Eddy So

A Current-Comparator-Based System for Calibrating Active/Reactive Power and Energy Meters

A system for calibrating active/reactive power and energy meters under sinusoidal conditions using a current comparator bridge is described. Measurement can be made at any power factor from zero lag through unity to zero lead, positive or negative power, at 100 to 120 V, 1 to 5 A, and 50 or 60 Hz. The system features a digital oscillator, a thermal rms ac/dc voltage comparator, an automatically compensated capacitor for producing an accurate and stable reactive component, and a microcomputer for control and data reduction. The systematic uncertainty of the calibration system is estimated to be not more than 15 parts per million (ppm).

The Application of the Current Comparator in Instrumentation for High Voltage Power Measurements at Very Low Power Factors

A current-comparator technique is applied to several auxiliary instruments which enables accurate high voltage power measurements to be made at very low power factors using precision wattmeters and precision bridges. The instruments include a high-voltage active-divider with a nominal output voltage of 100 V, a high-voltage inductive-quadrature-current reference source with current output ranges of 1 mA, 2 mA, and 10 mA, and a high-voltage high-capacitive-quadrature-current reference source with current output ranges of 0.1 A, 0.5 A, and 1 A. The current comparator is used in a feedback loop to correct the magnitude and phase of the associated outputs of these instruments to an accuracy of better than ±10 ppm (parts per million) and ±10 ¿rad respectively.

An electronically enhanced magnetic core for current transformers

Summary form only given. An electronic technique which greatly increases the apparent permeability of a magnetic core of a current transformer without a galvanic connection to either of the usual primary or secondary winding circuits is described. The number of turns and the turns ratio can be selected independently as desired. Means are available for examining the waveform of the magnetizing current for the presence of even harmonics, thus indicating possible remanence or direct currents in the windings. Application of the technique to transformer voltage dividers is also discussed. >

High-current high-precision openable-core AC and AC/DC current transformers

The application of an electronic technique, which greatly increases the apparent permeability of the magnetic core of a current transformer, to high-current high-precision openable-core AC and AC/DC current transformers is described. The openable-core AC/DC current transformer can be used to measure accurately alternating current only or direct current only, or both alternating and direct currents simultaneously. Test results of two prototypes, 5000 A/5 A openable-core AC and 2000 A/1 A openable-core AC/DC current transformers, indicate an AC current measurement accuracy of both types of transformers on the order of 10 p.p.m. and a DC current transformer of better than 100 p.p.m. >

Phase measurement of distorted periodic signals based on nonsynchronous digital filtering

Measurement of the phase angle between fundamental components of distorted periodic signals at power frequencies is described in the paper. It is based on a nonsynchronous multirate digital filtering algorithm, which is applied at the voltage and/or current signals to be measured. The digital filters implemented are designed to suppress the higher harmonics and ensure the accuracy of measurement. The measurement method is insensitive to frequency variations in a wide frequency band around the nominal frequency. A verification of the method has been performed by simulations and by measurements. The results of extensive performance evaluation are reported.

Compact Wideband High-Current (

In this paper, an overview of the development and performance of special compact-and-lightweight wideband high-current multistage current transformers for precise measurements of current harmonics at the National Research Council of Canada is described. These include current transformers with ratios of 1000 A/5 A and higher, with ratio errors of less than 5 10-6 in both magnitude and phase with burdens up to 0.5 Omega and at frequencies up to 5 kHz

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A high-accuracy system for calibration of electronic instrument transformers with digital output is described. Its design is based on International Electrotechnical Commission (IEC) standards 61850, 60044-8, and 60044-7. The performance of the calibration system has been evaluated. Its estimated relative uncertainty (2/spl sigma/) is within 40/spl middot/10/sup -6/ in magnitude and within 40 /spl mu/rad in phase.

1000 A) Multistage Current Transformers for Precise Measurements of Current Harmonics

This paper describes a high precision circuit for quadrature phase shifting in which frequency controlled signal amplification is introduced so that the amplitude of the phase shifted signal is not dependent on the frequency of the input signal. The implementation of the proposed quadrature phase shifter is aimed at high accuracy reactive power measurements in AC power systems. The implementation of the new phase shifter effectively reduces var/varh measurements to watt/watthour measurements. A prototype has been built and the test results are presented.

Calibration system for electronic instrument transformers with digital output

An electronically aided multistage technique is applied to a hand-held openable-core damp-on current transformer which enables accurate low current measurements to be made over a wide dynamic and frequency range of operation, for use in conjunction with highly accurate active/reactive power and energy meters, and harmonic power analyzers. The clamp on current transformer can be used to measure currents in the range from 1 A to 200 A, at frequencies between 50 Hz ad 5 kHz, with ratio errors of less than 50/spl times/10/sup -6/ in both magnitude and phase.

A high performance frequency insensitive quadrature phase shifter and its application in reactive power measurements

A current comparator technique for the measurement of resistance at 50-60 Hz with an accuracy of better than 10 ppm is described. The current in the unknown resistor is compared, using the current comparator, to the current in a reference resistor for the inphase component and to the current in a reference capacitor for the quadrature component or phase defect. Six-digit resolution is provided for both components. The bridge is direct reading in either per-unit resistance or conductance. Nominal ratios of 1,2,5,10,20,50, and 100 are available. An auxiliary two-stage current transformer provides extension of the ratio range to 10 000 and also of the maximum applied current to 100 A. The bridge is suitable for measuring resistances from 10 m¿ to 1 M¿.