WO2021110925A1

WO2021110925A1 - Electrical conductor

Info

Publication number: WO2021110925A1
Application number: PCT/EP2020/084652
Authority: WO
Inventors: Ashish Kumar; Shashank Mishra; Akshay BANKAR; Bhavesh GHAG
Original assignee: Eaton Intelligent Power Limited
Priority date: 2019-12-07
Filing date: 2020-12-04
Publication date: 2021-06-10
Also published as: GB202001037D0; GB2589645A

Abstract

The invention relates to an electrical conductor for alternating current applications, in particular for medium and high voltage alternating current applications, which electrical conductor comprises an elongate solid body having a substantially uniform cross-section of a steel core, an aluminum layer enveloping the steel core, and a copper layer enveloping the aluminum layer.

Description

Electrical conductor

The invention relates to an electrical conductor for alternating current applications, in particular for medium and high voltage alternating current applications.

Electrical switchgears are widely utilized for power distribution applications in various environments ranging from commercial, residential to industrial infrastructures. A typical switchgear consists of a number of electrical conductors which enable switchgear to safely distribute current across various feeder units.

In electrical switchgears, electrical resistivity, eddy currents and contact resistance generate heat within the enclosure of the switchgear resulting in a temperature rise. Typically, the electrical conductors also contribute to the thermal management within the enclosure by acting as heat sink to carry away the generated heat.

Furthermore, the electrical conductors are used to provide structural strength to the assembly in case of a short circuit.

In order to combine the functions of conducting the current, acting as heat sink and providing structural strength, it is well known in the prior art to use electrical conductors with a solid body of copper, which material combines these functions very well.

However, these solid copper electrical conductors give rise to the issue of a substantial weight and substantial costs, which is a substantial part of the overall costs of the switchgear.

For this type of applications, it is essential that the electrical conductor has a solid body to provide sufficient strength. So, stranded electrical conductors cannot be applied as such kind of stranded electrical conductors are typically designed for flexibility and the ability to resists frequent bending, movement and vibrations.

Using another kind of material for the solid body of the electrical conductor will typically increase the electrical resistance of the conductor, which will increase the generated heat. It is well known that copper has a very efficient electrical resistivity.

Accordingly it is an object of the invention to reduce or even remove the above mentioned disadvantages of electrical conductors according to the prior art.

This object is achieved with an electrical conductor according to the invention, which electrical conductor comprises an elongate solid body having a substantially uniform cross-section of a steel core, an aluminum layer enveloping the steel core, and a copper layer enveloping the aluminum layer.

When an alternating current is fed through an electrical conductor, then the skin effect and proximity effect will occur.

The skin effect is the tendency of an alternating electric current to become distributed within a conductor such that the current density is largest near the surface of the conductor, and decreases towards the core of the conductor.

The electric current thus flows mainly in a small portion of the skin of the electrical conductor, while on a small part of the electric current flows below beneath the skin and thus in the core of the electrical conductor.

The proximity effect is the effect that the current in an electrical conductor is concentrated in only a part of the electrical conductor due to the influence of currents flowing in nearby other electrical conductors, which is typical for switchgear.

Due to the skin effect and proximity effect, only a part of the prior art solid copper electrical conductor would be used. So, for a prior art conductor a portion of the copper is nonfunctional for the conductivity of current.

With the electrical conductor according to the invention, only the skin of the conductor is made of copper.

As the skin effect causes a main portion of the current to flow through the outer part of the conductor, only this portion is made from copper to have a low electrical resistivity for the main portion of the current.

The middle part of the electrical conductor according to the invention is made of aluminum. This will conduct the remaining portion of the electrical current. While aluminum has a higher electrical resistivity, the overall resistance of the electrical conductor will only increase marginally.

The aluminum portion of the electrical conductor according to the invention also has a good heat conductivity, but has a substantial lower strength. This is compensated by having a steel core, which has an excellent strength.

In a preferred embodiment of the electrical conductor according to the invention the cross-section is circular and wherein the steel core, aluminum layer and copper layer are concentrically arranged.

With a circular cross-section, the distribution of the current due to the skin effect will be even around the circumference of the cross-section. This allows for a minimal thickness to be used for the copper layer.

In a further preferred embodiment of the electrical conductor according to the invention the copper layer is cladded to the aluminum layer. By cladding the copper layer onto the aluminum layer, a fusion of the copper with the aluminum is obtained, such that no electrical surface resistance between the two layer occurs nor any heat conducting barriers are present.

In a further preferred embodiment of the electrical conductor according to the invention, the copper layer has a thickness between 5% and 20%, more preferably 10%, of the largest main dimension of the cross-section.

Preferably, the aluminum layer has a thickness between 50% and 70%, more preferably 60%, of the largest main dimension of the cross-section.

Within these ranges, an electrical conductor is obtained with a substantial reduction in weight, while having a low resistance due to the copper outer layer, having a good heat conduction due to the copper and aluminum layer, and a sufficient strength due to the steel core.

The invention also relates to a switchgear comprising:

- a number of busbars; and

- at least one of an electrical disconnect switch, a fuse or a circuit breaker electrically connected to at least one of the number of busbars, wherein at least one of the number of busbars is an electrical conductor according to the invention.

These and other features of the invention will be elucidated in conjunction with the accompanying drawings.

Figure 1 shows a cross-section of an embodiment of an electrical conductor according to the invention.

The electrical conductor 1, shown in cross-section in figure 1, has an elongate solid body with a steel core 2, an aluminum layer 3 enveloping the steel core 2 and a copper layer 4 enveloping the aluminum layer 3. The electrical conductor 1 has a circular cross- section with a diameter D. The thickness of the copper layer is t_c and the thickness of the aluminum layer is t_a.

As an example of the advantages of the invention, the electrical conductor 1 is compared to a prior art solid copper electrical conductor. Both conductors have a length of 1.23 m and a circular cross-section with a diameter of 20mm.

The thickness t_c of the copper layer of the electrical conductor 1 is 1.57mm, the thickness t_a of the aluminum layer is 6.43mm and the thickness or diameter of the steel core is 12mm.

Using a copper density of 8800 kg/m³, an aluminum density of 2700 kg/m³ and a steel density of 8050 kg/m³ will result in a weight of 13.74 kg for the prior art solid copper electrical conductor and 8.47 kg for the electrical conductor 1 according to the invention. A reduction in weight of 38.35%.

When an alternating current of typically 50Hz or 60Hz is fed through each of these electrical conductors, then the ohmic loss on the prior art solid copper conductor would be 431W in this example, while the ohmic loss on the electrical conductor 1 according to the invention would be 437W. Only an increase of 6W, i.e. 1.4%, which is insignificant.

Furthermore, it will be clear that due to the small amount of copper 4 in the electrical conductor 1, the costs are substantial lower than the costs of a solid copper conductor according to the prior art.

Claims

1. Electrical conductor (1) for alternating current applications, in particular for medium and high voltage alternating current applications, which electrical conductor (1) comprises an elongate solid body having a substantially uniform cross-section of a steel core (2), an aluminum layer (3) enveloping the steel core (2), and a copper layer (4) enveloping the aluminum layer (3).

2. Electrical conductor (1) according to claim 1, wherein the cross-section is circular and wherein the steel core (2), aluminum layer (3) and copper layer (4) are concentrically arranged.

3. Electrical conductor (1) according to claim 1 or 2, wherein the copper layer (4) is cladded to the aluminum layer (3).

4. Electrical conductor (1) according to any of the preceding claims, wherein the copper layer (4) has a thickness (t_c) between 5% and 20%, more preferably 10%, of the largest main dimension (D) of the cross-section.

5. Electrical conductor (1) according to any of the preceding claims, wherein the aluminum layer (3) has a thickness (t_a) between 50% and 70%, more preferably 60%, of the largest main dimension (D) of the cross-section.

6. Switchgear comprising:

- a number of busbars; and

- at least one of an electrical disconnect switch, a fuse or a circuit breaker electrically connected to at least one of the number of busbars, characterized in that at least one of the number of busbars is an electrical conductor (1) according to any of the preceding claims.