Title of the Invention
Insulator Clad Type Arrester
Background of the Invention
1. Technical Field to Which the Invention Belongs
The present invention relates to an improvement
of an insulator clad type arrester which is used, for
example, in an electric power generating plant or an
electric power substation and, in particular, relates
to an insulator clad type arrester of which outer
insulator sheath is formed of a polymer insulator.
2. Conventional Art
In an air insulated electric power generating
plant and substation, insulator clad type arresters
are primarily used so as to ensure coordination of
insulation in the electric power generating plant and
substation. These conventional insulator clad type
arresters, which are commonly employed, use porcelain
insulators for the outer insulator sheath. However,
an advantageous polymer insulator in view of its
mechanical performance is recently developed and is
gradually employed in place of the conventional
porcelain insulator.
Fig.8 shows an arrester which uses such polymer
insulator, wherein zinc oxide elements 80 are arranged
by piling up the same, an insulator cylinder 3 is
disposed so as to cover the piled up zinc oxide
elements 80, and further an outer insulator sheath 2
formed of a polymer insulator is disposed around the
outer circumference of the insulator cylinder 3.
Further, in the drawing, numerals 6 and 7 are metal
fittings and numerals 8 and 9 are explosion proof use
guides.
For such type of arresters, a zinc oxide element
80 having a discharge voltage of about 200V/mm for 1mA
is generally employed. Examples of this type of
arrester are disclosed in JP-A-2-97003(1990) and JP-A-
3-257720(1991).
In the above explained insulator clad type
arrester, the outer insulator sheath, namely the
polymer insulator shows water permeability which
likely affects adverserly to the insulation
performance of the arrester, therefore, such
undesirable effect has to be reduced. Further, in
order to reduce cost and weight of such arrester it is
desired to be able to utilize a high voltage zinc
oxide element having a discharge voltage of about
300V/mm for 1mA. However, if an arrester using such
zinc oxide elements having an increased discharge
voltage is merely constituted in a conventional
manner, the total piling up length of the zinc oxide
elements is shortened because of the increased
discharge voltage, on the other hand, the length of
the outer insulator sheath has to be determined in
view of decreasing insulation reduction due to
contamination thereof and in view of coordination to
the external insulation, therefore, the construction
thereof was difficult as well as the structure of a
possible construction tends to be complex. Further,
when a high voltage zinc oxide element having a
discharge voltage of about or more than 300V/mm for
1mA is used and if water permeates into the outer
insulator sheath, it was predicted that a shortage of
surface insulating strength of such element may be
caused.
Summary of the Invention
The present invention is carried out in view of
the above explained conventional problems and an
object of the present invention is to provide a
polymer insulator clad type arrester which reduces the
influence of water permeability of the polymer
insulator.
The present invention achieves the above object
with an insulator clad type arrester which includes
groups of arrester elements arranged by piling up
thereof and an outer cylindrical insulator sheath
disposed so as to cover the groups of arrester
elements and the outer cylindrical insulator sheath
being formed by a polymer insulator, wherein a water
absorbing agent is disposed inside the outer
cylindrical insulator sheath in an amount which can
absorb water permeating from the polymer insulator.
Further, in the present invention,
the groups of the arrester
elements are disposed in a distributed manner in the
piling up direction and a distributed electrode is
interposed between the distributedly disposed groups
of arrester elements. Further, a water absorbing
agent being disposed in each said distributed
electrodes.
Still further, in the present invention the water
absorbing agent is disposed inside the outer insulator
sheath in an amount equal to or more than the amount
of water permeating from the polymer insulator during
the life time thereof, each arrester element in the
groups of arrester elements is a high voltage zinc
oxide element having a discharge voltage of about
300V/mm for 1mA, the groups of the arrester elements
are disposed in a distributed manner in the piling up
direction, a pair of distributed electrodes are
provided at the top and bottom of each said
distributedly disposed groups of arrester elements,
and the water absorbing agent is disposed only in the
distributed electrodes which contact to end metal
members provided at the top and bottom of the outer
insulator sheath.
Moreover, in the present invention the diameter
of each of the distributed electrodes interposed
between the groups of arrester elements can be formed
larger than that of each of the high voltage zinc
oxide elements, or the diameter of either the
distributed electrodes positioned at the side of end
metal members provided at the top and bottom of the
outer insulator sheath or the distributed electrode
positioned at the bottom thereof can be formed larger
than that of each of the high voltage zinc oxide
elements. Still further, each of the distributed
electrodes interposed between the groups of arrester
elements is constituted by a metal cylinder having a
through-hole permitting communication between the
inside and the outside thereof and a pair of disk
shaped electrodes closing the top and bottom of the
metal cylinder, and the water absorbing agent being
received inside the metal cylinder.
Namely, with the thus constituted insulator clad
type arrester according to the present invention
through the distributed arrangement of the high
voltage zinc oxide elements the amount of the water
absorbing agent can be increased to an optimum amount,
and with this water absorbing agent water permeating
from the polymer insulator is sufficiently absorbed,
further the distributed arrangement of the groups of
the high voltage zinc oxide elements can properly
maintains coordination of insulation with the
potential distribution along the surface of the
polymer insulator when the polymer insulator is
contaminated, accordingly even in the arrester
employing the polymer insulator the adverse effect of
the water permeating from the polymer insulator is
reduced and the application of a high voltage zinc
oxide element having a discharge voltage of about or
more than 300V/mm for 1mA is enabled.
Brief Description of the Drawings
Fig.l is a vertical cross sectional side view
showing one embodiment of the insulator clad type
arresters according to the present invention ;
Fig.2 is a vertical cross sectional side view
showing a distributed electrode in the insulator clad
type arresters according to the present invention ;
Fig. 3 is a vertical cross sectional side view
showing another embodiment of the insulator clad type
arresters according to the present invention ;
Fig.4 is a vertical cross sectional side view
showing still another embodiment of the insulator clad
type arresters according to the present invention ;

Fig.5 is a vertical cross sectional side view
showing a further embodiment of the insulator clad
type arresters according to the present invention ;
Fig.6 is a vertical cross sectional side view
showing a still further embodiment of the insulator
clad type arresters according to the 'present
invention ;
Fig. 7 is a vertical cross sectional side view
showing another distributed electrode in the insulator
clad type arresters according to the present invention
; and
Fig.8 is a vertical cross sectional side view
showing a conventional insulator clad type arrester.
Description of Embodiments of the Invention
Hereinbelow, the present invention is explained
in detail with reference to embodiments as shown in
the drawings. Fig.l shows a cross sectional view of
such insulator clad type arrester.
[ Embodiment 1 ]
Fig.l shows one embodiment of the present
invention wherein a polymer insulator (an outer
insulator sheath) 1 is constituted by a weather proof
polymer cover 2 of such as EVT and HTV and an FRP
(Fiber Reinforced Plastics) cylinder 3. Groups of
zinc oxide elements 4 are distributedly arranged in
the polymer insulator 1 and a plurality of distributed

electrodes 5 are arranged in series between these
distributed groups of zinc oxide elements 4.
The zinc oxide element used in the present
embodiment is a high voltage zinc oxide element having
a discharge voltage of about or more than 300V/mm for
1mA, thereby the total length of the piled up high
voltage zinc oxide elements 4 is generally shorter
than that of the polymer insulator 1. Namely, the
polymer insulator 1 is required to have a length more
than a predetermined length so as to ensure the
insulating strength thereof even when the surface
exposed to the open air side of the polymer insulator
1 is contaminated. In other words, the length of the
polymer insulator 1 is long in comparison with the
total length of the high voltage zinc oxide elements 4
and a free space is generated in the polymer insulator
1 in the longitudinal direction thereof. Accordingly,
the plurality of distributed electrodes 5 can be
arranged so as to fill the free space in the polymer
insulator 1 along the piled up high voltage zinc oxide
elements 4.
End metal members 6 and 7 are secured at the top
and bottom of the polymer insulator 1, and the end
metal members 6 and 7 are respectively provided with
explosion proof use guides 8 and 9, and pressure
bursting valves 10 and 11. Although not illustrated,
the respective groups of zinc oxide elements 4 are
insterted into respective insulator rods which are
assembled with the respective distributed electrodes
5. These groups of zinc oxide elements 4 and
distributed electrodes 5 are retained between the end
metal members 6 and 7 of the polymer insulator 1 by a
spring 12. The inside of the polymer insulator 1 is
usually filled with nitrogen gas. Further, if
required a shield ring 13 (of which supporting metal
member is not illustrated) can be provided for the top
metal member 6 to thereby uniformalize static voltage
distribution along the groups of zinc oxide elements
4. The depth and pitch of ribs provided for the
wheather proof polymer cover 2 are determined
depending on the possible contamination conditions.
An exemplary structure of the distributed
electrode 5 is illustrated in Fig.2. At the top and
bottom of a metal cylinder 2 0 disk electrodes 21 and
22 are provided, and a through hole 2 3 is provided at
the metal cylinder 20. Inside the metal cylinder 20 a
water absorbing agent 24 such as zeolite and active
alumina is disposed. An insulator rod 25 is assembled
onto the top disk electrode 21 and by making use of
the insulator rod 25 doughnut shaped zinc oxide
elements 2 6 each having a center through hole are
inserted and piled up. The bottom electrode 22 is
provided with a supporting use hole 2 7 into which an
insulator rod 2 5 is insterted from downward.

An amount of water permeating through the polymer
insulator 1 is calculated according to the following
equation ;
m=k D S t/d ••• (1)
wherein, k:density of water, D:dispersion coefficient
of water in the polymer insulator, S:surface area of
the cylindrical portion of the polymer insulator,
t:expected life time of the arrester and d:thickness
of the cylindrical portion.
When great amount of water deposits on the side
surface of the zinc oxide element, the insulating
performance thereof reduces and in the worst case a
grounding accident may occurs. Accordingly, it is
required to place the water absorbing agent in an
amount more than the amount m which can absorb water
permeating during the expected life time of the
arrester so that in the present invention a
predetermined amount of the water absorbing agent 24
is placed inside the metal cylinder 2 0 of the
distributed electrode 5.
Further, when the groups of zinc oxide elements 4
are concentratedly arranged and further when the outer
surface of the polymer insulator is contaminated, a
potential difference is caused between the facing
inner surface of the polymer insulator and the zinc
oxide elements and a local discharge is induced to
thereby cause an insulation failure. Therefore, when

the groups of zinc oxide elements 4 are distributedly
arranged as illustrated in Fig.l, such insulation
failure can be avoided. If the number of distributed
groups of zinc oxide elements 4 is increased, the
effect caused thereby also increases. Further, ' as
illustrated in Fig.l it is preferable to begin with
respective distributed electrodes 5 for both ends of
the column of the groups of zinc oxide elements 4
within the polymer insulator 1 in view of reducing the
potential difference.
As will be understood from the above, according
to the present embodiment advantages, that the adverse
effect of water permeating through the polymer
insulator is reduced and a polymer insulator clad type
arrester which can utilize a high voltage zinc oxide
element having a discharge voltage of about or more
than 300V/mm for 1mA can be provided, are obtained.
Further, advantages, that with the provision of the
distributed electrodes cooling performance for the
high voltage zinc oxide elements is improved, is
obtained.
[ Embodiment 2 ]
Fig. 3 shows another embodiment. In the present
embodiment, no water absorbing agent is provided for
four center distributed electrodes 31 through 34.
Namely, the present embodiment represents a case in
which it is sufficient if the water absorbing agent is

placed in distributed electrodes 30 and 35 at
respective ends of the column of the zinc oxide
elements. The four center distributed electrodes 31
through 34 are solid so that an advantage, that the
groups of zinc oxide elements 4 are further
efficiently cooled, is achieved. Further, depending
on the circumfstances the water absorbing agent can
only be placed in the distributed electrode 35 at the
bottom end.
[ Embodiment 3 ]
Fig.4 shows still another embodiment. In the
present embodiment, the diameter of the distributed
electrodes 40 through 45 is determined larger than
that of the groups of zinc oxide elements 4.
Therefore, the zinc oxide elements 4 are further
efficiently cooled in comparison with the embodiment
1.
[ Embodiment 4 ]
Fig.5 shows a further embodiment. In the present
embodiment, only the diameter of distributed
electrodes 50 and 55 is determined larger than that of
the groups of zinc oxide elements 4. Four center
distributed electrodes 51 through 54 are solid,
therefore, the groups of zinc oxide elements 4 are
further efficiently cooled in comparison with the
embodiment 1 as well as a large amount of the water
absorbing agent can be placed in the distributed

electrodes 50 and 55 at both ends of the zinc oxide
element column in comparison with the embodiment 2.
Further, depending on the circumstances the water
absorbing agent can only be placed in the distributed
electrode 55 at the bottom end.
[ Embodiment 5 ]
Fig. 6 shows a still further embodiment wherein
groups of zinc oxide elements 60 are concentratedly
arranged and two distributed electrodes 61 and 62 are
used. The present embodiment is advantageous by its
simple structure and can be applied to a circumstance
of low contamination. In the two distributed
electrodes 61 and 62 the water absorbing agent in an
amount more than the amount m as defined equation (1)
above which can absorb water permeating during the
expected life time of the arrester is placed.
Further, depending on the circvmistances the water
absorbing agent can only be placed in the distributed
electrode 62 at the bottom end.
[ Embodiment 6 ]
Fig.7 shows another embodiment of the structure
for the distributed electrodes 5 which is applicable
when disk shaped zinc oxide elements with no center
through hole are used, wherein disk electrodes 21 and
22 are respectively provided with insulator rods 70
and supporting use holes 71 and disk shaped zinc oxide
elements with no center through hole 72 are piled up

and supported on the respective disk electrodes 21 and
22.
As explained herein above, with the arrester thus
constituted the water absorbing agent, in an amount
more than the amount of water defined by the equation
(1), namely in an amount equal to more than the amount
of water permeating from the polymer insulator during
the life time thereof, is placed inside the polymer
insulator, the groups of zinc oxide elements are
distributedly arranged therein, and further the above
water absorbing agent is distributedly disposed,
accordingly, the adverse effect of water permeating
through the polymer insulator is reduced as well as
the application of a high voltage zinc oxide element
having a discharge voltage of about or more than
300V/mm for 1mA is enabled.
As explained herein above, according to the
present invention, the adverse effect of water
permeating through the polymer insulator is reduced
and a polymer insulator clad type arrester can be
obtained in which a high voltage zinc oxide element
having a discharge voltage of about or more than
300V/mm for 1mA can be applied.

Claims
1. An insulator clad type arrester which includes
groups of arrester elements arranged by piling up
thereof and an outer cylindrical insulator sheath
disposed so as to cover the groups of arrester
elements and said outer cylindrical insulator sheath
being formed by a polymer insulator, characterized in
that a water absorbing agent being disposed inside
said outer cylindrical insulator sheath in an amount
which can absorb water permeating from said polymer
insulator.
2. An insulator clad type arrester which includes
groups of arrester elements arranged by piling up
thereof and an outer cylindrical insulator sheath
disposed so as to cover the groups of arrester
elements and said outer cylindrical insulator sheath
being formed by a polymer insulator, characterized in
that a water absorbing agent being disposed inside
said outer cylindrical insulator sheath in an amount
equal to or more than the amount of water permeating
from said polymer insulator during the life time
thereof.
3. An insulator clad type arrester which includes
groups of arrester elements arranged by piling up
thereof, an insulator cylinder disposed so as to cover
the groups of arrester elements and an outer insulator

sheath disposed around the outer circumference of the
insulator cylinder and said outer insulator sheath being
formed by a polymer insulator, characterized in that each
arrester element in said groups of arrester elements is a
high voltage of about 300V/inm for 1mA, said groups of the
arrester elements being disposed in a distributed manner in
the piling up direction and a distributed electrode being
interposed between said distributedly disposed groups of
arrester elements.
4. An insulator clad type arrester which includes
groups of arrester elements arranged by piling up thereof,
an insulator cylinder disposed so as to cover the groups of
arrester elements and an outer insulator sheath disposed
around the outer circumference of the insulator cylinder
and said outer insulator sheath being formed by a polymer
insulator, characterized in that said groups of the
arrester elements are disposed in a distributed manner in
the piling up direction, a distributed electrode being
interposed between said distributedly disposed groups of
arrester elements and a water absorbing agent being
disposed in said distributed electrodes.
5. An insulator clad type arrester which includes
groups of arrester elements arranged by piling up thereof,
an insulator cylinder disposed so as to cover the groups of
arrester elements and an outer insulator sheath disposed
around the outer circumference of the insulator cylinder
and said outer insulator sheath being formed by a polymer
insulator, characterized in that a water absorbing agent is
disposed inside said outer insulator sheath in an amount
equal to or more than the amount of water determined by the

following equation (1):
m = kDSt/d
wherein k: density of water, D: dispersion coefficient of
water in the polymer insulator, S: surface area of the
cylindrical portion of the polymer insulator, t: expected
life time of the arrester and d: thickness of the
cylindrical portion, and each arrester element in said
groups of arrester elements is a high voltage zinc oxide
element having a discharge voltage of about 300V/mm for
ImA.
6. An insulator clad type arrester which includes
groups of arrester elements arranged by piling up
thereof, an insulator cylinder disposed so as to cover
the groups of arrester elements and an outer insulator
sheath disposed around the outer circumference of the
insulator cylinder and said outer insulator sheath
being formed by a polymer insulator, characterized in
that each arrester element in said groups of arrester
elements is a high voltage zinc oxide element having a
discharge voltage of about 300V/mm for 1mA, said
groups of the arrester elements being disposed in a
distributed manner in the piling up direction, a pair
of distributed electrodes being provided at the top
and bottom of each said distributedly disposed groups
of arrester elements and a water absorbing agent being
disposed in each said distributed electrodes.
7. An insulator clad type arrester which includes
groups of arrester elements arranged by piling up
thereof, an insulator cylinder disposed so as to cover
the groups of arrester elements and an outer insulator

sheath disposed around the outer circumference of the
insulator cylinder and said outer insulator sheath
being formed by a polymer insulator, characterized in
that a water absorbing agent being disposed inside
said outer insulator sheath in an amount equal to or
more than the amount of water permeating from said
polymer insulator during the life time thereof, each
arrester element in said groups of arrester elements
is a high voltage zinc oxide element having a
discharge voltage of about 300V/mm for 1mA, said
groups of the arrester elements being disposed in a
distributed manner in the piling up direction, a pair
of distributed electrodes being provided at the top
and bottom of each said distributedly disposed groups
of arrester elements, and said water absorbing agent
being disposed only in said distributed electrodes
which contact to end metal members provided at the top
and bottom of said outer insulator sheath.
8. An insulator clad type arrester which includes
groups of arrester elements arranged by piling up
thereof, an insulator cylinder disposed so as to cover
the groups of arrester elements and an outer insulator
sheath disposed around the outer circumference of the
insulator cylinder and said outer insulator sheath
being formed by a polymer insulator, characterized in
that a water absorbing agent being disposed inside
said outer insulator sheath in an amount equal to or

more than the amount of water permeating from said
polymer insulator during the life time thereof, each
arrester element in said groups of arrester elements
is a high voltage zinc oxide element having a
discharge voltage of about 300V/mm for 1mA, said
groups of the arrester elements being disposed in a
distributed manner in the piling up direction, a pair
of distributed electrodes being provided at the top
and bottom of each said distributedly disposed groups
of arrester elements, and said water absorbing agent
being disposed only in said distributed electrode
which contacts to an end metal member provided at the
bottom of said outer insulator sheath.
9 . An insulator clad type arrester according to
one of claims 3 through 8 , characterized in that the
diameter of each said distributed electrodes
interposed between said groups of arrester elements is
formed larger than that of each said high voltage zinc
oxide elements.
10 . An insulator clad type arrester according to
one of claims 3 through 8 , characterized in that the
diameter of either said distributed electrodes
positioned at the side of end metal members provided
at the top and bottom of said outer insulator sheath
or said distributed electrode positioned at the bottom
thereof is formed larger than that of each said high
voltage zinc oxide elements.

11. An insulator clad type arrester according to
one of claims 3 through 8 , characterized in that each
said distributed electrodes interposed between said
groups of arrester elements being constituted by a
metal cylinder having a through-hole permiting
communication between the inside and the outside
thereof and a pair of disk shaped electrodes closing
the top and bottom of said metal cylinder, and said
water absorbing agent being received inside said metal
cylinder.
12 . An insulator clad type arrester according to
one of claims 3 through 8 , characterized in that said
distributed electrodes being disposed near end metal
members provided at the top and bottom of said outer
insulator sheath.

In order to reduce an adverse effect of water
permeating through a polymer insulator as well as to
provide a polymer insulator clad type arrester in
which a high voltage zinc oxide element having a
discharge voltage of about or more than 300V/mm for
1mA is applied, an insulator clad type arrester is
provided which includes groups of arrester elements 4
arranged by piling up thereof and an outer cylindrical
insulator sheath 1 disposed so as to cover the groups
of arrester elements 4 and the outer cylindrical
insulator sheath 1 being formed by a polymer
insulator, wherein each arrester element in the groups
of arrester elements 4 is a high voltage zinc oxide
element having a discharge voltage of about 300V/mm
for 1mA, the groups of the arrester elements 4 are
disposed in a distributed manner in the piling up
direction, a distributed electrode 5 is interposed
between the distributedly disposed groups of arrester
elements 4 and a water absorbing agent is disposed in
each distributed electrodes 5.