Application of the inductive high current testing transformer for supplying of the measuring circuit with distorted current

Abstract

The increasing number of non-linear loads and renewable energy sources causes a decrease in the power quality in the power networks. Therefore, tests of current transformers should be performed in similar conditions. This requires generation by a high current testing transformer of distorted currents that rms values are from a few hundred to several thousands of amperes with a given harmonics levels. However, its frequency band of operation is limited by inductances of its windings and connected load that result from the length and parameters of the used current track and connected device under test. To ensure the constant rms value of higher harmonic of distorted secondary current with the increase of its frequency proportional increase of the rms value of this harmonic in distorted primary voltage of the high current testing transformer is required. However, the maximum permissible value of primary voltage is limited by the dielectric strength of insulation of the primary winding. The purpose of presented studies is to determine the factors that condition the frequency band of operation of a high current testing transformer and limits the range of higher harmonics while testing of the transformation accuracy of instrument current transformers for distorted currents.

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

“…Meanwhile, if the rated secondary current of the tested CT is equal to 1 A, the combined uncertainties type B are respectively equal to ±0.01%, The step-up current transformer was previously tested during transformation of the distorted currents. In the paper [25], it was demonstrated that it is capable of wideband operation and shows no resonance in the tested frequency range of higher harmonics up to 5 kHz. Equations (1) to (5) are further used to determine values of the current and phase error of the transformation of harmonics of the distorted current.…”

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

“…The measuring circuit is supplied by the programmable power voltage source through the insulating transformer [33]. If required for testes rms value of the primary current exceeds 20 A application of the inductive high current testing transformer for supplying of the measuring circuit with distorted current is required [34]. The oscilloscope is used to determine the waveforms of the excitation current measured by the RD resistor and the secondary voltage measured by the differential connection of two voltage probes.…”

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

“…In the presented application, the tested wideband power source was used for generation of a distorted current for supplying the step-up current transformer required for testing the inductive current transformer's accuracy in transforming the harmonics [7,17]. Therefore, laboratory tests were performed in order to determine their frequency band of operation and the required rms values of the main and higher harmonics of the distorted output current of the step-up current transformer.…”

“…In Figure 9 the following new notations are used: L nf -compensation inductor for 50 Hz component; C C1 -compensation capacitors for 50 Hz component; C Ch -switchable capacitor for compensation of higher harmonics; CT-current transformer; and HCT-step-up current transformer. The frequency band of the HCT operation is reported in [17]. The transformation accuracy of the CT, similar to the one used in this measuring system, is analyzed in [7].…”

“…Therefore, a proper wideband programmable power source capable of generating the voltage of the required rms value with both main and higher harmonics is essential. Moreover, the wideband step-up current (or voltage) transformer is used [8,9,16,17].…”