Michal Kaczmarek

Simulation of the influence of conductive disturbances on accuracy of the voltage transformers during measurements of the power quality

Voltage transformers which are the source of the signals for electrical power network protection apparatus through transformation of high voltages to low voltages enables accurate measurement of high voltages and estimation of the power quality in the power network. Significant is then accuracy of the instrument transformer both in steady and transient states which means permissible values of the voltage error and the phase displacement during transfer of distorted voltages. These errors of the voltage transformers depends from the value and type of the loads of the secondary sides, frequency and value of primary voltages. Additionally, decrease of the power quality caused by nonlinear loads and conductive electromagnetic disturbances have an influence on the errors of the voltage transformer. Deterioration of the accuracy class is meaningful in honest estimation of the power quality.

Wide Frequency Operation of the Inductive Current Transformer with Ni80Fe20 Toroidal Core

Abstract—During transformation of the power frequency currents, inductive current transformers are characterized by the values of current errors and phase displacement, which determine their accuracy class. However, current transformers catalogues do not specify these metrological parameters of transformation for the sinusoidal signals at frequencies higher than 50 Hz (60 Hz). The aims of this article are the descriptions of the metrological and magnetic circuit properties of the inductive current transformers with an Ni80Fe20 toroidal core in condition of sinusoidal currents transformation of frequencies from 50 Hz to 20 kHz. Determined magnetization characteristics of tested current transformer magnetic circuit are the justification for the course of its measured wide frequency metrological characteristics. Moreover, they may be used in designing the current transformers with an Ni80Fe20 toroidal core for transformation of the above 50-Hz frequency currents. The classification procedure was used in this article to define the current transformers accuracy for wide frequency operation and measurement method for determining their current errors and phase displacement for transformation of sinusoidal signals at frequencies from 50 Hz (60 Hz) to 20 kHz are presented.

Method of current transformer metrological properties estimation for transformation of distorted currents

During transformation of power frequency currents inductive current transformers (CTs) are characterized by precise, acceptable in accordance with their accuracy class, values of current errors and phase displacements. CTs catalogues do not specify metrological properties of transformation for distorted currents. The aim of the paper is to present a new method for evaluating the metrological parameters of CTs during transformation of distorted currents based on determined values of the composite errors / transformer correction factors.

Analysis of operation of voltage transformers during interruptions and dips of primary voltage

Short transient states during interruptions and dips of the supply voltage of the voltage transformer are the cause of low power quality and source of impulsive conductive disturbances which are transferred to secondary side of the voltage transformer. Maximal values of these impulses are able to exceed even several times rated rms values of primary and secondary voltages. This may lead to abnormal operation of measuring and protection apparatus connected to the secondary side of voltage transformer or even to their damage. In this article used methods of measurements for calculation of the factor of transfer of impulsive disturbances from primary to secondary sides of voltage transformer are presented as well as results of analysis of the influence of construction parameters of windings and their operation conditions on the amount and quality of this transfer.

Analysis of the influence of the level of signal distortion on current error and phase displacement of the inductive current transformers

The aim of the paper is to present results concerning the influence of conductive disturbances on accuracy of transformation of distorted signal main harmonic through the inductive current transformers (CTs). Analysis of the results from the laboratory studies shows, that conductive disturbances in the CT primary current, in some measuring conditions, cause decrease of the accuracy of transformation of the main harmonic of distorted current. Determine of the current error and additionally phase displacement of the inductive CT for main harmonic of the transformed distorted current enables with the previously estimated value of the composite error calculation of the maximal changes in values of selected factors e.g. THDI used for characterization of the power quality caused by the usage of tested CT in indirect measuring system.

The influence of the method of winding construction on metrological properties of current transformers designed for systems of monitoring of power quality

Proper estimation of the power quality in case of high current strength or necessary of separation between tested and measuring circuits requires determine of the level of conductive disturbances through the current transformer. The scope of the article is description of the results of the comparative laboratory research on estimation of accuracy of transfer of distorted currents through current transformers with toroidal core and windings made typical from coil wire and with the aid of a new method from copper wattle. In the paper outcomes of analysis of the influence of the method of winding construction on metrological properties of current transformers during transfer of distorted currents are presented.

Simulation of voltage transformer operation in the external magnetic fields

In the article method and results of time-domain simulation in Matlab software of voltages on primary and secondary sides of the voltage transformer during its work in environments in which strong external magnetic fields are present. On the base of presented simulation results it is possible to determine the actual value of voltage on secondary side of the voltage transformer in dependence of actual value of voltage on primary side of the voltage transformer, load value of the secondary windings and external magnetic field strength. Time-domain simulation in Matlab software of voltages on primary and secondary sides of the voltage transformer also enables determine of phase displacement between actual values of these voltages.

Simulation of the voltage transformer metrological characteristics

In the article, results of simulation and laboratory research of designed voltage transformer are described. In the first part of the paper voltage transformer model is presented. Second part of the article is dedicated to voltage transformer model errors simulation. In the last section of this paper verification of simulation results is described. Correct simulation of the voltage transformer enables shorten design time and reduction of cost production.