1 General Information[edit | edit source]
Sometimes the customer's feeding cables are made of aluminium. In this case, certain rules must be followed, as the physical properties of the materials different.
The main reason why some customer choose the aluminium cables instead of copper cables is the cost, and sometimes also the lower weight of the material.
2 Connection[edit | edit source]
1 Carefully clean the stripped conductor end by scraping off the oxide layer, for example using a knife.
2 Immediately after removing the oxide layer, the conductor end must be coated with a neutral grease – for example, acid- and alkali-free petroleum jelly – and connected directly to the terminal.
No special terminal or clamp is required for the Wöhner main supply terminals. However, if the connection is made using cable lugs, special aluminium-copper cable lugs must be used.
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All connection points of aluminium conductors must be checked at regular maintenance intervals!
3 Correctly connecting al and cu[edit | edit source]
3.1 Aluminium and copper: how to connect them[edit | edit source]
- Combining aluminium and copper is problematic.
- High-quality Al/Cu compression cable lugs are perfect for coupling aluminium conductors with copper elements.
- A compound in the aluminium connecting material improves the contact properties.
- Aluminium-copper connectors are necessary for the skilled connection of aluminium and copper conductors.
We want to focus on the not-so-simple task of connecting aluminium and copper. As previously mentioned, aluminium is used quite often, but not always on its own. As copper has been the material of choice for decades, and continues to be used, there are problems in safely connecting both materials. In practice, electrical engineers are faced with this challenge more and more often.
Connecting aluminium and copper is required more often than you might think. For example, it is necessary if an aluminium ring conductor is located in an industrial area, but the adjacent plants are supplied via copper conductors. Even in transformer stations, aluminium conductors need to be connected to copper bars.
4 Aluminium/copper: a special connection[edit | edit source]
Aluminium has proven itself to be corrosion-resistant in practical situations. However, aluminium is generally an extremely reactive material that oxidises quickly. The durability of the material is down to a resistant oxide layer that is formed on its surface when atmospheric oxygen is applied – a process also known as self passivation.
If an electrically conductive liquid, such as condensation, comes into contact with an aluminium and copper connection, this results in an electrochemical reaction and the subsequent formation of contact elements. The difference in potential by means of the electrochemical series plays a key role in this process. The contact element is formed by the copper electrode (anode), the electrolyte (water) and the aluminium electrode (cathode).
The voltage generated as a result is shorted by the contact between copper and aluminium. The aluminium is deposited and/or corroded in line with the current flow that is generated. This process is visible as a vibrant oxidation mark and is applied to even the very smallest copper particles on the aluminium – with this being a permanent reaction as the copper does not therefore corrode. If there is an electrical connection, the consequence is an increase in the contact resistance, which can result in a temperature rise and, in the worst case scenario, a fire.
When combining copper and aluminium, it is therefore essential than you aim to prevent moisture from getting into the junction between both materials under any circumstances. In spaces where condensation builds up, you will therefore need to protect the contact point between copper and aluminium by way of special processing methods.
Use of aluminium/copper cable lugs and connectors is the most important step here. These items do not have any so-called creepage distances in which conductive liquid that is ultimately responsible for kicking off the oxidation process can accumulate. As a result, aluminium/copper compression cable lugs and connectors are also particularly suitable for use in offshore wind turbines. There is also the option to use tin plated aluminium cable lugs. This solution should only be used in spaces that are kept constantly dry, as even small amounts of damage to the tin layer are enough to start the contact corrosion process.
5 Al/Cu compression cable lugs[edit | edit source]
6 Aluminium conductors at a glance[edit | edit source]
Pursuant to DIN 60228, four different types of aluminium conductors are available – some of which require special processing methods. The following conductor types are available:
- single-stranded round conductors, class 1 (re)
- single-stranded sector shaped conductors, class 1 (se)
- multi-stranded round shaped conductors, class 2 (rm)
- multi-stranded sector shaped conductors, class 2 (sm)
The abbreviations and other information can be found among the markings on the Al/Cu compression cable lugs. This will help you to determine which cable lug is best for which aluminium connector.
The abbreviations and other information can be found among the markings on the Al/Cu compression cable lugs. This will help you to determine which cable lug is best for which aluminium connector.
The markings »8 KL16 50 rm 70 se« mean
- 8: Metric bolt dimensions of the connecting bolt bore (in this case M8 bolt)
- KL: Manufacturer code (Klauke in this particular instance)
- 16: Tool code
- 50 rm/sm: Nominal cross-section of the conductor in mm², when using a round or sector shaped multi-stranded conductor
- 70 re/se: Nominal cross-section of the conductor in mm², when using a round or sector shaped single-stranded conductor
7 Al/Cu connectors: securely joined[edit | edit source]
Klauke offers reduction connectors to ensure that aluminium and copper are securely joined.
Reduction connectors are often used in network repairs – more specifically in the production of non-tension connections for aluminium conductors in accordance with DIN EN 60228, and copper conductors in accordance with DIN EN 60228. The connectors are made of two components: aluminium parts (E-Al) and copper parts (pursuant to EN 13600). The aluminium side generally has a larger diameter, because the lower conductivity is compensated by a correspondingly higher nominal cross-section.
As with compression cable lugs, the aluminium side of the connector also contains a compound, which is prevented from running out and drying out by a protective cap.
To ensure safe results when processing the Al/Cu compression joints, follow the relevant copper and aluminium processing specifications.
When using compression connectors underground, make sure that the joints are protected from moisture. It is best if you use a cast resin joint. The joint permanently protects the connections from moisture, dust and the penetration of foreign bodies.
Lastly, an important note on aluminium and copper cable lugs and compression joints: Do not expose these products to bending stress, otherwise there is a risk of breakage at the contact point between the two materials. Use in the overhead line sector is therefore not possible.
8 Pressing al cable lugs[edit | edit source]
8.1 Light-weight and special processing qualities: aluminium cable lugs and connectors[edit | edit source]
- The benefit of aluminium conductors: their light weight and comparatively easy handling.
- According to the standards in place, aluminium conductors are available in four different designs that require different processing methods in places.
- The contact lubricant in aluminium connecting material improves the contact properties, thus enabling a smooth electrical connection.
9 Overview of aluminium conductors[edit | edit source]
9.1 Aluminium conductors are sold in four different variants, which sometimes require special processing methods in places:[edit | edit source]
- Class 1 single-stranded round shaped conductors (re)
- Class 1 single-stranded sector shaped conductors (re)
- Class 2 stranded round shaped conductors (rm)
- Class 2 stranded sector shaped conductors (rm)
These abbreviations can be found on the connectors and cable lugs along with other details. You will be able to use these details to work out which aluminium conductor is suitable for which connector and/or cable lug.
The marking on the aluminium compression cable lugs are roughly in line with those that can also be found on copper cable lugs. An example of this is as follows: “KL22 12-120 rm/ sm 150 re/se”
- KL: Manufacturer code (Klauke in this particular instance)
- 22: Tool code
- 12: Metric bolt dimensions of the connecting bolt bore (in this case M12 bolt)
- 120: Nominal cross-section of conductor in mm² (rm/sm)
- rm/sm: For stranded round shaped conductors and pre-rounded multi-stranded sector shaped conductors
- 150: Nominal cross-section of conductor in mm² (re/se)
- re/se: For single-stranded round shaped conductors and pre-rounded single-stranded sector shaped conductors
You may already have noticed that the nominal cross-sections of the se and re conductors are always one unit of measurement higher than the nominal cross-sections of the sm and rm conductors. The reason for this is quite simple: single-stranded conductors take up less volume than stranded conductors.
In order to maintain a secure connection, we recommend that you use hexagonal crimping dies according to DIN 48083 Part 4 or the EKM60ID indent crimping tool when processing compression cable lugs.
With regard to aluminium, there are special crimping dies whose crimp width is 7mm, which is 2mm wider than the crimp width of the crimping dies for copper connecting material. These larger crimp widths generate a larger contact surface that offsets the reduced conductivity of aluminium.
9.1 A contact lubricant for aluminium connecting materials[edit | edit source]
Commercially-available connecting material for aluminium conductors are coated ex-works with a special contact lubricant. During crimping, this destroys the non-conductive oxide layer, which forms on the surface of the aluminium after a short time. The lubricant improves the contact properties. The lubricant also prevents oxygen from penetrating the contact points. Re-oxidation is therefore avoided. The result is a flawless electrical connection. The majority of cable lugs are sealed with a plastic plug, which prevents the contact lubricant from drying out or leaking, and increases the durability of the lubricant.
Contact lubricant for aluminium connections contain corundum, a sand-like mineral which is characterised by its great strength and high wear and corrosion resistance, even in high temperatures. During the crimping process, the compound causes a kind of abrasive effect, which rubs and destroys the oxide layer. In addition, the lubricant allows better sliding friction between the conductor and the sleeve. A connector seizure is prevented, which in turn leads to the largest possible contact surface. In the case of multi-stranded conductors, the lubricant also spreads between the individual wires during the crimping process and seals them. This prevents the penetration of oxygen and moisture.
Another major advantage is that aluminium crimping joints can withstand greater current loads when coated with the contact lubricant than they can without it. We therefore recommend the basic use of cable lugs and connectors with contact lubricants. This will ensure that you will be safe when using a large number of cable lines.
10 Step by step: Processing aluminium compression cable lugs and connectors[edit | edit source]
10.1 Aluminium has special properties meaning that precise steps have to be taken for its processing. The ideal steps for obtaining a clean connection are as follows:[edit | edit source]
- Remove the insulation from the aluminium conductor.
- Treat the bright finish ends of the conductor, for example, carefully with a knife or a wire brush to roughly remove the oxidisation layer and to produce a clean contact surface. Ensure that when cleaning there are no metal residues left on the conductor, as otherwise this can cause contact corrosion.
- Insert the conductor into cable lug or connector up to the full insertion depth of the sleeve. The compound flows out of the sides and creates an exclusion of air, which prevents re-oxidisation.
- You can now make the hexagonal or indent crimping using the suitable crimping tool. Single and multi-stranded sector shaped conductors must be rounded with a suitable round press insert prior to crimping.
- Finally, remove any excess compound.
Alternative markings are provided on aluminium cable lugs for narrow and wide crimpings. The advantage of the wide variant is that the number of crimpings required is halved. However, note that a suitably strong crimping tool must be used for this.
