20 kV Cables

20 kV cable is one of the voltage ratings listed in IEC 60038 (IEC Standard Voltages) and one of those listed in IEC 60502 Part 2: Cables for rated voltages from 6 kV (Um = 7,2 kV) up to 30 kV (Um = 36 kV).

Voltage ratings covered by this IEC Standard include:

• 3.6/6 (7.2) kV
• 6/10 (12) kV
• 8.7/15 (17.5) kV
• 12/20 (24) kV
• 18/30 (36) kV

IEC (International Electrotechnical Commission) Standards are one of the most widely recognised sets of standards for electrical cables and systems The adoption of these standards ensures the safety, performance, and compatibility of electrical equipment and systems. 

A 20 kV (kilovolt) voltage rating is applied to a cable designed to operate in an electrical system where the nominal voltage is 20,000 volts.

IEC recognise 20 kV cables as being medium voltage cables, those with a voltage between 1 and 35 kV (1000 and 35000 V), used to form an important part of the electrical distribution system throughout many European countries.

Medium voltages are obtained from electrical substations, where electricity is transformed from high voltage (HV) to medium voltage (MV). 

20 kV Medium-voltage electric cables are typically used in large medium voltage power Distribution networks, between substations, local transformer stations and Industrial installations, they also find use for longer transmission distances.

Many European as well as other International Countries use this voltage rating, in the UK and parts of the old British Empire, different voltage ratings based upon BS (British Standards) are sometimes used.

When selecting or installing a 20 kV cable, it is essential to adhere to the relevant IEC cable standards to ensure the cable’s safety and performance. These standards cover aspects such as cable construction, insulation and sheathing materials, conductor size, current-carrying capacity, and give guidance on installation practices designed to prevent electrical failures and ensure the reliability of the whole of the electrical distribution system. Always consult the specific standards and local regulations applicable in your region or industry to ensure compliance and safety.

Tratos can supply a range of standard 20 kV cables, as well as bespoke deigns with:

Conductors

• Solid or stranded Aluminium conductors up to 3000 mm2.
• Stranded Copper conductors up to 3000 mm2.

Copper is by far the most widely used material for conductors in electric cables because its high electrical conductivity makes it a good conductor of electricity, only Silver has better conductivity. It is relatively soft and ductile, so it is easy to draw to size, and so it is an ideal material with which to make 20 kV cables.

Aluminium conductors offer a cost-effective alternative without compromising on performance.

Tratos Class 2 conductors are supplied water blocked.

Insulations systems

• Extruded semiconducting conductor screen.
• EPR or XLPE insulation
• Bonded or strippable extruded semiconducting insulation screen 
  • A metallic layer applied over either the individual cores or the core assembly collectively.

Both EPR and XLPE are cross-linked materials, having good mechanical properties coupled with excellent dielectric properties. Because of their elastomeric nature they withstand high temperatures without melting or excessively deforming. 

Because of their stable dielectric properties over a wide temperature range, EPR and XLPE are usually the insulation of choice for medium voltage and high voltage cables, although is some applications such as subsea EPR is preferred by some customers. Both materials are included in IEC Standards, British Standards as well as Specifications issued by the DNO’s.

The semiconducting compounds used by Tratos are fully compatible with the EPR and XLPE insulation.

Metallic screen

Tratos metallic screens can be a concentric layer of copper wires or one or more copper tapes. Other designs of screen can be supplied on request. 

When applied to each individual core the metallic screens ensure a uniform symmetrical stress within the insulation, they can also help electromagnetic interference.

When a collective screen is required, as well as a traditional tape screen, this can be supplied in the form of an aluminium or steel wire armour.

As the manufacturer Tratos can manufacture 20 kV cables with different screen resistance to meet the requirements of the installation or local regulations.

Assembly and finish

Single core Unarmoured:

• Metallic screened core as above
• Extruded outer sheath in PVC, MDPE or Low smoke, zero halogen emission.
• Radial and longitudinal Water blocking is available.

These single core unarmoured cables are both light and pliable to ease installation in applications where mechanical protection is not required.

Single core Armoured:

• Metallic screened core as above
• Extruded or taped inner covering.
• Aluminium metal wire armour.
• Extruded outer sheath in PVC, MDPE or Low smoke, zero halogen emission.
• Radial and longitudinal Water blocking is available.

These single core armoured 20 kV cables are an ideal choice for installations where mechanical protection is required.

Three core Individual core screens Unarmoured:

• Metallic screened core as above
• 3 cores laid up with non-hygroscopic fillers.
• Extruded outer sheath in PVC, MDPE or Low smoke, zero halogen emission.
• Radial and longitudinal Water blocking is available.

These three core unarmoured cables are both light and pliable to ease installation in applications where mechanical protection is not required.

Three core unscreened core, Collective screen in the form of an Armour:

• Unscreened core as above
• 3 cores laid up with non-hygroscopic fillers.
• Lapped inner covering. (an extruded inner covering can be supplied upon request)
• Galvanised wire collective screen applied as an armour.
• Extruded outer sheath in PVC, MDPE or Low smoke, zero halogen emission.
• Radial and longitudinal Water blocking is available.

The use of a collective metallic screen rather than an individual metallic screen around each core is preferred by some customers for 30 kV cables as it simplifies terminations.

Three core Individual core screens Armoured:

• Metallic screened core as above
• 3 cores laid up with non-hygroscopic fillers.
• Extruded inner sheath.
• Galvanised steel wire collective screen applied as an armour.
• Extruded outer sheath in PVC, MDPE or Low smoke, zero halogen emission.
• Radial and longitudinal Water blocking is available.

These 20 kV cables are popular for installations where maximum mechanical and electrical protection is required.

Sheaths

PVC sheaths should require no introduction, they have been used in the manufacture of electric cables since WW2.

PVC sheaths have good mechanical and ageing properties, with excellent resistance to ozone and weather, and specific resistance to UV can be achieved by including carbon black in the compound.

20 kV cable sheathed with PVC have good resistance to water but for prolonged or permanent immersion, an alternative sheathing material such as polyethylene is required. 

PVC has good resistance to chemicals but can be affected by solvents and some oils which tend to leach out the plasticiser and can cause the PVC to crack. Specific formulations can offer improved performance if required.

PVC compounds are classed as flame retardant, being self-extinguishing when the source of the flame is removed.

MDPE sheaths are popular as sheathings or coverings for both Energy and Telecommunication cables which are to be buried or drawn into ducts during installation. With the move away from lead sheaths Polyethylene is becoming the preferred sheathing material for installations where moisture or water are present continually, or for long periods of time. MDPE coverings also provide corrosion protection in installations where this is a problem. However, when used as a sheath or covering which will be exposed to UV, polyethylene sheaths must be compounded with carbon black or, if coloured, UV stabilisers.

Where increased resistance to radial water penetration is required, Tratos are able to supply cables in a “Glover Barrier” design, a thick polyethylene coated aluminium foil laminate bonded to an MDPE inner or outer sheath.

Low smoke, zero halogen sheaths are now the preferred choice for cables which need improved performance in the event of a fire. This has seen requirements for low smoke emission, low corrosivity when burnt, flame retardance and reduced propagation become clearly defined and increasingly specified in many areas of cable installation. This has removed halogenated compounds from many markets to be replaced by LSZH – low smoke, zero halogen – types. 

Depending upon the construction and compliance with local regulations cables can be installed in air, laid directly in ground, in cable ducts, indoors or outdoors.

Depending upon the construction 20 kV cables can be installed in air, laid directly in ground, in cable ducts, indoors or outdoors.

TECHNICAL CHARACTERISTICS

• Voltage Rating (Uo/U)(Um) 6/30 (12) kV
• Test Voltage 42 kV
• Temperature Rating
• Fixed: -20°C to +90°C
• Short Circuit Temperature +250°C
• Minimum Bending Radius 20 x overall diameter

For an in-depth technical specification, please consult our detailed PDF specification sheets.

Whether you require technical guidance or assistance in selecting the ideal 20kV cable for your application, our experts are at your service. As an Independent Distribution Network Operator (iDNO), power grid installer, or contractor, you can rely on our DNO MV specialists for invaluable insights and recommendations. Please do not hesitate to reach out to us for further information, and we will be delighted to support you in meeting your 20 kV cable and installation requirements.