SU69375A1 - The method of translation through synchronism of the electric drive, performed by the Kremer system - Google Patents

Description

In order to extend the range of speed control of an asynchronous motor in the Kremer system, which provides either a power condition (Fig. 1) or a moment constant (Fig. 2), it is desirable to use its speed zone more than synchronized.

The proposed method of translating the Kremer system through synchronism is based on the fact that the asynchronous motor 7 in this system is a dual power machine that has both synchronous and asynchronous modes. For speed control purposes, the Kremer system uses only synchronous mode. When trying to translate the Kremer system through synchronism, a single core transducer 3, as is well known, at low slip frequencies falls out of the synchronous mode. But at the same time, the induction motor 7 also drops out of the synchronous mode. This results in an area of approximately + 5% of the synchronous speed (L-C-B in the diagram of FIG. 3), th. a cut which the kremer system cannot go by itself.

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To translate the electric drive made by the Kremer system, through synchronism with the proposed method, it is required:

1) Near the synchronous speed of the asynchronous motor (point A in Fig. 3), one core converter 3 must be braked with the help of mechanical brake 4 in a certain, established by experience, position so that the maximum excitation current can flow through the rotor of the asynchronous machine.

2) Switch the auxiliary machine of the direct current 2 with the switch 5 and give with the help of the rheostat 6 a sufficiently high excitation current, established by experience, to synchronize the asynchronous motor 7. At this moment a constant flows through the rings of the single core converter 3 and the asynchronous motor 7 the current, under the influence of which the asynchronous motor is synchronized and approaches its work at point C (Fig. 3).

3) After synchronization of the asynchronous motor 7, it is necessary to un195

How much to reduce the excitation current of the auxiliary machine 2.

4) At the same time, it is necessary to force the excitation current of one of the core converter 3 by temporarily short-circuiting the resistance 8 with the switch 7.

5) After this, it is necessary to gradually release the brake 4 one core converter 3.

6) After synchronization of the induction motor, it is possible to set the desired excitation current of the auxiliary machine 2 according to the required speed of the entire unit.

The measures in clauses (3) and (4) are necessary in order to reduce the boundary speed of one core converter 3 operating at the time of going over synchronism, like a DC machine, so that it does not increase its speed too quickly, and however, the asynchronous motor 7 managed to change its speed following the change in speed of one of the core converters.

This is also promoted by: a) an increase in the fly-weight of one core converter and b) a somewhat increased friction in its bearings. Therefore, the Kremer system with a moment constant (Fig. 2) goes through synchronism much easier than a circuit with a constant power (Fig. I).

The author reports that the experiments fully confirmed all the indicated positions. With a system with constant power (Fig. 1), an asynchronous motor speed control was obtained in the range of 4: 1 (with the control limit being limited by the danger of engine spacing); in a system with a constant moment (Fig. 2), a range of 30: 1 (2000 rpm and bb rpm) was obtained.

During the test, the existence of synchronous and asynchronous modes of operation of the engines included in the Kremer system was fully proved.

The proposed method allows the transfer of an electric drive made by the Kremer system through synchronization with the simplest measures without special devices (except for a brake, which is not even required in some cases) and, thereby, significantly expands the range of speed control of an asynchronous motor even in already existing installation of kremer. This method can be used on rolling mills and other mechanisms.

Subject invention

A method of translating through synchronism of an electric drive made in a Kremer system, i.e., consisting of a working asynchronous motor, one core converter included in a rotor circuit of a motor and an auxiliary DC machine connected to a preg generator circuit through a collector, characterized in close to the synchronous speed of the motor 7, the converter 3 is braked, the excitation circuit of the direct current machine 2 is switched on and a sufficiently high excitation current is given to bring the motor 7 into synchronization and, after stizheni, several reduce excitation current machine 2 temporarily reinforce the excitation transducer J, then gradually ottormazhivaetsya converter 3 and, after passing through the matching engine 7, to give the machine 2 excitation of required engine speed corresponding 7.

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FIG. 2

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FIG. 3

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