Previous studies regarding static energy meter errors under non-sinusoidal load conditions have shown that these meters can produce erroneous readings. This paper describes an investigation done using loads consisting of a commercial lighting dimmer in combination with either a resistive heater or an array of various energy-saving lamps. Dimmer impedance and phase firing angle were gradually adjusted to change load conditions. Several meters showed dramatic variations in metering error under different load conditions. In the most extreme case, metering errors ranged from five times the energy consumed by the load to registering almost no energy. Though perhaps not typically found in households, the load combinations used in this study were able to highlight sensitivities of different static energy meters to changes in load conditions.
In this paper we present the design and implementation of a new flexible testbed for testing electricity meters with conducted EMI in the frequency range up to 150 kHz. This testbed is based on separate generation of voltage and current test signals with arbitrary waveforms. Different transconductance amplifiers were characterized for their suitability to generate the highly-distorted current waveforms required for advanced testing of electricity meters. The complete setup was validated by comparing test results on a meter showing error readings under conducted EMI with earlier test results obtained using a setup based on a power source in combination with real physical loads. The good validation results of the new testbed proof the setup is very suitable for advanced calibration or testing of static electricity meters under wideband conducted EMI. The setup and waveforms presented in this paper will be used as input for improved standardization of electricity meters type testing.
In 2015, the energy measurement of some static electricity meters was found to be sensitive to specific conducted electromagnetic disturbances with very fast current changes caused by highly nonlinear loads, leading to meter errors up to several hundred percent. This article describes new results on the electromagnetic compatibility (EMC) of 16 different meters from all over Europe when exposed to real-world disturbance signals. Those test signals were obtained from household appliances and onsite measurements at metered supply points all over Europe. The results show that also the interference signals recorded onsite can cause measurement errors as large as several hundred percent, even for meters that pass the present EMC standards. This unambiguously demonstrates that the present immunity testing standards do not cover the most disturbing conducted interference occurring in present daily-life situations due to the increased use of nonlinear electronics. Furthermore, to enable the adoption of potential new test waveforms in future standards for electricity meter testing, artificial test waveforms were constructed based on real-world waveforms using a piece-wise linear model. These artificial test waveforms were demonstrated to cause meter errors similar to those caused by the original real-life waveforms they are representing, showing that they are suitable candidates for use in improved standardization of electricity meter testing.
To compensate for the different transfer functions of the current and voltage input stages of static electricity meters, usually a time correction is applied, which is suitable for sinusoidal signals. However, for highly-distorted signals, in which the highfrequency content is significant, this method is insufficient and reading errors will not be fully compensated. For such waveforms, this paper describes two alternative methods to deal with the different input stages. The methods are implemented on a homebuilt waveform recorder, modified as static electricity meter, and validated by means of their influence on energy-reading errors for various waveforms and input stages (impedance and coupling). Apart from highly-distorted current signals, also the effect of finite source impedance is considered by modifying the voltage waveform accordingly, which potentially influences the observed meter errors as well. The inverse-filtering method is the most powerful method but is computationally intensive and, therefore, more suitable for high-accuracy power meters than for inexpensive electricity meters. The less computationally-intensive equivalent-filtering method shows very good results as well and is a better candidate to be implemented in electricity meters. The latter is especially relevant because of recent results showing that some electricity meters are sensitive to specific disturbances beyond the present standard test waveforms.
This paper presents a strategy for the description of new test waveforms for static electricity meters to be included in international standards. The need of extending the existing standardisation frame arises from several recent studies that have reported conducted electromagnetic interference problems of type-approved static electricity meters, resulting in significant errors in the measured electricity consumption. The proposed method is based on discrete wavelet transform and allows for a compact and parsimonious representation of test waveforms, suitable for inclusion in standards. Very few wavelet parameters are concentrating the relevant information to accurately reproduce all the characteristics that the meters need to be tested against. The same parsimonious description cannot be performed with the current practises based on Fourier transform methods since the new test signals need to be highly non-sinusoidal. The discrete wavelet transform is proposed as a more effective tool to sparsely describe the most relevant waveform features. The effect of different discrete wavelet transform decomposition settings on compactness and reconstruction accuracy is studied using suitable metrics. Finally, results from experimental validation with several different waveforms are presented to demonstrate that the error-inducing features can be preserved using only 0.1 % of the original signal information.
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