ANALYSIS OF MAGNETIC-FIELDS DUE TO 3-PHASE BUS BAR CURRENTS FOR THE DESIGN OF AN OPTICAL CURRENT TRANSFORMER

The de and ac magnetic fields due to transmission currents flowing thr ough bus bars arranged side-by-side are analyzed to design the three-p hase optical current transformer. The structure of optical current tra nsformer with a double core for magnetic shielding is proposed based o n the analysis of the interference effect of magnetic fields originate d in the three-phase transmission currents and those of the eddy curre nt fields induced by the component of three-phase ac fluxes perpendicu lar to the wide flat face of plate-form bus bar. It is shown that when a value of 100 is assumed as a relative permeability for the inner sh ield-core, the eddy current fields which hinder the exact measurement of transmission currents can be decreased by less than 1/10 in the spa ce between the inner core and the outer one, where the magneto-optical field sensor is arranged.