Calibration Of Current Transformers Research Articles

用于激光尾波场中电子束电荷测量的积分束流仪标定

用于激光尾波场中电子束电荷测量的积分束流仪标定

A Simple Method for the Calibration of Traditional and Electronic Measurement Current and Voltage Transformers

The calibration of measurement transformers represents a classical task in the practice of electrical measurements. Most commercial instruments that are expressly designed for this purpose found their working principle on a scheme that is based on the idea of Kusters and Moore. Although they can assure very high accuracy, the need to employ a high-performance electromagnetic circuit makes them very expensive and usually not suitable for measurements at frequencies that are higher than 50 or 60 Hz. For this reason, these kinds of instruments cannot be employed for the calibration of the new generation of current and voltage transducers, such as electronic measurement transformers, whose employment is growing in all the applications where wide bandwidth is required. In this paper, a new method for the calibration of electromagnetic voltage and current measurement transformers (VTs and CTs) and electronic voltage and current measurement transformers (EVTs and ECTs) is discussed, and a deep metrological characterization is carried out. The novelty of the proposed method is represented by a completely different approach to the measurement of the ratio and phase errors of the measurement transformers. The method is based on the proper digital signal processing of the signals that are collected at the secondaries of the transformer under test and of a reference transformer when the same signal is applied to their primary. Since no auxiliary electromagnetic circuits are required, this solution can be easily implemented in a simple and cost-effective way. In spite of its simplicity, the tests that are developed on a prototype clearly point out that the proposed system is suitable for the calibration of measurement transformers with precision class up to 0.1 in the frequency range from 50 Hz to 1 kHz.

Onsite Calibration of a Current Transformer Using a Rogowski Coil

This paper describes a reference current-measuring system for the onsite calibration of high-voltage current transformers. The reference current-measuring system consists of a Rogowski coil, a current shunt, two digitizing voltmeters, and a computer to control the voltmeters. The method of generation of the high current and the uncertainty of the calibration are discussed. The results of a calibration performed onsite on a 400-kV substation are presented. Uncertainties of 300 muA/A for ratio and 1 angular minute for phase displacement were achieved with this method onsite.

KRISS-NRC Intercomparisons of Calibration Systems for Instrument Transformers With Many Different Ratios at Power Frequency

An intercomparison of the calibration systems for instrument transformers between the Korea Research Institute of Standards and Science (KRISS) and the National Research Council of Canada (NRC), with many different ratios at 60 Hz, was performed using six portable transfer standards. The portable transfer standards consist of two current transformers (CTs) with current ratios of 5 A/5 A up to 20 000 A/5 A and four voltage transformers (VTs) with voltage ratios of 110 V/110 V up to 66 000 V/110 V. The comparison results for the CT calibration systems between the two institutes are in good agreement within 10times10-6 for ratio and 10 murad for phase for all the current ratios. The comparison results for the VT test systems also indicated good agreement within 35times10-6 for ratio and 35 murad for phase for all voltage ratios.

NRC-NIST intercomparison of calibration systems for current transducers with a voltage output at power frequencies

A number of international comparisons of current transformer calibrations at power frequencies were conducted in the past. However, all comparisons were done with a secondary current output of 5 A. This inter-comparison of current transformer calibration systems for power frequencies between the National Research Council of Canada and the National Institute of Standards and Technology, USA, was done with a primary current range of 100 A and a nonstandard secondary output signal of voltage range of 10 V. The comparison was implemented with a transfer standard consisting of a commercial current-comparator-based transimpedance amplifier, based on a development at the National Research Council of Canada modified to make the output voltage adjustable in magnitude and phase within a range of /spl plusmn/1 percent. The results indicate that there are no significant differences in the overall accuracy of calibration systems for current transducers with a voltage output at power frequencies in each laboratory.

Simple absolute method for current transformer calibration

A simple mains-frequency current transformer ratio build-up scheme has been developed which enables calibration by absolute means of ratios from 5 A:5 A to 500 A:5 A with uncertainties of 0.03 parts in 10/sup 6/ and 0.05 /spl mu/rad. The build-up is based on series-parallel interchange of primary windings of two-stage transformers with magnetically shielded second stages.

New comparator-type calibrator for instrument transformers

The principle of a novel comparator-type calibrator is described. It consists of a conventional current comparator-based high-precision current transformer calibration device with an additional current comparator and a current-voltage conversion circuits. The measuring range of the current is extended by the current comparator and that of the voltage by the resistances.

International Comparison of Current Transformer Calibrations

An international comparison of current transformer calibrations between five metrology laboratories has been conducted. The measurements were made at current ratios ranging from 1 A: 1 A to 200 A: 1 A at 10, 100, and 200 percent of rated current and from 5 A: 5 A to 200 A: 5 A at 1, 10, 100, and 200 percent of rated current, at a frequency of 50 Hz. Several ratios have also been compared at 60 Hz. Except at some low-level currents the results show very good agreement among the five laboratories. The current differences are typically within ±1 ppm and the phase displacements within ±1.5 μrad.

Method for the absolute calibration of current transformers

Method for the absolute calibration of current transformers

An Electronic Ratio Error Set for Current Transformer Calibrations

A direct-reading electronic ratio error set for current transformer calibrations is described. It is capable of generating direct and quadrature error currents from 1 ppm to 5 percent of transformer secondary currents up to 10 A. The uncertainty is less than one percent of the generated current. The set features electronic display of the direct and quadrature components with three digits each and is direct reading at 50, 60, and 400 Hz.

A precision current comparator for calibration of current transformers

The current comparator is a highly precise and stable a. c. current ratio measuring device. Essentially it is a 3-winding type current transformer, but with incorporation of additional windings its performance is greatly improved. The paper deals with the fabrication of a precise current comparator having ratios of 1/1 to 20/1 with a standard 5-Amp secondary winding. A 100/1 ratio has also been provided employing a bar primary. By suitable design it can be made more accurate than the best types of current transformers available. This inherent accuracy makes a current comparator an ideal device for calibration of current transformers in the laboratory or in industry. Several test results on such current transformers have been given.

A Phantom Burden for Current Transformer Calibration

A technique is presented for applying a burden to a current transf ormer being calibrated in which the power and reactive volt-amperes are returned to the supply rather than being absorbed in a passive network. The transfer is accomplished either by the magnetic shield if a compensated current comparator is used as the ratio standard, or by an auxiliary current transformer in circuits which employ other standards. Electronic circuitry provides the necessary volt-amperes for exciting the magnetic shield of the current comparator or the auxiliary current transformer, and the current transformer being calibrated, to produce the desired power transfer. The circuit requirements are analyzed and equipment which can develop burdens with both in-phase and quadrature components up to 10 ohms, at secondary currents up to 10 amperes, and for a 0.6 percent accuracy class current transformer or better, is described. The burden setting, which is independent of current, may be made by in-phase and quadrature dials to an accuracy of about one percent of full scale.

An International Comparison of Audio-Frequency Current Transformer Calibrations

A comparison of 1/1 ratio and 10/1 ratio current transformer calibrations at frequencies of 1, 5 and 10 kilohertz obtained by measurement techniques developed independently by the Physikalisch-Technische Bundesanstalt of West Germany and the National Research Council of Canada is presented. Discrepancies between the two laboratories of 0.03, 0.09 and 0.28 parts per million at 1, 5 and 10 kilohertz respectively are indicated. Uncertainties in the measurements which may account for these discrepancies are discussed.

A Wide Range Current Comparator System for Calibrating Current Transformers

This paper describes a new measurement system for the calibration of current transformers at 60 Hz for all ratios up to 10000/5 and higher and at four times rated current. For ratios up to 1200/5, no reference transformer is needed and the system is accurate to five parts per million (ppm). Most higher ratios can be measured using only one reference transformer. Included is an example of how a laboratory could use such a system to measure all ratios up to 8000/5, requiring a calibration of only one reference transformer on one ratio (4000/5).

Direct Reading Ratio-Error Sets for the Calibration of Current Transformers

Four different direct reading ratio-error sets, capable of generating measured complex fractions of an input reference current to a nominal accuracy of 1 percent of reading for such applications as current-transformer calibration, are described and analyzed. Construction and performance details for actual sets with 3 or more digit resolution in both direct and quadrature components from 0.1 parts per million to 10 percent of input currents up to 10 amperes at 50, 60, and 400 Hz, are given.

The Application of the Compensated Current Comparator to the Calibration of Current Transformers at Ratios Less than Unity

A technique is described for extending the range of the compensated current comparator so that it may be used for calibrating current transformers at ratios both greater and less than 1/1. The concept of providing compensation windings for both the primary and secondary ratio windings is introduced and a new method of correcting for the capacitance error due to burden is presented. Details on how a compensated current comparator previously developed for ratios from 1/1 to 240/1 may be adapted for this purpose are discussed and results of measurements at ratios down to 0.01/1 with this comparator are given.

The Application of Current Comparators to the Calibration of Current Transformers at Ratios up to 36000/5 Amperes

The design and construction of a multiratio, 36 000-ampex e compensated current comparator and the technique by which it may be cascaded with a second multiratio comparator to calibrate, with a single balance, power frequency current transformers at ratios up to 7200/1 are described. The first comparator has a distributed, single-turn primary winding and a sectionalized 1200-turn secondary winding that may be series-paralleled to obtain eight ratios from 120/1 to 1200/1. A 300-kVA 1100-volt transformer is included in the single primary turn to provide the power required for the calibrations. In size the device is 40 inches in diameter and 20 inches in height, and its weight is 2700 lb. The two comparators are cascaded at nominal currents up to 30 amperes by connecting the secondary winding of the first comparator to the primary winding of the second and by making corresponding interconnections between the two compensation windings. At balance, the actual current ratio of the standard composed of the two comparators in cascade, or the first comparator alone, differs from the corresponding turns ratio by no more than a part per million (ppm).

The Development and Performance of Current Comparators for Audio Frequencies

The design and construction of five different multiratio current comparators developed for use at audio frequencies is presented. The effectiveness of the various shields on the reduction of the current null detector error over the operating frequency range is shown. Equations are developed which illustrate the effect of several different arrangements of windings and grounded shields on the ratio winding error. All of the comparators are of the compensated type and each is rated at a secondary current of five amperes. Four have fixed primary windings which can be series-paralleled to obtain various ratios from 1 to 1 to 12 to 1. The fifth comparator is a feed-through type with a 100 turn secondary winding which provides ratios up to 100 to 1. Circuits are described which enable the calibration of these comparators to be performed, and the results of calibration at frequencies up to 16 kHz are given. A method of estimating the error at different ratios to within a part in a million, based on experimentally determined parameters and assumed uniform distribution, is also described. The main conclusion of the study is that for current transformer calibration the best design includes a grounded copper shield between the primary and secondary windings.

Correction [to "The compensated current comparator; A new reference standard for current-transformer calibrations in industry"

Correction [to "The compensated current comparator; A new reference standard for current-transformer calibrations in industry"

The Precise Measurement of Current Ratios

The development of the current comparator, a three-winding current ratio transformer, is reviewed and its characteristics as an alternating current ratio standard are analyzed. Particular attention is given to the use of magnetic shielding and its effect on the accuracy and usefulness of the device. Some error characteristics of three types of audio-frequency current comparators are given and possible applications discussed. These include the calibration of current transformers and impedance comparisons. The adaptation of this device to dc operation is made possible by modulation techniques. A 20 000-ampere self-balancing direct current comparator, designed specifically for the calibration in situ of transductors or direct current transformers, is described. The application of this comparator to the calibration of shunts at high currents also is discussed and some results presented.