Cable Insulation Materials - Open Electrical

7/28/2019 Cable Insulation Materials - Open Electrical

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Figure 1. Typical low voltage PVC cable

Figure 2. LV/MV cable for outdoor usage with PE sheath

Cable Insulation Materials

rom Open Electrical

The following materials are typically used for cable insulation:

Contents1 Thermoplastic

2 Thermosetting

3 Paper Based

4 Comparison of Materials

hermoplastic

Thermoplastic compounds are materials that go soft when heated and harden when cooled:

PVC (Polyvinyl Chloride) is the most commonly used thermoplastic insulator for cables. It is cheap, durable and widely available.

However, the chlorine in PVC (a halogen) causes the production of thick, toxic, black smoke when burnt and can be a health hazard in areas

where low smoke and toxicity are required (e.g. confined areas such as tunnels). Normal operating temperatures are typically between 75C

and 105C (depending on PVC type). Temperature limit is 160C (300mm2).

PE (Polyethylene) is part of a class of polymers called polyolefins. Polyethylene has lower dielectric losses than PVC and is sensitive to

moisture under voltage stress (i.e. for high voltages only).
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Figure 3. 3-phase EPR insulated cable for MV Figure 4. MV cable with XLPE insulation, 33 kV

hermosetting

Thermosetting compounds are polymer resins that are irreversibly cured (e.g. by heat in the vulcanization process) to form a plastic or rubber:

XLPE (Cross-Linked Polyethylene) has different polyethylene chains linked together (cross-linking) which helps prevent the polymer

from melting or separating at elevated temperatures. Therefore XLPE is useful for higher temperature applications. XLPE has higher

dielectric losses than PE, but has better ageing characteristics and resistance to water treeing. Normal operating temperatures are typically

between 90C and 110C. Temperature limit is 250C.

EPR (Ethylene Propylene Rubber) is a copolymer of ethylene and propylene, and commonly called an elastomer. EPR is more flexible

than PE and XLPE, but has higher dielectric losses than both. Normal operating temperatures are typically between 90C and 110C.

Temperature limit is 250C.

aper Based

aper Based insulation is the oldest type of power cable insulation and is still used mainly for high voltage cables. The paper insulation must be

mpregnated with a dielectric fluid (e.g. oil resin or a synthetic fluid). A lead sheath is commonly applied over the insulation to prevent water or moisture

ngress into the paper insulation, which is sensitive to moisture.
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Figure 5. Oil filled paper insulated cable, 66 kV

Comparison of Materials

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

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