting core and inside the secondary winding of the protecting core, and the measuring core and the protecting core have common inner yoke portions.

Abstract: A current transformer comprising a tubular main insulator, a number of first windings arranged around the main insulator, and a number of second windings arranged inside the main insulator. The second windings are arranged opposite their corresponding first windings so that the pairs of windings formed in this way are, in the direction of the axis of the main insulator, at a distance from each other. The primary windings are connected in series. A magnetic circuit related to each pair of windings consists of a first core portion that surrounds each first winding from the outside and has yoke portions, and of a second core portion covering each second winding and the main insulator from the inside and has likewise yoke portions. The subsequent cores, or core portions, have common intermediate yoke portions and the primary windings are arranged so as to magnetize both cores in the same direction.