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Impact of Fast-Front Overvoltage Transients on Electrical Oil-Paper Insulation Systems


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Title: Impact of Fast-Front Overvoltage Transients on Electrical Oil-Paper Insulation Systems

Professor K.D. Srivastava
The University of British Columbia, Vancouver,
B.C. Canada February 2015
  • 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.

  • The dominant electrical parameters, for all
    gaseous insulation are
  • the local electric field, and
  • the ambient gas pressure

  • 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
  • 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.

  • 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.

  • 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.

  • 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.

  • The most common example of an open atmosphere
    gaseous application is the aerial electrical
    power transmission/distribution line.

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  • 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.

  • Other common failure modes for aerial power lines
  • 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.

  • 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.

  • 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.

  • 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.

  • 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.

  • 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

  • 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

  • The breakdown voltage of an insulation system is
    a function of electric field non-uniformity.
    Local field enhancement can be a crucial factor.
    So is the applied voltage waveform, specifically,
    the rate-of-rise of voltage and the duration of

  • 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

  • The breakdown voltage of an insulation system is
    a function of electric field non-uniformity.
    Local field enhancement can be a crucial factor.
    So is the applied voltage waveform, specifically,
    the rate-of-rise of voltage and the duration of

  • The breakdown voltage is also dependent upon the
    surface area of the electrodes, larger the area,
    the lower is the withstand voltage.

  • 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.

  • 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.

  • 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!

  • 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!

  • 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

  • n n0 exp ax
  • Collisional Ionization in Nitrogen-Uniform
    Electric Field
  • n0 electrons initially at x 0
  • n electrons at x
  • a ionization coefficient for the gas

  • Ionization processes in a gas are
  • collisions
  • thermal
  • radiation, including photoionization and x-rays
    and nuclear radiations, including cosmic rays

  • De-ionization occurs through re-combination,
    thermal diffusion, loss of energy (cooling) at
    solid surfaces and at metal boundaries by
    conduction into the external electric circuit.

  • 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.

  • 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.

Flashover voltage in SF6, air and N2
Gas Spacer 0.1 MPa 0.2 MPa 0.3 MPa
SF6 With spacer 122 121 123
SF6 Without spacer 61 83 95
Air With spacer 53 62 61
Air Without spacer 46 57 66
N2 With spacer 36 54 50
N2 Without spacer 23 31 45
Cable Technology - 21st Century
  • 1960s-1980s Fluid filled systems for HV
    and EHV
  • 1980s-1990s Low loss PPL systems to match
    the paper laminates 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

  • 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

Power Ratings for conventional cable
  1. Paper fluid-filled 100
  2. PPL fluid-filled 120
  3. XLPE 110

Insulation Thickness for conventional cables
from 1990 to 1998
  • 500kV - from 35mm down to 25mm
  • 220kV - from 24mm down to gt20mm
  • 132kV - from 22mm down to gt15mm

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

Energy and Industrial Culture
  • Post World War II, energy (all forms) usage was
    growing at the rate of 3 per year, in
    industrial nations

  • 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!

  • 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.

  • 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)

Present Status of Conventional Cable Technology
  • Both oil-paper and polymeric cables up to 500 kV
    system voltage are in service and commercially
  • Experimental designs of oil-paper cable have been
    tested for both 750 kV and 1000 kV.

  • Cost differentials for such cable when compared
    to overhead lines are in excess of 251 (some
    estimates put this as high as 401).

  • 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.

  • 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.

  • 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.

  • Compressed gas cable technology has matured over
    the last 30 years, but its potential for bulk
    power transport is yet to be exploited and

  • 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!

  • 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?

  • 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.

  • What are the alternatives?
  • Three choices in technology
  • Conventional underground power cables
  • Compressed gas cables (SF6 - Sulphur
  • Superconducting cables

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Why GIS? Why GITL?
  • Land costs in urban areas
  • Aesthetically superior to air insulated
  • Not affected by atmospheric pollution

  • Completely sealed (metal-clad) permits very low
  • Demand for higher energy usage in urban areas
    requires increased transmission voltages for
    example, 420 kV

  • GITL
  • In addition to the advantages listed above for
    GIS, there is a need for non-aerial transmission
    lines near urban areas.

  • There are currently only two alternatives
  • Underground cablesconventional or
    superconducting, or
  • Gas Insulated Transmission Lines (GITL)
  • GITL, compared to underground cables, have the
    additional advantage of reduced ground surface
    magnetic fields.

Design Features of GIS/GITL
  • GIS/GITL installations have the usual components
  • Circuit breakers disconnect, earthing/grounding
  • Current and voltage measuring devices
  • Busduct sections
  • Variety of diagnostic/monitoring devices

  • 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.

  • 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.

  • 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.

  • Usually busducts are of rigid design although
    flexible and semi-flexible designs have been
    proposed. None are in use.

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Typical Cable Section
  • Growth of GIS

  • Growth of GIS Installations

  1. Current Transformer
  2. Potential Transformer
  3. Bus Section
  4. Cable Termination

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Expansion joint
  • 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.

  • 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).

  • 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.

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.

  • 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.

  • 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 oils-
    this is also an advantage.

  • Published good reviews of the current methods for
    measuring space charges in dielectrics. The
  • capability is as high as 2 micrometer, but the
    sample thickness for such high resolution is also
    low, (lt200 micrometer). Deconvolution of the
    measurements in some cases is necessary to get
    the actual distribution of the space charges
    within the sample.

  • 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.

Experimental Studies of Fast-Front Transients
inOil Impregnated Paper Insulation System
  • 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
  • Such equipment generates repetitive
    fast-front-transients, and those transients are
    known to cause failure of oil-paper insulation
    systems in motors and transformers

  • The impact of high power power-electronics
    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 oil-paper
    insulation systems, subject to fast-front
    transient overvoltages, have been undertaken for
    over 25 years.

  • In this paper, two such studies are described and
    the findings are discussed.

Re-striking process at opening of vacuum circuit
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
  • 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

  • Numerous equipment failures have been reported. A
    comprehensive laboratory study of such electrical
    insulation failures has been reported in Europe

  • 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

  • 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

  • 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

Figure 1a
Figure 1b
Figure 2a
Figure 2b
  • Figure 3 shows the test samples with noted visual

Figure 3
  • 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 fast-front overvoltage on electrical
    insulation systems

Figure 4
  • 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

  • A typical single fast-front pulse is also shown.
    Its peak magnitude and the rate-of-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.

  • 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.

  • 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

  • 1. The average value of breakdown was 3.2 kV
  • 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

  • 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.

  • The power loss measurements (Tan d) also show
    very significant increases.
  • The insulation paper samples were also inspected
  • The samples subjected to high frequency transient
    show signs of carbon deposits, perhaps due to
    local partial discharges.

  • 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.

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

  • 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 sulphur-hexafluoride gas,
    which is an electronegative gas.

  • 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

  • The experimental work was done at the BC Hydro
    research laboratory, Powertech Labs Inc., in
    Surrey, BC, Canada

  • A special pulse generator and a special electrode
    system were designed for this purpose

A special pulse generator and a special electrode
system were designed for this purpose
A special pulse generator and a special electrode
system were designed for this purpose
A typical fast-front impulse waveform
  • 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.

  • 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).

  • 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.

Effect of Risetime
Sample Layers FFI LI (base) SI
0.076 mm kraft paper one 0.85 1 1.15
0.076 mm kraft paper two 0.93 1 1.16
0.254 mm kraft paper three 0.93 1 1.17
0.254 mm kraft paper one 0.90 1 1.03
Results for Different Thicknesses of Kraft Paper
Sample FFI (kV/mm) LI (kV/mm) SI (kV/mm)
0.076mm 155 182 210
0.254 mm 142 156 160
Difference 8 15 24
Effect of Number of Layers on V50 Value (0.076 mm
thick kraft paper)
Sample FFI (kV/mm) LI (kV/mm) SI (kV/mm)
0.076mm 155 182 210
0.254 mm 142 156 160
Difference 8 15 24
V50 Results for Different Impregnants (0.076 mm
thick kraft paper)
Oil Type FFI (kV/mm) LI (kV/mm) SI (kV/mm)
Transformer Oil 155 182 210
High Fire Point Oil 190 201 196
Difference -18 -10 7
Discussion and Conclusions
  • In both case-studies described above, the
    laboratory investigations were triggered by a
    large number of equipment failures in the

  • In both case studies, the focus of the
    laboratory investigations has been the oil-paper
    insulations system, since it is very extensively
    used in a wide range of voltage classes from HV
    to UHV.

  • 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.

  • 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.

  • 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.

  • 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

  • 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.

  • Increasing the number of impulse applications at
    higher system operating voltage does reduce the
    safe impulse electric field magnitudes

  • The results for the power electronics application
    may also indicate longer term aging is present
    in lower system voltage applications.

  • 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.

  • Current work may provide a better understanding
    of the failure modes of the complex composite
    insulation systems.

  • 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

  • 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.

  • 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

  • Major long-term basic research and RD is
    currently underway. References are two such
    examples of research, development, fundamental
    measurement techniques and testing protocols.

Thank you!
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