Comparison of Reference Setups for Calibrating Power Transformer Loss Measurement Systems

A unique comparison has been performed of two reference setups for the calibration of industrial power transformer loss measurement systems (TLMSs). The setups are developed by the Van Swinden Laboratorium (VSL), Delft, The Netherlands and Physikalisch-Technische Bundesanstalt (PTB), Brunswick, Germany, with the aim to calibrate industrial TLMS as a complete system, rather than just via its individual components, with an uncertainty better than 50 μW/VA, for voltages up to 100 kV, currents up to 2 kA, and power factors down to 0. The results of the comparison show excellent agreement of the PTB and VSL reference setups, both for the individual components as for the complete system. The phase agreement in the VSL and PTB component calibration results is better than (2 ± 5), (5 ± 12), and (10 ± 15) μrad for all calibration points in current ratio, voltage ratio, and power, respectively. In the full system comparison, the difference in the results of the VSL and PTB systems is less than 12 μW/VA for currents up to 1000 A and voltages up to 70 kV, with a -7 μW/VA difference averaged over all comparison measurements. This is well within the present 25 μW/VA measurement uncertainty of each of the VSL and PTB reference setups.