US2279239A - High tension transformer - Google Patents

Description

A. MEYERHANS HIGH TENSION TRANSFORMER April 7, 1942 Fild 06x. 3, 1938 Patented Apr. 7, 1942 HIGH TENSION TRANSFORMER August Meyerhans, Rieden, near Baden, Switzerland, assignor to Aktiengesellschaft Brown, Boveri & Cie, Baden, Switzerland, a joint-stock company Application October 3, 1938, Serial No. 233,114 In Germany October 18, 1937 4 Claims.

The present invention relates to high tension transformers.

At the present time, the dimensions of transformers for high power above 10,000 kw. and for voltages of 100 kv and above are determined to a large extent by the extent of the insulating distances that are required in constructions now generally used. These constructions usually employ three upright cores arranged in one plane,

with the upper and lower cores connected by i a cross yoke. The low voltage windings are usually pushed over the cores and the high voltage windings are located outside of the low voltage windings with insulating cylinders between the two windings and between the cores and the low voltage windings, the insulating cylindersbeing spaced from each other and from the respective windings and cores to insure a free circulation of oil. A large pressure-proof oil chest is provided for housing the parts in-.

the ends of the winding, called the end distance.

A considerable insulating distance between the surface of the high voltage winding and the chest wall was also necessary and the lead in and connecting wires on the high voltage side required considerable space inside the chest. All of these insulating distances necessitated a definite minimum size for the transformer, its chest and the quantity of oil required.

Difficulties have been experienced in the transportation of these transformers because of their necessarily large size, special railway cars being required and it has also been necessary to construct the transformers in such a way that the prescribed railway clearance limits were not exceeded. Since it is not desirable in practice to ship large transformers disassembled, the insulators have been made removable or the construction altered to place them on the narrow side of the chest. The chest cover has also been made replaceable by a temporary flat cover in In addition the an effort to overcome shipping difficulties. The proposal to replace a single large three phase transformer by three single phase transformers is impractical and increases the space requirements for given power capacity and the same objection is raised against dividing the power between a number of transformers.

A primary object of the invention is to provide a large capacity transformer for the highest voltages which has considerably smaller dimensions than those heretofore employed for comparable voltages, thereby obviating the disadvantages of great bulk mentioned above.

In accordance with the invention, the problem of size reduction is treated and solved in a basically novel manner, it being treated purely as a problem of insulation. The large spaces which heretofore had to be provided for insulation are reduced to a minimum by a systematic graduation of the differences in potential inside the transformer so that leakage paths are eliminated to a great extent and the insulations are stressed chiefly in the direction of striking through.

The systematic graduation of the differences in potential can be accomplished, according to the invention, when either the core or the chest is brought to the high voltage potential and the potential between the two is diminished by stages in the radial direction from the high voltage potential to the ground potential. Specifically, the potential can fall either from the core to the chest or from the chest to the core.

In order to obtain the desired staging in potential according to the invention, the iron core of the transformer is divided up, perpendicularly to the axis of the column, into parts insulated from each other, which parts are brought to potentials differing from each other by electrical connection with points of the winding.

Other objects, advantages and novel features of the invention will become apparent during the course of the following detailed description thereof and upon reference to the accompanying drawing which illustrates preferred constructional examples of the invention.

In the drawing:

Figure 1 is a vertical sectional view of an oil transformer embodying the invention,

Figure 2 is a horizontal sectional view adjacent one end of a three phase transformer embodying the invention,

Figure 3 is an enlarged sectional View illustrating a detail of construction, and

Figure 4 is a vertical sectional view illustrating a regulating type transformer embodying the invention with the casing and lead-in omitted.

In the form of the invention shown in Figure 1, the central section or column 5 of the iron core is cylindrical and laminated radially or in evolvent form in known manner to reduce eddy current losses. The tubular passage 6 through the center of the column 5 serves for the circulation of oil, the cooling effect of which can be increased if some of the plates of the laminated column extend radially beyond others into the passage.

The column 5 is directly connected at I to lead-in conductor 8 which passes through insulator 9 to high voltage terminal I so that the column is brought to the high voltage potential. An annular core part I I which is mounted on and directly connected to the lower end of the center section 5 has the same potential as said section. The core part II is also preferably laminatedradially or in evolvent form and forms the magnetic connection between the oenter section 5 and a surrounding core yoke I22, preferably concentric with part II.

An upper annular core part l3 corresponding to part II surrounds the upper end of the center section 5 and an annular core yoke I 4 similar to yoke I2 surrounds the part I3. The upper core part I3 is separated from the center section by high voltage paper insulation I5 which is wound firmly on the center section and extends from a point above the section to the core part I I. The insulation I5 has sufficient resistance to withstand the full high tension voltage on core center 5.

A high voltage winding It is disposed around the core center 5 outside the insulation layer I5 between the core rings II and i3 and is electrically connected at its ends to the respective core .rings at .I I and lfirespectively. The high voltage Winding is wound in horizontal layers so that its potential constantly decreases from the core ring I I to the core ring I3. The winding I6 is formed with concentrically arranged cooling passages or slots I9 extending from end to end thereof and the core parts I I and I3 are provided with alined passages and 2|, respectively, to provide for circulation of oil to cool the winding.

Immediately surrounding the high voltage winding I6 and core parts II and I3 is a wound paper insulation forming an insulating sleeve 22 the ends of which project an appreciable distance above and below the core parts. The insulating sleeve is disposed inside the core yokes I2 and I4 so as to completely insulate the same from the core rings II and I3.

A low voltage winding 23 is disposed between the core yokes I2 and I4, outside of the insulation sleeve 22. The distance 24 between the outor surface of the low voltage winding and the Wall of the chest 25 will be governed by the magnitude of the voltage of the winding.

In use of the transformer with three phase current, the upper core rings 13 of the three phases can be connected to a star point or in certain cases can be grounded. In such cases, the insulationv above the rings I3 and I4 can be omitted.

Since some of the core parts 5, II, I2, I3 and I 4 carry high voltage, the core is mounted on powerful insulators 25 which may consist of alternate layers of wood and press board. Support for the upper end of the core is provided by insulators 27 carried thereby and springs 29 between these insulators and the cover 29 of the chest. The springs 28 absorb heat and short circuit forces and provide for expansion of the parts.

The distribution of potential in the use of the transformer of Figure 1 is as follows: The center core section 5 and lower core ring II have high voltage potential and this potential diminishes progressively in the high voltage winding to zero which is the potential of the core ring I3. The winding 23 has the potential corresponding to the lower voltage and the core yokes I2 and I4 are grounded. The chest 25 and its cover 29 are also grounded.

In order not to stress the oil too greatly in thick layers, the insulation sleeves I5 and 22 on the core parts and winding I6 are wound tightly, their thickness being based on the required test voltage. Due to the electrical oil stress at the ends, the insulating layers are made thicker toward their ends, as shown in Figure 3, and the gaps '30 between adjacent surfaces of the core rings are wedge shaped in section to accommodate the increased thickness of the insulation at this point. Protective rings 3| are disposed at the edges of the core rings to prevent leakage at these points.

The oil contained in the chest 25 circulates upwardly through the cooling passages I9 and 2t and down around the outside of the low voltage winding, it being understood that heat radiating pipes can be provided for dissipating the heat of the oil if desired.

In the embodiment of the invention illustrated in Figure 2, a three phase transformer is provided with the core centers or columns 32 arranged in triangular relation. Upper and lower triangular yoke plates 33 and-34, respectively, are provided, these being similar in form but unequal in size and serving as spacers for the core centers, the ends of the centers extending through openings in the yokes 33 and 34.

The upper yoke plate 33 is insulated from the core centers by wrapped paper insulation sleeves 35 which project above the yoke and core center and the yoke 33 forms the grounded star point of the high voltage windings 36 which surround the insulated center as in Figure 1 so that it replaces the separate upper core rings I3 and I4 of Figure 1.

Wrapped paper insulating sleeves 31 surround the high voltage windings 36 and terminate at the under side of the yoke 33. The low voltage windings 38 surround the insulating layer 31 as in the Figure 1. The lower yoke plate 34 corresponds to the core yoke I2 of Figure 1 and a core ring (not shown) corresponding to the ring II of Figure 1 is provided at the lower end of the core center in electrical connection with the center and with the lower end of the high potential winding. Central openings 39 and 40 in the yoke plates 33 and 34 respectively, serve for the circulation of cooling oil and also for the passage of clamping bolts, not shown, extending between the plates.

Since with grounded zero point, the stress on the outer insulation layer diminishes from the bottom towards the top, the thickness of this insulating layer can likewise be diminished in the same direction. If it is desired not to carry the high voltage current through the core center, an additional conductor can connect the inlet connection to the high voltage end of the high potential windings. This conductor can extend through the core center or the bore thereof. Also a copper plate could replace one or more of the iron plates of the core and be connected to the inlet and the high voltage winding.

Regulation of the structures thus far described by taps on the high voltage winding would disturb the regular potential distribution effected by. these structures. In the embodiment of the invention shown in Figure 4 provision for regulation at the high voltage side is made. The section 4| of the high voltage winding which is to be regulated is separated magnetically from the main section 42 of the high voltage winding by an intermediate core ring 43 and 9. corresponding outer intermediate yoke ring 44. The upper voltage regulating winding section 4| is surrounded by a low voltage primary winding 45 which is connected through a variable voltage divider 46 either in series with or counter to the main voltage as desired. The voltage divider 46 is connected across the low voltage winding 41, it can be a regulating transformer with or without stages or an inductance regulator.

The high voltage winding is connected to the lower core ring H at I1 and to the intermediate core ring 43 at 48. The high voltage regulating winding 4| is connected to core ring 43 at 49 and to core ring 13 at 50. By this construction, there is no change in the radial distribution of the potential.

Except for the regulating means described, the

construction of Figure 4 is the same as Figure 1 and corresponding reference numerals apply to corresponding parts.

In accordance with the invention, multi-phase transformers are also provided with the regulating means as described in connection with Figure 4.

In certain cases where a horizontal position of the core is desirable, forced circulation or" the oil may be desirable. However, the invention is not limited to oil filled transformers but may be employed in the construction of the dry type.

It will be noted that among the advantages of the invention heretofore set out, the arrangement permits of an especially small spacing of the windings and the oil chest can be made much smaller due to the low voltage winding being on the outside.

While preferred embodiments of the invention have been shown and described by way of illustration, it will be understood that various other modifications of the invention and changes in the details of construction may be resorted to without departing from the spirit of the invention within the scope of the claims.

I claim:

1. In a high potential transformer, an iron core comprising a cylindrical laminated core body, annular iron core sections surrounding said core body adjacent the ends thereof and in radially spaced relation to the walls thereof, a high potential winding on said core body disposed between certain of said core sections and having a high potential terminal and a low potential terminal, electrical connections between said terminals and the respective core sections between which the winding is disposed to establish on each core section a potential differing from that established on other core sections, and

a low potential winding surrounding said high potential winding in radially spaced relation thereto and between certain other of said annular core sections, which latter are radially spaced from said core sections connected to said high potential winding.

2. In a high potential transformer, an iron core comprising a cylindrical laminated core body, an annular core section surrounding said core body adjacent each end thereof, an insulating sleeve surrounding said core body extending substantially parallel to the axis thereof and extending between said core and at least one of said annular sections, a high potential winding surrounding said core body tightly engaging said insulating sleeve between said core sections, electrical connections between said core sections and spaced points on said winding to establish difierent potentials on said core sections, a second insulating sleeve surrounding and tightly engaging said high potential winding and said core sections connected thereto, other annular core sections concentric with said first mentioned annular core sections and radially spaced therefrom by said second insulating sleeve, and a low potential winding between said other annular core sections and tightly engaging said second insulating sleeve.

3. In a high potential three phase transformer, a plurality of iron cores disposed at the apices of an equilateral triangle, each of said cores comprising a central core body and a plurality oi core sections radially spaced from each other and from said central core body, means electrically insulating said core sections from each other, a high potential winding on each of said core bodies between certain core sections thereof, and means including electrical connections between said last mentioned core sections and the respective associated windings to establish on a section of each core a potential difierent from that established on another section thereof, certain of said core sections being in the form of triangular plates having openings therein receiving the ends of the core bodies.

4. In a high potential three phase transformer, a plurality of iron cores disposed at the apices of an equilateral triangle, each of said cores comprising a central core body and a plurality of core sections radially spaced from each other and from said central core body, means electrically insulating said core sections from each other, a high potential winding on each of said core bodies between certain core sections thereof, and means including electrical connections between said last mentioned core sections and the respective associated windings to establish on a section of each core a potential different from that established on another section thereof, certain of said spaced core sections being in the form of triangular yokes common to all three core bodies and having openings receiving the ends of the core bodies, said yokes having centrally disposed openings providing for the circulation of cooling oil and passage of clamping members extending between the yokes.

AUGUST MEYERHANS.

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