Theoretical meter circumvention/manipulation

[ruxton.stanislaw]

Hello,

I thought of an idea that could potentially be abused in photovoltaic net metering situations. This is all theoretical of course; I don't have the intention or means to do this.

Anyhow, the idea requires a peak use demand business meter on the same transformer as a typical net metering meter. The idea is to inject a relatively large amount of DC current on to one or all of the phases (as separate circuits) and complete the circuit on the other end of the peak use demand meter. The meter would see current going out of the solar meter and the peak use meter wouldn't care about the extra current coming in, unless it raised the peak use.

You would not be tampering with utilities, but rather, connecting a non-UL approved appliance to a circuit. There is for sure still fraud itself though.

Would this idea work? Does the current need to match the AC wave form? You could do the same thing with a lower voltage AC in phase. What do you think?

Cheers to us thinkers

 

[Carultch]

Would this idea work? Does the current need to match the AC wave form? You could do the same thing with a lower voltage AC in phase. What do you think?

That's precisely why this idea wouldn't work. Yes, the current has to match the AC waveform. The meter needs proper matching phases to each CT & voltage input, to tell the difference between apparent power and real power.

When we talk about current entering or exiting a point in an AC circuit, it is really just a discussion of current at the snapshot in time when the voltage is positive. The other half of the cycle, the voltage is negative and the AC current flows the opposite direction. It's the time average of the instantaneous product of current and voltage, that determines power. The meter measures this instantaneous product, and keeps track of the cumulative energy. If somehow the meter could measure DC current, the power would just add up to zero as it measures a pure AC voltage at the same time.

To inject a current through your meter in hopes of subtracting power from its reading, you'll ultimately need to produce the power you desire to subtract anyway. Utilities also usually don't allow unauthorized products in their metering enclosures, so sneaking another wire through the CT would not be allowed.

On top of that, power meters use current transformers (CT's) to measure a representative current for calculating power, so you don't need hundreds of amps worth of wiring on the circuit boards. Even self-contained meters, effectively have built-in CT's inside the globe. Transformers do not work with DC, and CT's are no exception. There are DC equivalents of CT's, called Hall Effect Sensors, but of course a meter that is built with AC in mind, won't have a DC equivalent of a CT.

 

[ruxton.stanislaw]

That's precisely why this idea wouldn't work. Yes, the current has to match the AC waveform. The meter needs proper matching phases to each CT & voltage input, to tell the difference between apparent power and real power.

...

To inject a current through your meter in hopes of subtracting power from its reading, you'll ultimately need to produce the power you desire to subtract anyway. Utilities also usually don't allow unauthorized products in their metering enclosures, so sneaking another wire through the CT would not be allowed.

I think we are on the same page, however, I am not talking about vandalising or interfering with the CT cabinet. And thanks for the reminder about DC not affecting a CT. My theory is to use the wire itself on the same phase, between the two buildings, with current in phase, as a circuit.

I drew a rough schematic; something like this, or vice versa. Perhaps modified slightly to arrive at what I have in mind, but would it work?

 

[Elect117]

I think the demand meter will still read the peak demand. Or it might read the max output of the solar if there is no load. Power flows both ways, and I don't exactly see how you would get around having a higher output on the solar than the loading on the load side of the demand meter. The KWH would split as it goes back to the utility by parallel conductors (not perfectly split since there is a transformer in there). At some point the demand meter might get a reverse power flow error or you could end up with a negative KWH. Most meters have tampering hardware in them now that alert the utility if there is something suspicious. They even have a DC offset alarm if someone tries to use a magnet to destroy the meter's register or cause the register to count down instead of up on the digital clocking.

At the end of the day, you can connect your solar to the load side of the demand meter and it would have the same effect. From my understanding.

 

[ruxton.stanislaw]

Let's simplify: assume there is one unloaded phase in both buildings for this exploitation; not a single breaker except for the circuit here which powers a high ampacity, current shunted 1:10 (12v) transformer. The person doing this will only operate when the peak demand meter is off-peak (for example, at night time). Then, it looks like the building is using 10x more power than it actually is, since it is a low voltage current relative to neutral. However, that can be ignored anyway because it is less than the peak usage so the data will be thrown out. The benefit is on the net metering side, where it looks like the building is exporting 10x more power than it actually is. And the power that it is exporting is useless, since it is just shorted out with the wild/random conductor leading to the other building.

I originally posted this in Campfire so it wouldn't inspire anyone up to bad on Google, but it was moved here (guessing because of the photovoltaic net metering context). However, not a single solar panel or inverter would be necessary for this exploitation - just the net metering program.

 

[jaggedben]

Sorry, I don't understand how your diagram isn't a dead short. Is there something not shown?

 

[ruxton.stanislaw]

Sorry, I don't understand how your diagram isn't a dead short. Is there something not shown?

Yes, it is a dead short with a low voltage, current shunted transformer (think similar to the neon sign transformers that can operated shorted at 100% duty cycle). It could be shunted or ballasted to 12 or 16 A for example, whatever the wiring will support

The point is, the meter sees an otherwise empty phase with 10 - 20 A of current flowing in the opposite (export) direction. It does not know the voltage or where it is flowing to, only that it is precisely in phase with the 120 V between the A phase and neutral.

 

[jaggedben]

Okay, so you didn't show the shunt, got it.

I think what I don't get is that you think the demand meter is not also a watt-hour meter. I will be both, right? So I see it coming out net zero on the net metering calc. That's assuming you even get paid the same for exports as you pay for imports, otherwise it's a net loss. Also if you did this at night and the utility has smart meters then you also have to explain how your solar system was outputting power at night.

I mean, I guess it's an interesting thought experiment that one can circulate useless current like this, and possibly mess up meter readings. But I don't see how it helps one 'get away with' anything in the real world.

 

[ggunn]

FWIW, this happened at a hotel in Mexico: A previous owner of the hotel had installed some sort of device (I was told it was magnetic) in the meter of the service which reduced the meter reading. When the utility found the device they determined that it had been in the meter since before the hotel changed owners, so they settled with the present owner for the estimated differential between what the meter had shown since the ownership change and what it should have read if the device were not in the meter. I don't know how the device worked.