Cross-Linked Polyethylene: How Does It Benefit Cable Assemblies

FACTS CHECKED BY  Jose George​

Insulation of cables and wires is an essential non-conductive material layer that resists the flow in electrical applications. There are different varieties of cable and wire. Recently, industries have been considering cross-linked polyethylene as an excellent choice for cable insulants. Conventional polyethylene also has good electrical properties, but its thermoplastic nature limits its applications. Let us see how polyethylene changes when it undergoes cross-linking and forms XLPE.

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What is Cross-linked Polyethylene / XLPE?

As the name suggests, cross-linked polythene is polyethylene having cross-links. Its abbreviated forms are PEX, XPE, and XLPE. It is like a thermosetting resin having three types of cross-linking. Based on the different cross-linking, PEX has three kinds: peroxide cross-linked, radiation cross-linked, and silane cross-linked polyethylene. You can use XLPE in pipework systems, hydronic radiant cooling and heating systems, insulation for high voltage cables, and domestic water piping systems. You can also use it for sewage and slurry transportation, offshore oil applications, and chemical transportation. Also, people use PEX plastic pipe in a residential piping system as an alternative to PVC, CPVC (chlorinated polyvinyl chloride), and copper tubing.

XLPE cable at the end

Image: XLPE cable at the end

Properties of Cross-linked Polyethylene

Due to the cross-linking, its chemical and mechanical properties change significantly. Let’s look into the different properties of XLPE.

  • Cross-linking increases abrasion resistance, low-temperature impact, scratch, brittle fracture, and environmental stress cracking. 
  • Cross-linking decreases the hardness and rigidity of polyethylene. 
  • Compared to thermoplastic polyethylene, PEX has more thermal resistance for extended periods in temperatures up to 120 degrees Celsius and for shorter periods in loads up to 250 degrees Celsius.
  • The increase in the cross-link density also increases the maximum shear modulus.
  • Cross-linking also resists dissolution; as a result, you will see enhanced chemical stability in PEX.

Common Types of XLPE Wire or Cable 

When XLPE is used for cable and wire applications, it mainly uses Low-density polyethylene. Such XLPE has excellent dielectric properties, and thus, you can use it for medium and high voltage cables. The XLPE cables have a maximum conductor temperature of 90 degrees Celsius with an emergency temperature rating of up to 140 degrees Celsius.

Sometimes, manufacturers modify the polymer structure during the manufacturing process to enhance productivity. For example, if you use XLPE in medium voltage applications, makers enhance its reactivity, resulting in higher line speeds. Also, manufacturers modify the insulation for high voltage and extra-high voltage cables to limit the quantity of gases byproducts.

As XLPE can work in low and very high temperatures, you can use it as insulation or jacket material. you can find their use in

Introduction to XLPE cable

Cross-linked cables mean cables with XLPE as their layer. These cables convert the linear molecular structure of polyethylene to the main network molecular structure by using different physical and chemical methods. This cross-linking process enhances the actual properties of polyethylene to better properties. The different production process of XLPE results in products with varied structural strength.

cutting an XLPE cable

Image: cutting an XLPE cable

XLPE cable performance

Here are some benefits of cross-linked polyethylene cables.

Flexibility: XLPE made with low-density polyethylene is quite flexible.

Heat resistance: As the cross-links form a net-like 3-D structure, the XLPE cable becomes highly heat resistant, and will not decompose below 300 degrees Celsius. The working temperature of the cable increases up to 90 degrees Celsius, and its thermal life rises to 40 years.

Insulation performance: Polyethylene (PE) already has good insulation properties, and with cross-linking, the insulation resistance becomes much better. Its dielectric loss tangent value becomes very small.

Mechanical properties: The cable’s mechanical resistance also increases due to the new chemical bonding. The formation of bonds improves its stiffness, hardness, impact resistance, tensile strength, and wear resistance. The structural integrity of XLPE cables overcomes the weaknesses of conventional polyethylene, which is prone to cracks and environmental stress.

Chemical resistance: The cross-linking of polyethylene makes XLPE strong acid and alkali-resistant, and oil resistant. It is less destructive to the environment as its combustion products are water and carbon dioxide.

What Is XLPE Cable Used?

XLPE cables are best used for power distribution and transmission applications. 

For external electrical cables, XLPE underground cables are the safest as they are more resistant to corrosion than any other cable. If you don’t want to replace or repair cables frequently, like in underground applications or concrete-filled power line channels, you can use steel wire armored XLPE cable.

An XLPE cable manufacturer follows all the standards while manufacturing an XLPE cable to give them unique qualities. These qualities make them ideal for applications that require high resistance to aging and stress cracking.

Further, using a 4-core XLPE cable in high-voltage applications is always better as it supports a broad voltage range.

You can also use it in applications at risk of fire, chemical stress, exposure to oil, and corrosive liquids. Lastly, you can also use an XLPE armored cable when you need a low smoke zero halogen cable.

How does the cable manufacturer make the XLPE Cable?

In the cross-linking process, molecules of materials’ long strands convert into ladder-type products. After this process, the molecules form a lattice that prevents them from slipping even at high temperatures. It means a cable with XLPE becomes highly heat resistant after this vulcanization process.

The cable manufacturer can change this molecular arrangement through physical or chemical processes. They expose cables to high energy like bursts of electrons or microwave radiation in the physical process. On the other hand, they add peroxide, saline, or chemicals to form cross-links in the chemical process.

Conclusion

Several applications use XLPE for electric insulation; however, their nature may vary according to the applications. Thus, you need an expert to pick a suitable XLPE cable for your job. Contact us today or request a quote.

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