GB2089582A

GB2089582A - Transformer with a Releasably Connectible Magnetic Circuit

Info

Publication number: GB2089582A
Application number: GB8135578A
Authority: GB
Original assignee: Ganz Villamossagi Muevek
Current assignee: Ganz Villamossagi Muevek
Priority date: 1980-12-01
Filing date: 1981-11-25
Publication date: 1982-06-23
Also published as: ATA496981A; DE3145596A1; GB2089582B; DE3145596C2; JPS57120315A; FR2495372B1; IT1172108B; AT380125B; HU188571B; CH659726A5; SE8106865L; FR2495372A1; IT8149784A0

Abstract

A large, e.g. oil-cooled, power transformer is assembled from at least two separately transportable units each comprising a magnetic circuit and associated transformer coils enclosed within a sealed tank. Parts of the magnetic circuit of each unit protrude from the associated tank via respective seals so that the protruding magnetic circuit parts of the two units can be releasably coupled together to provide a magnetic coupling between the two units. The invention has particular application to transformers which, due to their size and weight, would be impracticable to transport fully assembled. The self-contained transformer units of the invention can each be made of a conveniently transportable size for assembly at a user site into a larger multi-unit transformer while obviating the need to expose the working components of the transformer to the deleterious effects of draining and refilling the tanks with cooling oil as in existing systems. <IMAGE>

Description

SPECIFICATION Transformer with a Releasably Connectible Magnetic Circuit The invention relates to a transformer construction, the magnetic circuit of which can be disconnected for the duration of the transport and connected anew on the spot of application.

One of the characteristic features presently known energy systems lies in that the unit output of the electric equipment and thus of the transformers is showing a tendency to increase.

The reason for this is that between the mass of the transformers with a higher unit output, the price and the rating thereof there is a correlation: M=CrA=C2. pk wherein M stands for the mass of the transformer, A for the price, P for the rating c1 and c2 are constants, K is an exponent (always > 1).

The magnitude of the unit rating is determined by the transportable masses and dimensions permitted by the conveyance by railway, on public roads and by water. In general, an increase of the unit outputs has been obtained by building-in more material into the dimensions remaining at disposal and by the increase of the electric, thermal and mechanical loads. The process of the increase of the unit rating can be illustrated by the formula

where dP stands for the increment of the unit rating, i=1 ... n indicates the number of the components, by the change of which the increment of the rating can be achieved.

a stands for the load arising in the components, c' and c" are constants; and M=mass (as before).

From the correlation it becomes obvious thatthe increase of the unit rating becomes possible either by increasing the mass to be built-in or the load to be applied, or - as it is used to be in practice -- by the simultaneous application of both possibilities. The experience gained in connection with operational reliability of the transformers demonstrates that the increased loads and building-in a larger mass (at an unaltered load) are separately decreasing reliability and in case of simultaneous application deterioration of the operational-safety appears cumulatively. In general, decrease of reliability can be compensated by using new materials or technologies involving, however, in the majority of cases additional costs, accordingly, the economic advantages of the increment of the unit rating will be less.

The higher unit ratings appear on more and more higher voltage levels involving further difficulties. At a higher voltage level, into a given volume -- having been limited by the possibilities of transport -- a larger quantity of insulating material needs to be built-in. Accordingly, less space is left for the active materials, and as a consequence, the unit rating to be obtained will be also less.

The correlation between the transformer rating, which can be built-in into the limited volume and the nominal voltage of the transformer reads - in the first approximation as follows:- P=C3-C4U where P stands for the rating in MVA, U for the effective value of the voltage.

In case of Central European clearances and one-phase transformers C=2600 and C4=1 ,2.

That means that at 400 kV the limit rating equals to 2120 MVA, while at 1200 kV it reaches only the value 1 160 MVA.

For solving, the problem described, manufacturers of transformers have elaborated different methods. One group of such methods can be characterized in that essentially the transformer is manufactured in the traditional form but in larger dimensions; after having performed the trial tests in the plant, the transformer is delivered in a disassembled state to the place of application and there it is assembled anew. By the application of this method the difficulties in transport may be eliminated. The disadvantage, however, lies in that due to the larger masses of the construction with increased dimensions operational reliability becomes worse, in addition to this, local mounting requries additional expenditure of costs and time; beside the disadvantages mentioned above, double assembly, drying and filling up with oil considerably shorten the useful life of the insulating materials.

The other group of methods may be characterized in that the transformer is built in the traditional manner in larger dimensions, but by dividing the iron core and the tank structure the transformer is quasi sliced in several parts, which are closed for the duration of the transport in an airtight manner. On the place of application the transformer is assembled, assembly can be done more quickly than by using the previously described method, and the operations do not shorten the useful life to such an extent.

The disadvantage of said method lies in the deterioration of operational safety representing a side effect of building-in larger masses, and in the decreased reliability, (using better materials or more expensive technologies). In addition to these, this method also suffers from the local vacuum-drying and filling up with oil, both requiring more time and more costs.

The aim of the present invention is to at least partially eliminate the deficiencies of the known solutions. The aim set is achieved by a transformer which is built-up of units, the dimensions of which are determined by the possibilities of transport, as a consequence, its reliability can be characterized by the level of reliability associated with this dimension.

The single units of the new transformer construction have been developed in such a manner that after the first treatment with oil the coils with a liquid insulating material and with a part of the iron core form collectively a closed unit. The parts of the iron core protruding through a solid insulating plate from the closed system, are divided and can be connected to the units forming the remaining parts of the transformer with an abutting or laminated joint.

Accordingly, the invention relates to a transformer with a disconnectible magnetic circuit, with an iron core with a simple yoke, with an iron core with a frame or with a half-frame only, having been prepared in such a manner, in so far as the transformer consists of the disconnectible magnetic circuit with the yoke having been divided into an upper and lower part, of the columns interconnecting said parts of the yoke, while the parts of the yoke matching to each other are connected with one another after having penetrated the non-metallic insulating plates of the tank enclosing said parts of the yoke and the columns inbetween.

The invention will be described by means of a preferred embodiment, by the aid of the accompanying drawings, wherein Figure 1 shows the interconnection of two single-phase iron cores, Figure 2 shows a three-phase version, Figures 3, 4, 5 illustrate the different versions for joining the iron cores, Figure 6 shows a solution for sealing the part of the core protruding from the closed system, Figure 7 shows the subsequent closing and sealing of the assembled parts of the iron core.

As is to be seen in Figure 1, when instead of two single-phase units (the two upper transformers) the transformer according to the invention (the lower transformer) is chosen, - as weli in respect to material and dimensian -the outer column each closing the yoke of the two single-phase units and the corresponding fraction of oil and casings, respectively, can be saved.

Figure 2 shows an embodiment for the threephase version. The versions shown in Figures 1 and 2, respectively, may result in savings of about 20% in the material of the iron core, and about at least 5-1 0% may be saved in the price of the whole construction. These savings appear with the usual constructional form, when the insulating and conducting materials are used in the traditional quantity, but the mass of the iron core to be built-in is iess, accordingly no accessory deterioration or reliability due to the increased mass -- characterizing in general the increment of the unit output - can be observed.

With a transformer in accordance with the invention local treatment with oil becomes superfluous, since on the places where the two units are assembled, each tank is closed by an oiltight, electrically insulating plate. The stubs of the iron core penetrate said insulating plato to enable them to be connected to the other unit. In order to facilitate the assembly of the iron core, the yoke structure is formed at the place of connection with an abutted joint. Figure 3 gives an example for the abutting joint, showing a wedge-shaped abutting joint. The advantage of this solution lies in the easier joining in course of assembly.A further advantage of the wedge-shaped joint lies in that the excitation falling to the air-gap at the joints may be reduced, whilst the power effect between the surfaces will be also less, and accordingly a construction lower in vibration and noise can be obtained. The demand of excitation in case of a perpendicular abutting joint is given by:-

while in case of a joint at a angle it is given by:

where Bl stands for the induction of the y6ke, ,uO for the permeability of air, a for the average air-gap, being equal, whether a mitred or a perpendicular abutting joint is used with identical technologies.

The magnetic force arising on the place of the air-gap is given by:

in case of a perpendicular abutting joint, and in case of a wedge-shaped joint by:

In the formulae A stands for the iron-cross section of the yoke.

The effect of the arising highest ferromagnetic forces resulting in vibration and noise can be further decreased by means of the known iron core construction having been provided with a frame. In these constructions the fluxes in the individual frames have different phase positions, at the same time the resultant of the arising power effects is also smaller. In Figure 4 a slant abutting joint for the framed structure is shown, while Figure 5 shows a comb or rake-shaped abutting joint. In Figure 6 a preferred solution is shown for the sealing of the iron core protruding from the closed system. As can be seen in the figure, the iron core part 2 passes through the insulating plate 1. The seal 3 is compressed by the frame 4, accordingly, the oil can leak only through the iron core during the process of assembly.This leakage can be further reduced by applying known gluing technology generally used for the lamellae of the iron core. The air-tight closing plate 5 compietely eliminates oil-leakage during transport. After having finished assembly, the iron core 2 passing through the insulating plate 1, the seal 3 and the frame 4 remain in a sealed state in order to be able to maintain the cleanness of the active parts. In an assembled state a closing plate 5 isolates the space of the connected iron cores from the atmosphere; said space is filled up subsequently with oil for the improvement of cooling.

In Figure 7 the tank is indicated with 6, the part of the cover with 7.

The application of the solution according to the invention enables either the production of a single-phase unit with an increased rating using several units with lower rating, or the assembly of a three-phase transformer from single-phase units. The economic advantage of the solution manifests itself in savings in space and structural elements, while the technical advantage lies in keeping up the reliability being characteristic for smaller elements and reduced difficulties in transport, simultaneously enabling the production of transformers with a rating of up to 10 GVA in one single unit.

Claims

1. A transformer with a disconnectible magnetic circuit with an iron core and associated yoke, with an iron core with a frame or a halfframe, the disconnectible magnetic circuit of the transformer consisting of yokes each divided into an upper and a lower part, of columns connecting the yokes, and the parts of the yokes matching each other are connected after having penetrated non-metallic insulating plates of a vessel enclosing parts of the yokes and the columns therebetween.

2. A transformer as claimed in claim 1 , wherein the matching parts of the yokes of the disconnectible magnetic circuit are connected by means of a wedge-shaped or a comb or rakeshaped abutting joint.

3. A transformer as claimed in claim 1 or 2, wherein the matching yoke parts pass through the non-metallic closing plate in a sealed manner.

4. A transformer as claimed in any preceding claim wherein the space surrounding the matching yoke part is separated from the atmosphere by a sealed enclosure.

5. A transformer as claimed in claim 4, wherein the space surrounding the matching yoke parts is filled with cooling oil.

6. A transformer comprising at least two units, each unit comprising a magnetic circuit and associated transformer coil(s) enclosed within a sealed vessel, wherein parts of the magnetic circuit of each unit protrude from the associated vessel through respective seals and are releasably coupled together externally of the vessels to provide a magnetic coupling between the magnetic circuits of each of the units.

7. A transformer as claimed in claim 6, wherein the externally coupled magnetic circuit parts of the coupled units are enclosed within a sealed enclosure.

8. A transformer substantially as shown in and as hereinbefore described with reference to the accompanying drawings.

9. A unit suitable for use as one of said units in a transformer as claimed in claim 6. 7 or 8.