This paper presents a study on revenue active electrical energy meters. The huge installation along the distribution network of these devices made them a key element for energy billing, but also for monitoring the grid status. Hence, it is evident that the relevance of guaranteeing a trusty metering performance, and consequently a proper standardization, is needed. The operation of the meters is regulated by standards harmonized with the European Directive 2014/32/EU (known as MID). Still, and not infrequently, compliance to some legacy standards is declared on the device specifications. Thus, a brief comparison between the latest standards is presented. In particular, the focus was set on evaluating the potential impact of the harmonic disturbances on the energy meter accuracy, since they are omnipresent in the modern power networks. The evaluation has been carried out on three off-the-shelf class B meters by means of a new test procedure that considers realistic and quasi-realistic harmonic disturbances. Such tests showed that realistic harmonic disturbances affect significantly only some energy meters. Therefore, the standards should not neglect this kind of scenario.
The interpolated discrete Fourier transform (IpDFT) is one of the most popular techniques to estimate the parameters of a damped real-valued sinusoidal signal (DRSS). However, its accuracy is affected by strong noise presence and short observation windows. To this end, this letter proposes a novel twopoint IpDFT method, called I2pZDFT, for the parameter estimation of a DRSS. The proposed I2pZDFT uses the zeropadding technique to increase the sampling rate in the frequency domain. The conjugate symmetry and the parity of the zeropadded signal are utilized to eliminate the influence of the spectral leakage. Simulation results highlight that the proposed I2pZDFT outperforms the existing IpDFT-based methods in terms of noise immunity, especially in the case of observation windows as short as 0.5 ~ 1 cycles.
Even if their deployment in electrical medium voltage networks was not as extensive as could be expected at the beginning, Phasor Measurement Units are key elements for Smart Grid operation. An impressive amount of papers discusses their implementation and usefulness in medium voltage network and almost as many deals with their metrological characterization. Although it is well known that instrument transformers are the main source of uncertainty in PMU-based synchronized measurements, this topic is not sufficiently tackled in the scientific literature. In this paper, the attention is focused on the calibration of a measurement system made by a PMU and a low-power instrument transformer commonly employed in the Italian distribution network.
The paper addresses one of the new and most important issues arising when Low Power Voltage Transformers (LPVT) are used in power network substations for evaluating, among others, also the residual voltage. Conversely to opentriangle inductive instrument transformers, the use of phase voltage transformers for measuring the residual voltage gets challenging due to the very high accuracy required for the three LPVTs. In the paper, an analytical study will be presented along with simulation results in order to show the relationship between the accuracy class and the uncertainty affecting the residual voltage value.
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