The bandwidth of instrument current transformer for fault detection in distribution networks

Distribution network detection devices generally use two kinds of instrument current transformer (ICT), of which one is used to transform the travelling wave and transient signals, while the other is used to transform the power frequency signals. Such scheme is neither necessary nor economical. This paper analyses the influences of sampling resistance, stray capacitance and magnetizing inductance on the frequency characteristic of ICT. Considering that the fault zero sequence transient current has a large transient component and a small power frequency component, an ICT with wide-band frequency accuracy has been chosen. Practical experiments have been done. The technical parameters given by the instrument factory are only within 20-20 kHz. The characteristics in higher frequency are seldom reported due to the lack of test means. The experiments are based on a transient tester instrument and current amplifiers which can output a wide frequency-band current between 20 Hz-100 kHz up to 50 A. The experiments showed that the predicted results were in good agreement with the measured ones.