FIELD OF THE INVENTION:
[0001] The present invention relates to a high voltage composite insulator or more
particularly composite long rod (elongated) insulator (CLR) for ± 800 kV HVDC
transmission lines with a minimum level of electromechanical strength of 420 kN. Further,
the present invention also provides a fabrication method for manufacturing such electrical
insulators.
BACKGROUND AND PRIOR ART OF THE INVENTION:
[0002] Composite insulators have been witnessing increased popularity primarily because
of significant advantages, i.e., shorter string length under pollution, less weight, easy
manufacturing, lower price and no requirement for periodic cleaning etc. With the
advancement of new materials for interface, high-strength FRP support structures, HTV
silicone compounds etc., and also availability of new generation fabrication equipments
that facilitate manufacturing of composite insulators with precision with advanced quality
control in the course of manufacturing, its popularity has increased in recent years.
[0003] Composite insulator is normally fabricated by an injection molding method by
using an appropriate insulating polymeric material, such as, silicone rubber, ethylene
propylene copolymer (EPM), ethylene-propylene-diene copolymer (EPDM), and or
polyurethane, etc. structure of which is generated in the forms of sheds on the surface of
an elongated core rod of fiber-reinforced plastics (FRP).

[0004] US patent number 5540991A dated July 30, 1996 (by Koji Hayakawa et. al., NGK
Insulators Ltd., Japan) describes the fabrication of composite insulator that include a FRP
core rod and a sheath which is formed by integrally moulding an insulating polymeric
material to cover the core rod over substantially the entire length thereof. The sheath is
composed of a plurality of moulded portions which are aligned with each other in the axial
direction of the core rod. Adjacent moulded portions of the sheath are arranged relative to
each other so that a gap is left between the opposite ends of the moulded portions. The
gap is filled by a joint insulating material which is integrally united to the polymeric
material of the adjacent moulded portions.
[0005] In another invention by NGK Insulators Ltd., Japan (Tetsuhiko Abe et. al.), in the
patent number US5938998A dated August 17, 1999 describes the method and apparatus
for manufacturing composite insulators which include a FRP core rod covered by a sheath
and provided with a plurality of sheds which are made of an electrically insulating
polymeric material. The sheds are set on a support member arranged on a downstream
side of an extruder. The extruder is fed with a core rod and extrudes a polymeric material
to form a sheath on the core rod. The core rod with the sheath is moved toward the
downstream side through an opening in the support member. The sheds are sequentially
moved along the support member toward the downstream side and transferred onto
predetermined locations on the sheath that have passed through the opening and have
reached the downstream side. An assembly is thus formed which includes the core rod,
sheath formed on the core rod, and sheds transferred onto the sheath. The assembly is
then heated to vulcanize the sheath and adhere it to the core rod and the sheds.

[0006] US patent number 6930254B2 dated August 16, 2005 (by Electric Power Research
Institute, Andrew J. Philips et. al.) describes a composite insulator containing means for
providing early warning of impending failure due to stress corrosion cracking, flash-under,
or destruction of the rod by discharge activity conditions. In this invention, a composite
insulator comprising a fiberglass rod surrounded by a polymer housing and fitted with
metal end fittings on either end of the rod is doped with a dye-based chemical dopant.
The dopant is located around the vicinity of the outer surface of the fiberglass rod. The
dopant is formulated to possess migration and diffusion characteristics correlating to those
of water, and to be inert in dry conditions and compatible with the insulator components.
The dopant is placed within the insulator such that upon the penetration of moisture
through the housing to the rod through a permeation pathway in the outer surface of the
insulator, the dopant will become activated and will leach out of the same permeation
pathway. The activated dopant then creates a deposit or stain on the outer surface of the
insulator housing. The dopant comprises a dye that is sensitive to radiation at one or more
specific wavelengths or is visually identifiable. Deposits of activated dopant on the outer
surface of the insulator can be detected upon imaging of the outer surface of the insulator
by appropriate imaging instruments or the naked eye.
[0007] US patent number 20050120975A1 dated June 09, 2005 by Takanori Kondo, NGK
Insulators Ltd., Japan described how to prevent breakage of a cover member of a polymer
insulator caused by pecking by a bird, through use of an avian repellent which is carried
by the polymer insulator and an avian repellence maintained at least during construction
of power transmission equipment, thereby inhibiting pecking of the polymer insulator by

birds. The bird-pecking-preventive polymer insulator according to the invention includes
an insulator body, and a holding metal piece is fitted on each end of the insulator body,
the insulator body being composed of a core member is formed of a reinforced plastic
material and a cover member is formed of a rubber material and covering the periphery of
the core member, wherein the cover member is carries an avian repellent such as
capsaicin.
[0008] LS Cable and Systems Ltd. (Bok HeeYoun et. al.) in the patent number
US7165324B2 dated January 23, 2007 disclosed a method for manufacturing a composite
high-voltage insulators in which a plurality of skirts are manufactured and joined to a rod,
and more particularly to a method for manufacturing a composite high-voltage insulator in
which an expanding pipe is inserted into a plurality of skirts arranged in a line by a skirt
holder to expand the inner diameters of the skirts, so that the skirts are mounted on
precise positions of the rod, and an adhesive agent is easily applied, so that an interface
between different materials is not formed in order to improve reliability of insulator
products.
[0009] Patent No. WO2008074765A1 dated June26, 2008 (by Patrick Meier et. al., ABB
Research Ltd., Sweden) describes the manufacturing an electric insulator, comprising an
electric insulation and a semiconducting layer, forming on an outermost surface of the
insulator that faces the surrounding environment, wherein said semiconducting layer
comprises a polymer matrix, particles of a material that confers a semiconducting
character to said layer, said particles being dispersed in said matrix comprise
nanostructures. This invention is also related to the use of such an insulator in a moisture-
containing environment, in particular an environment that contains particulate matter that
will be deposited on an outer surface of said insulator, such as an out-door environment,

in which the semiconducting layer is subjected both to humidity and contamination.
[0010] Lapp Insulators Ltd., Germany by Heinz Denndörfeet. al., in the patent number
EP2243145B1 dated January 23, 2013 describes a field-controlled composite insulators in
which the materials of the fabricated insulators are greatly stressed by the
inhomogeneous distribution of the electric field across the surface thereof in the material
design. The field strength changes particularly in the region of the fittings due to the
transition from the insulating materials of the shields and the insulator core to a metal
material, due to the transition from the ground potential at the cross arm, or to the
conductor potential at that location, where the conductor cables are attached. A further
cause is the deposit of dirt, which is stress affecting an insulator overall. This invention
provides that a field control layeris disposed between the core and the protective layer, in
at least one section of the insulator, the said control layer comprising particles as the filler,
which influence the electric field of the insulator.
[0011] Another invention on similar field-controlled composite insulator by the Lapp
Insulators GmbH, Germany (Heinz Denndoerfe et. al.) under the US patent number
8637769B2 dated January 28, 2014 is reported that describes uses of materials which are
greatly stressed by an inhomogeneous distribution of an electrical field across a surface
thereof.
[0012] Another further invention on field controlled composite insulator by
Maschinenfabrik Reinhausen GmbH, Germany (Dieter Dohnal et. al.) in the patent number
DE102012104137A1 dated November 14, 2013 disclosed a configuration comprising e.g.
rod, core, shielding sheath and field control layer that is applied by plasma coating to the

core, where dielectric properties are controlled by geometric structure of field-control
layer. The field control layer is designed as active or excessive irregular stripe pattern that
extends diagonally, where thickness and width of the field control layer decrease or
increase over the length of the core. The field control layer is applied for dielectric barrier
discharge.
[0013] Patent number CN103165247B dated September 02, 2015 discloses the design of a
novel long-rod type porcelain composite insulator. The long-rod type porcelain composite
insulator comprises an insulator body, wherein an outer insulating umbrella skirt sheath is
arranged outside the insulator body; hardware fittings are cemented at two ends of the
body; a mounting inner hole of each hardware fitting is in a saw-tooth shape; and the
outlet end of each hardware fitting is in a circular arc shape, and a rectangular groove is
formed outside the outlet end. Due to the adoption of reasonable structural design and
high-quality production raw materials and the selection of an advanced manufacturing
process, the long rod type porcelain composite insulator has high electromechanical
properties. According to the long-rod type porcelain composite insulator, high-temperature
vulcanized silicon rubber is used as the outer insulating umbrella skirt sheath, high-
strength ceramic is used as internal insulation, and the end fittings are cemented by using
high-strength silicates through a amplitude varying process to manufacture the porcelain
composite insulator. As per the invented so-called‘long-rod porcelain composite insulator’,
the accidents of brittle failure and string breakage can be avoided, and the problem of
external insulation pollution flashover of the porcelain insulator is solved, so that the long
rod type porcelain composite insulator is high in mechanical and electrical properties and
is suitable for various extremely severe work conditions.

[0014] The manufacturing of composite insulators by utilizing specified materials, process
parameters along with designs for specified applications is a continued interest. The
applications of composite insulators are constantly being monitored by the End Users
depending on what kind of circumstances and difficulties they come across while these
composite insulators on the job and hence invention in this field have been taking place to
address new challenges and technical necessities. Further, as the environmental pollution
have witnessed to increase substantially in many parts across the globe, the composite
insulators are selected depending on the pollution level/type in the geographical regions
of the transmission line/s and hence composite insulators must be complied with specific
pollution norms depending on the geographical location of the transmission lines.
[0015] The present invention overcomes all the problem by providing a manufacturing
process of ± 800kV 420kN HVDC ‘composite long-rod’ (CLR) insulators by an injection
moulding process.
OBJECTS OF THE INVENTION:
[0016] It is therefore the primary object of the present invention to provide a high voltage
composite long rod (CLR) or elongated insulators for ± 800kV HVDC transmission lines
with minimum electromechanical strength of 420kN of the insulators.
[0017] Another object of the present invention to provide a high voltage CLR elongated
insulators, which has unique design that confirm HVDC applications with a voltage ratings
of ± 800 kV and counter electro-mechanical strength of 420kN of the fabricated CLR
insulators.

[0018] Further objects are to provide process parameters of the fabrication method in
order to manufacture defect-free ± 800kV 420kN HVDC CLR or elongated insulators.
SUMMARY OF THE INVENTION:
[0019] One or more drawbacks of conventional systems and process for a method for
manufacturing of composite long-rod (CLR) insulators are overcome and additional
advantages are provided through the method as claimed in the present disclosure.
Additional features and advantages are realized through the technicalities of the present
disclosure. Other embodiments and aspects of the disclosure are described in detail herein
and are considered to be part of the claimed disclosure.
A high voltage ± 800kV (voltage rating) 420kN (rating of electro-mechanical strength)
HVDC ‘composite long-rod’ (CLR) comprises of:
(i) plurality of insulation sheds, which is moulded by an additive-modified high
temperature vulcanized (HTV) silicone rubber material;
(ii) a core structure, which is an elongated ‘fibre reinforced polymer (FRP)’ rod
for holding the insulation sheds,
iii) metallic hardware, which are forged steel materials, fixed at the terminal
ends of the core rod and
iv) interface bonding/reinforcing agent which has been applied in the interface
region of the FRO rod & insulation sheds for strengthening interface bonding
respectively.
[0020] Various objects, features, aspects, and advantages of the inventive subject matter
will become more apparent from the following detailed description of preferred

embodiments, along with the accompanying drawing figures in which like numerals
represent like components.
[0021] It is to be understood that the aspects and embodiments of the disclosure
described above may be used in any combination with each other. Several of the aspects
and embodiments may be combined to form a further embodiment of the disclosure.
[0022] The foregoing summary is illustrative only and is not intended to be in any way
limiting. In addition to the illustrative aspects, embodiments, and features described
above, drawings and the following detailed description.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT OF THE
INVENTION:
[0023] While the embodiments of the disclosure are subject to various modifications and
alternative forms, a specific embodiment thereof has been shown by way of the figures
and will be described below. It should be understood, however, that it is not intended to
limit the disclosure to the particular forms disclosed, but on the contrary, the disclosure is
to cover all modifications, equivalents, and alternatives falling within the scope of the
disclosure.
[0024] It is to be noted that a person skilled in the art would be motivated from the
present disclosure to arrive at a process for manufacturing of long-rod composite
insulators for HVDC Applications. However, such modifications should be construed within
the scope of the disclosure.
[0025] As used in the description herein and throughout the claims that follow, the

meaning of “a,” “an,” and “the” includes plural reference unless the context clearly
dictates otherwise. Also, as used in the description herein, the meaning of “in” includes
“in” and “on” unless the context clearly dictates otherwise.
[0026] The terms “comprises”, “comprising”, or any other variations thereof used in the
disclosure, are intended to cover a non-exclusive inclusion, such that insulator, composite,
insulation, system that comprises a list of components does not include only those
ingredients but may include other ingredients not expressly listed or inherent to such
composite. In other words, one or more elements in a system proceeded by “comprises…
a” does not, without more constraints, preclude the existence of other elements or
additional elements in the system, apparatus or device.
[0027] The present subject matter relates to a novel high voltage composite insulators or
in particular to a composite long rod or elongated insulators (CLR) for± 800 kV HVDC
transmission lines with a minimum level of electromechanical strength of 420 kN of the
insulators. The said composite insulator comprises a core rod, plurality of insulation sheds
of which are continuously aligned towards the axial direction of the entire core rod and the
metallic hardware, which are fitted at the terminal ends of the insulator structure for
ohmic contacts respectively.
[0028] The said composite long rod (CLR) comprises of:
(i) plurality of insulation sheds, which is moulded by using an additive-modified (alumina,
silica etc.) hightemperature vulcanized (HTV) silicone rubber material such as methyl vinyl
silicone rubber,
ii) a core structure, which is an elongated ‘fibre reinforced polymer (FRP)’ rod up to a
length of 4.5 meter having diameter of 40 mm that holds the insulation sheds,

iii) metallic hardware, which are made up of forged steel materials, fixed at the terminal
ends of the core rodand
iv) interface bonding/reinforcing agent which has been applied in the interface region of
the FRP rod & insulation sheds for strengthening interface bonding respectively.
[0029] The metallic hardware parts are particularly made of forged-shell EN8 grade
material for ‘socket fittings’ at one terminal and EN13 grade forged shell is used as “ball-
fitting” at the other terminal end of the CLR insulator structure.
[0030] The insulation sheds which cover the entire length of core elongated FRP rod
surface, in which a plurality of sheds are formed by integrally molding an insulating
material, i.e., additive-modified silicone high-temperature vulcanized (HTV) rubber by an
injection molding machine at definite temperature/s with a definite period of curing time
of the HTV rubber material, prior surface.
[0031] The interface bonding or reinforcing material used for this purpose is a commercial
grade silane based catalyst-modified adhesive material such as alumina, silica etc in
xylene-solvent.
[0032] The each insulation shed of the composite insulator is aligned axially to the
adjacent shed by maintaining a pre-determined and equi-distance gap, all the area of FRP
rod of which is continuously moldedwith the same insulating material, i.e., additive-
modified silicone HTV rubber in a monolithic manner.The diameter of each adjacent
molded shed is also varied so that the diameter of each repeated insulation shed becomes
the same across the length of the FRP rod, which is integrally united throughout the
length of the FRP rod in the composite insulator body structure.
[0033] In accordance with another embodiment of the present invention there is

provided a fabrication method for manufacturing of a composite long rod (CLR) insulators
particularly useful in ± 800 kV HVDC transmission lines with a electromechanical strength
of 420 kN of the insulators.
[0034] The process comprises the steps of:
(i) placing of the metallic conductor fixed core FRP rod in a stainless steel die in an
injection moulding machine;
(ii) plurality of insulation sheds are formed by moulding of the additive modified HTV
silicon rubber material in form of round sheds at an elevated temperature and pressure on
the surface of core FRP (165-1750oC; 200-220 Bar);
(iii) surface treatment of the FRP rod to strengthen the bonding between the interface
region of silicone rubber insulation material and FRP rod;
(iv) heat treatment of surface of the rod by using a silane based catalyst modified
adhesive material;
(v) curing of the green insulator at an ambient temperature of 20-25°C and at a level of
humidity of 20-90%;
(vi) fitting both the terminal ends of the insulator with metallic hardware after cleaning
ultrasonically by using a non-aqueous solvent such as commercial grades of
trichloroethelene;
(vii) fixing the hardware at the terminal ends which is made out of forged shell material;
(viii) insulators are subjected to various testing such as electrical tests, mechanical tests,
vibration tests and pollution tests respectively by following validated testing procedures in
accredited laboratories.

[0035] The hardware fitting occurred at one end is known as ball fitting which at the other
end is known as socket fitting for the purpose of ohmic contacts in the transmission power
lines.
[0036] The fixing of hardware at the terminal ends of FRP rods is carried out by crimping
technique byusing appropriate metallic jaws and also by applying sufficient pressure in a
manner that the metallic hardware fixes at the terminal ends of the FRP rod.
[0037] The fabrication process allows the plurality ofinsulation sheds to get aligned
continuously throughout the FRP rod structure with nearly uniform thickness by
maintaining equal distance from one shed to another across the axial direction of the rod
that vary in diameter in alternate sheds repeatedly on the entire length of FRP core rod.
[0038] The fabrication process allows the plurality of insulation sheds to get aligned
continuously throughout the FRP rod structure with nearly uniform thickness of about
5mm by maintaining equal distance (pitch) from one shed to another of about 50mm
across the axial direction of the rod that vary in diameter in alternate sheds repeatedly
about 155 mm to about 125 mm on the entire length of FRP core rod, sheath of which has
a tapered angle about 10o at the top and about 5o at the bottom of each sheath, although
the fabrication process has the flexibility to alter all the parameters of the sheath
alignments including thickness & diameter of the insulation sheds in either way .
The plurality of insulation sheds is moulded by using the said additive-modified HTV
silicone rubber material in an appropriate stainless steel die in an injection mounding
machine in a temperature range of 165-175oC with curing time in the range of 650-750
seconds a counter injection pressure level in the range of 200-220 Bar.
[0039] Prior to the injection moulding for generating the insulation sheds on the core

FRP rod structure, metallic hardware conductors were fitted over the terminal-ends of the
FRP rod by a ‘crimping technique’ using an appropriate metallic jaw and also by applying a
crimping pressure level in the range of 150-170 Bar with holding time in the range of 5-10
seconds so that the metallic hardware fixes at the terminal ends of the FRP rod, although
the hardware could be fitted by any similar technique/s to that of the crimping technique,
described here.
[0040] The metallic hardware conductor-fitted FRP rod structure was placed in the
stainless steel mould for generating the plurality of insulation sheds by injection moulding
process, prior cleaning the said hardware ultrasonically by using a non-aqueous solvent,
i.e., trichloro-ethelene or similar solvent/s in order to remove any dirt/greasy matter from
the surface.
[0041] The surface treatment of the FRP rod was carried out by a chemical treatment
process, followed by using a silane-based catalyst-modified adhesive material in xylene
solvent, followed by a heat-treatment process at any temperature in the range of 100-
130oC for a period of 20-30 minutes, prior to the injection moulding process, which is
done for strengthening the bonding between the interface region of silicone rubber
insulation sheds & FRP rod in the composite insulator structure.
[0042] The HTV silicone rubber insulation material in the form of thin fibrous structure get
also formed on the surfaces of the insulation sheds during the injection moulding process.
These extra fibrous materials on the surface of moulded insulation sheds is termed as
‘flashes’, which were removed, after which the fabricated CLR insulators are preliminary
tested by NDT method for correctness of interfaces.
[0043] The fabricated insulators need to essentially pass all the type tests depending on the
application criteria after which it is confirmed for the desired quality with reliable

performance of the +800Kv 420Kn composite long-rod (CLR) insulators. The various tests
comprising design tests, type tests, electrical tests, mechanical tests, vibration tests and
pollution tests respectively by following validated testing procedures in accredited
laboratories.
[0044] The following examples will bring more detailed explanation about the novelty of the
fabrication process along for ensuring desired quality of the insulators with reliable
performance for applications.
Example 1:
In this example, composite long-rod’ (CLR) HVDC insulators having a total length
(including hardware fittings) about 13680 mm with counter i) creepage distance about
51,000 mm, ii) torsion load about 55 Nm, iii) coupling designation about 28 mm, iv)
voltage ratings of ± 800Kv and v) electromechanical strength of about485Kn is fabricated
by following an injection moulding technique.
The said ± 800kV 420kN HVDC ‘composite long-rod’ (CLR) insulatorsstructurally comprise
primarily, i) plurality of insulation sheds, which is moulded by using an additive-modified
high temperature vulcanized (HTV) silicone rubber material (chemically known as methyl
vinyl silicone rubber), ii) a core structure, which is anelongated ‘fibre reinforced polymer
(FRP)’ rod upto a length of 4.5 meter with counter diameter of about 40 mm that holds
the insulation sheds, iii) metallic hardware, which are forged steel materials, fixed at the
terminal ends of the core rodand another iv) interface bonding/reinforcing agent which is
used for strengthening interface bonding between silicone rubber and FRP rod
respectively.

The surface treatment of the FRP rod was carried out in order to strengthen the bonding
between the interface region of silicone rubber insulation sheds& FRP rod in the composite
insulator structure. Hence, the surface of the FRP rod was modified by a chemical
treatment process, followedby using a silane-based catalyst-modified adhesive material in
xylene solvent followed by a heat-treatment process at a temperature of 120oC for a
period of 20 minutes prior to the injection moulding process. Prior conducting the surface
treatment of the FRP rods, the rods were also cleaned with a non-aqueous solvent, i.e.,
iso-propyl alcohol.
Further, prior to the injection moulding for generating the insulation sheds on the core
FRP rod structure, metallic hardware fittingswere manually inserted over theterminal-ends
of the FRP rod, which was carried out by a so-called ‘crimping technique’ using an
appropriate metallic jaw and also by applying a crimping pressure of 150 Bar with holding
time of 5 seconds during crimping, so that the metallic hardware fixes at the terminal ends
of the FRP rod. The metallic hardware were cleaned ultrasonically by using anon-aqueous
solvent, trichloro-ethelene in order to remove any dirt/greasy matter from the surface.
However, similar other non-aqueous solvents can also be used for this purpose. Therefore,
hardware-fitted FRP rod structure was placed in the mould for generating the plurality of
insulation sheds by injection moulding process.The hardware material for‘ball fitting’ at
one end of the rod is EN19, while at another end of the rod, which is known as ‘socket
fitting’ is EN8 respectively. The total length including the hardware fittings of the
aforesaid ± 800kV 420kN HVDC CLR insulators is 13680mm.
In this example, the aforesaid ± 800kV 420kN HVDC composite long-rod insulator was
fabricated by placing the surface-modified core FRP rod by a chemical treatment

process in a stainless steeldie in the injection moulding machine,wherein the said additive-
modified HTV silicone rubber material is moulded in the form of round sheds at a
temperature of 170oCwith counter injection pressure of 210 Bar on the surface of core FRP
rod having curing time of 650 seconds.
The insulation sheds which cover the entire length of core elongated FRP rod surface, in
which a plurality of sheds are formed by integrally molding thesaid additive-modified
silicone high-temperature vulcanized (HTV) rubber material by the injection molding
machine, prior surface treatment of the FRP rod. During the molding process, the
insulation sheds got aligned to one another in the axial direction of the core FRP rod. The
injection moulding process that allowed the plurality of insulation sheds to get aligned
continuously throughout the FRP rod structure with nearly uniform thickness of 5mm by
maintaining equal distance (pitch) of 50 mm from one shed to another across the axial
direction of the rod that vary in diameter from 155 mm in alternate shed to 125mm
repeatedly on the entire length of FRP core rod, sheath of which has a tapered angle
about 10o at the top and about 5o at the bottom of each sheath. The shore hardness of
sheath HTV rubber material (post-curing) resulted in the range of 65-68.
The creepage distance of the aforesaid ± 800kV 420kN HVDC CLR insulators is 51000mm,
while the torsion load of the aforesaid ± 800kV 420kN HVDC CLR insulators is 55Nm.
After the injection moulding process, HTV silicone rubber insulation materialin the form of
thin fibers got deposited on the surface of the insulation sheds, which are termed as
‘flashes’, were removed from the surface. Therefore, the flash-free surfaces of the CLR

insulators are then subjected to routine visual checks & other routinetests, primarily,
mechanical test (tensile load) by NDT method (ultrasonically) for correctness of interfaces.
The fabricated insulators after the preliminary routine tests were then subjected to the next
level of testing, comprising various type tests, electrical tests, mechanical tests, vibration
tests and pollution tests respectively by following validated testing procedures in accredited
laboratories.
The fabricated insulator i.e., ± 800kV 420kN HVDC long-rod composite insulator has
passed through all the desired testing, i.e., mechanical, electrical, vibration and pollution
testing, therefore confirms its reliable performance as an insulator in ± 800kV HVDC
transmission lines having a counter electro-mechanical strength upto 420kN of the CLR
insulators.
Table 1 provides different properties of the following +800kV 420kN composite long-rod
(CLR) insulator fabricated in this example:
Table 1: Technical properties of the fabricated +800kV 420kN composite long-
rod (CLR) insulator under Example 1:

Sl. No. Description/Parameter Unit Value
1 Electro-mechanical strength
(Tensile) kN 485
2 Total length mm 13680
3 Creepage distance mm 51000
4 Coupling designation mm 28
5 Core diameter mm 40
6 Torsion Load Nm 55
7 Individual units/insulator No. 3
8 Corona rings/Insulator No. 6
9 Insulation Sheath - Big (Diameter) mm 155
10 Insulation Sheath – Small
(Diameter) mm 125
11 Pitch (Big Sheath to Big Sheath) mm 50
12 Insulation Sheath Thickness mm 06+0.5
13 Sheath (tapered) angle Degree 10 (at the top); 5
(at the
bottom)
14 Shore Hardness of the Silicone
Rubber Sheath (Post-curing) 65
15 DC Voltage rating kV +800

Example 2:
In this example, all other conditions remained the same to that of the Example 1, the
only difference is that the following parameters were varied during the injection
moulding process in order to get +800kV 420kN composite long-rod (CLR) insulators.
• Crimping pressure of the metallic hardware: 160Bar
• Injection moulding temperature: 165oC
• Curing time of the HT Silicone Rubber: 700 Sec
Table 2 provides different properties of the following +800kV 420kN composite long-
rod (CLR) insulatorfabricated in this example:
Table 2: Technical properties of the fabricated +800kV 420kN composite
long-rod (CLR) insulator under Example 2:

Sl. No. Description/Parameter Unit Value
1 Electro-mechanical strength of the
insulator (Tensile) kN 490
2 Total length mm 13680
3 Creepage distance mm 51000
4 Coupling designation mm 28
5 Core diameter mm 40
6 Torsion Load Nm 55
7 Individual units/insulator No. 03
8 Corona rings/Insulator No. 06
9 Insulation Sheath - Big (Diameter) mm 155
10 Insulation Sheath – Small
(Diameter) mm 125
11 Pitch (Big Sheath to Big Sheath) mm 50
12 Insulation Sheath Thickness mm 06+0.5
13 Sheath (tapered) angle Degree 10 (at the top); 5
(at the
bottom)
14 Shore Hardness of the Insulation
Sheath 67
15 DC Voltage rating kV +800

Example 3:
In this example, all other conditions remained the same to that of the Example 1, the
only difference is that the following parameters were varied during the injection
moulding process in order to get +800kV 420kN composite long-rod (CLR) insulators.
• Crimping pressure: 170Bar
• Injection moulding temperature: 175oC
• Curing time of the HT Silicone Rubber: 750 Seconds
The following +800kV 420kN composite long-rod (CLR) insulatorfabricated in this
example, showed the following properties, as per Table 3
Table 3: Technical properties of the fabricated +800kV 420kN composite
long-rod (CLR) insulator under Example 3:

Sl. No. Description/Parameter Unit Value
1 Electro-mechanical strength of the
insulator (Tensile) kN 500
2 Total length mm 13680
3 Creepage distance mm 51000
4 Coupling designation mm 28
5 Core diameter mm 40
6 Torsion Load Nm 55
7 Individual units/insulator No. 03
8 Corona rings/Insulator No. 06
9 Insulation Sheath - Big (Diameter) mm 155
10 Insulation Sheath – Small
(Diameter) mm 125
11 Pitch (Big Sheath to Big Sheath) mm 50
12 Insulation Sheath Thickness mm 06+0.5
13 Sheath (tapered) angle Degree 10 (at the top); 5
(at the
bottom)
14 Shore Hardness of the Insulation
Sheath 68
15 DC Voltage rating kV +800
The non-limiting advantages of the present invention are as follows:
The total length including the hardware fittings of the aforesaid ± 800kV 420kN HVDC

CLR insulators is 13680 + 500 mm, although the fabrication process has the flexibility to
alter the length of the fabricated insulators in either way and fabricate varieties of ±
800kV 420kN HVDC CLR insulators with variable total length of the insulators.
The creepage distance of the aforesaid ± 800kV 420kN HVDC CLR insulators is 51000 +
200mm, although the fabrication process has the flexibility to alter the creepage distance
of the fabricated insulators in either way and fabricate ± 800kV 420kN HVDC CLR
insulators with variable levels of creepage distance.
The torsion load of the aforesaid ± 800kV 420kN HVDC CLR insulators is 55+2 Nm,
although the fabrication process has the flexibility to alter the torsion load of the
fabricated insulators in either way and fabricate ± 800kV 420kN HVDC CLR insulators
with variable levels of torsion load.
The minimum electromechanical strength of the aforesaid ± 800kV 420kN HVDC CLR
insulators is 420kN, although the fabrication process has the flexibility to alter the
electromechanical strength upto 500kN of the fabricated insulators
The aforesaid ± 800kV 420kN HVDC CLR insulators have the following properties as per
the table 1.
The aforesaid ± 800kV 420kN HVDC CLR insulators become a suitable candidate as an
insulator in ± 800kV HVDC transmission lines.
[0045] Each of the appended claims defines a separate invention, which for infringement
purposes is recognized as including equivalents to the various elements or limitations
specified in the claims. Depending on the context, all references below to the

“invention” may in some cases refer to certain specific embodiments only. In other cases,
it will be recognized that references to the “invention” will refer to the subject matter
recited in one or more, but not necessarily all, of the claims.
[0046] Groupings of alternative elements or embodiments of the invention disclosed
herein are not to be construed as limitations. Each group member can be referred to and
claimed individually or in any combination with other members of the group or other
elements found herein. One or more members of a group can be included in, or deleted
from, a group for reasons of convenience and/or patentability. When any such inclusion or
deletion occurs, the specification is herein deemed to contain the group as modified thus
fulfilling the written description of all groups used in the appended claims.
[0047] The present disclosure provides a method for a high voltage composite long rod
insulator.
Equivalents:
[0048] With respect to the use of substantially any plural and/or singular terms herein,
those having skill in the art can translate from the plural to the singular and/or from the
singular to the plural as is appropriate to the context and/or application. The various
singular/plural permutations may be expressly set forth herein for sake of clarity.
[0049] It will be understood by those within the art that, in general, terms used herein,
and especially in the appended claims (e.g., bodies of the appended claims) are generally
intended as “open” terms (e.g., the term “including” should be interpreted as “including
but not limited to,” the term “having” should be interpreted as “having at least,” the term
“includes” should be interpreted as “includes but is not limited to,” etc.). It will be further

understood by those within the art that if a specific number of an introduced claim
recitation is intended, such an intent will be explicitly recited in the claim, and in the
absence of such recitation no such intent is present. For example, as an aid to
understanding, the following appended claims may contain usage of the
introductoryphrases “at least one” and “one or more” to introduce claim recitations.
However, the use of such phrases should not be construed to imply that the introduction
of a claim recitation by the indefinite articles “a” or “an” limits any particular claim
containing such introduced claim recitation to inventions containing only one such
recitation, even when the same claim includes the introductory phrases “one or more” or
“at least one” and indefinite articles such as “a” or “an” (e.g., “a” and/or “an” should
typically be interpreted to mean “at least one” or “one or more”); the same holds true for
the use of definite articles used to introduce claim recitations. In addition, even if a
specific number of an introduced claim recitation is explicitly recited, those skilled in the
art will recognize that such recitation should typically be interpreted to mean at least the
recited number (e.g., the bare recitation of “two recitations”, without other modifiers,
typically means at least two recitations or two or more recitations).
[0050] The above description does not provide specific details of manufacture or design of
the various components. Those of skill in the art are familiar with such details, and unless
departures from those techniques are set out, techniques, known, related art or later
developed designs and materials should be employed. Those in the art are capable of
choosing suitable manufacturing and design details.
[0051] The terminology used herein is for the purpose of describing particular
embodiments only and is not intended to be limiting of the present disclosure. It will be

appreciated that several of the above-disclosed and other features and functions, or
alternatives thereof, may be combined into other systems or applications. Various
presently unforeseen or unanticipated alternatives, modifications, variations, or
improvements therein may subsequently be made by those skilled in the art without
departing from the scope of the present disclosure as encompassed by the following
claims.
[0052] The claims, as originally presented and as they may be amended, encompass
variations, alternatives, modifications, improvements, equivalents, and substantial
equivalents of the embodiments and teachings disclosed herein, including those that are
presently unforeseen or unappreciated, and that, for example, may arise from
applicants/patentees and others.
[0053] While various aspects and embodiments have been disclosed herein, other aspects
and embodiments will be apparent to those skilled in the art. The various aspects and
embodiments disclosed herein are for purposes of illustration and are not intended to be
limiting, with the true scope and spirit being indicated by the following claims.

WE CLAIM:
1. A high voltage ± 800kV (voltage rating) 420kN (rating of electro-mechanical
strength) HVDC ‘composite long-rod’ (CLR) comprises of:
(i) plurality of insulation sheds, which is moulded by an additive-modified high
temperature vulcanized (HTV) silicone rubber material;
(ii) a core structure, which is an elongated ‘fibre reinforced polymer (FRP)’ rod
for holding the insulation sheds,
iii) metallic hardware, which are forged steel materials, fixed at the terminal
ends of the core rod and
iv) interface bonding/reinforcing agent which has been applied in the interface
region of the FRO rod & insulation sheds for strengthening interfacebonding
respectively.
2. The composite ± 800kV 420kN HVDC long rod insulator (CLR) as claimed in claim 1,
wherein the material for the plurality of insulation sheds is high temperature
vulcanized (HTV) silicone rubber material such as methyl vinyl silicone rubber, which
is modified by additive such as alumina, silica.
3. The composite ± 800kV 420kN HVDC long rod insulator (CLR) as claimed in claim
1, wherein the elongated ‘fibre reinforced polymer (FRP)’ rod having a length of 4.5
meter with core diameter of 40 mm that holds the insulation sheds, although the
fabrication process has the flexibility to vary the length and diameter of the core FRP
rod in the fabricated insulators in either way and fabricate ± 800kV 420kN HVDC
CLR insulators with variable levels of length & diameter of the FRP rod.
4. The composite ± 800kV 420kN HVDC long rod insulator (CLR) as claimed in claim

1, wherein the interface bonding/reinforcing agent is a silane-based catalyst-
modified adhesive in xylene-solvent.
5. The composite ± 800kV 420kN HVDC long rod insulator (CLR) as claimed in claim 1,
wherein the metallic hardware are forged steel materials, one end of the rod that is
fitted is EN19 grade forged steel known as ‘ball fitting’, while at another end of the
rod, which is known as ‘socket fitting’ is EN8 grade forged steel, although similar
metallic hardware fittings could be used for the purpose of ohmic contact.
6. A fabrication process for preparing of composite ± 800kV 420kN HVDC long rod
insulator (CLR) comprises the steps of:
(i) placing of the metallic conductor fixed core FRP rod in a stainless steel die in an
injection moulding machine;
(ii) plurality of insulation sheds are formed by moulding of the additive modified
HTV silicon rubber material in form of round sheds at an elevated temperature in
the range of 165-175oC and pressure about 200-220 Bar on the surface of core FRP
(iii) surface treatment of the FRP rod to strengthen the bonding between the
interface region of silicone rubber insulation material and FRP rod;
(iv) heat treatment of surface of the rod by using a silane based catalyst modified
adhesive material;
(v) curing of the green insulator at an ambient temperature;
(vi) fitting both the terminal ends of the insulator with metallic hardware after
cleaning ultrasonically by using a non-aqueous solvent such as tricholoroethelene
(vii) fixing the hardware at the terminal ends which is made out of forged shell
material;

(viii) insulators are subjected to various testing such as electrical tests, mechanical
tests, vibration tests and pollution tests respectively by following validated testing
procedures in accredited laboratories;
characterized in that, the fabrication process allows the plurality of insulation sheds to
get aligned continuously throughout the FRP rod structure with nearly uniform
thickness of about 5mm by maintaining equal distance (pitch) from one shed to
another of about 50mm across the axial direction of the rod that vary in diameter in
alternate sheds repeatedly about 155 mm to about 125 mm on the entire length of
FRP core rod, sheath of which has a tapered angle about 10o at the top and about 5o
at the bottom of each sheath, although the fabrication process has the flexibility to
alter all the parameters of the sheath alignments including thickness & diameter of the
insulation sheds in either way .
7. The process for preparing of composite ± 800kV 420kN HVDC long rod insulator (CLR)
as claimed in claim 6, wherein the plurality of insulation sheds is moulded by using the
said additive-modified HTV silicone rubber material in an appropriate stainless steel
die in an injection mounding machine in a temperature range of 165-175oC with
curing time in the range of 650-750 seconds a counter injection pressure level in the
range of 200-220 Bar.
8. The process for preparing of composite ± 800kV 420kN HVDC long rod insulator (CLR)
as claimed in claim 6, wherein the surface treatment of the FRP rod was carried out by
a chemical treatment process, followed by using a silane-based catalyst-modified
adhesive material in xylene solvent, followed by a heat-treatment process at any
temperature in the range of 100-130oC for a period of 20-30 minutes, prior to the
injection moulding process, which is done for strengthening the bonding between the

interface region of silicone rubber insulation sheds & FRP rod in the composite
insulator structure.
9. The process for preparing of composite ± 800kV 420kN HVDC long rod insulator (CLR)
as claimed in claim 6 , wherein prior to the injection moulding for generating the
insulation sheds on the core FRP rod structure, metallic hardware conductors were
fitted over the terminal-ends of the FRP rod by a ‘crimping technique’ using an
appropriate metallic jaw and also by applying a crimping pressure level in the range of
150-170 Bar with holding time in the range of 5-10 seconds so that the metallic
hardware fixes at the terminal ends of the FRP rod, although the hardware could be
fitted by any similar technique/s to that of the crimping technique, described here.
10. The process for preparing of composite ± 800kV 420kN HVDC long rod insulator (CLR)
as claimed in claim 6, wherein the fabrication of ± 800kV 420kN HVDC CLR insulators,
the metallic hardware conductor-fitted FRP rod structure was placed in the stainless
steel mould for generating the plurality of insulation sheds by injection moulding
process, prior cleaning the said hardware ultrasonically by using a non-aqueous
solvent, i.e., trichloro-ethelene or similar solvent/s in order to remove any dirt/greasy
matter from the surface.
11. The process for preparing of composite ± 800kV 420kN HVDC long rod insulator (CLR)
as claimed in claim 6, wherein the insulators have passed various tests comprising
design tests, type tests, electrical tests, mechanical tests, vibration tests and pollution
tests respectively by following validated testing procedures in accredited laboratories.