Proceedings of the Tomsk Order of the Red Banner of Labor Polytechnic Institute named after S. M. Kirov

Volume 212　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　1971

Brushless Synchronous Generator with Combined Magnetic and Electric Circuits with a Parallel-Series Circuit for Connecting the Windings on the Stator and Rotor

V. T. Karavaev

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

In the electrical combination of the windings of two different-pole electric machines [1], the number of turns of the exciter field winding and of the generator field winding depend, respectively, on the number of turns of the armature windings of the generator and the exciter; at the same time both the armature windings and the field windings have parallel branches.

The construction of a field winding with several parallel branches leads to the need to create a direct-current source of low voltage and high current, which reduces the regulating capabilities of the generator. Similarly, because the generator field winding has parallel branches, its resistance is small. Since this resistance is the load of the exciter, then, as experiment has shown, the exciter operates in a short-circuit mode, i.e., very far from the optimum. Studies have shown that in this case the exciter power amounts to more than 10% of the generator power. Thus, to increase the utilization of the brushless synchronous generator [1], it is necessary to increase the number of turns of the field winding of the exciter and generator.

In the research laboratory of the Department of “Electrical Machines and Apparatus” of the Kirov Polytechnic Institute, together with the Kirov Plant, a new brushless synchronous generator with rotating rectifiers and combined magnetic and electric circuits, with a new circuit for connecting the stator and rotor windings, shown in Fig. 1a, b, was created and tested.

The brushless synchronous generator is made on the basis of an AK 51/4 asynchronous motor with a phase-wound rotor and consists of two synchronous machines: a generator of normal construction and an exciter of inverted construction. The magnetic fluxes of two different-pole electric machines are combined in a common magnetic core. The windings of the electric machines are combined as follows: the field winding of the exciter with the armature winding of the generator, and the field winding of the generator with the armature winding of the exciter. The armature winding of the exciter operates through rectifier blocks made with D231A diodes according to A. N. Larionov’s circuit. The blocks are located on the rotor shaft under the end portions of the winding and feed the generator field winding with direct current.

A feature of the brushless synchronous generator under consideration is that the stator winding and the rotor winding are made of several combined parallel windings \(W_2\), \(W'_2\) and \(W_1\), \(W'_1\), connected according to the parallel-series circuit of Fig. 1a, Fig. 1b. With

(a)

(b)

Fig. 1. Schematic diagram of a brushless synchronous generator with combined magnetic and electrical circuits with a parallel-series connection scheme of the windings on the stator and rotor:
a — operating with separate loads, b — operating with a common load.

from the side of terminals \(A_2, B_2, C_2\) and \(A'_2, B'_2, C'_2\), the parallel combined stator windings \(W_2\) and \(W'_2\) perform the function of the armature windings of the generator, while with respect to terminals \(o_1, o_2\) and \(o'_1, o'_2\) they perform the function of the excitation windings of the exciter. The parallel combined rotor windings \(W_1\) and \(W'_1\), with respect to terminals \(A_1, B_1, C_1\) and \(A'_1, B'_1, C'_1\), perform the function of the armature windings of the exciter, while from the side of terminals \(o_3, o_4\) and \(o'_3, o'_4\) they perform the function of the excitation windings of the generator. In this case the armature windings of the exciter (terminals \(A_1, B_1, C_1\) and \(A'_1, B'_1, C'_1\)) and the armature windings of the generator (terminals \(A_2, B_2, C_2\) and \(A'_2, B'_2, C'_2\)) operate in parallel. The excitation windings of the exciter (terminals \(o_1, o_2\) and \(o'_1, o'_2\)) and the excitation windings of the generator (terminals \(o_3, o_4\) and \(o'_3, o'_4\)) are connected in series. Consequently, the number of turns of the excitation winding in the combined winding increases in direct proportion to the number of parallel windings selected in each individual case for the optimum operating mode of the exciter and generator.

With an increase in the number of turns of the excitation winding of the exciter, the excitation current decreases, which provides the possibility of regulating the generator voltage; and with an increase in the number of turns in the excitation winding of the generator, it becomes possible to match the load resistance (the resistance of the generator excitation winding) with the critical load resistance of the exciter, at which an exciter of a given volume delivers maximum power in the nominal operating mode of the generator.

It should be noted that the series connection of the excitation windings of the exciter from the side of terminals \(o_1, o_2\) and \(o'_1, o'_2\), included in the parallel combined stator windings \(W_2\) and \(W'_2\), is possible in the case when windings \(W_2\) and \(W'_2\), from the side of terminals \(A_2, B_2, C_2\) and \(A'_2, B'_2, C'_2\), each operate on separate loads, for example, active resistances \(R_{\mathrm{н}}\) and \(R'_{\mathrm{н}}\), or feed electric motors. In the general case, the number of turns in the parallel combined windings \(W_2, W'_2\) may be different; therefore the brushless synchronous generator can be made for several different voltages required in a number of special cases, which is a very effective means, since as a result additional voltage converters, which increase the weight of the power system as a whole, are eliminated. In addition, the armature windings of the generator (terminals \(A_2, B_2, C_2\) and \(A'_2, B'_2, C'_2\)) operate on a common load (Fig. 1b) if each phase of the parallel armature winding is connected in series to a capacitor, and the output plates of the capacitors \(C\) of each phase are connected to one another.

The series connection of the excitation windings of the generator with respect to terminals \(o_3, o_4\) and \(o'_3, o'_4\) is also possible only under the condition that the parallel armature windings of the exciter with respect to terminals \(A_1, B_1, C_1\) and \(A'_1, B'_1, C'_1\) are not electrically connected to one another. This condition is fulfilled when each parallel armature winding of the exciter operates on its own rectifier block \(B\) and \(B'\). The output terminals of the rectifier blocks \(B\) and \(B'\) are connected in parallel, since in this case the rectifiers of the combined blocks are connected in opposition. The rectifier blocks operate in parallel on a common load, which is the excitation winding of the generator.

Experience in making the parallel stator windings \(W_2\) and \(W'_2\) and rotor windings \(W_1\) and \(W'_1\) has shown that the slot fill factor of both the stator and the rotor, the technology, and the labor intensity of winding remain the same as in a brushless synchronous generator with one winding on the stator and one winding on the rotor [1].

LITERATURE

1. V. T. Karavaev, V. I. Popov. Brushless synchronous machine with combined magnetic and electric circuits. Transactions of the Gorky Polytechnic Institute named after A. A. Zhdanov, vol. 24, issue 7, Gorky, 1968.