Operation of inductive protective current transformer in condition of distorted current transformation

In the paper the influence of conductive disturbances on transformation of fault current by inductive protective current transformers is described. Analysis of the results from laboratory studies show, that for such condition primary current up to which the current transformer will comply with the requirements for composite/ratio error is decreased. This is caused by increased magnetic flux density in the magnetic core, which may even lead to its saturation. To perform worst case analysis the percentages of odd higher harmonics in distorted primary current for a required for tests THDI level were chosen in accordance with the limiting values presented in IEC 61000-3-12 standard, which defines the limits for harmonic currents produced by equipment connected to public low-voltage systems. Further research shown a significant impact of current transformer secondary winding load power factor on increase of the composite/ratio error with primary current distortion.