A measuring system to identify the frequency response of high current instrument transformers

In this paper a measuring system is presented to determine the frequency dependent transmission behaviour of high current instrument transformers (HCTs). Due to its high requirements, several components have been specially designed. These special requirements and the applied technical solutions are presented in this paper. Power amplifiers generate currents with a frequency range up to 40 kHz. The magnitudes of the generated currents are stepped up by using special transformers. A rigid Rogowski coil measures primary current and a shunt is used to measure the secondary current of the HCT to determine its frequency response. A special calibration concept of the used Rogowski coil and shunt ensure high accuracy (0.1 %) of the measuring system in a frequency range up to 40 kHz. Test measurements at a HCT with a rated primary current of 8 kA show the capability of the measuring system.