Self-healing high voltage electrical insulation materials

1. Self-healing high
voltage electrical
insulation materials
by Anujith.T
roll no. 12
S7-F
1

2. CONTENT
❖ INTRODUCTION
❖ SELF-HEALING TYPES
❖ ELECTRICAL TREE
❖ HOW IT WORKS
❖ MICROCAPSULES
❖ TESTING AND RESULTS
❖ ADVANTAGE AND DISADVANTAGE
❖ CONCLUSION
❖ REFERENCES
2

3. INTRODUCTION
● Self-healing materials have the structurally incorporated
ability to repair damage
● Micro cracking can lead to catastrophic failure of the
composites and shorten the service lifetime.
● To self-heal as a direct response to electrical degradation is
very attractive, especially in challenging environments.
3

4. WHY SELF-HEALING?
★ Traditional repairs are expensive
★ Sense and respond to damage,restore performance without
affecting inherent properties
★ No human intervention required
★ Provide early means of detection
4

5. TYPES OF SELF HEALING PROCESS
❖Microcapsule embedment
❖3D-microvascular embedment
❖Electro-hydranamics
5

6. ELECTRICAL TREE
In electrical engineering, treeing is an electrical pre-breakdown
phenomenon in solid insulation.
fig 1.electrical tree
6

7. CONTINUED....
❖ Damaging process due to partial discharges and progresses
through the stressed dielectric insulation
❖ It is a common breakdown mechanism and source of
electrical faults in underground power cables.
❖ Initiated at regions with high local electrical fields,
contaminations in the insulation or conducting
irregularities/protrusions or voids
7

8. CONTINUED….
Local partial discharges will cause chemical degradation and
disintegration of the polymer, thus further extending the tree
channels until final electrical breakdown occurs.
fig 2. microscopic image of an tree(500nm)
8

9. OCCURENCE
❖ Occur at the interface between insulation and conductor or
within the insulation system.
❖ Bulk or surface defects create excessive electrical stress that
initiates dielectric breakdown in a small region.
❖ Occurs through as additional small electrical breakdown
events (called partial discharges).
9

10. TREE GROWTH
❏ The insulation system will never be perfect
❏ Cumulative long term degradation of the insulation may
cause inception of electrical trees
❏ A tree or a bush grows depending on the electrical field
strength, frequency and voltage waveform
10

11. TYPES OF ELECTRICAL TREE
Bow-tie trees
● trees which start to grow from within the dielectric insulation and grow symmetrically outwards
toward the electrodes.
● no free supply of air which will enable continuous support of partial discharges.
● discontinuous growth, which is why the bow-tie trees usually do not grow long enough to fully
bridge the entire insulation between the electrodes, therefore causing no failure in the insulation.
Vented trees
● initiate at an electrode insulation interface and grow towards the opposite electrode.
● Having access to free air is a very important factor for the growth of the vented trees.
● grow continuously until they are long enough to bridge the electrodes, therefore causing failure in the
insulation
11

12. HOW IT WORKS
➢Microcapsules filled with a monomer (healing
agent) are added to the insulation materials
(epoxy) prior to casting.
➢ When cracks propagate in the material the
microcapsules will rupture, releasing liquid
healing agent into the crack.
12

13. CONTINUED...
❏ One or more of the branches of the electrical tree
will likely break a capsule filling the electrical
tree with the liquid monomer.
❏ The final step is the polymerization of the
monomer occurs upon contact with a catalyst
also added to the epoxy resin.
13

14. WORKING...
fig3.a. healing of an electrical tree explained
b.
14

15. CONTINUED..
● As the tree structure is interconnected, most of
the tree structure is likely to be filled.
● Depends on the partial pressure and viscosity of
the monomer and the surface tension of the
hollow tubes
● Also on the availability of monomer relative to
the dimensions of the hollow tubes
15

16. CONTINUED
● The filling itself should extinguish critical discharges,
making further growth less likely.
● Upon polymerization, further development of the electrical
tree should halt, or at least be significantly delayed
16

17. MICROCAPSULES
Constituents which combine to form the MICROCAPSULES
✓ Healing Agent- DICYCLOPENTADIENE(DTP)
✓ Microcapsule Shell- UREA-FORMALDEHYDE(UF)
✓ Chemical Catalyst -BIS(TRICYCLOHEXYLPHOSPHINE)
17

18. CONTINUED..
POLYMER MATRIX- EPOXY POLYMER
FIBER REINFORCEMENT - CARBON FIBER
fig 4.microscopic image of ruptured microcapsule
18

19. CAPSULES
fig 5.
microscopic image
of capsule
19

20. TESTING
TESTING SETUP FOR A EPOXY
POLYMER
1-optical microscope connect-
ed to computer
2-sample specimen
3-voltage source
4- variac
5-current sensing resistor
20
1
2
3
45

21. RESULT
An optical micrograph taken at 200X magnification reflecting a
range of characteristics for the interaction of electrical trees and
microcapsules as embedded in the epoxy matrix is shown
1. 2.
fig4.Optical micrograph obtained in a sample containing 1.no catalyst 2.catalyst
21

22. RESULT AND DISCUSSION
● the predominant trend for the present dataset is for the
electrical trees to be attracted by the microcapsules
● The electrical properties of the capsule material (complex
permittivity and conductivity) have not been measured as part
of this study, but will be so in the future.
● electrical trees were repeatedly observed to enter
microcapsules and subsequently seemed to stop growing.
22

23. ADVANTAGES
● anything that cannot be reached at the moment of
damage can be repaired
● less cost in maintenance
● lifetime of the insulation material is increased
23

24. DISADVANTAGES
❖ this method self healing is very
expensive
❖ only 70-80% strength was obtained after self-
healing process
24

25. CONCLUSION
❖ Electrical trees formed by faults/contaminants inside the
insulation material can be stopped/delayed by the introduction
of microcapsules containing a healing agent.
❖ They may be healed before growing to sizes that could
sustain partial discharges and thus the inception of electrical
trees.
25

26. REFERENCES
[1] B. J. Blaiszik, S. L. B: Kramer, S. C. Olugebefola, J. S. Moore, N. R. Sottos, S. R. White, "Self-Healing
Polymers and Composites," in Annual Review of Materials Research, Vol 40. vol. 40, D. R. Clarke, et al., Eds.,
ed Palo Alto: Annual Reviews, 2010, pp. 179-211.
[2] S. R. White, N. R. Sottos, P. H. Geubelle, J. S. Moore, M. R. Kessler, S. R. Sriram, E. N. Brown, S.
Viswanathan, "Autonomic healing of polymer composites," Nature, vol. 409, pp. 794-797, Feb 2001.
[3] S. Van der Zwaag, Self Healing Materials: an Alternative Approach to 20 centuries of Materials Science.
Dordrecht: Springer, 2007.
[4] L. A. Dissado and J. C. Fothergill, Electrical Degradation and Breakdown in Polymers. London, United
Kingdom: The Institution of Engineering and Technology, 1992.
[5] R. Schurch, "Techniques for Electrical Tree Imaging," IEEE International Conference on Imaging Systems
and Techniques (IST), pp. 409-414, 2012
[6] J. Holton and E. Ildstad, "Electrical tree growth in extruded polypropylene," presented at the 2010
International Conference on Solid Dielectrics, Potsdam, Germany, 2010.
244
26

27. 27

28. 28