Following is a description
of a compact high power, high voltage, electrostatic induction
generator that I am presently working on and building. The metal
rotor of this generator is at earth ground potential so that it can
be driven directly from a mechanical motor without any hazardous
voltages being present in the mechanical mounting and powering of the
generator. The rotor and stator plates are laser cut out of aluminum
sheets, and are separated by "KAPTON" (Polyimide)film
sheets, and the entire assembly is encased and runs in a cooling,
lubricating, and insulating oil bath. The rotor and stator plates
have the insulating films laminated on them so that the moving parts
in contact with one another are all insulating sheets, and therefore
no "shavings" or metal particles should be produced to
cause breakdown problems.
The switching diodes are
high voltage diodes of the type that are used in X-ray power supplies
and can withstand at least 100KV PIV. The physical dimensions of the
generator described are approximately 10"x10"x4" thick
including the housing.
Rotor and Stator
laser cut from one sheet Polyimide insulating sheet
A stack of ten rotor and
stator plates were assembled onto a drive shaft, and the maximum and
minimum capacitor values of the variable capacitor were determined by
measuring the capacitive reactance at the two settings.
The power output
capability of this type of generator increases linearly with increase
in rotation speed and the number of sectors on the plates, and the
number of plates. The highest voltage output voltage to input
voltage ratio attainable is directly related to the capacitance ratio
of the variable capacitor.
Losses in this generator
are from diode leakage currents, and dielectric leakage and losses.
Assembled
Rotor and Stator Stack
Schematic of Generator
The Supply Voltage Storage
Capacitor is initially charged with respect to a neutral voltage
ground by the high voltage 20KV trickle supply through the resistor.
The charge on the capacitor is Qs = Cs*V = 1mC (Coulomb). Also,
and at the same time, the Variable Capacitor is being charged through
the high voltage diode D1, and the output storage capacitor remains
uncharged, but both sides of it are raised to the 20 KV supply
voltage potential. When the variable capacitor is at its maximum
value, the charge held on it is: Qv = Cv*V = 64uC.
As the rotor of the
variable capacitor turns, it goes through six cycles of maximum and
minimum capacitance per revolution, because of the six sectors on
each plate. The rotor turns at 1800 RPM, so the frequency of the
capacitor cycle is 180 HZ.
Since the diode D1 blocks
reverse current back into the supply capacitor when the variable
capacitor moves to minimum value, mechanical energy is required to
turn the rotor and overcome the attraction of the rotor plates to the
stator, and is the conversion means to produce electrical energy from
mechanical energy. Also, the voltage starts increasing across the
variable capacitor in accordance with V = Q/Cv , as long as the
charge on the capacitor remains constant. As the capacitor decreases
in capacitance, and the voltage across it increases, diode D2 is
forward biased and the current flowing through it charges the High
Voltage Storage Capacitor, raising the voltage across it, and some of
the current flows through the load resistor. The maximum voltage
that can be developed across Cv is equal to Vmax = (Cmax *
20KV)/Cmin. For this particular generator design, the maximum
voltage is 98.5KV, and the maximum voltage that can be developed
across the storage output capacitor is 98.5KV - 20KV = 78.5KV. So
until the storage capacitor reaches this potential, current will flow
from the variable capacitor into the storage capacitor on each cycle,
raising the storage capacitor voltage. Also, some of the current
will flow through the load resistor as well. This process will
continue until the current being supplied by the variable capacitor
reaches an equilibrium with the current passing through the load
resistor at some stable voltage across the capacitor. For this
illustration, we will pick a resistor which will cause a
stabilization voltage of 40KV across the capacitor, and a maximum
voltage of 60KV across the variable capacitor (which is under the
98.5KV max & assures current flow into the load and storage
capacitor).
To see what current would
be flowing through the load at the point of equilibrium, we will have
to look at the charge levels on the variable capacitor at the maximum
and minimum levels of capacitance at various voltages.
At 20KV potential and
maximum capacitance: Qmax = 20KV * 3.2E-9F = 64uC
At 60KV potential and
minimum capacitance: Qmin = 60KV * 6.5E-10F = 39uC Therefore, 64uC
- 39uC = 25uC of charge is transferred per cycle or,
25uC * 180 Hz = 4.5 mA
current goes into the load at 40 KV and 180
Watts is delivered to the load. The
load resistor value would be 40KV/4.5mA = 8.9Mohms
At 50KV output voltage
(still 28.5 KV below max available), the power output is:
64uC - 45.5uC = 18.5uC ,
18.5uC * 180 = 3.33mA , 3.33mA * 50E3V = 167Watts Resistor
Value = 15 Mohms
At 30KV output voltage,
the power output is: 64uC - 32.5uC = 31.5uC ,
31.5uC * 180 = 5.67mA , 5.67mA * 30E3V = 170
Watts Resistor
Value = 5.3 Mohms
Notice that both the
charge current and load current flow back into the Supply Storage
Capacitor in the negative direction at the minimum variable
capacitance point, replenishing the lost charge required to supply
the variable capacitor at its maximum capacitance point in the cycle.
And while running, the generator draws no average current from the
trickle 20KV supply. It is needed just to replenish any leakage
current in the diodes or dielectrics, and set the initial supply
voltage on the storage capacitor. Also notice that the maximum power
output peaks where the operating voltage on the variable capacitor is
about at 2/3 of the maximum voltage attainable on it.
Copyright Dan Bowlds 2011
