High Voltage Cable Insulation Material Construction

High Voltage Cable Insulation Construction

Cable Insulation Construction for High Voltage Power cable


Cable insulation is used to provide electrical good and safe separation between conductors of a cables. Numerous types of cable insulation materials like-XLPE, Elastomer, Rubber or PVC have been employed since the historical development of cables. During recent years, there has been some consolidation in the types of insulation used.


Code: IS: 7098, 8130, 14494 / IEC: 60502 / BS: 6622/BS: 7835;
Material Used: PVC, XLPE, Rubber, Elastomer, EPR;
Used for Voltage level: LV ,MV & HV Cables;


Purpose of uses:
Cable Insulation main Purpose is to withstand the electrical field (voltage) applied to the cable end for it's design life in its intended installed environment;


Cable insulation will be an extruded layer of XLPE, Elastomer, Rubber or PVC applied over conductor screen under triple extrusion process along with conductor screen and insulation screen;

There are different Type of Insulation Material used for cable but widely used are XLPE, PVC, Elastometer, EPR & Rubber.
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Comparison of Cable Insulation Materials

A comparison of common insulating materials is as follows:
MaterialAdvantagesDisadvantages
PVC
  • Cheap
  • Durable
  • Widely available
  • Highest dielectric losses
  • Melts at high temperatures
  • Contains halogens
  • Not suitable for MV / HV cables
PE
  • Lowest dielectric losses
  • High initial dielectric strength
  • Highly sensitive to water treeing
  • Material breaks down at high temperatures
XLPE
  • Low dielectric losses
  • Improved material properties at high temperatures
  • Does not melt but thermal expansion occurs
  • Medium sensitivity to water treeing (although some XLPE polymers are water-tree resistant)
EPR
  • Increased flexibility
  • Reduced thermal expansion (relative to XLPE)
  • Low sensitivity to water treeing
  • Medium-High dielectric losses
  • Requires inorganic filler / additive
Paper / Oil
  • Low-Medium dielectric losses
  • Not harmed by DC testing
  • Known history of reliability
  • High weight
  • High cost
  • Requires hydraulic pressure / pumps for insulating fluid
  • Difficult to repair
  • Degrades with moisture

 Cross-Linked Polyethylene: (XLPE)

They are known as PEX or XLPE Cable. It is form of polyethylene with cross links;

XLPE creates by direct links or bonds between the carbon backbones of individual polyethylene chains forms the cross linked polyethylene structure;

The result of this linkage is to restrict movement of the polyethylene chains relative to each other, so that when heat or other forms of energy are applied the basic network structure cannot deform and the excellent properties that polyethylene has at room temperature are retained at higher temperatures;

The cross linking of the molecules also has the effect of enhancing room temperature properties;

The useful properties of XLPE are temperature resistance, pressure resistance (stress rupture resistance), environmental stress crack resistance (esc), and resistance to UV light, chemical resistance, oxidation resistance, room temperature and low temperature properties;

XLPE cables work for the working voltage of 240 V to 500 KV.
The Jacketing Material can be of PVC / Flame Retardant / Flame Retardant Low Smoke / Zero Halogen (LSOH);

Applications: Fire Survival, Under Water Cables, Underground burial, installation on trays and ducts;
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2Y
2Y
2X
O2Y
LDPE
HDPE
VPE

Low density
Polyethylene
High density
Polyethylene
Cross Linked
Polyethylene
Foamed
Polyethylene
Density g/cm3
0.92-0.94
0.94-0.98
0.92
≈0.65
Breakdown Voltage KV/mm (20oC)
70
85
50
30
Specific Volume Resistivity Ω cm (20oC)
1017
1017
1012-1016
1017
Dielectric Constant 50 Hz (20oC)
2.3
2.3
4-6
≈1.55
Dielectric Loss Factor (tan δ)
2 x 10-4
3 x 10-4
2x 10-3
5 x 10-4
Working
Temperature
Permanent oC
-50 +70
-50 +00
-35 +90
-40 +70
Short Time oC
+100
+120
+100
+100
Melt  Temperature +oC
105-110
130
-
105
Flame Resistance
Flammable
Flammable
Flammable
Flammable
Oxygen Index LOI (% O2)
≤22
≤22
≤22
18-30
Heating Value H0 MJ.kg-1
42-44
42-44
42-44
42-44
Thermal Conductivity W.K-1.m-1
0.3
0.4
0.3
0.25
Corrosive Gases In Case Of Fire
No
No
No
No
Radiation Resistance max Mrad
100
100
100
100
Tensile Strength N/mm2
10-20
20-30
12.5-20
8-12
Elongation At Break %
400-600
500-1000
300-400
350-450
Shore Hardness
43-50 (D)
60-63 (D)
40-45 (D)
-
Abrasion Resistance
Medium
Good
Medium
-
Water Absorption %
0.1
0.1
0.1
-
Halogen Free
Yes
Yes
Yes
Conditional
Weather Resistance
Medium
(Black: Good)
Medium
(Black: Good)
Good
-
Cold Resistance
Good
Good
Good
Good


Polyvinyl chloride (PVC)

They are known as PVC insulated cables are widely used in various fields;

PVC’s relatively low cost, biological and chemical resistance and workability have resulted in it being used for a wide variety of applications;

For electric cables the PVC is mixed up with plasticizers. PVC has high tensile strength, superior conductivity, better flexibility and ease of jointing;

PVC is a thermoplastic material, therefore care must be taken not to overheat it; it is suitable for conductor temperatures up to 70°C. PVC insulated cables should not be laid when the temperature is less than 0ºC because it becomes brittle and is liable to crack.

Applications: Low voltage copper conductor PVC cables are extensively used for domestic home appliances wiring, house wiring and internal wiring for lighting circuits in factories, power supply for office automation, in control, instrumentation, submarine, mining, ship wiring applications etc.
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PVC Insulation Materials 

Y
Yw
Yw
Yk
PVC
PVC
PVC
PVC
Polyvinylchloride
Compounds
Heat-resistant
90oC
Heat-resistant
105oC
Cold
Resistant
Density g/cm3
1.35 - 1.5
1.3-1.5
1.3-1.5
1.2-1.
Breakdown Voltage KV/mm (20oC)
25
25
25
25
Specific Volume Resistivity Ω cm (20oC)
1013-1015
1012-1015
1012-1015
1012-1015
Dielectric Constant 50 Hz (20oC)
3.6-6
4-6.5
4.5-6.5
4.5-6.5
Dielectric Loss Factor (tan δ)
4 x 10-2 to 1 x 10-1
4 x 10-2 to 1 x 10-1
4 x 10-2 to 1 x 10-1
4 x 10-2 to 1 x 10-1
Working
Temperature
Permanent oC
-30 +70
-20 +90
-20 +105
-40 +70
Short Time oC
+100
+120
+120
+100
Melt  Temperature +oC
>140
>140
>140
>140
Flame Resistance
Self Extinguishing
Self Extinguishing
Self Extinguishing
Self Extinguishing
Oxygen Index LOI (% O2)
23-42
23-42
24-42
24-42
Heating Value H0 MJ.kg-1
17-25
16-22
16-20
17-24
Thermal Conductivity W.K-1.m-1
0.17
0.17
0.17
0.17
Corrosive Gases In Case Of Fire
Hydrogen Chloride
Hydrogen Chloride
Hydrogen Chloride
Hydrogen Chloride
Radiation Resistance max Mrad
80
80
80
80
Tensile Strength N/mm2
10-25
10-25
10-25
10-25
Elongation At Break %
130-350
130-350
130-350
130-350
Shore Hardness
70-95 (A)
70-95 (A)
70-95 (A)
70-95 (A)
Abrasion Resistance
Medium
Medium
Medium
Medium
Water Absorption %
0.4
0.4
0.4
0.4
Halogen Free
No
No
No
No
Weather Resistance
Medium
(Black: Good)
Medium
(Black: Good)
Medium
(Black: Good)
Medium
(Black: Good)
Cold Resistance
Moderate - Good
Moderate - Good
Moderate - Good
Very  Good

Elastomer Insulated cable

These cables are suitable for use where the combination of ambient temperature and temperature-rise due to load results in conductor temperature not exceeding 90°C under normal operation and 250°C under short-circuit conditions;

This insulation shall be so applied that it fits closely on the conductor (with or without either separator or screen) but shall not adhere to it. The insulation, unless applied by extrusion, shall be applied in two or more layers and it is applicable to cables with a rated voltage up to 1 100 volts;

Applications: Welding Cables, Ship wiring cables, Pressure Tight Cables and cables for submerged connection, Railways locomotives and coach wiring cables, Mining Cables.

Elastomere Materials

G
2G
3G
4G
5G
6G
NR
SBR
SiR
EPR
EVA
CR
CSM
Natural Rubber
Styrol-
Butadiene Rubber
Compounds
Silicone Rubber
Ethylen-
Propylene

Rubber
Compounds
Ethylene-
Vinylacetate

Copolymere
Compounds
Poly-
Chloroprene

Compounds
Chloro-
Sulfonated

Polyethylene
Compounds
Density g/cm3
1.5-1.7
1.2-1.3
1.3-1.55
1.3-1.5
1.4-1.65
1.3-1.6
Breakdown Voltage KV/mm (20oC)
20
20
20
30
20
25
Specific Volume Resistivity Ω cm (20oC)
1012-1015
1015
1014
1012
1010
1012
Dielectric Constant 50 Hz (20oC)
3-5
3-4
3-3.8
5-6.5
6-8.5
6-9
Dielectric Loss Factor (tan δ)
1.9 x 10-2
6x 10-3
3.4 x 10-3
2 x 10-2
5 x 10-2
2.8 x 10-2
Working
Temperature
Permanent oC
-65 +60
-60 +180
-30 +90
-30 +125
-40 +100
-30 +80
Short Time oC
+120
+260
+160
+200
+140
+140
Melt  Temperature +oC
-
-
-
-
-
+160
Flame Resistance
Flammable
High Flash Point
Flammable
Flammable
Self
Extinguishing
Self
Extinguishing
Oxygen Index LOI (% O2)
≤22
25-35
≤22
≤22
30-35
30-35
Heating Value H0 MJ.kg-1
21-25
17-19
21-25
19-23
14-19
19-23
Thermal Conductivity W.K-1.m-1
-
0.22
-
-
-
-
Corrosive Gases In Case Of Fire
No
No
No
No
Hydrogen Chloride
Hydrogen Chloride
Radiation Resistance max Mrad
100
50
200
100
50
50
Tensile Strength N/mm2
5-10
5-10
5-10
8-12
10-20
10-20
Elongation At Break %
300-600
300-600
200-400
250-350
400-700
350-600
Shore Hardness
60-70 (A)
40-80 (A)
65-85 (A)
70-80 (A)
55-70 (A)
60-70 (A)
Abrasion Resistance
Moderate
Moderate
Moderate
Moderate
Medium
Medium
Water Absorption %
1.0
1.0
1.0
1.0
1.0
1.5
Halogen Free
No
Yes
Yes
Yes
No
No
Weather Resistance
Moderate
Good
Very Good
Good
Very Good
Very Good
Cold Resistance
Very Good
Very Good
Good
Good
Moderate
Moderate

Polyvinyl chloride (EPR).

For high-voltage cables the insulation is ethylene propylene rubber (EPR) and for low-voltage cables it is polyvinyl chloride (PVC);

EPR has good electrical properties and is resistant to heat and chemicals; it is suitable for a conductor temperature up to 85 ºC.

Rubber Insulated cable

These are used in electric utilities such as the generation and transmission of electricity. Long service life under normal environment in Nuclear and conventionally powered generating stations plus safety considerations are the significant factors of these electric appliances;

When exposed to fire, Silicon offers circuit integrity, low smoke evolution, and freedom from halogen acids.

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