Inductive current transformer accuracy of transformation for the PQ measurements

2020

Sensors

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.

Section: Introductionmentioning

confidence: 85%

“…The magnetic core of the developed wideband inductive CT presented in Figure 1a is made of Ni80Fe20 tape [14]. Its quality preliminarily determines the current and voltage errors of the transformation of sinusoidal, as well as distorted, current.…”

Section: Wideband Self-calibration Of Inductive Cts With Application mentioning

confidence: 99%

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

Stano

2020

Sensors

“…Distortion of current in the power network causes the needed for control of the level of higher harmonics to ensure required power quality [1][2][3]. Mainly used inductive current transformers (CT) are able to provide wideband operation with their accuracy class determined for sinusoidal current of frequency 50 Hz [4][5][6][7][8][9]. Therefore, the measurement error of non-sinusoidal electrical power and energy is not increased [10].…”

Section: Introductionmentioning

confidence: 99%

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

Stano

2020

IEEE Access

The novelty of the paper contributes to the increase of the reliability of the methods used for evaluation of the inductive CTs accuracy of transformation of the distorted current. The results of performed analyses shows that the values of current and phase errors of transformation of the low order higher harmonics by inductive CT depends significantly from the phase angle between transformed higher harmonics of the distorted primary current and the self-generated higher harmonics of the secondary current. Moreover, higher harmonics of the distorted primary current may increase the peak value of the magnetic flux density in the magnetic core. Then the impact of the self-generated low order harmonics resulting from the nonlinearity of the magnetic core on values of current and phase errors of transformation of the higher harmonics of the distorted primary current is increased. Proposed evaluation procedure enables determination of the maximum values of current and phase errors of transformation of the higher harmonics of the distorted primary current. It is essential to determine the accuracy class. In such approach the impact of the secondary current's distortion caused by the nonlinearity of the magnetic core and the influence of the harmonic distortion on the peak value of the magnetic flux density are considered. Therefore, transformation accuracy of tested CT is ensured for specified range and type of the load of the secondary winding, rms values of primary current and its distortion. INDEX TERMS inductive current transformer, nonlinearity of magnetic core, transformation accuracy, distorted current, power quality, composite error, current and phase errors at harmonics.

“…Instrument transformers are widely used to decrease the value of the voltages and currents from the power grid to the levels appropriate for measuring and to protect circuits. Most of them are inductive and the non-linearity of the magnetization curve of their magnetic core causes the need for testing their transformation accuracy in the full range of the primary current/voltage [1][2][3]. Due to the large number of non-linear devices, the quality of the electrical energy in the power networks is deteriorated and thus the signal transformed by the instrument transformers is distorted.…”

Section: Introductionmentioning

confidence: 99%

“…In the case of inductive current transformers this may even have a negative impact on their transformation accuracy of the main component of the distorted current [2]. Of course, ratio and phase errors in the transformation of higher harmonics are usually different than determined for sinusoidal signals [3][4][5][6][7][8][9]. However, the 0.1 and 0.2 accuracy classes of inductive current transformers designed for transformation of sinusoidal currents of frequency 50 Hz may be preserved to 5 kHz [7].…”

Section: Introductionmentioning

confidence: 99%

Comparison of the Wideband Power Sources Used to Supply Step-Up Current Transformers for Generation of Distorted Currents

2020

Energies

In this paper a comparison of the wideband power sources of a pulse width modulation (PWM) inverter and a power supply composed of an audio power amplifier and a two-channel arbitrary generator is discussed. Their application is to supply a step-up current transformer for generation of the distorted current required to test the transformation accuracy of the distorted currents of the inductive current transformers. The proposed equations allow to calculate the maximum rms values of higher harmonic of distorted currents for its required main harmonic component. Moreover, they also enable the calculation of the maximum rms values of the main harmonic of the distorted current for which the required higher harmonic component may be obtained. This defines the usable bandwidth of the tested power source for their specific load. During work on high inductive impedance, the maximum voltage is the limitation that determines the higher harmonic value. While for resistive loads, the maximum current and the transistor’s slew rate are the limiting factors. The usage of the compensation system for the inductive reactance of the step-up current transformer under supply significantly increased its maximum output current. Its rms value with a 10% higher harmonic component up to 5 kHz was almost 400 A instead 100 A for the PWM-based power source and about 800 A instead 200 A for the power supply system with the audio amplifier.