IT202000016903A1 - ELECTRICAL CONDUCTORS FOR POWER TRANSFORMERS WITH HIGH ELECTRICAL AND THERMAL CONDUCTIVITY. - Google Patents

Description

BRIEF DESCRIPTION OF THE INVENTION

The present invention relates to a process for making electrical conductors for high conductivity power transformers. electrical and thermal, enhanced through the deposition of copper and graphene.

In particular the present invention ? is it an industrial process for the production of rectangular conductors in copper and/or aluminum covered by graphene GNP (Graphene NanoPlatelets) with different thicknesses in order to increase the conductivity? thermal and electrical of said rectangular conductors which are then used in all the windings for electric machines, transformers, generators, motors and in particular power transformers.

By applying graphene on the surface of the rectangular conductor ? is it possible to increase the conductivity? electric and then allow the same passage of current in a section pi? small and, at the same time, improve the conductivity? thermal. This means being able to create a conductor with the same electrical performance but much more? small in size and therefore much less expensive. Furthermore, the best conductivity? Thermal insulation allows for better heat dissipation and better prevention of hot spot damage and thermal aging.

In particular, for power transformers ? extremely important to be able to design and build machines more and more? efficient and less expensive, in our case why? the total volume of transformers having a significantly reduced total volume.

FIELD OF THE INVENTION

The transformer? a static electric machine powered by alternating current, based on the phenomenon of electromagnetic induction, intended to transform, between the primary circuit (input) and the secondary circuit (output) of the transformer, the voltage and current factors of the electric power.

The transformer then transfers electrical energy from one electrical circuit to another that has a different voltage, by coupling them inductively, without the transformer windings touching each other.

An electric current transformer in the primary winding generates a changing magnetic flux in the transformer core and consequently a changing magnetic field across the secondary winding (Faraday's law and Lenz's law). This changing magnetic field induces an electromotive force, or voltage, in the secondary winding. This effect? called mutual induction.

The transformer? therefore a machine capable of operating essentially in alternating current, why? it generally exploits the principles of electromagnetism linked to variable flows. The efficiency of a transformer? very high and the losses are very low (in iron, due to the effect of hysteresis and eddy currents, and in copper due to the Joule effect).

To reduce the decrease in efficiency, a transformer must have the following characteristics:

? windings:

or as few turns as possible

o minimum length: the winding wire must be as short as possible; generally this depends on the section and the shape of the core, square or (better still, where possible) circular. ? Nucleus:

or a suitable section;

o as short a length as possible;

or in ferromagnetic material in such a way as to have an electrical resistance as much as? possible high, to minimize losses due to the Joule effect and a coercive force as much as? possible low, and to have a hysteresis loop the pi? tight as possible (and therefore of the lowest possible magnetic losses).

? Cooling: cooling ? necessary to avoid overheating of the transformer due to the dissipated power. ? particularly important in transformers operating at high powers. The cooling can to be:

o air - typical solution of normal civil transformers and for small powers;

or in an oil bath? the transformers work in an oil bath inside suitably shaped metal casings to facilitate heat dispersion;

o forced oil bath - compared to the oil bath system, there are also pumps for the forced circulation of the oil and a system of external fans to increase heat removal;

or in resin - compared to other systems, the windings are immersed in a special resin, which causes them to dissipate heat. This resin takes the place of oil. From the resin transformer you can get benefits on the dimensions, given that they are slightly larger? smaller than an oil transformer.

For this purpose, various types of transformers are recognized according to their cooling method. The type of cooling is recognized by an acronym made up of two or four letters (two if the transformer has a single cooling, four if the cooling is double). Specifically, in the acronym the first letter shows what type of substance is being used for cooling (e.g. oil, resin, air), the second letter shows the type of circulation of the fluid inside the transformer (natural circulation or forced). For this purpose, transformers of the type are recognised:

? AN: with natural air circulation (not forced);

? ON: natural oil circulation;

? AF: with forced air circulation;

? ONAN: circulation of air and natural oil;

? OFAF: with forced air and oil circulation.

NOTE TECHNIQUE

WO2014/141071 describes a method for the preparation of coated metal foams (by an electrodeposition process) with a metal matrix and graphene.

EP0859381A1 describes an electrical conductor for low voltage windings (and high currents) which allows greater heat exchange, maintaining the same performance as a transformer which however? has a much larger footprint. There? allows you to create a power transformer with reduced dimensions, thus saving? large quantities of copper during the construction of said transformer.

No electric conductors and/or power transformers object of the present invention are described or suggested in the art.

DESCRIPTION OF THE INVENTION

The present invention relates to a process for making electrical conductors for high conductivity power transformers. electrical and thermal, enhanced through the deposition of copper and graphene.

In particular the present invention ? is it an industrial process for the production of rectangular conductors in copper and/or aluminum covered by graphene GNP (Graphene NanoPlatelets) with different thicknesses in order to increase the conductivity? thermal and electrical of said rectangular conductors which are then used in all the windings for electric machines, transformers, generators, motors and in particular power transformers.

By applying graphene to the surface of the rectangular conductor, ? is it possible to increase the conductivity? electric and then allow the same passage of current in a section pi? small and, at the same time, improve the conductivity? thermal. This means being able to create a conductor with the same electrical performance but much more? small in size and therefore much less expensive. Furthermore, the best conductivity? Thermal insulation allows for better heat dissipation and better prevention of hot spot damage and thermal aging.

? therefore object of the present invention the realization of rectangular metal conductors for transformers (metal strips) electroplated with graphene, obtained through the following processing steps:

PHASE 1 ? Wire rod drawing.

The metal rod is drawn with special dies in synthetic diamond and/or tungsten carbide, using an emulsion bath of water and oil.

The drawing phase? necessary to reduce the diameter of said metal rod until it reaches a circular section having a diameter of 1.8 mm.

In accordance with the present invention, metal rod is defined as a rod made of metallic material, which usually has a cylindrical shape.

Said wire rod:

? ? generally circular in section, with a diameter between 8 mm and 20 mm;

? ? made of a metal selected from the group comprising: aluminium, silver, nickel, gold, copper and/or alloys thereof; preferred are copper and aluminum.

PHASE 2 ? lamination and edging.

The metal rod obtained at the end of phase 1 is modeled through a rolling and edging process obtaining a ?rectangular? which complies with the IEC (International Electrotechnical Commission) tolerance standards and has the following characteristics:

? width between 2 mm and 25 mm;

? length between 2 mm and 25 mm;

? thickness between 0.9 mm and 8 mm.

PHASE 3 ? static firing in an inert atmosphere (nitrogen).

The metal strip obtained at the end of phase 2 is subjected to a firing thermal cycle, characterized by the following temperatures and time intervals: firing at a temperature of 550°C for a period of 4 hours (parameters usually used for copper strips) using an electric furnace for static firing in an inert atmosphere (nitrogen), to bring the metal back to a soft and malleable physical state.

PHASE 4 ? electrodeposition of the metal strips.

The metal strip obtained at the end of phase 3 is coated through successive steps:

Step 1 - the metal strip is covered with a "first metal layer", deposited using a physical deposition technique (PVD/physical vapor deposition) or with a chemical deposition technique (CVD/chemical vapor deposition) as described in Adv. Mater. 2000, 12, No. 9;

Step 2 - on the first metal layer of ?Step 1? a ?second layer of metal (or its alloys) and graphene? is deposited/stratified, using the electrodeposition technique described in WO2014141071, in which the metal associated with the graphene can be the same or different from the one used in Step 1;

Step 3 - on the second layer of ?metal and graphene? of ?Step 2? is a ?third metallic layer? deposited/stratified? (or its alloys) through a further electrodeposition process as described in WO2014141071, or a chemical or physical vapor deposition process through the PVD or CVD procedure as described in http://www.mag-data.com/technical-details /introduction-to-polymeric-films/; Journal of Materials Chemistry C Volume 4 Number 37, 7 October 2016, Pages 8585?8830; and/or Adv. Mater. 2000, 12, No. 9.

The metallic material of the first, second and third layer is selected from the group comprising: aluminium, silver, nickel, gold, copper and/or their alloys; the metal of the first layer pu? be equal to or different from the metal of the second layer, which in turn can be equal to or different from the metal of the third layer.

PHASE 5 ? insulation of the electrodeposited strips through taping. The electrodeposited metal strip obtained at the end of step 4 is insulated through a taping process using a material selected from the group comprising: pure cellulose paper for oil impregnation, aramid paper, mica tape and/or polyamide tape.

PHASE 6 ? Coupling of the metal strips with obtaining the power transformer.

The strips obtained at the end of phase 5 are grouped/coupled (depending on the transformer to be made) in helical windings, disc windings or other types of windings, with the desired power transformer being obtained.

Said power transformer ? usable in the industrial, energy, naval and/or aerospace fields and having better conductivity characteristics? electrical, thermal, power dissipation and efficiency compared to current transformers on the market.

The increase in conductivity? electric power of the metal straps and of the power transformer, obtained at the end of phases 5 and 6 of the process of the present invention, has led to a reduction of the resistivity? of the initial material (copper) between 5% and 9%. To this reduction of resistivity? is associated, on an equal footing? section, a decrease in the heat generated by the Joule effect, also between 5% and 9%. Furthermore, an appropriate sizing and optimization of the shapes of the contacts and the geometry of the surrounding areas has contributed, in addition to a further reduction of at least 5% of the thermal load, also to a homogenization of the temperatures with a reduction of the hot spots.

? a further object of the present invention is the metal strip obtained at the end of step 5, which can be used for making the windings of electric machines, transformers, generators and/or motors.

Claims (7)

1. Process for the preparation of a power transformer, including the following processing steps: ? PHASE 1 ? wire rod drawing; ? PHASE 2 ? lamination and edging; ? PHASE 3 ? static firing in an inert atmosphere; ? PHASE 4 ? electrodeposition of metal strips; in which said phase 4 comprises the following steps: - Step 1 ? the metal strips are covered with a first metal layer, deposited using the physical vapor deposition (PVD) technique or the chemical vapor deposition (CVD) technique; - Step 2 - a second layer of metal and graphene is deposited on the first metal layer of Step 1, using the electrodeposition technique; - Step 3 - a third metal layer is deposited on the second metal and graphene layer of Step 2 using the physical vapor deposition, chemical vapor deposition or electrodeposition procedure; and in which: - the metallic material of the first, second and third layer? selected from the group comprising: aluminium, silver, nickel, gold, copper and/or their alloys; - the metal material of the first layer can? be equal to or different from the metal of the second layer, which in turn can be equal to or different from the metal of the third layer; ? PHASE 5 ? insulation of the electrodeposited strips through taping; ? PHASE 6 ? Coupling of the metal strips with obtaining the power transformer. 2. Process of claim 1, wherein the metal rod of step 1: ? ? circular section, with a diameter between 8 mm and 20 mm; ? ? made of a metal selected from the group comprising: aluminium, silver, nickel, gold, copper and/or alloys thereof; preferred are copper and aluminum; ? it is drawn with synthetic diamond and/or tungsten carbide dies, using an emulsion bath of water and oil. 3. Process of claim 1, wherein the metal strip obtained at the end of step 2 has a width of between 2 mm and 25 mm, a length of between 2 mm and 25 mm and a thickness of between 0.9 mm and 8 mm . 4. Process of claim 1, wherein the firing of step 3 takes place at a temperature of 550°C for a time period of 4 hours, using an electric oven for static firing. 5. Process of claim 1, wherein the taping of step 5 is carried out using a material selected from the group comprising: pure cellulose paper for oil impregnation, aramid paper, mica tape and/or polyamide tape. 6. Process according to claim 1, wherein the strips obtained at the end of step 5 are grouped/coupled in coils of the helical and/or disk type. 7. Metallic strip obtained at the end of step 5, usable for making windings of electric machines, transformers, generators and/or motors, for use in the industrial, energy, naval and/or aerospace fields.