conductor insulation

Conductor insulation Property

conductor insulation property

What are the main property of insulating material?

1-Insulator material must have high insulation resistance to avoid leakage current.

Insulation Resistance

As conductor of the wire are at higher potential and outer side of wire insulation material at lower potential due to this there are chance of current flow from higher to lower potential.
But we do not want that current will flow through the insulator because if there is very small flow of current it cause power losses and potential drop, therefore we use the material which have very high resistance as an insulator.
NOTE:-Megger is an insulation tester which is used to measure insulation resistance of the cable which is generally in mega-ohm(M&#8486).

2-Insulator material must have high dielectric strength.

Dielectric Strength

The dielectric strength is the maximum electric field strength that it(insulator) can withstand without experiencing failure of its insulating properties.
or
Dielectric Strength of an insulator is the maximum strength of field(i.e Electrical field), it can withstand without becoming a conductor. 
if electric field is above the Dielectric Strength then breakdown occur and insulator behave just like an conductor.

3-Insulator material must have low relative permittivity(dielectric constant)

Relative permittivity(dielectric constant)

Dielectric constant is the ratio of force between the charges at some distance apart in the AIR to same charges kept at same distance but in other medium.
It is normally indicated by Er(Relative permittivity).
The large the dielectric constant, more charge can be stored and as the value of dielectric increase its capacitance also increase.
NOTE:-XLPE have 2.2 dielectric constant at 1kHZ where as dielectric constant of EPR is between 2.8 to 3.2.

4-Insulator material must be Non-hygroscopic.
Non-hygroscopic material having little or no tendency to absorb moisture.

5-Good mechanical strength

6-Non-inflammable:-not catching fire easily.

7-The cost of insulator should be economically

8-Oil Resistance:-If we are going to use our cable in chemical processing industry,food beverage industry,automative assemblies utilizing various cleaning solvents in that case our cable must be oil resistance.

NOTE:-We use some standards and specifications for insulation material such as For PVC power cables we use IS:5831 and for XLPE power cables we use IS:7098 and for Rubber-based power cables, we use IS:9968 and other relevant specifications. There are some international standards also which form by International Electro-technical Commission's(IEC) such as IEC 60228 for EPR Cables

Which material is used to insulate cables?

Mainly most of our insulation material are polymer of plastic and we can divide plastic into 2 type.
1-Thermoplastic:-A Thermoplastic is a material that softens when heated and becomes firm when cooled
e.g:-PVC, PUR, TPE
2-Thermoset plastics:-Thermoset plastics always remain in a permanent solid state.
e.g:-XLPE, EPR, Silicone Rubber

We have lage number of different types of insulation material some of them are very popular such as polyvinyl chloride(PVC), Cross-linked polyethylene(XLPE),EPR(Ethylene Propylene Rubber).

polyvinyl chloride(PVC)

PVC is world third-most widely use synthetic plastic polymer because of Cheap, Durable, Widely available. The maximum operating temperature for PVC is 70°C for general-purpose 85°C for heat-resisting purpose.

Short circuit temperature for PVC

160 for 5 second  

PVC Disadvantages
Highest dielectric losses, Melts at high temperatures(as it is a thermoplastic), Contains halogens.

Cross-linked polyethylene(XLPE)

The Cross-linked polyethylene(XLPE) are ideal for transmission and distribution of power most of HT and LT cables are insulated by XLPE because of Low dielectric losses, Improved material properties at high temperatures. The maximum operating temperature for XLPE 90°C.

Short circuit temperature for XLPE

250 for 5 second

XLPE Disadvantages
Does not melt but thermal expansion occurs, Medium sensitivity to water treeing (although some XLPE polymers are water-tree resistant) and not very flexible.

EPR(Ethylene Propylene Rubber)

EPR is also a very popular material in cable industries because of excellent flexibility, Reduced thermal expansion (relative to XLPE), Low sensitivity to water treeing etc. The maximum operating temperature for EPR 90°C. It is also know as Tough Rubber Sheathed(T.R.S) cable.
EPR Disadvantages
Medium-High dielectric losses, Requires inorganic filler/additive 

Silicone Rubber

Silicone insulated cables have an outstanding thermal range of -90°C to 200°C+. This temperature range demonstrates it's greater resistance to heat than PVC insulated cables. Silicone test leads offer superior flexibility and softest surface than the PVC alternative.

PUR Cable(Polyurethane Cables)

PUR cables has very good mechanical characteristics property such as high abrasion resistance, tear resistance and this has toughness for cable jacketing. Cable with PUR installation is harder to strip.

In machining applications PUR becomes the cable to use owing to its better resistance to cutting and hydraulic oils, therefore PUR cables are very well suited for flexible applications in robotics, machine tools and metal cutting manufacturing.

Polyurethanes displayed excellent antibacterial, Polyurethane limits the growth of bacteria and microbes which makes the sheathing material particularly to use in the food & beverage industry, clean rooms, and complying with the hygiene requirements of production lines.

PUR cables can operate between -40°C and +125°C.

But Polyurethanes(PUR) insulation is very costly and mostly used as a jacketing material instead of insulation.

Thermo-Plastic Elastomers(TPE)

Thermoplastic elastomers (TPE), also known as thermoplastic rubbers.

TPE cables are resistant to inorganic oils, organics oils, heat resistance, flame resistance, moisture resistance and deep-freeze applications better than PUR.

But the cost of TPU cables is relatively high. TPE is eco-friendly and non-toxic recyclable plastics.

TPE is often used in more robust applications that feature fast movements such as conveyor systems and crane systems,materials handling or low temperature applications.

As TPE is also a thermoplastic so it melt down at high temperature.

Electron Beam Cross Linked (EBXL) Cables

The Electron Beam Cross Linked (EBXL) Cables are the Cables in which cross-links between the molecules is formed by the help of E-Beam Technology E-Beam Technology
In E-Beam Technology we use electron-beam accelerator with variable energy 1 to 3 MeV and power of 100 KW. This electron accelerator give us a number of high energy electron and when our polymer(made of hydrocarbon) is exposed on the beam of high energy electron the weak bond between hydrogen and carbon is break and strong bond between carbon and carbon remain unaffected. These free hydrogen ion react with each other and form a cross-links between the molecules.
This cross-linking makes the polymer dimensionally more stable. Therefore it improve thermal, chemical, barrier, impact wear and other mechanical properties. As a result we get cables with the advantages of increased life, higher temperature withstand capability, higher current carrying capacity, improved physical properties with reduced thicknesses in these cables.
It is also better than conventional method of cross-linking based on thermally induced chemical reaction(or chemical cross-linking). Which is carried out at high temperature due to which there is some degradation of polymer. Whereas E-beam cross-linking carry out at room temperture by the help of electron-beam accelerator within few second.

Feature of Electron Beam Cross Linked (EBXL)

• EBXL is environment friendly and very reliable.
• current carrying capacity to more than double.
• Increase in Abrasion resistant
• Increased the life of cable more than 50 years.
• Cross-linked cables have already been adopted in all critical applications such as railways, defense, solar power, nuclear power, Marine and Automobile.

Why high voltage is used for power transmission?

As when current flow through a wire there is some losses such as copper losses.

power loss( or Copper losses)=I2R.

When voltage increase current in line goes down and voltage drop also goes down. Therefore we use high voltage for power transmission.

CABLE POWDER

In the manufacturing of cables different types powder are used such as:-
Talcum powder
It is used where low current is supplying for example in our Computer power supply cable. It protect internal wire to attached each other and jacket of the cable
Magnesium Oxide
It is mostly used. It is used where high current is flowing and cable temperature is high as magnesium Oxide reduce the temperature of the cable. It also work as very good insulator. magnesium Oxide also have fire resistant property. Magnesium Oxide also provide additional flexibility to our cable.
Swellable Powder
It Block water and protects our cable from moisture.
Chalk Powder
It have very good fire resistance property.

INSULATION AND SHEATHING

For Insulation and sheathing we mostly follow stranded IS:5831-1984 (and it also written as "PVC Type 'ST2' as per IS:5831/84")

Insulation Material

PVC Type A-------------General purpose insulation for conductor temp. 70°C under 3.3 KV.
PVC Type B-------------Insulation for conductor temp. 70°C and voltage upto 3.3KV and above.
PVC Type C-------------Heat Resistance Insulation for conductor temperature 85°C and 105°C and voltage upto 1100V.
PVC Type D-------------Flexible insulation for conductor temp. 70°C and voltage up to 3.3KV.
XLPE----------90°C.
Rubber-EPR IE-1----------90°C.
EPR MV-105---------------105°C.

Silicon Rubber--------------150°C.
Teflon------------------------450°C.

sheathing Material

PVC Type ST1:-General purpose sheath for conductor temperature 70°C.
PVC Type ST2:-Heat Resisting sheath for cables with maximum conductor temperature 90°C.
FR PVC Type ST2:-Additional property fire resisting, and Anti-Rodent.
FRLS PVC Type ST2:-Additional property fire Retardant low smoke sheath.
PVC Type ST3:-General purpose flexible sheath for conductor temperature 70°C.
ST7:-ST7 is used for PE (PE types HDPE, LDPE and MDPE).
ST8:-It is halogen free (or LSZH) with maximum conductor temperature 90°C.

Examples

For better understanding have to observe some of the data from datasheets of the cable
50 x 3.5 Core Alum. Armd

• Voltage Grade V:-1100V
• Conductor material:-H2/H4 Grade Aluminium as per Class 2 of IS: 8130/84,latest
• Insulation:-XLPE as per IS 7098(Pt-1)/88
• Inner Sheath:-Wrapping of Tapes
• Outer Sheath:-PVC Type 'ST2' as per IS:5831/84
• Max. conductor temp. under normal operating conditions: 90°C, [short circuit temp.=250°C]

1.5 x 3 Core Cu Armd Str. Cond. Frls Cable

• Voltage Grade V:-1100V
• Conductor material:-Plain annealed Copper as per Class 2 of IS:8130/84
• Insulation:-XLPE as per IS 7098(Pt-1)/88
• Inner Sheath:-Extruded PVC Type ST2 as per IS:5831/84
• Outer Sheath:-Extruded FR-LSH PVC Type ST2 as per IS:5831/84
• Max. conductor temp. under normal operating conditions: 90°C, [short circuit temp.=250°C]

1.5 x 1 P Overall Shielded Armd Frls Cable Red

• Voltage Grade V:-300/500V
• Conductor material:-Plain Stranded Copper as per IS: 8130
• Insulation:-PVC Type A
• Inner Sheath:-Extruded PVC Type ST1 as per IS:5831
• Outer Sheath:-Extruded FRLS PVC Type ST1 as per IS:5831
• Max. conductor temp. under normal operating conditions:70°C, [short circuit temp.=160°C]

1.5 x 4 Core Cu Braided Flex Cable Black

• Rated Voltage:-1100V
• Conductor material:-Plain annealed high conductivity Flexible copper conductor as per Class 5 of IS 8130/2013 latest
• Insulation:-PVC Type A
• Sheath:-Extruded FRLS PVC Type ST1 as per IS:5831/84
• Max. conductor temp. under normal operating conditions:70°C, [short circuit temp.=160°C]

0.5 x 2 Core Cu Flex PVC Cable Black

• Rated Voltage:-1100V
• Conductor material:-Plain annealed high conductivity Flexible copper conductor as per Class 5 of IS 8130/2013 latest
• Insulation:-PVC Type 'D'
• Sheath:-Extruded PVC Type 'ST3' as per IS:5831/84
• Max. conductor temp. under normal operating conditions:70°C, [short circuit temp.=160°C]

1.5mmX2core FS(EPR-LSZH-LSZH) ARMD CABLE

• Voltage Grade V:-1100V
• Conductor material:-Annealed Tinned Class -2 Copper to IEC 60228
• Insulation:-EPR as per IEC 60502-1
• Inner Sheath:-Extruded LSZH Type ST8 as per IEC 60502-1
• Outer Sheath:-Extruded LSZH Type ST8 as per IEC 60502-1
• Max. conductor temp. under normal operating conditions: 90°C, [short circuit temp.=250°C]
• Fire Performance Circuit integrity test:-IEC 60331 (750°C for 90minutes) and Glass mica Tapes to meet the fire resistance requirements

EXTRUSION

Extrusion is a process where molten polymer is forced through a die to produce a components of a fixed cross-sectional area such as tubes and pipes. The product which are formed by help of Extrusion process are known as extruded product. The Crosshead Extrusion process is widely used to coat wire and cable with a polymer.