Method and screen for shielding a current transformer as well as current transformers with such shielding

摘要

A current transformer comprising a circumferential core (12) and a through-going conductor (14) forming the primary winding of said transformer, and a secondary winding (16) wound on defined portions of the core (12) whereas the remaining portion of the core (12) is not covered by windings an provides a yoke (18), should be protected against exposure to environmental fields, especially when it forms part of a three-phase system with closely arranged conductors involving strong current intensities. According to the invention, the yoke or yokes exposed to foreign magnetic fields are completely or partially shielded by means of one or more shields (50) of a ferro or ferrimagnetic material neither extending over nor covering any windings or portions of windings. By foreign magnetic fields is meant fields beyond the field caused by a current in the primary winding of the transformer. In this manner the current transformer can meet the desired measurement accuracy.