Some electronic power meters as used by utilities can give readings that are more than five times higher than actual energy consumption when the measured waveform is nonsinusoidal.
So say researchers at the University of Twente (UT) in the Netherlands who collaborated with the Amsterdam University of Applied Sciences (AUAS) to measure the accuracy of various brands of power meters. UT Professor Frank Leferink estimates that potentially inaccurate meters have been installed in at least 750,000 Dutch households.
Researchers tested nine different electronic meters manufactured between 2004 and 2014. The meters were connected to a range of power-consuming appliances that included energy saving light bulbs, heaters, LED bulbs and dimmers. The researchers then compared the actual consumption of the system with the electronic energy meter’s readings.
Five of the nine meters gave readings that were much higher than the actual amount of power consumed. Some setups gave readings that were off by more than a factor of five. Conversely, two of the meters gave readings that were 30% lower than the actual amount of power consumed.
The greatest inaccuracies arose when dimmers combined with energy saving light bulbs and LED bulbs were connected. Researchers attribute the inaccurate readings to the nonsinusoidal waveforms that arise in the case of triac dimming and switching power supplies that lack adequate power factor compensation. The designers of modern energy meters have not made sufficient allowance for switching devices of this kind, researchers say.
When researchers dismantled the energy meters tested, they found that the meters associated with excessively high readings contained a Rogowski Coil current sensor. Meters associated with excessively low readings sensed current with Hall effect sensors. Researcher Leferink points out that “The energy meters we tested meet all the legal requirements and are certified. These requirements, however, have not made sufficient allowance for modern switching devices”.
The study, entitled Static Energy Meter Errors Caused by Conducted Electromagnetic Interference, published in the IEEE Electromagnetic Compatibility Magazine. The Van Swinden Laboratory (the Dutch Metrology Institute), which carried out a countercheck, confirmed the results.
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