No, under no circumstances will the mains be electrically modified, and that includes tapping in an AC transformer or sensor wire.
Doesn't change the nature of the project. 3ph 208v = 120v legs most likely. Not important.
The current sensor is not an issue. That's straightforward and there's several options. Sensing the wire's electric field, not magnetic field (current) without electrically clipping onto the mains is the problem.
Hall Effects only sense magnetic field from current. They cannot sense the voltage at all, AC or DC. It is impossible to determine voltage, phase angle, or power factor, or power from a Hall Effect.
As you can tell this is not a simple question, if it were readily solvable I'd have already done it.
There are noncontact voltage sensors used for determining if an AC wire is "hot" without finding copper to probe. They are not remotely accurate for measurement, but they are not applied in a consistent manner. AFAIK they are still reliable for detecting zero crossing. I'm wondering if the sensing is applied in a fixed installation (no distance or geometry variations) if it can't simply be calibrated and become an accurate voltage measurement.
Hi,
Oh so it is the voltage measurement you are after, as well as the current. Usually the voltage would be assumed and then just measure the current.
So it is starting to sound like you are asking too much from anyone except an engineering firm that is wiling to take the contract and study ways in which this could be done.
The measurement you talk about is just too riddled with constraints, which start to make it physically impossible. You can usually have one constraint and still get away with different kinds of tricks, but once you get too many constraints it starts to make it a very tough problem to solve, which may not have any good solution.
For example, you say that you need to measure the voltage right at the mains, yet you cant do anything to the wiring. Well if you have two single wires where one is hot and one is neutral then you might use a differential capacitive coupling setup, where you run a pickup along each wire. It must be differential because you need the voltage between the two wires not the voltage to physical ground. But because you cant alter the wiring and it must be close to the source, that means the sense pickup would probably be too small and more important the hot and neutral wires will be too close together to pick up the signal. The only possibility is to try to sense at the very outside edges of the two wires, the place where the surfaces are farthest apart. But the problem here is you cant get to the wires individually either it sounds like, so you'd have to wing it by building a sensor and placing it along the wire at different places and hope to find a good spot, and then epoxy it to the wire. The other problem is the insulation thickness will be more because of the outer cable, and the ground wire inside the cable might interfere too much too. Also even with a longer pickup, if the internal wires twist then the pickup signal will be diminished unless the pickup sense area can twist with the wire, and that will be hard to do because you can not see inside the wire. Maybe multiple pickups, where each one is adjusted separately along the wire, and each one is kept relatively short.
So with all these constraints the best you could do would be to build up a sensor and amplifier, use DSP to calculate the quantities needed, and move the sensor up and down the wire to see where you might pick up the signal best, then attach it permanently. It must be extremely physically stable or the calibration will change.
To increase the capacitance for the pickup try to make it as long as possible, probably in the shape of two long C shaped metal pieces that cup the wire on each side, one C on each side. It's hard to say how well this will couple and how much will be picked up because the two wires being close together will cancel out some of the field. If the wires could be separated it would work better.
By all means tell us how this works out if you try it. Remember you can always try it at home first too, just by using some lamp cord. Later move to some Romex cable and try that. If you next tell me that they are using BX cable then all bets are totally, totally, totally, and completely, off.