Saytaro Kon

ECT Evaluation by an Error Measurement System According to IEC 60044-8 and 61850-9-2

A high-accuracy error measurement system for calibration of digital-output equipped electronic current transformers (ECTs) is described. The system has been developed in conformity with the requirements for digital information networks in IEC 61850-9-2 and for accuracy class and error measurement procedures in IEC 60044-8. The system has also been designed to achieve simultaneous and synchronous samplings between an ECT/MU and a reference measuring unit, a procedure for capturing and filtering sampled value (SV) packets and data processing using the discrete Fourier transform with error compensations for an integrating analog-to-digital converter. The system employs a prototype commercial digital-output equipped ECT consisting of an optical current transformer (OCT) and a merging unit (MU). The error sources of the system are discussed for the error compensations and uncertainty estimations. Based on the principle of the system, the accuracy and temperature dependence of the prototype OCT/MU are evaluated and are confirmed to be within the limits of errors of accuracy class 0.2S.

Uncertainty Evaluations of an AC Shunt Calibration System With a Load Effect Reduction Circuit

An ac shunt calibration system at the National Metrology Institute of Japan (NMIJ) has been developed. The uncertainties of the system were estimated 3.4 μΩ/Ω for in-phase and 8.6 μrad for quadrature at 55 Hz/5 A. Meanwhile, the enhancement of the system is planned up to 10 kHz/10 A. For this goal, the accuracy and high-frequency performance of the buffer amplifier, which have the largest influence on the uncertainties, have been improved by developing a load effect reduction (LER) circuit. The LER circuit cancels out the effect of output impedance of the buffer amplifier. The effect of the circuit on the buffer amplifier allows the uncertainties of the ac shunt calibration system to be reduced into 2.6 μΩ/Ω and 8.2 μrad at power frequencies.

AC shunt calibration using a current‐bridge method and its validation

An AC shunt calibration system using a current-bridge method is developed, and its measurement uncertainties are estimated. A comparison of the calibration results obtained using the current-bridge method with the results using DC resistance and AC–DC difference methods was performed to verify the system. These comparison results show that the current-bridge-based system performs well with small measurement uncertainties for both the AC resistance and phase angle of the AC shunts up to 1 kHz.

Load characteristics of two-staged inductive voltage dividers

The load dependence of two-staged inductive voltage dividers (IVDs) for both in-phase and quadrature components up to 10 kHz are examined. The IVD ratio errors deviate from the calibrated values because of the relationship between the IVD output impedance and the loads when the IVD is used in some applications. Therefore, evaluations of the loading effects on the IVDs are an important issue. To detect the very small variation with loads, another calibrated IVD is used. The in-phase components of the IVD with resistive loads remain constant up to 10 kHz, and those with capacitive loads increase rapidly over 1 kHz. The error values depend on the load values. The quadrature components with resistive and capacitive loads change proportionally with the frequency. The errors due to the loads are not small and are significant for some applications that use IVDs.

Verification and uncertainty evaluation of an ac shunt calibration system at power frequencies

An ac shunt calibration system has been developed at NMIJ. The calibration results were discussed with dc calibration results and the expanded uncertainties (k=2) of the system have been estimated to be less than 3.4 µΩ/Ω for ac resistance and 8.6 µrad for phase angle.

Characterization of High-Accuracy, Wideband Transconductance Amplifiers up to 100 kHz

A highly precise and accurate system comprising several ac shunts and an inductive voltage divider (IVD) is proposed for characterizing high-accuracy, wideband transconductance amplifiers (TCAs). Frequency characterization of the shunts and the IVD confirms the wideband (up to 100 kHz) performance of the proposed system. Evaluation of two TCAs up to 100 kHz with the proposed system reveals frequency-, current-, and load-dependent properties as well as phase shifts between the input voltage and the output current. The results for the load dependence show that the load differences have a limited impact on the phase shifts up to 10 kHz.

Uncertainty estimations of an evaluation system for a high accuracy and wideband transconductance amplifier

An evaluation system for high accuracy transconductance amplifiers has been developed. The system has a standard ac shunt and inductive voltage divider for precise evaluations. The measurement capabilities of the system are 4.1×10^-6 (k = 2) for in-phase component, 9.1×10^-6 (k = 2) for quadrature component at power frequencies, and 13×10^-6 for inphase component, 45×10^-6 (k = 2) for quadrature component at 3 kHz.

AC characterizations of current shunts

The dependence of cage-type AC shunt resistance and phase angle on frequency and input current is examined in this paper, for shunts with different current ratings. The AC resistance of shunts remains constant for up to 1 kHz, but the phase angle changes proportionally to the frequency. The results of current dependencies on AC resistance are consistent with each other within measurement uncertainties between 1 A and 10 A. The phase angle does not depend on the current, for values up to 10 A. The effects of current heating of shunts are also evaluated. The thermal time constant of shunts is found to be approximately 200 s and does not depend on the shunts and the input current frequency.

Characterization of a current shunt and an inductive voltage divider for PMU calibration

This paper describes a phasor-measurement-unit (PMU) calibration method and presents the measurement results of the characteristics of an inductive voltage divider (IVD) and a current shunt. The frequency characteristics of an IVD and a current shunt were evaluated up to 10 kHz in terms of PMUs. The in-phase components of the IVD were less than 0.39 ppm, whereas its quadrature components reached 0.53 ppm at 10 kHz with small measurement uncertainties. The measurement uncertainty of the current shunt reached approximately 14 ppm at 10 kHz. These results imply that the frequency characteristics of the IVD and current shunt were found to be sufficient for the evaluation of PMUs.

Frequency characterizations of voltage and current transducers for evaluation of phasor measurement units

This paper describes a phasor measurement unit (PMU) evaluation method and presents the measurement results of the frequency characteristics of an inductive voltage divider (IVD) and a current transformer (CT). Frequency characteristics up to 3 kHz of an inductive voltage divider and a current transformer were evaluated in terms of ph as or measurement units, which play an important role in smart grids. The in-phase components of the inductive voltage divider were less than 0.1 ppm, whereas its quadrature components reached 0.22 ppm at 3 kHz. The in-phase and quadrature components of the current transformer reached approximately 10 ppm at 3 kHz, with large measurement uncertainties. While the frequency characteristics of inductive voltage dividers were found to be sufficient for the evaluation of phasor measurement units, the results show that improvements in the frequency characteristics of current transducers are needed for successful phasor measurement unit evaluation.