William J. M. Moore

On the Definition of Reactive Power Under Non-Sinusoidal Conditions

A new method of defining reactive power under non- sinusoidal conditions is proposed. It consists of sub- dividing the current into components which would have the same waveform as the current in a resistance and either an inductance or a capacitance when the voltage is applied to them, and into a residual component. An instrument for subdividing and measuring each current component and its corresponding power is described. The method permits the power system operator to determine if the possibility of improving the power factor by means of a shunt capacitance or inductance exists and to easily identify the proper value required to realize the maximum benefit.

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 development of the current comparator, a high-accuracy A-C ratio measuring device

The current comparator is a stable, sensitive, and reliable magnetic device, which may be used for a-c ratio measurements of high accuracy. The sources of error in such a device are discussed, and methods are proposed for minimizing their effect. The design of a 2,000-amp (ampere) feed-through current comparator based on these investigations is described, and test results are given which indicate that its over-all accuracy at 60 cps (cycles per second) is better than 0.2 ppm (part per million) for all ratios from 1:1 to 400:1, irrespective of distribution of the primary winding.

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. >

A Direct-Reading AC Comparator Bridge for Resistance Measurement at Power Frequencies

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¿.

A Comparison of Instrumentation for Measuring the Losses of Large Power Transformers

The results of a comparison of several different types of equipment and techniques for measuring the short circuit (copper) and open circuit (iron) losses of a large power transformer are presented. The measurements were made on a 233-MVA, 735-kV, single phase, 60-Hz power transformer with a short circuit power factor of 1.3%, at currents up to rated, and open circuit voltages to 115 percent of the rating. The short circuit tests were performed using two current comparator type high-voltage capacitance bridges, a thermal wattmeter, an electro-dynamic wattmeter system with conventional instrument transformers and a new semi-automated digital wattmeter system. For the open- circuit tests only the three wattmeters were employed. The average discrepancy between the five measuring systems used in the short circuit tests was less than 1% and between the three systems in the open circuit tests less than 0.5 %.

An international comparison of power meter calibrations conducted in 1987

The results of an intercomparison of power meter calibrations conducted during 1987 between the National Research Council of Canada, Ottawa, the US National Bureau of Standards, Gaithersburg, the Physikalisch-Technische Bundesanstalt, Braunschweig, and the Institut Mihailo Pupin, Belgrade, are described. The comparison was implemented by a transfer standard consisting of a time-division multiplier watt-converter developed at the Institut Mihailo Pupin. The measurements were made at 120 V, 5 A, and 50 and 60 Hz, at power factors of 1.0, 0.5 lead and lag, and 0.0 lead and lag. An agreement between the laboratories of better than 20 ppm is obtained. >

Measurement of Shunt Reactor Loss at High Voltage with an Alternating Current Comparator Bridge

The application of a high voltage capacitance bridge based on the current comparator to the measurement of the loss angle of high voltage shunt reactors is described. Measurements on three core-less 55 MVA, 735 kV single phase shunt reactors are discussed and a comparison is made with the results of a calorimetric determination of loss which indicates agreement to better than 2 percent. Other bridge techniques for this type of measurement are reviewed.

Measurement of short circuit load losses in large three phase power transformers using an alternating current comparator bridge

The application of a high-voltage alternating-current-comparator capacitance bridge to the measurement of the short circuit load losses of large three phase power transformers at rated current is described. Input of the transformer current to the bridge is provided through a 1000/1 ratio two-stage current transformer with a single turn primary winding Insulated for 50 kilovolts. Voltage input is provided through a loss-free gas dielectric capacitor which serves as the reference. Measurements on typical transformers ranging in size from 450 MVA to 750 MVA; with currents from 600 to 2100 amperes and short-clrcuit power factors from one percent to four percent, are discussed. Comparisons to appropriately corrected wattmeter measurements (aided by low-loss capacitors connected in parallel with the transformer) indicate an overall agreement of better than one percent.

A current comparator for the precision measurement of D-C ratios

A magnetic d-c ratio device has been developed that is capable of attaining accuracies approaching 1 part per million. The operating characteristics and some of the design problems are discussed, and construction details of an experimental model, rated at 4,000 ampere-turns and capable of handling ratios up to 400 to 1, are given. The use of this device for the scaling of fundamental resistance standards is proposed