SHOCK GENERATOR—AN ENERGY STORAGE DEVICE AND SOURCE OF 100 MJ

G. A. Sipailov, K. A. Khor’kov, V. Z. Khor’kova

(Presented by the scientific seminar of the Departments of Electrical Machines and General Electrical Engineering)

Periodic pulses of strong current are used to power electrophysical installations for studying the properties of substances in superstrong magnetic fields, to power the solenoids of installations for controlled thermonuclear reactions, and to power the windings of charged-particle accelerators. Numerous circuits with oscillatory contours, as well as special electrical machines, are used as sources of strong pulsed currents.

The use of special synchronous machines as sources of strong pulsed currents, which have been called shock generators, was initiated by Academicians P. L. Kapitsa and M. P. Kostenko. They designed the world’s first shock-power generator, from which current pulses of duration about $0.02$ sec with an amplitude of $72\,000$ A at a voltage of $2.2$ kV were obtained. In 1939, at the Elektrosila plant, the single-phase shock generator TO-12-2 was manufactured. This shock generator made it possible to obtain current pulses with an amplitude of $280\,000$ A at a voltage of $2.37$ kV [1, 2, 3].

However, despite their advantages, shock generators have still not found wide application. This is explained, on the one hand, by the imperfection of the existing switching equipment and, on the other, by the traditional use of capacitor banks as energy storage devices. Economic calculations show that at an energy of the order of $1$ MJ the cost of a capacitor bank and of a shock generator is approximately the same. As the power required from the storage device increases, the advantages of the shock generator become indisputable.

Physics today has posed the problem of creating an energy storage device of $100$ MJ. Scientists throughout the world are working on solving this problem. At present it appears inexpedient to create a capacitive storage device for such energies. Therefore, searches are being conducted in the field of developing special electromechanical and inductive storage devices [4, 5]. For a number of years we have been carrying out research on special pulsed synchronous generators—shock-power generators. Comprehensive investigations have made it possible to develop a methodology for the optimal design of these generators, to estimate the energy capabilities of various structural versions of shock generators, and to develop a number of schemes for transmitting energy from the generator to the load.

This article presents the results of investigations of the energy capabilities of various structural designs of shock-power generators.

It is known that the storage of energy in rotating flywheel masses is the most effective. The density of kinetic energy of rotors is determined by the relation

\[ \Delta T=\frac{\gamma}{16}\left(\frac{\pi D_p}{p}\right)^2\cdot 10^4,\ \frac{\text{J}}{\text{cm}^3}, \tag{1} \]

where \(D_p\) is the diameter of the rotor barrel;
\(p\) is the number of pole pairs of the machine;
\(\gamma\) is the density of the rotor material,

and for two-pole machines with a rotor diameter of \(1.2\ \text{m}\) reaches up to \(69.3\ \text{J}/\text{cm}^3\). For comparison it should be noted that the energy density in capacitors is only \(0.02\)—\(0.26\ \text{J}/\text{cm}^3\).

The rotors of shock generators of limiting dimensions can store energy up to \(600\ \text{MJ}\) in a two-pole version and more than \(1000\ \text{MJ}\) in a multipole version [6].

The task of the designer is to ensure the maximum possible conversion of the stored kinetic energy into electromagnetic energy. When a shock-power generator operates into a matched inductive load, the energy delivered to the load is determined by

\[ Q_{\text{н}}=\frac{U_{mo}}{2\omega} I_{\text{н}}^{t} k_{\text{з}}, \tag{2} \]

where \(U_{mo}\) is the voltage amplitude at the terminals of the single-phase stator winding of the shock-power generator in the no-load mode;
\(I_{\text{н}}^{t}\) is the amplitude of the current pulse;
\(k_{\text{з}}\) is the current damping coefficient;
\(\omega\) is the angular frequency of the voltage.

For a constant value of the voltage at the terminals of the stator winding, the current amplitude and, consequently, the fraction of the rotor kinetic energy converted into electromagnetic energy of the stator winding are determined by the magnitude of the inductive transient reactance of the machine. Comprehensive measures must be taken to reduce this reactance. First of all, the generator must have a powerful damper system on the rotor. This reduces the inductive transient reactance to the value of the inductive leakage reactance of the stator winding. The latter can be reduced by shielding the end portions of the stator winding with current-conducting caps and by reducing the height of the stator slot while simultaneously increasing its width.

The limiting dimensions of a shock generator are determined by the permissible value of the outside diameter of the rotor, which, on the one hand, is limited by the permissible load on the retaining rings and, on the other, by the permissible deformations of the rotor forging. A number of firms manufacture turbogenerator rotors assembled from several parts pressed onto a central shaft. For superpower generators a welded-rotor technology is being developed. A calculation of the limiting diameters of the retaining rings \(D_{\text{б}}\), the rotor barrel \(D_p\), and the limiting lengths of the active part of the rotors, performed by specialists of Brown Boveri [7], showed that at a rotor speed of \(3000\ \text{rpm}\) rotors are realistically feasible with \(D_{\text{б}}=1310\ \text{mm}\), \(D_p=1280\ \text{mm}\), \(l_1=11000\ \text{mm}\), and at \(n=1500\ \text{rpm}\): \(D_{\text{б}}=2370\ \text{mm}\), \(D_p=2250\ \text{mm}\), \(l_1=11900\ \text{mm}\).

From shock-power generators made in the dimensions given above, it is possible to transfer to a matched inductive load, in one current pulse, an energy of 60 and 100 MJ, respectively. Still greater electromagnetic energy can be obtained from an 8-pole shock generator with dimensions \(D_p = 3900\) mm, \(l_1 = 12000\) mm, namely 140 MJ. In addition to the possibility of increasing the electromagnetic energy in a single pulse by increasing the dimensions of the generator, there is the possibility of increasing the energy by reducing the inductive resistance of the stator winding and increasing the induction in the air gap of the machine. The latter leads to the creation of a shock generator with a smooth armature.

Calculations show that from a shock generator with a smooth armature (toothless stator), with dimensions \(D_p = 1250\) mm, \(l_1 = 6000\) mm, it is possible to obtain an energy of up to 100 MJ, which is three times greater than from a shock generator with a toothed stator in the same dimensions. Raising the induction in the air gap of a shock generator with a smooth armature to 2.4 T makes it possible to attain a value of the energy delivered by the generator to the load of up to 200 MJ.

When a shock generator is connected directly to an inductive load, in the best case an energy equal to

Table 1

one fourth of the electromagnetic energy of a sudden short circuit is transferred to the load. To increase the fraction of the energy transferred to the inductive load during one half-period of the emf, we proposed and investigated a circuit for the joint operation of a shock generator and a capacitor bank [9]. The fraction of the energy transferred to the load can be increased by a factor of three or more by applying preliminary charging of the capacitor bank. In this case the capacitance must be calculated for 25–30% of the energy transferred to the load.

Of greater importance is the circuit for accelerated accumulation of energy in an inductive load, consisting of a shock generator, a capacitor bank, a switching device, and a load [8]. The inductance of the load is taken to be several times greater than the inductance of the generator. This makes it possible, upon reaching in the generator–load circuit the same currents as with a matched load, to transfer to the load, over several accumulation periods, practically the entire reserve of electromagnetic energy of the rotor of the shock generator, i.e., to transfer to the load an energy of several hundred MJ. Table 1 gives the values of the load inductance \(L_{\mathrm{n}}\) as fractions of the inductance of the shock generator \(L_{\mathrm{g}}\), the number of accumulation cycles \(m\), the magnitude of the energy transferred by the generator to the load \(Q_{\mathrm{n}}\), and the magnitude of the energy for which the capacitor bank \(Q_c\) must be designed, as a percentage of \(Q_{\mathrm{n}}\). As the generator, a shock generator with a smooth armature of the above dimensions was adopted: \(D_p = 1250\) mm, \(l_1 = 6000\) mm. Calculations show that over 6 accumulation periods the shock generator transfers to the load practically the entire reserve of electromagnetic energy of the rotor.

Thus, we have shown that the problem of accumulating and transferring energy of hundreds of megajoules to an inductive load can be solved at the present stage of development of electrical machine engineering.

References

1. P. L. Kapitza. Proc. Roy. Soc., A, 115, No. 772, 1927.

2. M. P. Kostenko. Electrical Machines (Special Part). GEI, 1949.

3. E. G. Komar. Shock generators of the Elektrosila plant. VEI, No. 1, 1940.

4. Energy storage in rotating electrical machines. Express information Electrical Machines, No. 36, 1970.

5. L. P. Poberezhsky. On inductive energy-storage devices. Proceedings of the Moscow Power Engineering Institute, “Electric Power Engineering,” issue 45, 1963.

6. G. A. Sigailov, K. A. Khorkov. Specific energy of a shock generator. Proceedings of TPI, vol. 132, 1965.

7. Limiting powers of two- and four-pole turbogenerators. Express information Electrical Machines, No. 11, 1970.

8. G. A. Sigailov, K. A. Khorkov, V. V. Ivashin, A. V. Loos. Device for storing energy in an inductive load. Author’s certificate No. 184334.

9. G. A. Sigailov, K. A. Khorkov, V. V. Ivashin. Method of transferring energy to an inductive load from a shock-power generator. Author’s certificate No. 192922.