SOME PROBLEMS IN THE STUDY OF A MULTIPOLE ELECTROSTATIC GENERATOR

A. P. KONONOV

(Presented by the scientific seminar of the Department of Theoretical Foundations of Electrical Engineering)

To study the operation of a multipole generator, an experimental model was built with a cascade connection of conveyor conductors with three pairs of poles. The generator rotor, 140 mm in diameter, was made in the form of a disk of epoxy resin with rods embedded in it, 25 mm long and 4 mm in diameter. The stator was made in the form of split rings of organic glass. The inductors were filled with epoxy resin with a silicon-carbide filler in order to create a semiconducting layer, which serves to distribute the potential uniformly in the generator.

Fig. 1. Connection diagrams of an electrostatic generator with different numbers of pole pairs: a) with one pair of poles \(p = 1\), b) with two pairs of poles \(p = 2\), c) with three pairs of poles \(p = 3\).

In the experimental model, contact commutation was used; the brushes for it were made of metal mesh. The design of the generator made it possible to implement various connection diagrams, the operation of which is described below.

An experiment was carried out on the test generator to measure the short-circuit current with different numbers of pole pairs \((p = 1;\ p = 2;\ p = 3)\).

The generator connection diagrams are shown in Fig. 1.

The values of the short-circuit current as a function \(I = f(U_{\mathrm{в}})\) are presented in the graph of Fig. 2. From this graph it is evident that the current in the generator does not increase in direct proportion to the number of pole pairs, as would be expected from theoretical calculations. When comparing dependences 2 and 4, 3 and 5 (Fig. 2), it may be noted that the experimental characteristics lie considerably lower than the calculated ones. This reduction of current, as indicated in [1], occurs because of the reduction in the working surface of the rotor occupied by the inductors.

Further investigation of the generator showed that the current in the generator described above can be made equal to the calculated value (for \(p = 2,\ p = 3\)) if the polarity of the excitation voltage is reversed.

When the generator operates according to the diagram of Fig. 3a, its external characteristic in the form of the dependence \(U_{\mathrm{н}} = f(I_{\mathrm{н}})\) is presented in the graph of Fig. 4 (curve 1). If the generator operates according to the diagram of Fig. 3b, then its characteristic for each pair of poles is shown by curve 2 in Fig. 4.

Fig. 2. Graph of the dependences \(I = f(U_{\mathrm{в}})\), obtained according to the diagrams of Fig. 1. Experimental: 1) at \(p = 1\), 2) at \(p = 2\), 3) at \(p = 3\); calculated: 4) at \(p = 2\), 5) at \(p = 3\).

When comparing dependences 1 and 2 (Fig. 4), a decrease in current is observed when the generator operates according to the diagram of Fig. 3b. This decrease in current can be explained as follows.

If the generator operates with only one pair of poles (Fig. 3a), then the external field forces do not hold the charges on the carriers. A current value arises in the generator close to the calculated one (curve 1, Fig. 4).

When the generator operates according to the diagram of Fig. 3b, the presence of a constant positive potential \(+U_{\mathrm{в}}\) located beyond the loaded pole leads to retention of part of the charges on the carriers, which causes a decrease in the current in the generator.

This is confirmed by the generator operating diagram in which the polarity of the excitation voltage is reversed (Fig. 3c).

In this diagram the constant negative potential \(-U_{\mathrm{в}}\) does not retain the negative charges on the carriers and thereby increases the generator current (curve 3, Fig. 4).

Thus, by changing the polarity of the excitation voltage in multipole generators, one can obtain an increase in current directly proportional to the number of pole pairs and, correspondingly, increase the generator power.

In addition, such a generator provides voltage at the output terminals—

Fig. 3. ESG connection diagrams: a) independent circuit of one pair of poles, b) circuit with the same excitation polarity, c) circuit with different excitation polarity.

Fig. 4. Graph of the dependence
$U_{\mathrm{n}} = f(I_{\mathrm{n}})$: 1) for independent operation of one pair of poles, 2) during operation of a multipole generator with the same excitation polarity, 3) during operation of a multipole generator with different excitation polarity.

with different polarity. The circuit of a multipole generator of this type with the number of pole pairs \(p = 4\) is shown in Fig. 5.

Electrostatic high-voltage direct-current generators with different polarity are used in electrostatic separation of materials [2] and in electrofilters.

Fig. 5. Circuit of a multipole ESG with different excitation polarity.

Conclusions

1. Alternating reversal of the polarity of the excitation voltage leads to an increase in the current in the generator proportional to the number of pole pairs.

2. The indicated reversal of the polarity of the excitation voltage makes it possible to take the voltages \(+U_n\) and \(-U_n\) from the generator terminals.

References

1. V. I. Levitov and A. G. Lyapin. Electrostatic Generators with a Rigid Rotor, TsNIIpriborelektroprom, 1963.

2. Application of Electric-Field Forces in Industry and Agriculture, materials of the International Colloquium in Grenoble, VNIIEM, 1964.