Current Transformers (CT) and Voltage Transformers (VT) are the primary sensing elements in electric power systems. While their performance at a single frequency Is well known, it is necessary to analyze the performance of CTs and VTs for harmonic excitation. A single virtual instrument that can be used for performance measurements of Instrument Transformers (IT) in addition to analyzing the magnetic characteristics of cores is proposed. Experimental results are shown to validate the proposed method. © 2004 IEEE.