INTRODUCTION TO DESIGN AND ENGINEERING OF ELECTRICAL
INSULATION SYSTEMS FOR POWER NETWORKS
Professor K.D. Srivastava
The University of British Columbia, Vancouver, B.C. Canada
February 2015
Introduction
• At this Seminar on Insulation Technology,
our principal motivation is to describe a
design approach for large complex power
apparatus, and in the process we use our
accumulated previous experiences as best
as we can.
2
• The dominant electrical parameters, for all
gaseous insulation are:
• the local electric field, and
• the ambient gas pressure
3
• These two parameters, jointly for any
insulating gas, determine the initiation of
the ionization process, when free
electrons are present in the space where
sufficiently high electrical field is present.
• The geometry of the metallic electrodes
that create the high electric field “space”
play a crucial role in determining the
necessary local electrical field for the
gaseous insulation.
4
• The necessary initiatory electrons are
present in the high electric field space
either by cosmic radiation or by cold
electron emission from a metallic surface
that is subjected to high electric field or to
high temperature, or both.
• The gaseous insulation medium may be
open, such as open air atmosphere, or
may be enclosed within a container.
5
• The ionization characteristics of an
insulating medium are determined by its
intrinsic physio-chemical properties and its
surrounding environmental context, that
is, its specific usage for an electrical
apparatus.
• If the electrical field is sufficiently high the
insulating medium goes through a physical
process of rapidly enhancing the ionization
processes and creating a highly conducting
gaseous channel, that is, an arc.
6
• The final stages of insulation failure for all
types of electrical insulation media
(gaseous, liquid or solid) happens in a
gaseous phase.
• Also, as mentioned earlier, in all electrical
apparatus designs at least one solid
insulating surface is subjected to the full
design voltage of the specific apparatus.
7
• The most common example of an open
atmosphere gaseous application is the
aerial electrical power
transmission/distribution line.
8
9
• The electrical conductors are supported by
post insulators, or suspension insulators or
bushings at other high power apparatus
such as transformers, circuit breakers or
gas-insulated or air-insulated busbars at
substations. The support insulators are a
weak link in the insulation system. The
surface flashover strength is significantly
less than that of a gaseous gap between
the electrical power conductors, or
between the live conductors and the
ground.
10
• Other common failure modes for aerial
power lines are:
• surface pollution on the support insulators
from the ambient atmosphere
• icing of the insulator surfaces under low
temperature weather and icicle formation
• ice formation also increases the conductor
sag, thus reducing the air/gas clearance to
ground.
11
• also, under stormy conditions the live
conductors also swing (often called
“galloping”). This may cause mechanical
failure or flashover to another phase of a
three-phase 60Hz AC system.
• at some parts of the right-of-way there may
be large trees and other tall vegetation. The
right-of-way has to be regularly maintained
and kept clear.
12
• All insulation systems are also subject to
power system generated high voltage
transient overvoltages. The impact of such
system disturbances is discussed later in
this lecture. Lightning strikes will also
generate high voltage transients on aerial
power lines and the connected apparatus
such as transformers, circuit breakers, and
other equipment in a substation.
13
• However, we recognize that technology
very often depends upon a complex set of
phenomena not fully understood and are
not accessible for measurements and
observation. Nonetheless, based on our
accumulated experiences and continuing
analyses and reinterpretations, we can still
model them with reasonable accuracy.
14
• This also informs us about the mutual
interdependencies amongst the various
critical "elements" that enable the
device/apparatus to function and, in
addition help the operators understand
the ageing of the device and its various
'failure' modes . This methodology may be
described as engineering modeling
utilizing statistical methods.
15
• In electrical power apparatus three types
of insulation are used:
• gaseous
• insulating liquids
• solid insulating materials
• Interfaces between different insulation
media present significant design
challenges
16
• always one solid insulator interface, which
has significant tangential surface electric
field, and is often subjected to the full
design voltage of the specific apparatus.
The final breakdown stages always occur in
a gaseous phase
17
• The breakdown voltage of an insulation
system is a function of electric field nonuniformity. Local field enhancement can
be a crucial factor. So is the applied
voltage waveform, specifically, the rate-ofrise of voltage and the duration of
application.
18
• The density of the insulation medium also
plays an important role. In liquids and
solids local density variations occur, and
molecular interactions would play a role in
the failure processes.
19
• The breakdown voltage of an insulation
system is a function of electric field nonuniformity. Local field enhancement can
be a crucial factor. So is the applied
voltage waveform, specifically, the rate-ofrise of voltage and the duration of
application.
20
• The breakdown voltage is also dependent
upon the surface area of the electrodes,
larger the area, the lower is the withstand
voltage.
21
• Local field enhancement would contribute
to free electrons in the insulation material.
The mean free path, in dense media is
quite small (~0.5 to 2 nm), so the initial
free electrons are likely to get “trapped” or
“thermalized”. This process often leads to
“regions” of lower density in the insulation
and, is known to initiate the breakdown
process.
22
• In electrical insulation, subjected to
repetitive fast-front transients, the initial
measurable indication is Partial
Discharges(PD) in the insulation, such as
motors driven by pulse modulated power
electronics. It is important to understand
the precursor deterioration processes. For
example, generation of localized pockets
of space charges. These charge
accumulations lead to PDs and eventually
failure of the apparatus.
23
• Oil-paper electrical insulation systems have
been in use for over a century! Although
electrical grade cellulose based paper quality
has considerably improved, its aging in
service is predominantly impacted by water,
oxygen, oil acids, particulate impurities
created by other materials present in the
design, temperature of operation and the
electrical and mechanical stresses it is
subjected to in its working life. One such
process of degradation is polymerization!
24
Polymerization
• Cellulose is a polymer, composed of
repeating glucose molecule. The numbers
of glucose monomer in a polymer's chain
is called the degree of polymerization. The
DP number of unused paper is around
1,000. As the paper ages the DP value
drops, and at DP around 200, the paper is
at the end of its useful life!
25
• It would be useful to explain the basic
physical process of how a gaseous gap
between two conductors, which have a
high electric field between them,
sparkover. The following illustrate the
basic processes:
26
n = n0 exp αx
Collisional Ionization in Nitrogen-Uniform
Electric Field
n0 = electrons initially at x = 0
n = electrons at x
α = ionization coefficient for the gas
27
• Ionization processes in a gas are:
• collisions
• thermal
• radiation, including photoionization and xrays and nuclear radiations, including
cosmic rays
28
• De-ionization occurs through recombination, thermal diffusion, loss of
energy (cooling) at solid surfaces and at
metal boundaries by conduction into the
“external” electric circuit.
29
• Some gases are electronegative, that is,
affinity of molecules for “free” electrons in
the ambient gas. Examples are oxygen and
sulphur hexafluoride (SF6). This capture of
electrons by neutral molecules slows down
the ionization process, since molecules are
heavier and move slowly when an electric
field is applied.
30
• A single electron, in a uniform electric
field, multiplies exponentially – it is often
called an “avalanche” – and it has a
positive and negative charge carrier
separation. Negative at the “head” and
positive at the “tail”.
31
Flashover voltage in SF6, air and N2
Gas
SF6
Air
N2
Spacer
0.1 MPa
0.2 MPa
0.3 MPa
With spacer
122
121
123
Without spacer
61
83
95
With spacer
53
62
61
Without spacer
46
57
66
With spacer
36
54
50
Without spacer
23
31
45
32
Cable Technology - 21st
Century
• 1960s-1980s: Fluid filled systems for HV
and EHV
• 1980s-1990s: Low loss PPL systems to
match the paper laminate’s
performance for EHV
• 1970s-1990s: Parallel development of
XLPE systems from MV up
to EHV 275kV XLPE cables
in service. In Japan 500 kV
XLPE installed
33
• 1970s-1990s: Gas-filled (SF6) short lengths
installed. Many lab models
for higher voltages, including
three phase designs in a
single duct. Also, SF6 /N2
• 1990s:
500 kV mass impregnated
paper for submarine DC
systems in the Baltic Sea
• 1970s-1990s: Low temp. cryogenic/supercon.
designs tried. 1990s witnessed
the phenomenal growth in HTS
technology
34
Power Ratings:
for conventional cable
technologies
1. Paper fluid-filled
100%
2. PPL fluid-filled
~120%
3. XLPE
~110%
35
Insulation Thickness: for
conventional cables from 1990
to 1998
500kV - from ~35mm down to 25mm
220kV - from ~24mm down to >20mm
132kV - from ~22mm down to >15mm
36
Design Stresses:
for conventional cables
Paper - from 10kV/mm to ~15kV/mm
PPL - from ~18kV/mm to ~20kV/mm
XLPE - from ~5kV/mm to ~35kV/mm
[Theoretical maxm. stress in 100% SF6 is
~89kV/cm.bar]
37
Energy and Industrial Culture
•
Post World War II, energy (all forms)
usage was growing at the rate of ~3%
per year, in industrial nations
38
•
But in industrial nations electricity
usage was growing by more than 7%
by displacing other forms of energy
•
With oil crisis of 1970s and the
growing environmental movement,
the energy picture is very different
now!
39
•
In Europe (Western) and North
America the electricity usage is
almost constant. In developing
countries, however, the usage is
growing between 7 and 10% per year.
•
With declining “confrontation”
between major world powers, the
prospects for rapid world economic
growth are pretty good.
40
•
The availability of useful forms of
energy is not equal worldwide, and
there are major geographical barriers
to the movement of energy in the
world.
•
There is considerable world
experience in transporting oil, natural
gas and electricity over long distances
(thousands of km)
41
Present Status of “Conventional”
Cable Technology
•
Both oil-paper and polymeric cables up
to 500 kV system voltage are in service
and commercially available.
•
Experimental designs of oil-paper cable
have been tested for both 750 kV and
1000 kV.
42
•
Cost differentials for such cable when
compared to overhead lines are in
excess of 25:1 (some estimates put this
as high as 40:1).
43
•
Cellulose paper will have to be replaced
by synthetic polypropylene paper or a
composite.
•
Impregnating mineral oil will have to be
replaced by more acceptable (from
environmental point-of-view) alkyl
benzenes.
44
•
At such high operating voltages the
margin to the high voltage “intrinsic”
breakdown is lower. Hence very high
oil pressures (~20 atmospheres) and
very high quality control is needed.
45
•
Technology of making joints is still in an
experimental/development stage.
•
Conventional cable technology is very
well established and over the past 100
years there have been many
technological improvements.
46
•
Compressed gas cable technology has
matured over the last 30 years, but its
potential for bulk power transport is
yet to be exploited and developed.
47
•
High temperature superconductor
technology is developing rapidly but
[is] not yet fully commercially viable for
bulk power transport.
•
None of the above three are free from
technological areas of concern!
48
•
Geographically and technologically
South Africa has the potential and
opportunity to play an important
strategic role.
•
This prospect raises the technological
and economic question of:
 How does one move large amounts
of electrical energy to major urban
centres?
49
•
Over sparsely populated areas,
overhead lines are, perhaps, the only
proven and economic option for long
distances.
•
However, near urban centres overhead
lines are no longer acceptable to the
communities for environmental and
aesthetic reasons.
50
•
What are the alternatives?
•
Three choices in technology:
 Conventional underground power
cables
 Compressed gas cables (SF6 - Sulphur
Hexa-fluoride)
 Superconducting cables
51
52
53
54
55
56
57
58
59
60
Why GIS?
Why GITL?
•
Land costs in urban areas
•
Aesthetically “superior” to air insulated
substations
•
Not affected by atmospheric pollution
61
•
Completely sealed (metal-clad) permits
very low maintenance
•
Demand for higher energy usage in urban
areas requires increased transmission
voltages; for example, 420 kV
62
GITL
•
In addition to the advantages listed above
for GIS, there is a need for non-aerial
transmission lines near urban areas.
63
•
There are currently only two alternatives:
 Underground cables–conventional or
superconducting, or
 Gas Insulated Transmission Lines (GITL)
•
GITL, compared to underground cables,
have the additional advantage of reduced
ground surface magnetic fields.
64
Design Features of GIS/GITL
•
GIS/GITL installations have the usual
components:
•
Circuit breakers; disconnect,
earthing/grounding switches
•
Current and voltage measuring devices
•
Busduct sections
•
Variety of diagnostic/monitoring devices
65
•
Installations from distribution voltages
right up to the highest transmission
voltages (765 kV) have been in service for
30 years or more. Both isolated-phase and
three-phase designs are in use.
66
•
SF6 is the insulating medium at a pressure
of 4 to 5 atmospheres. GITL units are
factory-assembled in lengths of 40 to 50
feet.
67
•
The phase conductor is almost always of
aluminium. The outer enclosure is also of
aluminium, although earlier designs used
mild steel. For lower voltages, stainless
steel has also been used.
68
•
Usually busducts are of rigid design
although flexible and semi-flexible designs
have been proposed. None are in use.
69
70
Typical Cable Section
71
72
Growth of GIS
Growth of GIS Installations
Before 1985 January
After 1985 January
Voltage
GIS
CB-Bay-Yrs.
GIS
CB-Bay-Yrs.
1
230
28669
731
28215
2
227
21252
382
12808
3
123
10362
147
5678
4
45
3870
65
2904
5
26
3252
37
1273
6
-
-
2
200
751
67,405
Total
51,078
Voltage Class
1
60 – 100 kV
2
100 – 200 kV
3
200 – 300 kV
4
300 – 500 kV
5
500 – 700 kV
6
>700 kV
73
5.
Current Transformer
6.
Potential Transformer
7.
Bus Section
8.
Cable Termination
74
75
76
77
78
79
80
81
82
83
84
85
Expansion joint
SF6
• Sulphur hexafluoride is a man-made gas,
and it is an electronegative electron
attaching gas. It has been in industrial use
for almost a century. Since its introduction
in major equipment for electrical power
industry, it has raised some serious
environmental concerns.
86
• Before WWII it was mainly used as a tracer
gas. With the advent of nuclear power
generation, its use increased for refining
uranium ore. It is included in the Kyoto
Protocol.
• SF6 is an excellent electrical insulating gas
and has been used in power circuit
breakers, gas insulated substations (GIS)
and more recently in Gas Insulated
Transmission Lines (GIL).
87
• Its main physical properties are:
• basic electric breakdown strength 89 kV/cm
• normal condensation temperature 63°
• Its thermal properties are also very
favourable for application in GIS/GIL.
However, under arcing conditions its
byproducts are both corrosive and toxic.
The operative standards require it to be
reclaimed and recycled.
88
Oil-Paper Composite Insulation
• There have been investigations for
assessing the usefulness of vegetable oils
in electric power apparatus as an
impregnating insulation medium. The
main components of such oils are
triacylglycerols, the fatty acid components
vary quite a lot. These are more prone to
oxidation.
89
• The three main chemical processes of
insulation degradation are called
hydrolysis, oxidation and pyrolysis. The
degradation by-products are carbon
monoxide, carbon dioxide, various organic
acids, water, and free glucose molecules.
Free glucose molecules can decompose
further into a class of compounds called
furans. These different compounds can be
monitored and analyzed in the context of
insulation deterioration and the applied
external stresses.
90
• In the longer term the higher fatty acid
content protects the paper surface from
further degradation, and also lowers the
water content in the treated paper
insulation. For similar reasons the Furanic
content, at the same level of DP, is also
less in paper treated with vegetable oilsthis is also an advantage.
91
• Published good reviews of the current
methods for measuring space charges in
dielectrics. The resolution
• capability is as high as 2 micrometer, but
the sample thickness for such high
resolution is also low, (<200 micrometer).
Deconvolution of the measurements in
some cases is necessary to get the actual
distribution of the space charges within
the sample.
92
• Accumulated pockets of charge in
composite and solid insulation systems
have a very significant impact on
• the electric breakdown, aging and
dielectric losses. For the oil-paper
composites the energy loss is very
important. However, for the longer-term
failure modes the frequency of partial
discharges (PDs) accelerates the failures.
93
Experimental Studies of FastFront Transients in
Oil Impregnated Paper
Insulation System
94
• In modern electric power systems there is
a significant increase of power electronics
devices such as :
• inverters/converters for HVDC
• numerous applications for renewable
energy apparatus
• Such equipment generates repetitive fastfront-transients, and those transients are
known to cause failure of oil-paper
insulation systems in motors and
transformers
95
• The impact of high power powerelectronics devices adds to the impact of
vacuum interrupters and compressed gas
insulated substations equipment which are
known to generate fast-front transient
overvoltages.
• In Europe and Canada aging studies of oilpaper insulation systems, subject to fastfront transient overvoltages, have been
undertaken for over 25 years.
96
• In this paper, two such studies are
described and the findings are discussed.
97
Re-striking process at opening
of vacuum circuit breaker
98
Applied voltage: 300kV, 0.4 MPa (SF6)
(81kV/div, 20 ns/div
FTO waveform measured by 1-GHz surge sensor
Source: M.M. Rao & M.S. Naidu, III Workshop on EHE Technology,
Bangalore, India, 1995.
Case Study A: High Power
Electronic Switching Systems
• Industrial applications high capacity power
electronics devices are now ubiquitous
• Many components of such energy
conversion systems make extensive use of
composite oil-paper insulation in motors
and transformers
100
• Numerous equipment failures have been
reported. A comprehensive laboratory
study of such electrical insulation failures
has been reported in Europe
101
• The technology of power inverters and
converters is very well established in
power systems and numerous industrial
applications. It utilizes fast solid-state
switching devices, such as rectifiers,
thyristors, inverted gate bipolar transistors
(IGBT) and MOSFETS. Pulse width
modulation methodology is commonly
used
102
• A high quality AC waveform switching
device operates at higher frequencies up
to 10 kHz
• In one study the rise time of a “square
wave” was changed and the impact on the
time to failure was measured; the
insulation tested was for an adjustable
speed motor
103
• The circuit diagrams for these test voltages
are shown in Figures 1a & 1b, and Figures
2a & 2b show the actual applied voltages
to the insulation test samples
104
Figure 1a
105
Figure 1b
106
Figure 2a
107
Figure 2b
108
• Figure 3 shows the test samples with
noted visual differences.
109
Figure 3
110
• Figure 4 shows that the time to failure
decreases as the rate of rise of the applied
voltage pulse is increased. In the European
study, a spark generator has been
designed to observe the impact of fastfront overvoltage on electrical insulation
systems
111
Figure 4
112
• Two different types of test voltages used in
the experimental work:
• a combination of power frequency (50Hz)
with a superimposed high frequency
modulating signal
• a double-exponential fast-front impulse
• The modulated power frequency
waveform is 50Hz with a peak magnitude
of 5 kV. The modulating frequency is 10
kHz with a peak magnitude of 1 kV.
113
• A typical single fast-front pulse is also
shown. Its peak magnitude and the rateof-rise of fast-front can be varied. The
modulated power frequency waveform is
used for insulation aging studies, and the
single double exponential pulses are used
to explore the physical processes for
insulation deterioration. Single pulse
polarities can also be reversed.
114
• In the European studies kraft paper
0.06mm in thickness was used and was
impregnated with Shell Diala B. the AC
breakdown of the paper sample is 3.2 kV
rms. The IEC standard IEC 60243 was
followed for these studies. Both positive
and negative voltage polarities were used.
115
• When oil-paper insulation samples were
subjected to a modulated power
frequency voltage and fast repeating
higher frequency components, ranging
between 0.5 kHz and 10 kHz of bipolar
pattern, rate of rise 1 kV/µs and average
magnitude of 1 kV:
116
• 1. The average value of breakdown was 3.2
kV superimposed
• 2. At 5 kHz, 8 kHz and 10 kHz, with a peak
transient magnitude of 1 kV and power
frequency magnitude of 2.91 kV, the average
time to insulation failures were 22, 12.5 and
10.1 hours respectively.
117
• In the absence of high frequency
superimposed transients, the power
frequency breakdown delay was about 168
hours. Clearly the observed failures in service
may be attributed to the high frequency
transients generated by power electronics
high speed switching.
118
• The power loss measurements (Tan δ) also
show very significant increases.
• The insulation paper samples were also
inspected visually
• The samples subjected to high frequency
transient show signs of carbon deposits,
perhaps due to local partial discharges.
119
• It should be noted that in these European
studies, the fast-front transient is
superimposed on top of the power frequency
(50 Hz) applied voltage. This is very different
from the case study B, described below,
where the magnitude of the fast-front
transient is significantly higher than the
power frequency applied voltage.
120
Case Study B: GIS Fast-front
Transient Impact on Oil Paper
Insulation
• Numerous failures of transformers and their
bushings connected to compressed gas
insulated substations have been reported, for
system voltages from 220 kV to 765 kV
121
• Field tests showed that fast-front transients,
up to 1.2 per unit peak voltages with a
risetime of 25 ns could be attributed to GIS
disconnect switch operation. The principal
gaseous insulation in GIS is sulphurhexafluoride gas, which is an electronegative
gas.
122
• In 1980 the Canadian Electrical Association
sponsored a laboratory study to explore the
possible behavior of oil-paper insulation
when repetitive fast-front impulses were
applied to samples of oil-paper insulation
123
• The experimental work was done at the BC
Hydro research laboratory, Powertech Labs
Inc., in Surrey, BC, Canada
124
• A special pulse generator and a special
electrode system were designed for this
purpose
125
A special pulse generator and a special
electrode system were designed for
this purpose
126
A special pulse generator and a special
electrode system were designed for
this purpose
127
A typical fast-front impulse
waveform
128
• The fast-front high voltage pulse generator,
for peak voltages up to 100 kV, could be
synchronized with a half wave 60 Hz power
source and is capable of generating impulses
at the rate of 1500 pulses per minute, that is
up to 2.5 million per day.
129
• In addition to the custom built pulse
generator tests were also done with DC and
60 Hz voltage and standard lighting impulse
1.2/50µs and 5.7/130µs and switching
impulses and a fast-front impulse (10 ns/2500
µs).
130
• Test samples were one, two and three layers
of 0.076 mm thick kraft paper, one layer of
0.254mm thick kraft paper, one layer of 0.76
mm thick Nomex paper and one layer of
0.254mm thick polyester sheet. Two kinds of
impregnants were used: standard
transformer oil and a high fire-point oil.
131
Effect of Risetime
Sample
0.076 mm
kraft
paper
0.254 mm
kraft
paper
Layers
FFI
LI
(base)
one
0.85
1
1.15
two
0.93
1
1.16
three
0.93
1
1.17
one
0.90
1
1.03
SI
132
Results for Different
Thicknesses of Kraft Paper
Sample
FFI
(kV/mm
)
0.076mm
155
182
210
0.254 mm
142
156
160
Difference
8%
15%
24%
LI
SI (kV/mm)
(kV/mm)
133
Effect of Number of Layers on V50
Value (0.076 mm thick kraft paper)
Sample
FFI
(kV/mm
)
0.076mm
155
182
210
0.254 mm
142
156
160
Difference
8%
15%
24%
LI
SI (kV/mm)
(kV/mm)
134
V50 Results for Different Impregnants
(0.076 mm thick kraft paper)
Oil Type
FFI
LI (kV/mm)
(kV/mm)
SI (kV/mm)
Transformer Oil
155
182
210
High Fire Point
Oil
190
201
196
Difference
-18%
-10%
7%
135
Discussion and Conclusions
• In both case-studies described above, the
laboratory investigations were triggered by a
large number of equipment failures in the
industry
136
• In both case studies, the focus of the
laboratory investigations has been the oilpaper insulations system, since it is very
extensively used in a wide range of voltage
classes from HV to UHV.
137
• As the equipment use continues, in time,
pockets of space charges develop in the
insulation systems. These space charge
discontinuities play a very major role in the
aging and failure modes of the apparatus and
equipment.
138
• Several factors, including the quality of
materials, the sample preparation, the
applied voltage magnitude and waveform
and the number of fast-front pulses and the
intervals between the impulses are just a few
factors that would impact the aging
phenomena is the field.
139
• There are some overall impacts of fast-front
repetitive applications on power apparatus
and devices. For example, the breakdown
electrical strength reduces as the risetime
gets shorter.
140
• Both the European results and the Canadian
results confirm this, albeit that the voltage
magnitudes and the context of the operation
of the specific equipment are quite different
141
• In another aspect these are different since
the power system operating voltages are
vastly different, in the case of European
investigation and the Canadian one.
142
• Increasing the number of impulse
applications at higher system operating
voltage does reduce the safe impulse electric
field magnitudes
143
• The results for the power electronics
application may also indicate: longer term
aging is present in lower system voltage
applications.
144
• The breakdown phenomena have to be
studied in order to understand the deeper
physical/chemical processes that may be
determining the deleterious impact on
insulation ageing and useful lifetime of
composite oil-impregnated paper/cellulose
insulation systems.
145
• Current work may provide a better
understanding of the failure modes of the
complex composite insulation systems.
146
• It is evident from the accumulated results of
laboratory studies and the industry's
manufacturing, testing and field experience
that the impregnated oil-paper insulation
system is a very complex combination of
material, processing technologies and very
poorly understood physical and chemical
processes during manufacturing and contexts
under which the equipment is used in the
field.
147
• The equipment designers, manufacturers and
industrial users, for almost over a century,
have oversimplified the physical/chemical
framework under which in practice the
insulation must operate in apparatus and
equipment. The focus has been on adopting a
phenomenological approach.
148
• A very useful set of design criteria, material
selection, manufacturing practices and
development testing protocols have served
the industry well. The good news is that, in
the last several decades very useful research
and development has taken place in
industrial countries.
149
• Major long-term basic research and R&D is
currently underway. References are two such
examples of research, development,
fundamental measurement techniques and
testing protocols.
150
Thank you!
151