Suppliers, Distributors and Exporters of HT Cables/MV Cables

HT Cables or High Tension Cables are cable defined as per IS 7098 Part II having voltage grade from 3.3kv to 33kv. Cables of similar voltage range are also defined as MV Cables or Meduim Voltage Cables as per IEC-60502 part 2, BS-6622 & BS-7835

Traditionally Paper/Oil Insulation systems have been used in HT Cables/MV Cables. However, since the advent cross-linked polyethylene (XLPE) have been used as an insulation material. In most countries, the use of polyethylene have been limited to the cross-linked version (XLPE) due to major advantage XLPE

Cross-linked polyethylene is also considered to be the material of choice due to its ease of processing and handling as compared to paper/oil. In addition, the low dielectric losses of cross-linked polyethylene which become increasingly important with increase in voltage as well as high intrinsic electrical strength makes it the favored material for the range of medium & high-voltage applications.

Power Cables are generally selected considering the application. However, following factors are important for selection of suitable cable construction required to transport electrical energy from one end to the other.

• Maximum operating voltage
• Fault level
• Load to be carried
• Possible overloading duration & magnitude
• Route length and voltage drop
• Mode of installation considering installation environment such as ambient & ground temperature chemical & physical properties of soil
• Flame retardant properties

Guidelines for Selection of Cables

Since a wide range of HT cables are manufactured, it is important that while placing enquiries or orders, as much information as possible shall be given, so that the enquiries and orders are dealt quickly and efficiently.

1. Voltage Grade

Voltage grade of HT cable as per following table

• 2. Relevant Indian Standard :
  IS 7098(Part-2)-1985 or International standard-IEC- 60502(Part-2), BS-6622 & BS:7835.
  Any other International standards or as per customer specification for e.g. UL 1072 ANSI/ACEA, etc.
• 3. Number of Cores - Single & Three.
• 4. Conductor :
  Size-35 Sq.mm to 1000 Sq.mm in Single Core Cables & 35 Sq.mm to 400 Sq.mm in 3Core cables.
• 5. Conductor Material - Copper/Aluminium
• 6. Type of Insulation - XLPE
• 7. Type of Inner Sheathing - PVC Wrapped/PVC Extruded.
• 8. Type of Armour - Unarmoured/Strip Armoured/Round Wire Armoured.
• 9. Type of Outer Sheath :
  PVC/Flame Retardant/Flame Retardant Low Smoke/Zero Halogen (LSOH).
• 10. Length of cable required in one drum length.

Conductor

The conductors are Stranded Class2 Annealed Plain/Tinned Copper/Aluminium. All sizes of conductors of single or three core cables for HT cable are circular compacted.

Conductor construction and testing comply to IS 8130-1984 as amended up to date & as per IEC: 60228.

Conduct Semi- Conductive – Insulation – Insulation Semi-Conductive

The Three layers are extruded in one step using the state-of-art Catenary Continuous Vulcanization (CCV) technology with advanced automatic concentricity control system which can guarantee the highest quality of the insulated conductor.

Over the metallic conductor, an extruded layer of cross linked semi-conducting compound is applied. This layer acts to smooth out any irregularities and thus reduces the probability of protrusions into the insulating layer. Such protrusions into the insulation or into the semi-conducting layer increase the localized stress that may exceed the long-term breakdown strength of the insulation, so the semi-conductive layer is acting as a stress control layer.

Each core conductor is insulated by extruded high quality XLPE conforming to IS:7098/Part 2 and IEC 60502-2, the insulating compound is a developed material suitable for application through CCV technology. The insulation thickness is selected based on the designated voltage rate complying with IS:7098/Part 2 and IEC 60502-2.

Over the insulation, an extruded layer of cross linked semi-conducting compound is applied. This layer, which has a very smooth surface, is a transition from the insulating material where the electric field exists to a conductive metallic screen, where the electric field is zero, so it will reduce the stress enhancement at the insulation layer. The insulations shield layer could be bonded to the insulation or strippable type for easily removable to facilitate splicing and terminating.

Metallic Screening/Shielding

The metallic screening over insulation semi-conductive layer is necessary to cancel out the electric field outside the cable and to provide a low resistance path for charging current to flow to ground. When the screening bonded to earth it will also carry out the short circuit fault current. Below are the methods of metallic screening

• Copper Tape: an annealed Copper tape is applied helically with a suitable overlap.
• Copper Wire: helically applied and binded with a Copper tape to achieve electrical contact

Cable Assembly

For 3 core cable, the screened cores will have identification tape (Red, Yellow & Blue) under the metallic screen, then the cores are laid up together to form the laid up cable cores. Non-hygroscopic polypropylene filler is applied between laid up cable cores to provide a circular shape to the cable.

Inner Sheath

Extruded inner sheath serves under cable armouring to protect the laid up cores and as a separation sheath. The Inner sheath is an extruded PVC type ‘ST2’ as per IS 7098 Part 2.

Armouring

The cable intended for tray application is protected enough and does not require armour in general, while it is recommended to have armour for the cable intended for Direct Burial Application. The armour provides mechanical protection against crushing forces. Armour also can serve as an Earth Continuity Conductor (ECC). Armouring is applied over the inner sheath and normally comprises of Galvanized Steel Strips for multi core cables and galvanized steel wire can be offered as per customer requirements. For Mining use and other special applications, double Wire/Strip armoured cables with Tinned Copper wires can also be offered. Single core armoured cables are provided with non-magnetic armour consisting of hard drawn flat or round aluminium wires to avoid magnetic hysteresis losses on A.C. System.

Outer Sheath

It is the outer protection part of the cable against the surrounding environment.

• A tough Outer Sheath of Heat Resisting PVC compound (Type ST2) as per IS:7098 Part 2 is extruded over the armouring in case of armoured cables or over non-magnetic metallic tape covering the insulation screening in case of unarmoured single core cables.
• Outer sheath can be FR/FRLS/LSOH depend upon customer requirement.
• When the cable is required to anti-termite/anti-vermin, a special additive is added to the sheathing compound.

Lead Sheath (Optional)

Upon request a layer of lead is extruded over the bedding layer.

HT Cables designed to be used underground directly, buried in ducts, trenches or in tunnels for electric power transmission at high voltage, finds its applications in

• Transmission of Power from 3.3kv to 33 KV
• For power distribution by utilities to residential, commercial complexes & Industries consuming bulk power.
• For Large & Medium industries where equipment’s require power at high voltage
• Solar & Thermal Power Plants

Contact us for more information on HT Cables/MV Cables or to discuss your requirements. Enquiries are solicited for India, UAE and Africa on following Email id web@aakashpower.com