PULSED POWER GENERATOR MODEL

G. A. Sipailov, K. A. Khorkov, A. I. Verkhoturov,
A. V. Loos

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

Pulsed power generators are special synchronous machines of the turbogenerator type, whose normal operating mode is a sudden short circuit or connection to a single-phase load for a time approximately equal to one period of the emf. In principle, pulsed power generators may be either single-phase or three-phase machines. In the latter case, however, only two phases are used in operation, while the third phase is a reserve phase.

In designing pulsed generators—when choosing the ratios between the stator bore diameter and the length, between the slot height and their width, when selecting the numbers of stator and rotor slots, the air-gap magnitude, the types of stator and rotor windings, etc.—one must proceed from the condition of obtaining the maximum electromagnetic energy produced during one first half-period of the emf.

From this point of view, as studies [1–7] have shown, a single-phase generator with a single-layer winding occupying \(2/3\) of the total number of stator slots has substantial advantages.

For experimental verification of the basic principles of the theory and design of pulsed power generators on the basis of the recommendations developed [1–7], a prototype generator was designed and manufactured within the dimensions of the MTV-612 crane electric motor. A general sectional view of the pulsed power generator model is shown in Fig. 1.

The choice of rotor design depends on the purpose of the generator. For example, in the Kapitsa–Kostenko generator, in order to obtain constancy of the current amplitude over a certain interval of time, the rotor has two independent excitation windings [8]. However, in most applications of pulsed power generators, their rotor may be the same as in interrupting-power generators, that is, with one excitation winding. In all cases the generator rotor must have a powerful damping winding, serving to reduce the subtransient reactance of the generator and to suppress the backward-synchronous field of the armature reaction.

The rotor of the model is made analogous to the rotors of interrupting-power generators. The total number of tooth divisions of the rotor is \(Z'_2 = 32\); the number of slots filled with the excitation winding is \(Z_2 = 20\).

The shape of the rotor slot was chosen from the condition of obtaining the maximum slot area:

\[ \frac{h_n}{b_n} = \frac{Z'_2}{2\pi}. \]

Fig. 1. General view of the pulsed generator in section.

In order to improve the utilization of the rotor and to optimize the parameters of the damping winding, the upper parts of the rotor slots occupied by the damping rods were somewhat widened. In the model, the damping winding is uniformly distributed around the circumference of the rotor and occupies 26% of the area of its slot. In the slot portion the damping winding is made in the form of flat copper bars laid one on another without insulation; in the end portion, in the form of solid arc-shaped segments with projecting fingers, which enter the slot portion in an overlap with the damping bars. The rotor slots are wedged with copper wedges. The end portions of the field winding and of the damping winding are enclosed in retaining rings made of a nonmagnetic aluminum–magnesium alloy.

Fig. 2. Generator stator slot.

The stator of the pulsed generator is made similarly to the stator of generator TO-12-2 [9]. To reduce additional losses and e.m.f. pulsations due to stator slotting, the stator slots are made semi-closed (Fig. 2). The ratio of the slot height to its width was taken equal to two. The total number of stator slots is 36; the number of slots filled with the stator winding is 24. The principal geometrical dimensions of the model are: \(D_a = 493\) mm, \(l = 515\) mm, \(D = 275\) mm.

The stator winding is single-phase, single-layer, concentric, with separated end portions. On the outer and inner sides the end portions are supported by conical rings made of aluminum alloy. The surfaces of the cones facing the end portions are covered with two layers of micanite segments. The end portions are wedged with special spacers and filled with a special cold-setting compound, which turns the conical part of the winding into a single rigid frame (Fig. 1).

Special attention was paid to the reliability of fastening the end portions of the stator winding on the lead side. The fastening assembly consists of three rings: an inner, a central, and an outer ring. In the central ring, slots are milled for the winding rods emerging from the stator slots (Fig. 3). In these slots the rods are securely fastened by means of the inner ring. The connecting forks are located between the central and outer rings. Thus, the soldering points of the rods and forks are moved far away from the frame and are readily accessible. Soldering was carried out by gas welding with copper–phosphorus solder. Figure 4 shows the fastening assembly of the end portions of the stator winding.

The rotor is mounted in pedestal bearings. The machine was assembled on a steel plate 60 mm thick, installed on a concrete foundation. In order to eliminate the influence of the mechanical action of the generator pulses on the foundation of the building in which it is installed, the concrete base of the generator is separated from the building foundation by elastic gaskets. On the same plate with the generator are installed the load and an asynchronous motor that drives the generator rotor at a speed close to 3000 rpm. Blocks of a 1.5-GeV synchrotron electromagnet with switchable field windings were used as the load. During operation of the generator, the drive motor is disconnected from the mains. Switching the generator on and off is carried out by an ion-mechanical switching device.

At the moment of interruption of the stator circuit of the generator, the field winding

Fig. 3. Central ring.

Fig. 4. Fastening of the end portions of the stator winding.

…of it, supplied from the exciter unit, terminates with the field-suppression resistance.

Experimental investigations of the model showed good agreement between the calculated and experimental parameters of the machine (Table 1).

The oscillogram (Fig. 5) presents the curves of the excitation current and the generator surge current. The emf amplitude with the generator fully excited reaches 410 volts; the amplitude of the sudden short-circuit current is 21,500 amperes. The preliminary conducted…

Fig. 5. Oscillograms of the excitation current and the generator surge current.

tests of the pulsed-power generator model showed its good technical characteristics.

Table 1

where

\(r_1,\ r_2\) — active resistances of the stator and excitation windings,

\(x_{s1}\) — leakage resistance of the stator winding,

\(x_d\) — direct-axis synchronous reactance of the generator,

\(x''_d\) — direct-axis subtransient reactance of the generator.

REFERENCES

1. G. A. Sipailov, K. A. Khorkov. On higher harmonics in the emf curve of a generator. Interuniversity Collection of Works, issue 3, Novosibirsk, 1963.

2. G. A. Sipailov, K. A. Khorkov. Specific energy of a pulsed generator. Izvestiya TPI, vol. 132, 1965.

3. G. A. Sipailov, K. A. Khorkov. Power, energy, and machine constant of a pulsed generator. Izvestiya TPI, vol. 132, 1965.

4. G. A. Sipailov, K. A. Khorkov. On the choice of the principal dimensions of a pulsed generator. Izvestiya TPI, vol. 132, 1965.

5. G. A. Sipailov, K. A. Khorkov. On the choice of the stator winding of a pulsed generator. Izvestiya TPI, vol. 138, 1965.

6. G. A. Sipailov, K. A. Khorkov. On the choice of the rotor winding of a pulsed generator. Izvestiya TPI, vol. 138, 1965.

7. G. A. Sipailov, K. A. Khorkov. On the choice of the air-gap size of a pulsed generator. Izvestiya TPI, vol. 138, 1965.

8. M. P. Kostenko. Electrical Machines, Special Part. GEI, 1949.

9. E. G. Komar. Pulsed generators of the Elektrosila plant, VET No. 1, 1940.