High Voltage High Power Induction Generator

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