Transporting and Accessing Charge at EHV, Part II

Fig. 2.  Charge transfer to a dissectible capacitor within a high-voltage dome

Current carried in metal-wire conductors

Figure 2 above shows in schematic form one method of accessing charge that has been brought into the interior of a dome already at very high voltage. The charge is brought from an external source (the battery B) as a current in ordinary metallic conductors, which are initially connected to the plates of a dissectible capacitor within the dome.

Dissectible capacitor

The dissectible capacitor is an old concept, dating back to the Leyden Jars of the mid 18th century. The version shown in Figure 2 consists of two metallic plates of area A separated by a distance d, with a dielectric of constant κ and thickness b between the plates. (b must be sufficiently less than d to avoid charge transfer by corona discharge from the plates to the dielectric at any time. This unwanted effect usually does occur when Leyden Jars of traditional design are dissected — for example see the MIT video at https://www.youtube.com/watch?v=9ckpQW9sdUg).

After the plates have been charged, one of them is disconnected from the source, and removed as far as possible from the rest of the device, as shown dashed, so that (most of) its charge can then be delivered through an electrical connection to the dome. As we have seen previously, by Gauss's law, this delivery of charge must occur, no matter what voltage the dome has already acquired.

After this, the movable plate is returned to its original position, reconnected to the external source and the operating cycle continues.

Force through distance

It could be objected that force must be exerted through a distance, i.e. that energy must be expended, to separate out the movable charged plate. That is correct, and no doubt there would be no net energy gain if this process was not occurring within a dome already at very high voltage. But it is, and the higher the dome voltage, the higher the net energy gain as the plate's charge is transferred to it.

Charge accumulation on fixed plate

A more serious problem involves getting rid of undesired charge that would otherwise build up on the fixed plate. This could be neutralised against Earth via switch S, once per cycle, but even so, problems could still remain in accessing the desired charge at low energy penalty. However, I'm certainly not convinced that any such problems are insoluble. Experiments would be necessary to decide this.

Example calculation

When assembled, the capacitor obeys the formula given in Figure 2, where:—

C = capacitance
κ = dielectric constant
ε₀ = permittivity constant = 8.854 × 10^-12 farad/meter
A = area of plate
d = plate separation
b = dielectric slab thickness

Substituting "reasonable" values: A = 0.01m², κ = 5.4, d = 1mm, b = 0.8mm in this formula, we get:— 

C = 255.6pF.

If the external source charges the capacitor to a voltage V of say 1kV, we would get:—

q = CV = 2.556 × 10^-7 coulombs.

If the capacitor could be charged/discharged say 100 times/sec, we would get:—

I = dq/dt = 25.56 microamps.

This is a very small current, still typical of what is usually encountered in electrostatic machines employing isolated "static" charge carriers.

Next time I'll look into the possibility of using a similar approach to this, to achieve far higher levels of current and power.