SU57985A1 - Device for straightening and inverting three-phase AC - Google Patents

Description

A common disadvantage of six phase current rectifying circuits is the high harmonic content of both rectified voltage and primary current. Eliminating or compensating for these harmonics in a six-phase scheme requires additional costs and in a number of schemes is associated with a decrease in operating flexibility. Therefore, the literature recommends the use of high power, preferably twelve-phase circuits, in the rectification.

The subject of this author's certificate is a device for straightening and inverting three-phase alternating current, which has several advantages over known straightening schemes, due to the original switching circuit of the secondary windings of the supply transformer and the rectifiers.

The invention is explained in the accompanying drawing, depicting the circuit diagram of the device, and is as follows. The primary winding / rectifying (supply) transformer can be connected either in a star or in a triangle; On the secondary side, the transformer has two three-phase windings 2 and 5 of half power, one of which is connected to a star, the second - to a triangle (it is also possible to connect the second winding to a zigzag or any other connection that provides a phase shift of 30 °). Each of the mountain windings is connected to rectifying valves 4 according to the principle of the three-phase Gretz circuit and, therefore, gives a rectified voltage of six-phase waviness. The rectified voltages of each winding, shifted in phase one against the other by 30 °, are connected in series (in cascade); The resulting DC voltage is twice as high as the rectified voltage of each winding and, due to the aforementioned phase shift, has a waviness corresponding to the twelve-phase mode. The content of higher harmonics in the primary current also corresponds to the twelve phase mode. The proposed scheme is intended to convert averages.

and high powers at high and superhigh voltages and, in particular, for the purposes of energy transfer by rectified high voltage currents.

Compared with the known twelve-phase rectification schemes, the proposed scheme, according to the author's instructions, has the following advantages.

1. Design simplicity: while existing circuits are either a combination of two structurally separate transformers, or require the Bt oriental winding to be divided into 18-24 branches located on different cores and connected in a very complicated way, in the proposed scheme only one transformer with two three-phase secondary windings connected in a standard way.

2. Good use of typical transformer capacity: existing schemes require, due to poor use of active materials, an increase in the typical power of the transformer by 27-60% against the power of rectified current, the proposed scheme requires an increase in the typical transformer power by only 3%.

3. The absence of special suction transformers or chokes required for most existing twelve-phase circuits.

4. The absence of a sharp increase in voltage when approaching idle, reaching in existing schemes 10-24%.

5. Small reverse voltage on rectifying valves; the reverse voltage is about four times less than in other twelve-phase circuits. Even in comparison with the Gretz three-phase circuit, the reverse voltage is reduced by a factor of two. At low voltages, this advantage is not essential; at high and ultrahigh voltages, it is of decisive importance, since it allows

receive from the same rectifier two to four times higher voltage.

Compared with the series of phases of the secondary winding of the transformer, similar to the scheme described in the author's certificate No. 12817, the proposed scheme of cascade connection of two separate secondary windings of the transformer has the following advantages: primary current, requires fewer valves, gives less reverse voltage and increased transformer usage, etc.

The disadvantages and limitations of the proposed scheme are as follows:

1, The total fall in the arc is four times the fall of the R arc of one valve. This circumstance speaks against the application of the circuit at low voltages; at high and superhigh stresses, it is insignificant.

2. The possibility of using mercury rectifiers with multiple anons in one vessel is excluded. At voltages of the order of 15–20 kV and above, this circumstance is also insignificant, since single-gate valves are always used for such voltages.

The subject matter of the invention.

A device for straightening and inverting a three-phase alternating current with twelve single-phase rectifiers and with a power transformer having two secondary windings, characterized in that said windings connected to a star and a triangle, respectively, to middle points of two groups connected in series rectifiers, each of which consists of three parallel connected rectifier pairs.

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