Current-measuring circuits flawed, potentially over-charge homes, study finds
A recent study from researchers at University of Twente (UT) and Amsterdam University of Applied Sciences (AUAS) has found that three-phase static (electronic) energy meters, which are replacing traditional electromechanical meters, can exaggerate energy consumption by as much as 582 per cent.
Estimates of the number of households in the Netherlands with smart meters range from 750,000 to 1.5 million. In the US, smart meter penetration at the end of 2016 has been estimated at 70 million, according to the Edison Foundation [PDF].
The government of the Netherlands aims to replace at least 80 per cent of the energy meters in the country with smart meters by 2020, in keeping with EU goals. EU authorities suggest that smart meters, on average, result in energy savings of 3 per cent.
But as researchers Frank Leferink, Cees Keyer, and Anton Melentjev report, “Some consumers are complaining about their energy bills after replacement of the energy meter, because the registered energy is higher with the static meter compared to the old Ferraris meter.” Smart meter billing problems have also been documented in the US.
Some of the past flaws found in static meters have been attributed to electromagnetic interference, which has been addressed over the years.
The researchers suggest that present flaws are made more difficult to detect by insufficiently broad testing and opaque industry practices.
They point out that makers of the smart meters covered in the study test their equipment under ideal conditions, with consistent voltage and load, but fail to consider other scenarios.
They also observe that faulty smart meters tend to get scrapped instead of being offered for examination and that utilities don’t make their equipment available for testing, don’t document the devices well, and tend to rely on proprietary software.
Among the 10 models tested, the issue appears to be a component known as the Rogowski Coil, one of the four-types of current sensors used in static meters. The three others are: the shunt resistor, the current transformer, and the Hall effect-based current sensor.
“The reason for faulty readings appears to be the current sensor, and the associated circuitry,” the researcher paper states. “As a Rogowski coil results in a time-derivative of the measured current, the measured voltage has to be integrated. Probably active integration is used instead of passive integration, and the input electronics are pushed in saturation caused by the high rise-time of the current.”
While the highest deviation between actual energy consumption and reported energy consumption was 582 per cent, some of the meters made errors in favor of the customer. Two reported about 32 per cent less usage than actually occurred. ®