Measurement of Ratio Error and Phase Displacement of DC Tolerant Current Transformers

Two main errors exist in the current transformers: the ratio error and the phase displacement. DC tolerant current transformers are used in modern electricity meters. This brings some advantages but at the same time increases ratio error and causes higher but almost constant phase displacement. Therefore it is important to measure both errors. The indirect method of these errors measurement the errors has been tested on a commercial DC tolerant current transformer with manufacturer declared errors and the calculated errors were in very good accord with the declared parameters. This way the verify of the indirect method was proven and it has been used for further measurements. The measurements have been done with four DC tolerant current transformers that use cores made by different manufacturers. The cores have had different permeability and the results have shown the dependence of measured errors on permeability. Next, phase displacement of three of four measured current transformers have been found almost constant, which is important to the current transformers used in the electricity meters.