Abstract
<p class="Abstract"><span lang="EN-US">The manuscript presents a method for the metrological characterisation of the commercial AC comparators used to calibrate current transformers. The theoretical basis for simulating the difference between two almost identical currents has been outlined, as well as the mathematical models for both a ratio error and a phase displacement has been derived. The measurement setup, consisting of conventional measuring instruments, has been described with a detailed presentation of its parameters. The sources of uncertainty have been distinguished and analysed with determining the current phase shift which led to a significant increase of relative measurement uncertainty. The simulation of measurement results was yielded in two ways: physically using a method presented and virtually using a Monte Carlo method. The second method confirmed that evaluating the measurement uncertainty through derived sensitivity coefficients is correct enough. The simulation results in the range from 1 to 1200 parts per million for both ratio error and phase displacement motivated the use of a comparator characterised through the proposed method for accurate measurement, especially for very low errors.</span></p>
Highlights
The energy sector deals with electricity accounting for accurate settlements and monitoring the dynamic events for power quality assurance
The researchers have offered alternative approaches to determining the metrological characteristics of instrument transformers, such as the application of a quasi-balance technique using the virtual instrument [8], or low cost efficient digitiser [9], or a method based on the low-voltage reciprocity principle [10], or a calculation of the errors based on the excitation table [11]
This paper proposes a method that allows achieving a measurement uncertainty of several tenths of μA/A when calibrating a commercial current transformers (CT) calibration unit under ordinary laboratory conditions
Summary
The energy sector deals with electricity accounting for accurate settlements and monitoring the dynamic events for power quality assurance. The accuracy of measuring instruments is steadily increasing and researchers continue to find the approaches for minimising the errors of equipment, in particular those of instrument transformers [4]. PTB (Germany) laboratory declared measurement uncertainty in on-site calibrating the isolating CTs slightly less than 40 μA/A [6]. A sampling current ratio bridge for the calibration of CTs was developed at VSL (Netherlands) laboratory. The researchers have offered alternative approaches to determining the metrological characteristics of instrument transformers, such as the application of a quasi-balance technique using the virtual instrument [8], or low cost efficient digitiser [9], or a method based on the low-voltage reciprocity principle [10], or a calculation of the errors based on the excitation table [11]
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