Everything you need to know about MV XLPE Cables
Many of our valued customers have raised queries about the best type of cable for their medium voltage applications and are often confused about what MV XLPE cables are, what are their applications and benefits. Since MV XLPE cables are not commonly used, many people are quite unfamiliar with them. This article looks into the definition and purposes of the MV cables and addresses all the common concerns of our customers and beyond related to MV XLPE cables. Yet if there is something else that you want to know about MV XLPE cables, feel free to ask in the section below and we will get back to you shortly.
What are Medium Voltage XLPE Cables?
As the name suggests, medium voltage XLPE cables are XLPE cables that are designed specifically to carry medium voltages. The XLPE-insulation processes excellent electrical, thermal, and mechanical characteristics at medium voltages. Medium voltage XLPE cables have widely replaced the traditional classic paper insulated medium voltage cables in many different sectors. The medium voltage XLPE cables have many advantages over paper insulated and PVC cables which will be discussed later in this article.
The figure above shows the different components of armoured XLPE cables. It can be seen that there are several insulation layers that protect the core conductor of the wire. The several layers of insulations and protections ensure that the MV cables perform even during extreme conditions.
What is the crosslinking of XLPE?
Polyethene (PE) is a long-chain polymer that is manufactured via long-chain polymer that is manufactured through the polymerization of ethylene gas. Though PE was a quite popular and cheap method of insulation as opposed to paper insulation, a significant issue with PE was that in its thermoplastic state, the operational temperature was limited to just 70˚C. This issue was solved with the use of crosslinked polyethene (XLPE), which had the ability to have better thermal ratings combined with freedom from hydraulic problems. The use of armoured XLPE cables allowed for the maximum operating temperatures of 90˚C along with 250˚C short circuit ratings.
The polymers that are used in the MV XLPE cables are manufactured by high-pressure tubular reactors. The crosslinking of LDPE with DCP (DiCumylPeroxide) to make XLPE was first done by Precopia and Gilbert in 1955; however; its commercial use can only be seen for the past two decades.
Properties of MV XLPE Cable
Medium voltage cables with XLPE insulations have superior properties as compared to other conventional MV cables in the market. Armoured XLPE cables do not melt and have better thermally resistance. MV XLPE cables can also deliver results even when exposed to temperatures up to 120°C. XLPE insulated cables can also sustain temperatures for up to 250°C without mechanical or electrical loads. XLPE power cables are also much more flexible and durable as compared to other types of cables. Being very flexible, these wires can easily make to the parts that are hard to access and can also be easily bundled together for storage. MV XLPE cables can also be used for underground power transmission and often find their use in underwater applications.
Due to their excellent properties, the medium voltage cables insulated with XLPE can see their use in smart grid applications as they can outperform almost all the types of cables available in the market today. They have far better current and voltage transmission capabilities and thus can easily adapt to the modern high demand industrial applications. The XLPE cables are also termed by many as the cables of the future due to their superior working ability. With more and more countries and cities going towards a modern look, more and more power transmission is now seeing their power delivery underground. Overhead medium voltage cables not only pose a threat to the locals in cases of accidents but also fail to function properly during any natural disasters. On the other hand, underground XLPE cables can function during adverse conditions.
Testing procedures for MV XLPE cables
XLPE cable manufacturers incorporate a number of different high-performance tests to ensure that the MV XLPE cables can perform as expected even under extreme conditions. The following are some of the many tests that XLPE cable manufacturers test their wires with;
These are the tests that are conducted to monitor the overall function and quality of the MV cables. Routine tests include conductor resistance tests, high voltage tests, insulation tests, and numerous voltage tests.
These tests are carried out on MV XLPE cables to make sure that any new design changes conform to proper performance thresholds.
XLPE cable manufacturers carry out type tests on MV cables to validate and calibrate the MV cable design and working capacity. Type tests for MV XLPE cables include thermal stability tests, bending tests, heat distortion test, dielectric thermal resistance tests, and impulse voltage tests.
Several tests are carried out on the MV cable to ensure that the cable is performing as expected after it is installed. Common post-installation tests include conductor resistance tests, diverter tests, and verification tests.
At SSGcables, we incorporate state of the art testing procedures to ensure that the cables manufactured by us conform to the high standard of the market. We expose our cables to stringent standards to ensure that our products are able to meet the high expectations of our customers. The main testing equipment used by us are;
- Impulse test systems
- Partial discharge test system
- C high voltage test system
- Capacitance and power factor measuring bridge
- C Long Time test system
Benefits of MV XLPE cable
There are many different benefits of using MV XLPE cables instead of conventional medium voltage cables. The benefits of using XLPE cables are;
The XLPE power cables can easily bend in a wide radius and also adjust to sharp turns via elbow joints. XLPE insulated cables can also handle short radius turns with the aid of metal braces. With high flexibility, MV XLPE cables are the preferred choice of cables over others.
The XLPE cables can run direct from the distribution point to the outlet fixture without the need for it to be spliced or cut. This reduces the MV XLPE cables from becoming potentially weak at certain points. Alongside this, the direct routing of the XLPE insulated cable also reduces the installation times, thus reducing the installation costs.
- Improved water-tree resistance
MV XLPE cables have better water-tree resistance as compared to traditional insulating materials such as PVC, PE, and EPR. Water treeing is a common defect in electric wires which is a result of the imperfections in the insulation of wire where fracture lines occur and grow in the direction of the electric field, thus increasing electrical stress.
- No metallic sheath required
MV XLPE cables do not require a metallic sheath. Therefore, XLPE cables are free from failures related to metallic-sheathed cables such as fatigue and corrosion. However, some cable manufacturers do add metallic sheath to the XLPE insulated wires as an added protection and better durability.
The MV XLPE cables can be used for underground cabling systems. This allows for power delivery even during extreme weather conditions. Since XLPE cables are insulated quite good, they are the cables of choice for power delivery using underground means. The following image illustrates that the power delivery in the urban areas is ensured even during adverse weather conditions. On the other hand, if power delivery was done overhead, there is a high chance that the systems might have failed.
Underground power delivery using MV XLPE cables
Structural design and performance of MV XLPE cables
The performance of XLVE medium voltage cables conform to the international standards includes IEC 60502 and 60840.
The medium voltage cables with XLPE insulation, in general, have circle conductors with multiple cores. The conductors can be compacted stranded copper or stranded aluminium. XLPE cable manufacturers during construction must take special care to make sure that no small profile that is free from sharp objects that may damage the insulation when the conductors are exposed to high electrical stresses.
All MV cables with XLPE insulation are manufactured with extruded cross-linked semiconducting screens to protect the primary solid XLPE insulation. The conduction screens in these armoured XLPE cables fill the small gaps between the wires and are then able to provide a smooth circular exterior around the conductor. This process eliminates the concentration of the electrical stress around the conductor. The XLPE power cables carrying designed for medium voltage can have either bonded or strippable insulation screens; it is up to the customers on which one to get for their applications. As seen from the image below, the medium voltage cables with XLPE insulations come in many different categories. Ranging from a single copper conductor to multiple copper cores, the XLPE coating can be done easily on all types.
Different types of MV cables with XLPE insulations
Where are MV XLPE cables used for?
Apart from the fact that MV XLPE cables are used to carry medium voltages from point A to point B, the XLPE cables are used in locations that exposes the cables and wire to several different scenarios. The MV XLPE cables are used for;
- High abrasion and stresses
- Long term medium voltage applications
- Extreme temperature, both high temperatures and low
- Chemicals and other hazardous materials
- Power delivery to of the grid units
- Long term exposure to liquids
- Hard access points requiring medium voltage
How MV XLPE cables prevent charge accumulations?
XLPE insulated cables are known to prevent charge accumulations due to their construction. The MV XLPE cables offer extra protection to prevent any charge accumulation along the cable. Though many other cables require additional materials for the charge accumulations, the XLPE medium voltage cables are built in such a way that they automatically prevent the accumulation of electric charges. A typical XLPE cable is constructed using the following;
- Aluminium or copper conductor
- Conductor shield
- Insulation and its shield
- XLPE jacketing
Armoured XLPE cables help reduce the effects of imperfection on the MV cable or the effects of the cable coming in contact with the ground potential, i.e. at locations where voltage can accumulate. Though XLPE cable manufacturers such as SSGcables take utmost care to have even distribution of insulation, there still are points on cables where there might be a slightly thinner jacket or contact with the ground; hence at that location, there is a lower point of resistance. At such locations, electrical charges may try to accumulate. T
Therefore, medium voltage cables with XLPE insulations, since having thicker and much more even insulations reduces the charge accumulations in the wires. Our cables go through rigorous tests to ensure that the cable is performing as per expectation and no charge accumulation is taking place throughout the cables. At SSGcables, only the best and fully tested cables reach the customers as safety and quality are our top priorities.
Why is termination critical for medium voltage XLPE cables?
It is important that the termination process is carried out for MV XLPE cables. A proper termination process makes sure that the ends of the wires are properly closed and attached to switchgear for further power distribution. The smallest of imperfections in these cables, even a speck of contaminations, a small cut or nick can lead to a cable failure. Hence, a skilled person may take around an hour to fully terminate an assembly as everything has to be precise or cable failures may occur. Tests such as ‘high-pot test’ are commonly carried out to ensure that the cables are properly installed and ready for use.
What are the differences between XLPE and PVC insulation?
XLPE, as explained previously, is cross-linked polyethylene while PVC stands for polyvinyl chloride insulation. The main difference between the two is that XLPE cables can be used for both high- and low-tension applications as its structure provides excellent resistance to stress, abrasion, and general wear and tear. Other differences include;
- XLPE cables are more environmentally friendly as it does not contain chloride
- XLPE insulated cables have a longer life than PVC insulated cables
- XLPE insulated cables have better moisture and thermal resistance as compared to PVC.
- MV XLPE cables are much more flexible and can reach hard to access locations.
- XLPE cables can also be bundled together to save space
- XLPE cables are slightly more expensive than PVC insulated medium voltage cables
Industrial applications of Medium voltage XLPE cables
Due to their excellent physical properties, MV XLPE cables are cables of choice for many different applications. Some of the common industrial applications include;
- Power supply both via overhead and underground systems
- Power supply during wet or cold weather. The MV XLPE cables tend to operate easily under wet, damp, and cold conditions without showing signs of degradation
- To remote area – being robust and durable, armoured XLPE cables can easily power supply to off the grid locations such as small substations
- Power supply to regions with extreme weather conditions
- XLPE coated medium voltage cables see their heavy use in the mining industry.
Why XLPE insulated cables over other cables?
The XLPE insulated cables have superior characteristics as compared to other types of cables which makes them favorable in the market. The XLPE insulated medium voltage cables have a minimal voltage drop. It is because the voltage feeder lines have lower current; therefore, it results in lower voltage drops. Being XLPE insulated, the cables can sustain the medium voltage for longer durations. The MV XLPE cables also have far better flexibility as compared to other cables since XLPE can bend and make the tight turn without adversely affecting the conductor inside. Alongside this, the XLPE has better protection against external factors which greatly reduces the effects on the conductors. XLPE cables can also withstand extreme abuse and last longer; thus; it makes them the cables of choice for a wide array of applications.
Reasons for XLPE cables failure?
Though XLPE insulated cables are build to last and sustain long term exposure to harsh conditions, naturally, even the strongest cables tend to fail or degrade over the passage of time. There are several reasons why XLPE cables or any other cable may fail. Some of the common factors why MV XLPE cables fail are;
Degradation due to age
With constant use, the service life of the XLPE insulated cables tends to reduce. If the use of the cable is outside the stated working conditions, then the wire can degrade rapidly and thus reduce their overall working timespan. Hence, it is a must that the wires are operated as instructed by the XLPE cable manufacturers.
XLPE power cables may not perform well and cause short circuits if they are exposed to extremely high voltages. The medium voltage XLPE insulated cables are designed for medium voltages only. It must be ensured that they are not exposed to high voltages or unexpected voltage surges. It is common for the MV XLPE cables to fail if it is subjected to high voltages. Many users incorrectly install it at high voltage applications which results in the wire being electrically overloaded, thus resulting in the wire degradation. XLPE cable manufacturers highly recommend using their medium voltage cables at medium voltage applications only.
It is important that the XLPE MV cables are installed properly via trained professionals. If these cables are not installed properly, then it is highly likely that they may fail over subsequent usage. Improper installation may also result in these cables to fail abruptly. For the safety of the assembly and the personnel, it must be ensured that the proper installation of the cables is being carried out.
Updates for Medium voltage XLPE cables
With the demand for power on a steady rise due to the rapid urban development, the MV XLPE cables have also evolved. In the future, it is expected that much more energy-efficient medium voltage XLPE cables will come into the market. Currently, the MV cables fail to function properly when exposed to high voltages or when there is charge accumulation. It is expected that the XLPE cables of the future will have better operation envelopes and can outperform any other cable available in the market today.
The automotive industry has also become electric, which means that now more and more cars are in demand of power both at home and at specified power stations. With such a high and constant demand for power, it is important that the cables are also up to the requirements in the market. The upcoming versions of medium voltage XLPE cables can cater to this need and work exceptionally well under high loads for longer periods of time.
We at SSGcables are manufacturers and suppliers of high-quality MV XLPE cables. We have decades of experience in MV cable research, development, and manufacturing. Therefore, from conductor selection to sheathing to complete cabling, we execute a full set of strict controls over the quality of our components at each stage of manufacturing. At SSGcables, we have excellent sourcing and supply chain at each production stage, which ensures cost-savings, excellence, and value-adding solution so that we can deliver what we promise to our customers.
We would love to work closely with you to offer the best MV XLPE cable or any other cable to fit your requirements and deliver you our best in class products.
You might be interested in these XLPE insulated cables:
Low Voltage Power Cable
Medium Voltage VFD Cable
Medium Voltage Power Cable