Tatsuji Yamada

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.

High-Accuracy Estimations of Frequency, Amplitude, and Phase With a Modified DFT for Asynchronous Sampling

High-accuracy frequency, amplitude, and phase estimation methods for asynchronous sampling are presented. The proposed estimation methods are based on phase difference estimation, compensation of number of samples, and a modified discrete Fourier transform. This study focused on processing signals in substation automation systems that comply with IEC 61850. Some simulation tests were conducted in cases of pure and distorted sinusoids, and the frequency, amplitude, and phase errors of the fundamental and harmonics are evaluated at fundamental frequencies around 50 Hz at fixed sampling rates of 4 kHz and 12.8 kHz (i.e., 80 and 256 samples per period). Dependence of each estimation accuracy on a fraction of number of samples is discussed.

Demonstration of a 10 V programmable Josephson voltage standard system based on a multi-chip technique

We have demonstrated a programmable Josephson voltage standard (PJVS) operation up to 10.84 V using a multi-chip technique. We combined two PJVS chips fabricated using NbN/(TiNx/NbN)2 junction technology. Each PJVS chip was mounted on a single chip carrier using bonding wire, and the two chip carriers were connected by a simple Cu lead wire, and mounted on a cryocooler. High-precision measurements confirmed flat voltage steps for all 22 cells, with a peak-to-peak variation of 100 nV and wide margins of at least 0.35 mA. We also confirmed the stability of the voltage steps in spite of a temperature and RF frequency variation of ± 0.1 K and ± 0.1 GHz, respectively.

Error and Uncertainty Estimations for A Passive-CC-Based AC Current Ratio Standard at High Audio Frequencies

This paper describes a development framework for alternating current ratio standard working at high audio frequencies. To realize this, first, a calibration method for frequency-dependent balancing current generators (BCGs) producing error currents to balance current comparators (CCs) is proposed. Second, the BCG error correction is made not only for the current transformer (CT) calibration but also for the CC self-calibration. Third, practical capacitive error corrections are also proposed to be introduced for the CT and CC calibrations. Finally, in consideration of the BCG error, capacitive error, and compensated CC error, a proposed way of calculating CT error and estimating its uncertainty is described.

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.

Bilateral Comparison Of AC Current Ratio Standards up to 700 HZ Between NMIJ and NRC

A binary type self calibrateable AC current comparator (CC) was developed at NMIJ. In order to confirm the reliability of the new AC current ratio standard at NMIJ, a bilateral comparison was conducted with NRC using an error compensating current transformer. The paper describes an error estimating procedure for the CC and the results of the bilateral comparison

A high audio-frequency inductive voltage divider standard up to 100 kHz

A high audio-frequency inductive voltage divider (IVD) and its calibration system at the frequencies from 10 kHz to 100 kHz have been developed in order to establish the high audio-frequency ac metrology. Design of the constructed IVD and its calibration circuit are described.

Calibration methods of a CC and BCG for a high-accuracy AC current ratio standard up to 4 kHz

This paper describes calibration methods of current comparators (CCs) and balancing current generators (BCGs) accompanied with them, for establishing a high-accuracy ac current ratio standard up to 4 kHz. The CC calibration is explained mathematically according to the self-calibration procedure that NMIJ has been exploiting. The BCG calibration is based on measurement of the conversion ratio. The technique with a CC and CT is unique in terms of the fact that the uncertainty can be ignored against the CT calibration.

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.