The growing integration of renewable energy sources into national power grids is impacting electricity quality, primarily due to the widespread use of electronic power converters. These converters, which rely on switching components, can introduce high-frequency harmonics, reaching up to 150 kHz, into the grid. However, the current international standards and state-of-the-art literature on instrument transformers (ITs) provide limited guidance on methods, techniques, parameters, and metrological requirements necessary for power quality (PQ) measurements at frequencies above tens of kilohertz. In response, this article presents an example of cost-effective measurement setup used to test four medium-voltage low-power ITs (LPITs) within the frequency range of (9–150) kHz. A detailed uncertainty analysis is conducted using both standard accuracy indices [ratio error (RE) and phase displacement (PD)] and less common indices (composite error). Finally, this article discusses an approach to the uncertainty evaluation for high-frequency components. The results demonstrate the method’s applicability, replicability, and value for end users.