The growing presence of power electronic converters has introduced new challenges for power quality, particularly due to distortion at frequencies above 2 kHz. To address this issue, the definition of accuracy classes for instrument transformers has been extended to include frequencies beyond the fundamental (wideband classes). However, simple and credible methodology for characterizing the ratio error and phase displacement of instrument transformers is still under development. This paper focuses on current transformers and presents a test setup developed to identify their frequency response characteristics. Using this setup, the frequency response of six conventional current transformers was measured up to 20 kHz, corresponding to wideband class WB2. In addition, the influence of key test signal parameters, such as current magnitudes and the number of distortion components, was evaluated. The results reveal significant differences between current transformers with turn ratios below and above 100, with the latter showing indications of resonance behavior. In contrast, the influence of fundamental current magnitude remains negligible up to 20 kHz.