Sampling Primary Power Standard from DC up to 9 kHz Using Commercial Off-The-Shelf Components

Abstract

In the framework of the empir projects myrails and windefcy, metas developed a primary standard for electrical power using commercial off-the-shelf components. The only custom part is the software that controls the sampling system and determines the amplitude and phase of the different frequency components of voltage and current. The system operates from dc up to 9 kHz, even with distorted signals. The basic system is limited to 700 V and 21 A. Its power uncertainty is 15 μW/VA at power frequencies and increases to 1.8 mW/VA at 9 kHz. With the extension up to 1000 V and 360 A, the system reaches power uncertainties of 20 μW/VA at power frequencies, increasing to 510 μW/VA at 9 kHz. For higher voltages or higher currents, the same principle is used. However, the uncertainties are dominated by the stability of the sources. The voltage and current channels can also be used independently to calibrate and test power quality instruments. Thanks to a time-stamping system, the system can also be used to calibrate phasor measurement units, which are synchronised to utc.

Measurement Setup for a DC Power Reference for Electricity Meter Calibration

“…In this sense, a crucial role is played by the feedback loop: the instrument transformer (either voltage divider or current transformer) and the digitizer are periodically calibrated against the national reference standards for voltage and current. Moreover, the uncertainty contribution and the uncompensated bias introduced by the sampling process and the following non-linear fit procedure are also periodically evaluated according to the method presented in [18].…”

DC active electrical energy meters: Accuracy tests

“…The model equation (5) shows how the error F depends on the different input quantities. The symbol P DUT (t) denotes the instantaneous power measured by the DUT, P Ref (t) that measured by the reference.…”

“…The first term in (5) is the contribution of most interest since it is related to the comparison of the DUT with the reference. The quantities related to the DUT are E Res,DUT , n DUT , t DUT,0 and t DUT,1 .…”

“…With the increasing spread of electric vehicles, the measurement of DC active electrical energy [1], [2] becomes relevant for billing purposes again [3], [4]. While primary standards for power and energy at DC exist [5], common, automatised meter calibration and testing systems, for instance for use by verification authorities, are suitable for AC only. The design characteristics of modern active electrical energy meters for DC applications differ very much from those used until some decades ago.…”

Calibration of a Digital Current Transformer Measuring Bridge: Metrological Challenges and Uncertainty Contributions

“…It is also worth noticing that the sine fitting procedure returns the value of the amplitude, frequency and initial phase of the fundamental component. Therefore, by comparing the phase at the two channels, we can retrieve the phase contribution of the amplifier only with a standard uncertainty of 0.03 µrad [24]. • Measuring bridge (DUT): A ZERA WM3000I (ZERA, Konigswinter, Germany) with a current input range from 1 mA to 15 A.…”