Iron Core for a Stationary Induction Apparatus

This invention relates to an iron core for a stationary induction apparatus, such as a transformer or a reactor.

A laminated core for a stationary induction apparatus, such as a transformer or a reactor, has usually been formed from high-grade silicon steel sheets which contribute to energy and resource saving. Another material has recently been developed for use in the manufacture of an iron core for a stationary induction apparatus. It is a magnetic thin strip which enables a reduction in the electrical loss of the core to 20 to 80% of the electrical loss of a silicon steel sheet core.

The construction of these iron cores will be described with reference to FIGS. 1 and 2. In FIG. 1, 1a to 1d indicate silicon steel sheets, and in FIG. 2, 2a to 2d designate thin magnetic steel sheets cut from, for example, a thin amorphous magnetic strip, thin ferronickel strip or thin quenched ferrosilicon strip. 1a and 1b, or 2a and 2b are leg members, and 1c and 1d, or 2c and 2d are yoke members connecting the leg members 1a and 1b, or 2a and 2b. The core members 1a to 1d, or 2a to 2d are laminated with a minimum joint clearance to form a laminated core for a stationary induction apparatus.

The laminated core composed of silicon steel sheets as shown in FIG. 1 can be efficiently produced, since it is easy to obtain a desired shape. It is, however, very difficult to obtain a laminated core having a small loss, since it is presently difficult to expect any further improvement in the magnetic properties of silicon steel sheets.

It is easy to obtain a laminated core having a small loss from thin amorphous magnetic steel sheets as shown in FIG. 2, since they ensure a small electrical loss. A further improvement in their properties can be expected. A thin magnetic strip is produced by cooling hot molten material rapidly as it is blown against a roller or the like moving at an ultrahigh speed. This method involves a lot of technical difficulty, and presently enables the production of only a magnetic core material having a thickness of, say, 100 .mu.m and a width of, say, 2 inches. The production of a laminated core from this material involves a great deal of difficulty.

It has hitherto been impossible to obtain an inexpensive laminated core for a stationary induction apparatus having a small electrical loss if only either silicon steel sheets or thin amorphous magnetic strips are employed. The former material has the disadvantages of failing to achieve a satisfactory reduction in electrical loss, while the latter has the disadvantage of being very low in workability.

This invention provides an iron core for a stationary induction apparatus comprising alternately laminated thin amorphous magnetic strips and silicon steel sheets. It is low in electrical loss, and high in workability.

FIG. 1 is a top plan view of a conventional iron core composed of silicon steel sheets;

FIG. 2 is a top plan view of a conventional iron core composed of amorphous magnetic thin strips;

FIG. 3 is a top plan view showing an embodiment of this invention;

FIG. 4 is a sectional view taken along the line IV--IV of FIG. 3; and

FIGS. 5 and 6 are top plan views showing other embodiments of this invention.

The invention will be described with reference to the drawings. In FIG. 3, 11a to 11d indicate silicon steel sheets laid in a plurality of layers, and 21a to 21d denote thin amorphous magnetic strips laid in a plurality of layers. They are juxtaposed in a single layer as shown in FIG. 4. 11a, 11b, 21a and 21b are leg members, and 11c, 11d, 21c and 21d are yoke members connecting the leg members 11a, 11b, 21a and 21b. They are laminated with a minimum joint clearance.

The thin amorphous magnetic strips 21a to 21d are presently available only in a thickness of 100 .mu.m and a width of 2 inches, as stated before. The silicon steel sheets 11a to 11d are available in a thickness of 0.28, 0.30 or 0.35 mm. Therefore, the strips 21a to 21d are employed in a plurality m of layers and a plurality n of rows, as shown in FIG. 4, depending on the thickness of the silicon steel sheets 11a to 11d, and the capacity of the core required. This arrangement enables utilization of the advantages of the two kinds of materials employed, i.e., the small electrical loss of the thin amorphous magnetic strips and the high workability of the silicon steel sheets.

Although the thin amorphous magnetic strips are disposed inwardly of the silicon steel sheets according to the embodiment hereinabove described, it is possible to dispose thin amorphous magnetic strips 41a to 41d outwardly of silicon steel sheets 31a to 31d, as shown in FIG. 5. It is also possible to obtain the same results by disposing thin amorphous magnetic strips 51a to 51d between silicon steels sheets 61a to 61d, and 71a to 71d, as shown in FIG. 6.

Although the invention has been described with reference to iron cores for single-phase transformers, it is equally applicable to laminated cores for other stationary induction apparatuses, such as a polyphase transformer having three or more phases, or a reactor.