Electronic – High voltages vs. Energy loss

If you are only confused by the "test particle," then you can think of it similarly to a multimeter. With a multimeter, you can probe a circuit to determine a voltage at one part of a circuit relative to another. With a test particle (or test charge, as I got used to hearing), you place it at a point in space, and "observe" it's behavior to see how electric (or magnetic) fields are oriented.

Like charges repel each other, so if a test charge would tend to move in a certain direction in space, then either that direction contains a negative charge (assuming you use a positive test charge), or the opposing direction contains a positive charge.

The movement of a test charge will always oppose the energy gradient (in three dimensions, energy is a scalar field, so the spatial derivatives are your forces, since energy divided by length is force). Thus, a test charge will move in the direction that achieves it's lowest energy state.

In a vacuum (such as space), ionized particles can move freely. The test charge is usually assumed to be in a state such that it can move freely. This doesn't necessarily correlate to anything real, but is a hypothetical state so the fields can be analyzed easily. You are correct in that circuits don't involve the movement of atoms or positive charges, but rather electrons (due to d-block delocalization, but that's chemistry) move. The positive charges (protons) are held in a crystalline lattice, which is why they don't move. In a conductor, electrons can move freely, so they move in response to an applied electric (or changing magnetic) field.

In free space, however, a test charge (which is really an ion, or a proton, or a positron, or a myriad of other positively charged particles) is not constrained by the bonds that hold metal atoms in place, so it can move in response to an applied field. Specifically, interactions governed by photons cause particles to exchange energy, creating the field gradient mentioned before. Therefore, test charges in free space move similarly to how electrons move in a metal (or another conductor).

While this is a convention (positive charges just seemed to be more reasonable when a lot of this math was derived), you could physically create a positively charged particle and observe it's trajectory. You could even do this at home. You'd be using a Cloud Chamber and a Beta emitter to see them.

I hope this was helpful! Let me know if you need any more clarification.

Having designed a number of energy meters over the years, I can say with authority that reactive energy (Q) is not the same as exported energy (PE), in fact it has basically nothing to do with it. What you need is an energy meter that has separate counters for imported real energy (P) and exported real energy (PE).

Reactive power is basically only relevant for industrial metering, but in case you're interested, an energy meter can additionally have up to four counters for reactive energy (Q), these being, in order of real world relevance, inductive (QIND) and capacitive (QCAP), exported inductive (QEIND) and exported capacitive (QECAP). When there are six registers in total, the sign of real power is used to select which registers are accumulated.

Most important, however, is that when money is involved (the meter is used for billing), the exact meter brand and model must be accepted by your power grid company. If money is involved, they may also come and seal the meter themselves with their own seal, although the practice varies from company to company in different countries.

When you're reading the registers, be sure to note the difference between instantaneous power (P) and accumulated energy (W). The register names for instantaneour powers might be something like P, PE, Q, QIND, QCAP and the energies might be something like W, WE, WQ, WQIND, WQCAP etc.