Approach of obtaining the error of current transformers through the measurement of turns correction factor and impedance

Abstract

The error detection platform for current transformers (CTs) typically measures CT error by using the comparison method provided by International Electrotechnical Commission (IEC) 61869–2. It uses a more accurate standard CT as reference and the error of tested CT is obtained through comparison. This paper proposes an alternative approach of determining CT error by measuring the turns correction factor and magnetizing impedance. The measurement of magnetizing impedance is essentially equivalent to the excitation current measurement method. Therefore, high current sources are not required. More importantly, the measurement process requires only an impedance measurement instrument and a millivoltmeter, eliminating the need for constructing a complex system, and on-site CT error measurement can be realized. This method has engineering practical value. This paper firstly derives formulas for CT error in terms of turns correction factor and impedance. The turns correction factor is measured through the proposed differential voltage method, while the impedance is measured by using an impedance measurement instrument. Additionally, the measurement uncertainty introduced by the nonlinearity and impedance measurement instrument is analyzed. The final CT error results indicate that the proposed method yields comparable accuracy to the comparison method.