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Smart energy meter shows energy generation instead of consumption

An energy meter that indicated that hundreds of watts are generated, while in reality no PV panels or a small windmill are part of the system. On the contrary: in reality, a small amount of power is consumed. This can happen using the comnination of a dimmer and some household equipment, together consuming about twenty Watt. Depening on the actual setting of the dimmer, the energy meter gives the correct read-out, a consumption that is twenty times higher, or even hundreds of Watts generated power. Researchersof the University of Twente present and explain this effect on the large online conference on electromagnetic compatibility, EMC 2021.

‘The meter is running back’, we used to say when energy was generated: the dial of the electricitymeter turned the other way round, which was a great way of visualizing the power generated by e.g. solar panels. Today’s smart meters have a display, and they show the energy that is fed back, on a display. Earlier UT research, on intelligent electricity meters, indicated that the errors can be huge: they then show substantial under- or overconsumption of hundreds of percents. As the researchers now found, they can even show a negative amount of energy, as if electronics would generate power instead of using it.

This effect happens when a remotely controlled dimmer is used in combination with some kind of household equipment.  In fact, the dimmer is only used for switching on an off. But even in this situation, the dimmer appears to dim for a few percent. For the equipment, this has no direct consequences, but for the measurements the smart meter shows, it indeed has. It can make the difference between a readout that is fully correct, a readout that indicates far too much power and a readout that actually shows energy production. After consumers noticed this in their home setting, Frank Leferink’s lab tested it using both an idealized situation as well – with a simulated mains voltage and no further load - as a fully operational mains environment with all kinds of devices working.

According to the researchers, this has to do with the rapid current pulses formed by the combination of the dimmer and the device. Like many home devices and battery chargers, this devices also has a switching power supply: it will work the same for various mains voltages (110 V, 230V) by switching rapidly. Thus, it is no linear load anymore, like many loads used to be. The dimmer, in turn, can take action at several moments of the sinusoidal shape of the net voltage. This moment determines the measured outcome: roughly from minus 400 to plus 400 Watt.

The result is that, caused by complex loads like switching power supplies, LED’s, dimmers, the electricity supplies encounter a load that is far more complex than before. An average electricity meter will determine the overall current using a coil. Is this too simple and cheap, it will not be prepared for the complexity of today’s net loads. Many of the smart energy meters were upgraded and have the lastest ‘immunity norm’, but even for this article a meter was used, built in 2019.

The other side of the medal is that the equipment we use on the net, should meet the standards as well. A recent publication of ‘Netbeheer Nederland’ (Netherlands Grid Management) also points at that. The combination of equipment and a dimmer that is not used for dimming, may be a bit out-of-the-ordinay. But imagine you use a remotely controlled device for several purposes: you dim a few lights, switch on and off another type of device, all in one. So, this situation may not be that extraordinary after all.

The paper ‘How to earn money with an EMI problem: static energy meters running backwards’, by Tom Hartman, Bas ten Have, Niek Moonen and Frank Leferink, will be presented at het IEEE Symposium on Electromagnetic Compatibility, Signal & Power Integrity, georganiseerd samen met EMC Europe. Dit is een online conferentie.

ir. W.R. van der Veen (Wiebe)
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