UDC 621.313.3.002.24

INFLUENCE OF EXTERNAL FACTORS ON THE OUTPUT PARAMETERS OF A SELF-EXCITED ESG

Yu. G. Leleko

(Presented by the scientific seminar of the Department of TOE and the laboratory of rotary ESGs, Research Institute of Nuclear Physics)

External factors that affect the output parameters of an ESG, without changing its geometry and operating principle, and by changing which we have the possibility of regulating the current or voltage at the generator output, include: the load on which the generator operates and whose resistance may change during operation; the pressure inside the generator housing and the chemical composition of the gas used as the working medium; and the supply voltage of the motor, which affects the rotor speed. The influence of some of these quantities on the output parameters has been examined in detail as applied to generators operating with an external excitation source [1, 2]; the influence of others has been studied less thoroughly. However, when investigating the operation of a small-size self-excited ESG, it is evidently impossible mechanically to transfer the degree of influence of each of them from one type of ESG to another. In this connection it is necessary to consider the influence of these factors on the output parameters specifically of a small-size self-excited ESG.

To resolve these questions, experiments were carried out with a small-size self-excited ESG, the design of which is described in [3]. The generator operated into an active load, whose resistance could be varied from 16.6 GΩ to 41.4 GΩ, which corresponds to a change in load current from 0.9 to 3 μA for a generator stabilized at an output voltage of 40 kV. In this case, in the continuous-operation mode, the change in the load voltage is within ±5%. On a specially made divider consisting of active resistances, whose design made it possible to change the load resistance within the range 10–80 GΩ without stopping the generator, the dependence of the output voltage on the value of the load resistance was determined. Figure 1 presents these data for a generator with a load voltage of 40 kV at different values of the pressure inside the housing. For a generator without an additional brush, the load voltage increases sharply with increasing load resistance. When an additional brush is introduced, the potential of the excitation inductor remains practically constant; consequently, the load voltage also does not increase with increasing load resistance. In this case the excess charge from the inductor is removed through the additional brush. The change in load voltage in these experiments amounted to 7–10% of the nominal value.

In studying the influence of gas pressure inside the generator housing, a number of experiments were carried out with several generators and with different gases as the working medium. From their results one may draw a conclusion confirming the earlier conclusion made for externally excited generators, namely that the most acceptable gas is hydrogen [1, 3]. For the other gases used in the experiments, the dependences have the same character as for hydrogen.

Figure 2 shows the load characteristics of the generator at different pressures and for two values of the motor supply voltage.

Fig. 1. 1 — 7 ati, 2 — 6 ati, 3 — 5 ati, 4 — 4 ati, 5 — 6 ati without an additional brush

Fig. 2.

\[ \left. \begin{array}{l} 1 \text{ — } 7\ \text{ati}\\ 2 \text{ — } 6\ \text{ati}\\ 3 \text{ — } 5\ \text{ati} \end{array} \right\} \quad \text{at } U_{\mathrm{dv}} = 12\ \text{V} \]

\[ \left. \begin{array}{l} 4 \text{ — } 7\ \text{ati}\\ 5 \text{ — } 6\ \text{ati}\\ 6 \text{ — } 5\ \text{ati} \end{array} \right\} \quad \text{at } U_{\mathrm{dv}} = 8\ \text{V} \]

When the pressure inside the housing changes, the magnitude of the output voltage and current changes regardless of whether an additional stabilizing brush is used or not. Indeed, a change in the electric strength of the working medium when the pressure is decreased, for example, increases the charge leakage from the transporters of the auxiliary rotor at the same potential on them, and this leads to a decrease in the potential on the excitation inductor and, accordingly, to a decrease in the load current and voltage.

The regulating effect of the additional brush appears only when the pressure is increased above the values required to obtain the regulated output voltage. In this case, no increase in voltage above a certain limit is observed, since, with a constant gap, the additional brush–collector of the auxiliary rotor does not reduce, to a sufficient degree, the leakage of charges from the transporters of the auxiliary rotor when the electric strength of the medium is increased.

The rotational speed of the rotor, to which the load current varies proportionally, is of great importance for obtaining stable characteristics during continuous long-term operation of the generator. Since it is impossible to measure directly the number of revolutions of the generator rotor during its operation under load, the rotor speed was estimated from the current consumed by the motor during operation. For this purpose, when the generator was operated with only one rotor (without the housing and the external stator), the dependences of the rotor speed on the volta-

…of the motor supply voltage and on the current consumed at constant supply voltage. On the basis of these data, dependences were plotted of the rotor rotational speed on the motor supply voltage and on the current consumed by it; these make it possible, with a sufficient degree of accuracy, to determine the rotor rpm when operating under load. Thus, for example, during prolonged operation of the generator in the load mode, the current consumed by the DPR-32-N-1 motor is 60 mA, which corresponds to a rotor rotational speed of approximately 6000 rpm. When the consumed current is increased by 50%, the rotor rotational speed decreases by 40–45%. Figure 3 shows the dependences of the load voltage of a generator adjusted to the nominal voltage of 30 kV on the motor supply voltage for several values of load resistance. The generator operated in compressed hydrogen at up to 6 ati. The dependences presented show that, for a generator with an additional corona brush, when the motor supply voltage is varied from 6 to 20 V and the load current is varied from 0.5 to 2 μA, the load voltage increases by approximately 7% of the minimum value. When the generator operates without the additional brush, the load voltage rapidly increases to values sufficient for a discharge to occur along the collector of the main rotor.

Fig. 3. 1. \(R_{\mathrm{n}} = 55\ \mathrm{G\Omega}\), 2. \(R_{\mathrm{n}} = 41.4\ \mathrm{G\Omega}\), 3. \(R_{\mathrm{n}} = 16.6\ \mathrm{G\Omega}\), 4. \(R_{\mathrm{n}} = 41.4\ \mathrm{G\Omega}\) without the additional brush.

The investigations carried out of the operating mode of the motor showed that, during prolonged continuous operation for several tens of hours, the thermal state of the motor does not affect the output parameters of the generator. At the same time, at practically constant supply voltage, the motor current changes with a change in the magnitude of the load voltage, and this dependence is the stronger, the higher the magnitude of the output voltage. At constant load voltage, the motor current also remains constant. The reason for such a dependence apparently lies in the fact that ionization processes in the brush–collector system, whose intensity depends on the magnitude of the load voltage, have a definite influence on the current of the drive motor. When the load voltage is increased, the intensifying ionization processes increase the motor current, and conversely. The use of an additional corona brush, which makes it possible to stabilize the load voltage within certain limits, also limits the increase in motor current; consequently, when determining the rotor rotational speed it is necessary to take into account the influence of ionization processes on the motor current. This can be done if the volt–ampere characteristic of the corona discharge between the collector plates of the main rotor and the brushes is known. When an additional corona brush is used, such values of the output voltage can be set at which ionization processes do not yet affect the motor current; this makes it possible not to take them into account when determining the rotor rotational speed.

Thus, the investigations carried out make it possible to conclude that external factors have practically no effect on changes in the generator output parameters when an additional corona-producing brush is introduced into the auxiliary-rotor system. This brush makes it possible to stabilize the magnitude of the generator output voltage within preset limits under practically any changes in external factors, and to regulate the load voltage from zero to values at which gas discharges occur inside the generator. In order to obtain a voltage of 30 kV, the length of the gap of the additional brush–collector plate must be on the order of 1–1.5 mm, and for a voltage of 40 kV, 3.0–3.5 mm when hydrogen at a pressure of 6 atm is used as the working medium. The only exception is a change in the pressure inside the generator housing, which causes a change in the load voltage (more significant when the pressure is reduced).

However, in the practical application of generators in industrial installations, the pressure inside the housing will not change; and, in order to maintain a constant pressure value in the generator, appropriate measures are provided for monitoring it and maintaining it at a constant level.

REFERENCES

1. A. F. Kalganov. Development and investigation of certain types of rotary ESG. Dissertation, Tomsk, 1962.

2. V. I. Levintov, A. T. Lyapin. Electrostatic generators with a rigid rotor. Part 1, Moscow, TsINTI Elektropron, 1963.

3. Yu. G. Pelekh. Problems in the investigation of a small-sized self-excited electrostatic generator. Izv. TPI, vol. 227, 1972.