A Novel Combined Alternate Current Sensor for Variable-Frequency Scenario

Abstract

Recent developments of variable frequency applications have accelerated the demand to look at the measurement technology on variable frequency signals. Most low voltage (LV) circuit breakers are designed to operate at a fixed frequency. Therefore, it is necessary to propose a variable-frequency measuring concept for LV protection devices. In this paper, we propose a novel combined alternate current sensor based on the Rogowski coil and iron-cored current transformer (CT), which can provide a high accuracy within the frequency range of 0.2Hz-200Hz and amplitude (up to several hundreds of kA). For the iron core CT, it covers the small current at ultra low frequency. For the Rogowski coil, it covers other current levels. In order to achieve the performance, an improved compensation method for the iron core CT is used to obtain higher accuracy and a combined integration method for the Rogowski coil is applied to expand the band of frequency, especially at ultra low frequency.