High-Frequency Current Transformer Design and Construction Guide

High-frequency current transformers (HFCT) are well suited as sensors for measuring transient current signals on power cables, such as partial discharges (PD). If the HFCT is well designed and its measurement bandwidth matches the bandwidth of the signal to be measured, high sensitivities can be achieved. However, optimizing the HFCT design for a specific measurement bandwidth is a difficult task because various design parameters affect its transfer function. In addition, there is little helpful literature on the relationships between HFCT design and resulting sensitivity/bandwidth. To give guidance and fill this research gap, this article aims to provide all the necessary information on HFCT development. For this purpose, an analytical HFCT model is derived and validated with measurements from various self-made HFCT sensors. The method for measuring their transfer function (or transfer impedance) is presented and the measurement data of all our manufactured prototypes are given. Based on these data, valuable relationships between various design parameters and the HFCT transfer function are analyzed. Based on our experience, detailed information about the sensor manufacturing process is provided. The developed HFCT model is an effective tool to simulate and optimize the sensor transfer function before it is built. In this way, HFCT sensors can be designed quickly and cost-effectively specifically as required.