HORIZONTAL TYPE OF INDOOR SWITCHGEAR FOR 3–10 kV

I. D. Kutyavin

The development of indoor switchgear for 3–10 kV electric power stations has until now followed the path of complicating its design. An example of this is the four-story switchgear with MGG circuit breakers [L—5, Fig. 25]. A certain simplification of them through the use of a hall-type building with removable partitions, recommended by the basic provisions for the design of thermal power stations, does not change the situation.

The process of developing switchgear has until now been accompanied by preservation of the basic principle of the mutual arrangement of the elements of the circuit, in which the busbars are mounted on the upper floor, the circuit breakers on the middle floor, and the reactors on the lower floor (in a three-story switchgear). Such a principle for the layout of switchgear could be called vertical. Switchgear with a mixed arrangement of elements is used to a limited extent, for example with a checkerboard arrangement of circuit breakers and reactors on the lower floor or with detached reactor chambers [L—3, Fig. 5]. However, these simplified switchgears can be used only for stations of small and medium capacity.

The chief disadvantages of the vertical type of switchgear are the many stories and the large number of corridors, which leads to poor utilization of the building volume, to excessive consumption of conductor and other materials, and complicates operation. These disadvantages are so substantial that the use of the vertical type of switchgear can be justified only when using large-volume oil circuit breakers, which require explosion chambers or corridors.

At the present time, the main type of circuit breakers used for power stations are oil-free and low-oil-volume oil circuit breakers, which do not require explosion chambers or corridors and allow servicing from one side, making it possible to simplify the design of switchgear considerably.

Simplification of the design and reduction of the dimensions of switchgear can be achieved only by a radical change in the manner of mutual arrangement of the elements. For example, in contrast to the vertical type of switchgear, one could propose a horizontal type, in which all the elements of the circuit are located on one floor. Sketches of such switchgears are shown in Figures 1, 2, 3, 4, and 5. These sketches have been made with maximum simplifications and have insufficiently developed assemblies, but nevertheless from them one can form an idea of the fundamentally new type of switchgear and of its principal qualities.

As can be seen from the figures presented, the busbars are mounted in the left corridor on a frame made of structural iron and are covered on the corridor side by protective mesh screens. The bus disconnectors are placed between the busbar systems on the dividing wall and

on the corridor side are likewise enclosed by mesh screens, and are separated from one another and from the busbars by removable light partitions. The operating mechanisms for controlling the disconnectors are mounted on the frame.

On the other side of the dividing wall are the circuit-breaker chambers, separated by removable partitions.

Fig. 1 shows a switchgear installation that can be used at small stations isolated from the system, with VMG and MGF-11 circuit breakers and with non-reactorized feeders, and also as switchgear for the auxiliary services of large stations. In terms of compactness of equipment arrangement, this switchgear approaches a complete switchgear installation

Fig. 1

Fig. 2

and, for VMG circuit breakers, can be executed with a cell pitch of 1.2 m and a specific cell volume of 26 m³. With a two-row arrangement of the switchgear, the cell volume will be reduced to 20 m³. It is interesting to note, for comparison, that a single-row complete switchgear installation with VMG circuit breakers [L-4, Fig. 11] has a cell pitch of 1.2 m and a specific volume of 17 m³, while a two-row one has a cell volume of 14 m³. When MGF-11 oil circuit breakers are used, this switchgear will have a cell pitch of 1.5 m and a specific cell volume of 36 m³. A two-story switchgear installation of the vertical type with MGF-11 circuit breakers [L-5, Fig. 12] has a cell pitch

Fig. 3

kV, 1.5 m, and a specific volume of 37 m³ with the servicing corridors 1.2 m wide. If the width of the servicing corridors of the switchgear shown in Fig. 1 is reduced to 1.2, then the specific volume of a cell will decrease to 26 m³, which indicates the clear advantage of this switchgear over the vertical type.

The switchgear for a station with VMG and MGF-11 circuit breakers and with reactor-protected feeders is shown in Fig. 2. The reactors, line disconnectors, and cable potheads are located in the forechambers and require a wider cell (2–2.5 m) than the circuit breakers; therefore the cells of reactor-protected feeders must alternate with non-reactor-protected ones. The line disconnectors and cable potheads of non-reactor-protected feeders are placed

Fig. 4

in meter-wide forechambers located between the reactor ones. With such an arrangement of circuit breakers and reactors, the average cell pitch can be made 1.5–1.6 m, and the specific volume of a cell 68 m³. For comparison, let us note that the so-called “simplified universal” type of switchgear with vertical arrangement of equipment, intended for VM-23 and MGF-11 breakers [L-2, Fig. 1], has a nominal cell pitch of 1 m and a specific volume of 104 m³; only a switchgear with remote reactor chambers [L-3, Fig. 5] approaches the switchgear of Fig. 2 in terms of specific cell volume.

Figure 3 shows a single-row switchgear with MGG-type circuit breakers. The busbars of this switchgear are arranged vertically and are separated by removable shelves. In all other respects the layout principle is analogous to the preceding one. The cell pitch of this switchgear is 2.2 m and the specific cell volume is 124 m³.

A double-row horizontal-type switchgear with MGG-type circuit breakers can be made according to Fig. 4, in which the busbars have a single-row arrangement and individual servicing corridors. On the second floor are located MGG-223 type feeder circuit breakers and reac-

tors; moreover, opposite each reactor cubicle there are two chambers, one of which, 2 m wide, is for the feeder circuit breaker MGG—223, and the other, with a pitch of 1.6 m, is for the busbar drop to the MGG—229 circuit breaker located on the lower floor. The line disconnectors and cable bushings are installed in the compartments of the first floor, arranged two opposite each MGG—229 cell. Beneath the compartments there is a tunnel for

Fig. 5

power cables, while the tunnel for control and measuring cables is located behind the MGG—229 circuit breakers. The switchgear has a nominal cell pitch of 1.8 m and a specific cell volume of 119 m³. This switchgear can be used instead of the so-called “heavy” type switchgear [L—1, Fig. 11], which has a nominal cell pitch of 1.25 m and a specific cell volume of 210 m³.

Finally, Fig. 5 shows a sketch of a horizontal switchgear station with MGG—229 type circuit breakers, having an American switching scheme. The cell pitch of this switchgear is 2.3 m and the specific cell volume is 190 m³.

Conclusion

The proposed horizontal type of indoor switchgear, in terms of the required building cubage, is the most economical of all existing types. For example, the double-row switchgear shown in Fig. 4 gives a saving in the cubage of the building of one cell, compared with the “heavy” type switchgear [L—1, Fig. 11], of 91 m³. Assuming the cost of one cubic meter of switchgear building to be 70 rubles, we obtain a saving per cell of 6 to 7 thousand rubles, and for the entire switchgear building, 100–200 thousand rubles.

The proposed type of switchgear also has other advantages over the vertical type. The principal ones are the following:

1. The switchgear occupies at most the two lower floors of the building, while the remaining floors may be used for the control board and other purposes.
2. The small number of corridors and floors facilitates operation of the switchgear and reduces the consumption of conductor and other materials.
3. Simplicity of the building structure and of equipment installation.
4. Simplicity of servicing and repair of busbars and bus disconnectors.

LITERATURE

1. I. I. Gurvich et al.—Fundamental questions in the design of high-pressure thermal power plants, 24–50 thousand kW. Elektricheskie stantsii, 10, 1941.
2. L. I. Dvoskin—A simplified design of switchgear for 6–10 kV. Elektricheskie stantsii, 10, 1941.
3. P. D. Bogachev and A. P. Nazarov—Compact generator-voltage switchgear for small- and medium-capacity power stations. Elektricheskie stantsii, 10, 1941.
4. I. I. Pokrass—Complete switchgear with low-oil-volume circuit breakers. Elektricheskie stantsii, 5, 1941.
5. I. I. Greben—Switchgear for new types of high-voltage apparatus, GONTI, 1938.