XLPE

1. NOVEL INSULATION MATERIALS
FOR HIGH VOLTAGE CABLE
SYSTEMS

2. OUTLINE
• Introduction
• Limitations of XLPE
• Thermoplastics
 Polyethylene
 Polypropylene
• Conclusion
• References

3. INTRODUCTION
• Most common polymeric insulation material.
• Produced with high throughput and well-controlled extrusion
technology .
• Base for this insulation is polyethylene (PE).
• Crosslinked either with peroxide cure , or by grafting silane
onto the polymer chains, and the use of moisture-based cure .

4. PEROXIDE CURE
• Organic peroxide is added to polyethylene
• Dicumyl Peroxide(DCP) is the most commonly used cross
linking agent.
• Cross linking occurs at 150-200 °C
• Cropensity for premature crosslinking (scorch) .
• peroxide mediated crosslinking generates byproducts
(acetophenone, cumyl alcohol, methylstyrene, and methane).

5. MOISTURE CURE
• Silane is added to the polyethylene in the polymerization
process
• Simpler curing process
• Cross linking occurs at 90 °C in water bath
• Increased risk of water tree formation

6. BENEFITS OF XLPE
• Improved thermal stability
• High melting point
• Cost effective

7. LIMITATIONS OF XLPE
• Thermal expansion
• Cause damage to the sheath and joints
• If the insulation system is subjected to mechanical forces
between 90 to 100°C, mechanical damage can result

8. POLYETHYLENE
• Produced by the
polymerization of monomer
ethylene
 Branched LDPE
 Linear HDPE

9. LOW DENSITY POLYETHYLENE
• Obtained by polymerization of
ethene under high pressure.
• Chemically inert and tough but
flexible
• Poor conductor of electricity
• having density between 0.91 and
0.923 g/cm3
• much lower crystalline content
compared to HDPE

10. HIGH DENSITY POLYETHYLENE
• Obtained by polymerization of
ethylene under low pressure
• Density between 0.94 and 0.98 g
/cm3
• Higher crystalline content

11. BLENDING OF HDPE AND LDPE
Fig: Differential scanning calorimetry trace of the melting behavior of samples
isothermally crystallized at 124°C for different high-density polyethylene
(HDPE)/low-density polyethylene blend compositions

12. NANOSCALE INCLUSION OF LDPE
Figure 4. Scanning electron microscopy graph showing the crystalline high-
density polyethylene “skeleton” structure, which is embedded in the
noncrystalline majority component low-density polyethylene

13. • Rise to an increase in breakdown strength of 24% compared
with a material of the same molecular composition
• Tree growth rates being significantly reduced in PE blends
compared to XLPE
• Nanoscale inclusion of the LDPE provide low temperature
flexibility
• HDPE crystals gives good high temperature mechanical
integrity
• This integrity is retained to some 30°C above the melting
temperature of XLPE

14. POLYPROPYLENE
• Polypropylene, a synthetic resin built up by the
polymerization of propylene.

15. PROPYLENE BASED SYSTEMS
• Difference between polyethylene and polypropylene:
 The melting temperature of isotactic polypropylene (iPP) is much higher
than that of HDPE.
 iPP tends to form particularly large spherulites. The benefit is that the
material is intrinsically clean.
 The synthesis method of PP does not produce branched molecular
structures akin to LDPE
 Manipulating the structure and properties of PP is much more difficult
than in PE

16. • propylene-based systems in cable applications is driven by two factors:
 high melting temperature of PP (above 160°C) provides the potential for
much higher cable current ratings.
 Apparent cleanliness of PP exhibits excellent electrical properties for
correctly designed systems.
• A widely accepted strategy for the design of propylene-based systems for
use in cable applications is to blend iPP with a more flexible, lower
crystallinity copolymer.

17. Scanning electron microscopy graph showing (a) isotactic polypropylene after
isothermal crystallization at 120°C, showing clear interspherulitic boundaries; (b)
polypropylene blend with 12% ethylene, showing clear phase separation, resulting in
electrically weak regions

18. Fig: (Left) Electric breakdown strength of polypropylene and high-density polyethylene
samples of different thickness as function of spherulite mean diameter size . (Right)
Illustration of the breakdown path along the weak boundaries

19. Scanning electron microscopy graph showing (a) isotactic polypropylene blend system with
ethylene/propylene copolymer, virtual elimination of weak boundaries; (b) example of
successful polypropylene blend without phase separation.

21. CONCLUSIONS
• It is now possible to formulate thermoplastic polymer blends
that are able to overcome the limitations of XLPE.
• These new materials promise more sustainable systems , both
economically and environmentally and provide greater design
freedom for HV and extra high voltage AC and DC cable
developments.

22. REFRENCES
• Thomas Andritsch , Alun Vaughan ,and Gary C. Stevens , “Novel Insulation
Materials for High Voltage Cable Systems” ,IEEE Electrical Insulation Magazine, Vol.
33, No. 4 , 2017.
• C. D. Green, A. S. Vaughan, G. C. Stevens, A. Pye, S. J. Sutton, T. Geussens, and M.
J. Fairhurst, “Thermoplastic cable insulation comprising a blend of isotactic
polypropylene and a propylene-ethylene copolymer,” IEEE Trans. Dielectr. Electr.
Insul., vol. 33, no. 3, pp. 639–648, 2015.
• P. J. Caronia, J. M. Cogen, and P. Dluzneski, “Novel polymer crosslinking chemistries
for cable insulation,” in Electr. Insul. Conf., 2014, pp. 392– 396.

23. THANK YOU !