Harmonic and Rectangular Pulse Reproduction Through Current Transformers

摘要

Current transformer (CT) measuring properties for harmonic reproduction and rectangular pulse reproduction were investigated. Results show that harmonics are reproduced through CT with less error than the fundamental frequency component when the secondary load is purely resistive. With an inductive secondary load, CT accuracy deteriorates as the frequency increases. A CT is saturated at higher voltage levels with harmonics than it is with the fundamental frequency. The secondary current distortion, when a CT is subjected to a series of rectangular pulses, is determined by the ratio of the pulse duration to CT time constant. The rectangular pulses caused by traveling wave reflections on a power transmission line can be reproduced through CT with negligible distortion due to the short pulse duration, the large CT time constant, and the negligible influence of the secondary winding to ground capacitance. The maximum pulse amplitude and duration permitted to avoid saturation were found. Analysis indicates that the rectangular pulses caused by traveling waves along the transmission line can be reproduced through the CT without saturation if maximum pulse amplitude is less than or equal to the maximum rms value of the ac current rated for CT accuracy.