High Voltage Cable Insulation Material 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:

Material	Advantages	Disadvantages
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.