Wideband Self-Calibration Method of Inductive CTs and Verification of Determined Values of Current and Phase Errors at Harmonics for Transformation of Distorted Current

Abstract

Self-calibration of a designed wideband inductive current transformer (CT) was carried out in the ampere-turns condition. This method does not require a reference transducer. The values of current and phase errors at the harmonics of frequencies from 100 Hz to 5 kHz were determined for the distorted primary current of the rated main frequency equal to 50 Hz. These results were verified based on the comparison of values measured between two CTs and calculated as the difference between values obtained from their calibration. Moreover, from vectorial diagrams drawn for transformation of the higher harmonics, the source of the change in the values of current and phase errors with frequency is explained. Furthermore, the method for calculation of the values of the corresponding harmonics of the current associated with the active power losses in the core and the magnetization current is presented.

Nonlinearity of Magnetic Core in Evaluation of Current and Phase Errors of Transformation of Higher Harmonics of Distorted Current by Inductive Current Transformers

“…However, during the tests resistive loads are used not to additionally increase the secondary voltage and the magnetic flux density for transformation of the higher harmonics of the distorted primary current. Selected objects of the research have the primary and the secondary currents ratio equal to 1 in order not to require reference current transformer, as it could be expected to affect the results of the research [32]. In the measuring circuit presented in Fig.1 the differential connection is made in accordance with the standard IEC 61869-2 [30].…”

A Simple Method for Compensating Harmonic Distortion in Current Transformers: Experimental Validation

“…The main reason is often supposed to be the bandwidth limitation [ 16 ] due to the dynamics of the CT; techniques aimed at compensating its frequency response can be found in the literature [ 17 , 18 , 19 ]. However, (weak) nonlinearities are also present even when the core operates well below saturation [ 20 , 21 ]; their impact is significant as long as the measurement of low-order harmonics is concerned. In principle, they can be mitigated through a specific design of the CT [ 20 ] or by adopting signal processing techniques that enable significantly more accurate harmonic measurements.…”

“…However, (weak) nonlinearities are also present even when the core operates well below saturation [ 20 , 21 ]; their impact is significant as long as the measurement of low-order harmonics is concerned. In principle, they can be mitigated through a specific design of the CT [ 20 ] or by adopting signal processing techniques that enable significantly more accurate harmonic measurements. In this respect, [ 22 ] proposes to compensate for nonlinearities through frequency-domain linearization around a specific working condition, defined by the amplitude of the fundamental component.…”

Transformation of Transient Overvoltages by Inductive Voltage Transformers

“…The inductive instrument transformers are subject to many nonlinear effects causing problems in the accurate measurement of PQ issues [ 4 , 6 , 7 , 8 , 9 , 10 , 11 , 12 ]. The rms values of the slow-front transient overvoltage in the secondary circuit of the inductive voltage transformer results from the internal resonance caused by the simultaneous presence of inductances and capacitances in the inductive voltage transformer (VT) [ 6 , 7 , 12 , 13 , 14 , 15 , 16 ].…”