Branislav Djokic

Calibration of Rogowski coils at power frequencies using digital sampling

A new high-accuracy system for power-frequency calibration of Rogowski coils is described in this paper. The calibration system is based on nonsynchronous digital sampling. An automated prototype of the calibration system operates at currents of up to 2000 A. A semiautomated system is capable of operating at currents of up to 60 000 A. The best uncertainty (k = 2) of the calibration system is estimated to be better than 50 muA/A for magnitude and 50 murad for phase.

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.

Calibration of Rogowski coils at frequencies up to 10 kHz using digital sampling

A high-accuracy system for calibration of Rogowski coils at frequencies up to 10 kHz, based on a reference current transformer, an I/V converter, and a digital sampling system, is described in the paper. The calibration system has been automated and its performance evaluated. At the frequency of 10 kHz, the calibration system is capable of generating currents up to 100 A. At power frequencies, it is capable of generating currents up to 2,000 A. The best uncertainties (k=2) of the calibration system are estimated to be less than 500 μA/A for magnitude and 500 μrad for phase at 10 kHz, and an order of magnitude better at power frequencies.

Calibration system for electronic instrument transformers with digital output

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.

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

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.

To What Extent Can the Current Amplitude Linearity of Rogowski Coils Be Verified

Calibrations of Rogowski coils at power frequencies are often performed at currents of only tens of amperes even though the coils are used at currents larger by two to three orders of magnitude, or even more. The assumption of an ideal linearity versus current amplitude is true for ideal coils. This paper addresses the question on practical significance as to what extent the current amplitude linearity of real Rogowski coils can be verified at power frequencies. For this task, several different types of Rogowski coils were evaluated using a digital sampling system, with the best calibration uncertainties (k = 2) of 50 μA/A for magnitude and 50 μrad for phase and the estimated linearity better by a factor of two or more.

An Optically Isolated Hybrid Two-Stage Current Transformer for Measurements at High Voltage

The development of a high-voltage reference current measurement system for on-site/in-situ calibrations in power systems is described in the paper. The system is based on an optically isolated hybrid two-stage current transformer with electronic circuitry that performs A/D conversion. It features a fiber optic link for data transmission to a ground station, and a laser-driven fiber optic link for supplying power to the electronic circuitry of the remote module at high voltage. The ratio accuracy of the current measurement is estimated to be better than 100middot10-6

Calibrations of Resistance Welding Equipment With High Pulsed Currents

Rogowski coils are widely used as high pulsed current sensors in resistance welding applications. The operating conditions of the coils determine the requirements for their calibration. A new calibration system has been developed at National Research Council (NRC) Canada for calibrating current sensing coils and weld current monitors (WCMs) used in AC resistance welding. The calibration system, which includes a high-current source and a coaxial copper cage, has been evaluated at peak pulsed currents of up to 80 kA at 60 Hz. The expanded measurement uncertainties (k = 2) have been estimated to be less than 350 μA/A for magnitude. A method for the calibration of WCMs separately from their Rogowski coils at conditions that correspond to those obtained at high pulsed currents but without the need to use actual high pulsed currents has also been developed.

Development of a low-frequency quantum-based AC Power Standard at NRC Canada

A development of a new low-frequency quantum- based AC Power Standard at the National Research Council of Canada (NRC) is described in the paper. It uses programmable Josephson voltage standard (PJVS) for providing AC voltage with quantum accuracy, highly stable magnetic devices such as voltage and current transformers for scaling output signals to low levels, and digital sampling for comparison of low-level output signal replicas with the PJVS output.

Two methods for improved measurements of reactive power and reactive energy insensitive to frequency variations

The paper describes the implementation of successive frequency-to-voltage and voltage-to-frequency conversion used to achieve a wideband frequency multiplication allowing reactive power and reactive energy measurements in the range of 40 Hz to 70 Hz of the input signal frequency. It also describes a phase shifting method which provides independence of the shifted signal of the capacitor value used in the phase shifter. This feature ensures long term stability and wide temperature operating range of the meter while retaining high accuracy.