Dissertation defense, March 2020

1. THE IMPACTS OF IMPURITIES AND THERMAL
HISTORY ON THE ELECTRICAL CONDUCTION
AND CHARGE TRAPPING CHARACTERISTICS IN
CROSSLINKED POLYETHYLENE THIN FILMS
Student: Roger C. Walker II
Chair/Adviser: Dr. Michael Lanagan
Committee Members: Dr. Ramakrishnan Rajagopalan, Dr. Ralph Colby, and Dr. Mike Chung
Department of Materials Science and Engineering
Penn State University
1

2. Submarine power cable
Crosslinked polyethylene (XLPE) enables high voltage
power cable insulation
Sources: T. J. HAMMONS (2003) Power Cables in the Twenty-First Century, DOI: 10.1080/15325000390234445; https://wiki.openelectrical.org/index.php?title=Cable_Construction
Power cable insulation needs:
• High breakdown voltage
• Negligible dielectric loss
• Low conductivity
• Simple manufacture
• Reliability
• Low cost
• Simple maintenance
• Environmental friendliness
Many power cable insulation needs can be easily addressed using
XLPE due to its properties, and so it has become commonly used
Electronic
polarization only
→ low loss;
highly insulating
Simple manufacture;
connected branches
improve stability,
claimed to also
reduce conductivity
Schematic structure
of XLPE
-(CH2-CH2)n-
Ethylene repeat unit
Promotes reliable performance
at high voltages
2
The structure and properties of
crosslinked polyethylene make it
suitable for addressing these needs

3. Improving the quality of XLPE is key for its development
Sources: T. J. HAMMONS (2003) Power Cables in the Twenty-First Century, DOI: 10.1080/15325000390234445; LONG-LIFE XLPE INSULATED POWER CABLE; https://en.wikipedia.org/wiki/Submarine_power_cable
An improved control and understanding of this material
can make a big impact both scientifically and socially
3
Reduction in cable thickness enabled by removing macroscopic defects,
which also helps to enable the use of higher and higher voltages
Mitigating defects is key for enabling high performance
As macroscopic
defects are removed...
...microscopic defects
become more important.
This material can support a transition
to renewable energy... If kept clean!

4. The crosslinking process controls the structure of XLPE
4
At elevated temperatures (150 to 220°C), the
O-O bond breaks apart and crosslinks can form
DCP + heat →
Two reaction pathways proceed, leaving behind DCP byproducts in XLPE
DCP and byproduct images sourced from Sigma-Aldrich
1) β-scission
DCP radical Acetophenone (ACP)
+
Methyl
radical
Methyl radical attacks LDPE
chain or branch, creating
methane and a reactive site.
Two reactive sites → crosslink.
2) No β-scission
DCP radical attacks LDPE chain
or branch, taking hydrogen
and creating reactive sites.
Two reactive sites → crosslink.
Cumyl alcohol (aCA)
Dehydration
Methylstyrene (aMS)
+ H2O
Water
Low-density polyethylene (LDPE) is commonly
converted to XLPE using dicumyl peroxide (DCP)
1 to 2 wt% DCP
LDPE XLPE

5. Think about why ACP conductivity is so high (protons?)
DCP byproducts have a notable impact on performance
5
Sources: T. Andrews et al, "The role of degassing in XLPE power cable manufacture," doi: 10.1109/MEI.2006.253416; Y. Maeno et al, "Effects of crosslinking byproducts on space charge formation in crosslinked
polyethylene," doi: 10.1109/TDEI.2005.1394019; Y. Sekii et al, "The effects of material properties and inclusions on the space charge profiles of LDPE and XLPE," doi: 10.1109/CEIDP.2002.1048876; Computational
Materials Science 163 (2019) 134–140135; Computational and Theoretical Chemistry 1117 (2017) 188–195
Compound
Melting Point
(°C)
Relative
Permittivity
Conductivity
(S/m)
Proportion in
XLPE cable (wt%)
Response to water
Ionization
Potential (eV)
Polyethylene ~105 2.3 ~10-15 98 Hydrophobic -
Acetophenone 20 17.4 ~10-6 1.2 Hydrophilic (strong) 9.2
Cumyl alcohol 32 5.6 ~10-8 0.6 Hydrophilic (weak) 8.7
Methylstyrene -24 2.3 ~10-12 trace Hydrophobic 8.2
Goal: correlation to induced trap states within crosslinked polyethylene
General impact: increased conductivity, introduce trap states, cause space charge buildup → aging, degradation, early failure
generates ions in the presence of
moisture → bulk space charge forms
Acetophenone (ACP)
traps charge injected from electrodes;
decomposes into aMS and water
Cumyl alcohol (aCA)
assists XLPE carbonyl groups in
trapping carriers; no impact on own
Methylstyrene (aMS)

6. Degassing is used to mitigate the influence of byproducts
6
In order to address these byproducts, commercial XLPE must be degassed
Sources: T. Andrews et al, "The role of degassing in XLPE power cable manufacture," doi: 10.1109/MEI.2006.253416; J. APPL. POLYM. SCI. 2017, DOI: 10.1002/APP.44525; https://en.wikipedia.org/wiki/Submarine_power_cable
Elevated temperature and reduced
atmospheres are combined to force
out-diffusion of DCP byproducts
Factors influencing degassing time
Byproduct removal in XLPE cable insulation
Byproducts are still retained after degassing... Need to understand their impacts!
Remove DPMP
Remove DPMP
Thick cables are hard to fully degas

7. Byproducts are key determinants of electrical properties
The main goal of this work was to understand how one specific factor
impacts charge transport and trapping in XLPE: DCP byproducts
7
Objective: analyze the impacts of chemistry on XLPE electrical properties
How do each of the major DCP byproducts impact
charge storage and transport processes within XLPE?
What can influence their concentration?
1. Initial DCP concentration
2. Thermal history (degassing)
3. Intentional addition (soaking)
Adds byproducts... Removes byproducts...

8. I combined multiple types of processing and analysis into a
comprehensive study
8
Polyethylene
Melt pressing
(XL is here)
Aluminum
Polyethylene
Aluminum
Contacting
65°C,
72
hours
Polyethylene
Degassing
Polyethylene
Soaking
Focus on thermal
history Focus on byproducts
Analysis of polyethylene at various
conditions and electric fields
→ Systematically study each impact
Electrical
characterization
1. Broadband dielectric
spectroscopy
2. Conduction current
measurement
3. Thermally stimulated
depolarization current
4. Current-voltage
measurement
Physical
characterization
1. Thermogravimetric
analysis
2. Infrared spectroscopy

9. Equipment for Broadband Dielectric
Spectroscopy (BDS) analysis (Chapter 3)
Equipment for Conduction Current Measurement (CCM)
and Current-Voltage Measurement (IVM) analysis
(Chapters 4 and 6)
For more details, see the dissertation
AC and DC analysis were both applied to XLPE
9
Short discussion will be done first

10. Equipment for Thermally Stimulated Depolarization Current (TSDC) analysis
(Chapter 5)
The primary focus of this talk will be on the results from TSDC analysis
Focus is on analyzing how charge storage changes in XLPE
10

11. Effects of residual molecules
on the dielectric response of
polyethylene
Dissertation Chapter 3
Technique: Broadband Dielectric Spectroscopy (BDS)

12. Polarizable species determine the dielectric response
12
In broadband dielectric spectroscopy (BDS), the capacitance (shown here as the permittivity) is
measured as a function of the frequency and is influenced by the available polarization mechanisms.
Equipment for BDS analysis
Source: ISIJ International, Vol. 51 (2011), No. 11, pp. 1766–1772
Frequency
range for
analysis
Ultraviolet light
(PHz)
Infrared light
(GHz – THz)
Microwaves
(MHz – GHz)
Radio waves
(Hz – MHz)
Exhibited in
polyethylene
(intrinsic)
Exhibited in
polyethylene
(impurities)
𝐿𝑜𝑠𝑠 =
𝜀𝑟
′′
𝜀𝑟
′
+
-
𝜀 = 𝑛2
+
+
+

13. BDS is used to measure the dielectric loss...
13
The capacitance of LDPE and XLPE samples is measured using this technique and then translated
into other metrics such as loss, conductivity, and so on in order to analyze the dielectric properties.
Low frequency, used
for conductive losses
High frequency,
used for capacitance
Loss data taken at f ≤ 10 Hz
Equipment for BDS analysis

14. ...and analyze the temperature-dependent capacitance
14
The temperature coefficient of capacitance (TCC) can be measured using temperature-dependent
BDS and characterizes how sample capacitance changes in response to variable temperatures
Source: A G Cockbain and P J Harrop 1968 J. Phys. D: Appl. Phys. 1 1109
TCC is defined as: 𝑇𝐶𝐶 =
1
𝐶′
𝜕𝐶′
𝜕𝑇
=
1
𝜀′
𝜕𝜀′
𝜕𝑇
+ 𝛼𝑇
The temperature dependence of capacitance is controlled
by the temperature dependence of the permittivity, which
can be determined from the Clausius-Mossotti equation:
𝜀 − 1
𝜀 + 2
=
𝛼𝑚
3𝑉𝜀𝑜
𝜕
𝜕𝑇 𝜕𝜀
𝜕𝑇
= (𝜀 + 2)(𝜀 − 1)
1
3𝛼𝑚
𝜕𝛼𝑚
𝜕𝑇
− 𝛼𝑇
↓
𝑇𝐶𝐶 =
(𝜀 + 2)(𝜀 − 1)
𝜀
1
3𝛼𝑚
𝜕𝛼𝑚
𝜕𝑇
− 𝛼𝑇 + 𝛼𝑇
Polyethylene has only electronic polarization…
Assume polarizability (αm) does not vary with T and εr ≈ 2
𝐓𝐂𝐂 ≈ −𝛂𝐓
Equipment for BDS analysis

15. BDS experimental approach
15
Initial tests with as-received and degassed
polyethylene
Impacts of the crosslinking process:
increased DCP concentrations
Impacts of a DCP byproduct: acetophenone
(ACP)

16. The TCC of polyethylene: physical origins
16
Source: A G Cockbain and P J Harrop 1968 J. Phys. D: Appl. Phys. 1 1109; J. Polym. Sci. Polym. Phys. Ed., 22: 835-846.
𝑇𝐶𝐶 ≈
(2 + 2)(2 − 1)
2
−𝛼𝑇 + 𝛼𝑇
𝐓𝐂𝐂 ≈ −𝛂𝐓
For polyethylene, the TCC values
extracted from BDS are a match for αT
TCC data can be used to analyze
the structure of polyethylene
and compare between samples
LDPE data taken at f = 1 kHz
𝑇𝐶𝐶 ≈ −2𝛼𝑇 + 𝛼𝑇

17. TCC of polyethylene: impacts of residual byproducts
17
Byproducts fill in the voids present within XLPE, aiding thermal expansion
BDS data taken at f = 1 kHz
TGA data
Byproducts
Annealing
TGA data obtained by Hossein Hamedi

18. TCC of polyethylene: impacts of DCP concentration
18
If degassing is successful, then what led to these changes?
BDS
data
taken at
f = 1 kHz
TGA data
More DCP → More byproducts However, degassing = only trace concentrations
TGA data obtained by Hossein Hamedi

19. TCC of polyethylene: impacts of DCP concentration
19
Greater DCP concentrations increase this concentration of residual byproducts
TGA: Degassing apparently removes >99% of byproducts
FTIR: Chemical group associated with ACP is still present
↓
There should be a population of trapped byproducts
that cannot be removed by degassing
BDS
data
taken at
f = 1 kHz
ACP FTIR data
More DCP → More byproducts Degassed samples still show byproducts...
FTIR data obtained by Hossein Hamedi

20. TCC of polyethylene: impacts of DCP concentration
20
Residual byproduct concentrations have been confirmed by other researchers
BDS
data
taken at
f = 1 kHz
More DCP → More byproducts
Source: Chong et al.: Heat Treatment of Cross-linked Polyethylene and its effect on morphology and space charge evolution
Removal of byproducts from XLPE thin films
crosslinked with initial 2% DCP by weight.
1.4% of the weight can be removed from
these samples, matching the TGA data.
Fewer byproducts
More byproducts

21. Impacts of byproducts and annealing on the dielectric loss
21
Annealing reduces the loss...
Loss data taken at f ≤ 10 Hz
Loss data taken at f ≤ 10 Hz
...and byproducts increase it

22. Excess acetophenone causes space charge buildup in XLPE
22
Space charge buildup due to acetophenone is a hazard for XLPE!
Acetophenone (ACP)
incorporated by soaking
for two hours at 50°C
Space
charge
buildup
Space
charge
buildup
Polyethylene
Excess ACP directly
contributes to the
buildup of space charge

23. Summary of the effects of residual molecules on the
dielectric response of polyethylene
23
In general, the dielectric properties of polyethylene are dominated by residual molecules
Residual DCP byproducts
Features
1. Trapped inside microvoids
present within XLPE films
2. Increases TCC magnitude
at elevated temperatures
Initial DCP concentration
Features
1. Increases the loss when
above a threshold (≈7%)
2. Alters the TCC at both low
and high temperatures
Acetophenone
Features
1. Result of the crosslinking
process, found in voids
2. Leads to space charge
buildup at low frequencies

24. Electronic and ionic traps in
polyethylene active in
different temperature ranges
Dissertation Chapter 5
Technique: Thermally stimulated depolarization current (TSDC)

25. TSDC directly analyses charge storage and polarization
processes within dielectric materials
25
Steps
1. Apply a poling voltage (Ep) at the poling temperature
(Tp) for some amount of time (tp) to introduce charges
2. Cool the sample with the applied voltage on
3. Lock in stored charges by holding the sample at the
storage temperature (T0) with no poling
4. Measure the current released by stored charges as the
sample is heated at some ramp rate (β)
Polyethylene Polarization
+
+
-
-
+
+
+
+
-
+
Charges move in response
to the applied stresses
Tp
T0
Ep
β
tp
Polarization
Charging
Depolarization
Discharging
tp
Parameters
Tp = 90°C
Ep = 10 kV/mm
tp = 15 minutes
T0 = -150°C
β = 2.5°C/min
Responses (L to R): charge injection; dipole orientation;
space charge polarization; ionized impurities

26. TSDC directly analyses charge storage and polarization
processes within dielectric materials
26
Plan: expand the range of
examined temperatures
Steps
1. Apply a poling voltage (Ep) at the poling temperature
(Tp) for some amount of time (tp) to introduce charges
2. Cool the sample with the applied voltage on
3. Lock in stored charges by holding the sample at the
storage temperature (T0) with no poling
4. Measure the current released by stored charges as the
sample is heated at some ramp rate (β)
Tp
T0
Ep
β
tp
Polarization
Charging
Depolarization
Discharging
tp
Parameters
Tp = 90°C
Ep = 10 kV/mm
tp = 15 minutes
T0 = -150°C
β = 2.5°C/min
Responses (L to R): charge injection; dipole orientation;
space charge polarization; ionized impurities
Polyethylene Depolarization
+
+
+
+
-
+
Originally: + Originally: -

27. TSDC directly analyses charge storage and polarization
processes within dielectric materials
27
Plan: extract energy of trap states in XLPE
Heterocharge
Homocharge
Steps
1. Apply a poling voltage (Ep) at the poling temperature
(Tp) for some amount of time (tp) to introduce charges
2. Cool the sample with the applied voltage on
3. Lock in stored charges by holding the sample at the
storage temperature (T0) with no poling
4. Measure the current released by stored charges as the
sample is heated at some ramp rate (β)
Arrhenius fit is used to extract
the activation energy (EA)
𝑖 𝑇 = 𝑖0 exp −
𝐸𝐴
𝑘𝐵𝑇
Homocharge (negative current) vs heterocharge (positive
current) is defined by charge relative to the electrode
Homocharge
+
+
Originally: +
+
+
Heterocharge
-
-
Originally: +
-
-

28. TSDC experimental approach
28
Initial tests with degassed LDPE and XLPE
Thermal history: degassing at 65°C vs 90°C
Impacts of byproducts: ACP and aMS
Impacts of poling parameters on d-XLPE

29. Impact of polarity and crosslinks on charge storage
29
Three distinct homocharge peaks found in both LDPE and XLPE
Degassed XLPE Degassed LDPE

30. High temperature peak originates from charge injection
30
Prior TSDC studies for XLPE focus on cables
Goal: add focused TSDC analysis on
the impact of DCP byproducts
Cyclical TSDC of XLPE cable section
Traps at amorphous-
crystalline interfaces,
including defects
Stored charge in
crystalline regions
and amorphous-
crystalline interfaces
Charge injection from the
semiconducting electrodes
Repeated anneals led
to reduced stored
charge in crystals and
greater injected
charge at electrodes
Sources: J. Polym. Sci. B Polym. Phys., 41: 1412–1421. doi:10.1002/polb.10489; J. Polym. Sci. B Polym. Phys., 42: 4164–4174. doi:10.1002/polb.20268
Heterocharge
Homocharge
Types of traps in XLPE active at high temperature
e-
e-
e-
-
Charge injection from the
semiconducting electrodes
Traps at amorphous-crystalline
interfaces, including defects
Stored charge in crystalline regions
and amorphous-crystalline interfaces
Crystal
Crystal
Crystal
Crystal
Amorphous
e-
-
e-
e-

31. Raising the degassing temperature impacts the spectra
31
Changing the thermal history alters charge storage and suggests certain origins
Major change
to this peak
Not much change
with this peak
Potential origins for these peaks
Source:
https://polymerdatabase.
com/polymer%20physics
/GlassTransition.html
Chain Motions
Low temperature peak
characteristics
• Intensity not impacted by
density of crosslinks
• Intensity not impacted by
degassing temperature
• Observed not far from Tg
Impurities
Medium temperature
peak characteristics
• Reduced intensity in LDPE
• Reduced intensity with
harsher degassing
• Observed near or just
below room temperature

32. The origins and energies of the three distinct peaks
32
Measured energies match
well with other techniques
e-
e-
e-
H2O
Charge Injection
Impurities
Chain Motions
Source:
https://polymerdatabase.
com/polymer%20physics
/GlassTransition.html
Matches with
literature?
Yes!
(~1 eV)
Yes!
(~0.4 eV)
Yes!
(0.1–0.2 eV)

33. The origins and energies of the three distinct peaks
33
Chain Motions Impurities Charge Injection
Peak Origin Temperature Range (°C) Measured Energy (eV) Reference Energy (eV) Source
Charge Injection 93.54 ± 3.00 0.968 ± 0.495 1 [1,2]
Impurities 11.57 ± 4.39 0.387 ± 0.135 0.4 [3]
Chain Motions -65.57 ± 6.34 0.219 ± 0.080 0.1 – 0.2 [4,5]
Source:
https://polymerdatabase.com/polym
er%20physics/GlassTransition.html
Sources: 1) C. G. Garton and N. Parkman, "Experimental and theoretical investigation of conduction in polyethylene from 4 MV/m up to 'intrinsic' breakdown,“; 2) Journal of Materials Science volume 51, pages
506–512(2016); 3) H. Hamedi et al., "Electric Field Assisted Transport of the Crosslinking Byproducts in Low-Density Polyethylene,“; 4) Polymer 40 (1999) 6405–6416; 5) J. Polym. Sci. B Polym. Phys., 34: 641-648
Next step: focus on this peak!

34. Soaking XLPE in liquid byproducts to analyze their impact
34
Polyethylene
Soaking
ACP aMS
Steps
1. Degas beforehand as normal (65°C, 72 hrs)
2. Bring liquid byproduct to 50°C
3. Let polyethylene soak for two hours
4. Apply electrical contacts as normal
To examine the impact of byproducts, add them to degassed films
aCA
XLPE sample soaked with aCA
with evaporated electrode
XLPE sample (not soaked)
with evaporated electrode
XLPE sample soaked with ACP
with evaporated electrode
Successfully incorporated two
byproducts → study their impact

35. Impact of added methylstyrene (aMS) to d-XLPE
35
aMS
Changes
1. Spectra remains similar to degassed samples
2. Significant increase of trapped charge for the
middle temperature peak → additional states
aMS: alters extent of trapped charge
Significant
increase

36. Impact of added acetophenone (ACP) to d-XLPE
36
ACP
Changes
1. Spectra now exhibits only one main peak →
ACP presence can determine if peaks appear
2. Heterocharge is observed → solvation reaction
ACP: alters trapping characteristics
Homocharge
Heterocharge

37. 37
Sources: Phys. Chem. Chem. Phys., 2019,21, 22888-22894; J. Phys. Chem. A 1997, 101, 4384-4391; Journal of Electroanalytical Chemistry 554/555 (2003) 133/143; Chemical Physics Letters 519–520 (2012) 1–17
C=O --- H-O | strong hydrogen bond
C-H --- O-H | weak hydrogen bond
Reaction = negative heterocharge
Impact of added acetophenone (ACP) to d-XLPE
ACP
Changes
1. Spectra now exhibits only one main peak →
ACP presence can determine if peaks appear
2. Heterocharge is observed → solvation reaction
ACP: alters trapping characteristics
→ +
+
-
Energy = 0.8 eV
2 𝐻2𝑂 → 𝐻3𝑂+
+ 𝑂𝐻−
Energy = 0.7 eV
Two possible reaction mechanisms exist

38. 38
Sources: Y. Sekii et al, "A study on the space charge formation in XLPE“, doi: 10.1109/CEIDP.2001.963583; Y. Sekii et al, "The effects of material properties and inclusions on the space charge profiles of LDPE and
XLPE,“ doi: 10.1109/CEIDP.2002.1048876; Journal of Electroanalytical Chemistry 554/555 (2003) 133/143; Chemical Physics Letters 519–520 (2012) 1–17
More moisture → more heterocharge; can be absorbed by additives or produced by decomposition
ACP markedly enhances conductivity in
H2O when compared to other byproducts
Impact of added acetophenone (ACP) to d-XLPE
ACP
Changes
1. Spectra now exhibits only one main peak →
ACP presence can determine if peaks appear
2. Heterocharge is observed → solvation reaction
ACP: alters trapping characteristics
Heterocharge origin = H2O dissociation
PEA data
2 𝐻2𝑂
𝐴𝐶𝑃
𝐻3𝑂+
+ 𝑂𝐻−
𝑎𝐶𝐴
𝑑𝑒𝑐𝑜𝑚𝑝𝑜𝑠𝑒𝑠
𝑎𝑀𝑆 + 𝐻2𝑂
Reaction Energy = 0.7 eV
Negative ions trapped,
move upon heating

39. 39
w/ H20
w/o H20
Variation in
hydration
ACP
Changes
1. Spectra now exhibits only one main peak →
ACP presence can determine if peaks appear
2. Heterocharge is observed → solvation reaction
ACP: alters trapping characteristics
Impact of added acetophenone (ACP) to d-XLPE

40. Impact of byproducts within as-received samples
40
Similar spectra to
degassed sample w/ ACP
r-XLPE
Tmax: 26.44 ± 2.63 °C
EA: 0.675 ± 0.023 eV
d-XLPE
Tmax: 11.57 ± 4.39 °C
EA: 0.387 ± 0.135 eV
Annealing and removal
changed the trap states
Impurity-related peak had altered characteristics
between degassed and as-received samples

41. Summary of the impact of byproducts
41
aMS: alters extent of trapped charge
Contributes mainly to impurity peak
Impurities
Not studied in
detail here
Source: N. Hirai, R. Minami, T. Tanaka and Y. Ohki, "Chemical group in crosslinking byproducts responsible for charge trapping
in polyethylene," in IEEE Transactions on Dielectrics and Electrical Insulation, vol. 10, no. 2, pp. 320-330, April 2003.
Solubility
1. ACP → similar concentration as the as-received →
similar results between as-received and soaked
2. aMS →much greater concentration than in cables
→ significantly increased current when soaked
Difference due to higher solubility

42. 42
ACP: alters trapping characteristics
Determines if certain peaks appear
Sample
Peak Temperature
(°C)
Peak Energy (eV)
r-XLPE 26.44 ± 2.63 0.675 ± 0.023
d-XLPE and d-LDPE 93.54 ± 3.00 0.968 ± 0.495
d-XLPE and d-LDPE 11.57 ± 4.39 0.387 ± 0.135
d-XLPE and d-LDPE -65.57 ± 6.34 0.219 ± 0.080
d-XLPE w/ ACP 14.11 ± 10.59 0.670 ± 0.154
d-XLPE w/ aMS 90.57 ± 5.86 1.496 ± 0.567
d-XLPE w/ aMS 14.11 ± 3.59 0.351 ± 0.092
d-XLPE w/ aMS -71.07 ± 0.93 0.252 ± 0.023
Summary of the impact of byproducts

43. Impact of the TSDC poling parameters on the peaks
43
By varying the poling parameters, more information can be gleaned
Varied parameters
Ep = 10, 15, 20 kV/mm
Tp = 50, 30 °C
Right image made by Dr. Priyanka Dash (2013); further discussion can be found in the literature review and the dissertation work of Dr. Wei-En Liu (2009).
Temperature-dependence clarifies the origins of these two peaks
Defect Dipoles
Trapped Charges

44. Summary of the electronic and ionic traps in polyethylene
active in different temperature ranges
44
In general, three types of stored charge can be observed in polyethylene samples via TSDC
Source for polymer rotations image: https://polymerdatabase.com/polymer%20physics/GlassTransition.html
Chain Motions
Features
1. Observed close to the glass
transition (e.g. -65°C)
2. Not significantly impacted
by thermal history
3. Is influenced by byproducts
(reduced impact)
4. Origin: defect dipoles
Impurities
Features
1. Observed near room
temperature (e.g. 10-20°C)
2. Is influenced by thermal
history (reduced impact)
3. Is influenced by byproducts
(enhanced impact)
4. Origin: trapped charges
Charge Injection
Features
1. Observed at high
temperatures (e.g. 90°C)
2. Is influenced by thermal
history (reduced impact)
3. Is influenced by byproducts
(reduced impact)
4. Thermally activated

45. The Impacts of Impurities and Thermal History
45
Sources: https://wiki.openelectrical.org/index.php?title=Cable_Construction
XLPE enables power cable insulation...
...but has issues in dealing
with residual byproducts
Each byproduct
has its own impact
on the properties
Methylstyrene
Aids in charge trapping
Acetophenone
Promotes space charge
Control over thermal history is
needed to mitigate the impact
of these polar additives and
improve the overall properties
Submarine power cable

46. Publications in Progress
46
Based on Chapter 5 (presented today)
Based on Chapter 4
Based on Chapter 3 (presented today)

47. Presentations
47
Presented at the International Conference
on Broadband Dielectric Spectroscopy 2018
in Brussels
Presented at the International Conference on Dielectrics 2018 in Budapest
Presented at the Conference on Electrical Insulation and
Dielectric Phenomena 2019 at Pacific Northwest National Lab
Would have been presented at the
American Chemical Society National
Meeting 2020 in Philadelphia

48. Future Work
48
Other important areas that could be explored
1. Antioxidants
How do these molecules,
often used in cables, alter
the electrical properties?
3. Electrodes
e-
e-
e-
-
Charge injection from the
semiconducting electrodes
Does switching electrodes
alter the charge storing
characteristics of XLPE?
2. Time-dependence
What is the
timescale at which
charges are trapped?

49. Acknowledgements
Thanks for listening!
49
PSU – Dr. Lanagan’s Research Group
• Dr. Michael Lanagan
• Hossein Hamedi
• Cesar Nieves Sanabria
Financial Support provided by...
Additional support provided by...
• Penn State ECL
• Penn State Nanofab
• Dr. Eugene Furman
• Van Duin group