Nonlinearity of the magnetization characteristic of the magnetic core in calculation of current error and phase displacement values of inductive CTs

This paper explores the implications of employing a load exhibiting a power factor of 1 to test the transformation accuracy of an inductive current transformer with an apparent power below 5 VA. It offers an explanation of the change in current error and phase displacement correlates with the load power factor. The impact of the load power factor on the secondary winding on the accuracy of inductive CT is investigated in detail. The paper introduces a newly developed method that allows for the calculation of current error and phase displacement values for any power factor with consideration of the nonlinearity of the magnetization characteristic of the magnetic core. To ensure required accuracy of calculations of utmost significance is the potential RMS value modification of the magnetic core excitation voltage, which may further impact the transformation accuracy. Consequently, the operational conditions during the test are modified, and, owing to the nonlinearity of the magnetization characteristic of the magnetic core, the values of current error and phase displacement are also changed-not only due to a different load power factor connected to the secondary winding of the tested inductive current transformer. To maintain consistent operational conditions for a given secondary winding load power factor, the resistance connected to the secondary winding during the accuracy test with the power factor equal to 1 should be corrected. Moreover, the findings of this paper lead to the conclusion that evaluation of the transformation accuracy of inductive current transformer for both secondary winding load power factors is essential to ensure its reliable future operation in real conditions with the required accuracy class.