Estimation of Broadband Transfer Function of HFCT Using Time Domain Measurements

The presence of partial discharges (PD) in high voltage insulation is one of the prime factors responsible for equipment failure. High-Frequency Current Transformer (HFCT) is a simple and relatively cheap instrument that can be used for the detection of partial discharges. However, it is very important to characterize or identify the transfer function of HFCT for the identification of PD. PD current pulses have a wide frequency band and hence the measurement of the wideband transfer function will be advantageous in providing better resolution for the PD current pulses. This paper focuses on the characterization of the transfer function of the HFCT using an innovative method. In this work, an HFCT sensor has been excited with two different pulses with two different ranges of frequency content (20 kHz- 10 MHz and 1 MHz – 500 MHz) and the response signals are measured. Combining these responses, the transfer function is estimated, covering a much wider range than the frequency range of individual excitation pulses. The identified transfer function shows very good matching with experimental measurements.