Corona control ring having elongated water discharge holes

A corona control ring has a corona control ring main body and a water discharge hole having an elongated shape like a racetrack. The corona control ring main body includes a bottom portion and an inner wall portion and an outer wall portion respectively arranged at an inner edge portion and an outer edge portion of the bottom portion. The water discharge hole is arranged in the bottom portion. A depression portion is formed in the corona control ring main body by the inner wall portion, the outer wall portion and the bottom portion. Accordingly, the present invention provides a corona control ring which can suppress a corona discharge even during rain fall.

BACKGROUND OF THE INVENTION 
(1) Field of the Invention 
The present invention relates to a corona control ring which is installed 
along with insulator apparatuses, phase-to-phase spacers or the like for a 
power-transmission line and is used for reducing corona discharge. 
(2) Related Art Statement 
Along with insulator apparatuses for insulating power-transmission lines or 
phase-to-phase spacers used for preventing contact between the 
power-transmission lines by keeping a distance constant between the 
power-transmission lines, the corona control ring is sometimes used for 
preventing corona discharge near metal fittings arranged at both end 
portions at which an electric field may be concentrated. 
As a corona control ring mentioned above, there is known a ring shaped bent 
metal pipe. However, in this case, it is necessary to bend each pipe 
individually, and thus productivity decreases. Therefore, generally, use 
is made of a corona control ring formed by casting a device having a shape 
shown in FIGS. 8 and 9. In the embodiments shown in FIGS. 8 and 9, a 
corona control ring main body 22 of a corona control ring 21 has a 
circular shape in a plan view. A part of the corona control ring main body 
22 has a cut out portion. There are also embodiments without a cut out 
portion. A depression portion 23 is arranged in the corona control ring 
main body 22 to reduce the weight of the corona control ring 21. Since 
there is the depression portion 23, the corona control ring main body 22 
is "U" shaped in cross section, comprising a bottom portion 24 having an 
arc shape in cross section 35 and a pair of side wall portions 25 
extending upward from the edge portions of the bottom portion 24. 
The corona control ring 21 is secured to upper and lower end portions of, 
for example, a phase-to-phase spacer (not shown) by means of a securing 
portion 26 extending from the side wall portion 25 of the corona control 
ring main body 22. The corona control ring 21 is secured to the 
phase-to-phase spacer such that the depression portion 23 faces upward at 
an upper end portion as shown in FIG. 8 and downward at a lower end 
portion. In this case, since the projection portions of the upper and 
lower corona control rings 21 are arranged face to face, it is possible to 
suppress corona discharge from the corona control ring 21 itself. 
In the embodiment shown in FIG. 8, since the depression portion 23 of the 
upper corona control ring 21 faces upward, water gathers in the depression 
portion 23 when there is rain fall. The water gathered in the depression 
portion 23 tends to corrode the corona control ring main body 22. To 
eliminate the problem mentioned above, a plurality of water discharge 
holes 27 each having a small diameter are arranged in the bottom portion 
24 of the corona control ring main body 22 to discharge the water 
therethrough. In the embodiment shown in FIG. 8, four water discharge 
holes 27 are arranged. 
However, if the number of the water discharge holes 27 is only three or 
four, a total amount of area of the water discharge holes 27 is low 
compared to the area of the depression portion 23. Therefore, if a rain 
fall is hard, an amount of water gathered in the depression portion 23 is 
larger than that of water that can be discharged through the water 
discharge holes 27, such that water pools in the depression portion 23. In 
this case, water pooled in the depression portion 23 is gathered at the 
water discharge holes 27, and is discharged collectively through the water 
discharge holes 27. The water discharged from the water discharge holes 27 
then becomes a projection shape at which an electric field concentrates, 
and thus corona discharge is liable to be generated. Therefore, noise due 
to the corona discharge causes signal jamming of television, radio or the 
like. Moreover, radiation due to the corona discharge is disturbing to 
nearby inhabitants. 
Further, since it is not possible to discharge the water pooled in the 
depression portion 23 completely by means of the water discharge holes 27 
mentioned above, the corona control ring main body 23 tends to corrode. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to eliminate the drawbacks 
mentioned above and to provide a corona control ring which can suppress 
corona discharge even during rain fall. 
According to a first aspect of the invention, a corona control ring 
comprises a corona control ring main body having a tubular shape, 
comprising a bottom portion and an inner side wall portion and an outer 
side wall portion respectively arranged at an inner edge portion and an 
outer edge portion of said bottom portion, and a water discharge hole 
having a racetrack shape arranged in the bottom portion along an extended 
direction of the corona control ring main body. 
Moreover, according to a second aspect of the invention, a corona control 
ring comprises a corona control ring main body having a tubular shape, 
comprising an outer bottom portion and an outer wall portion arranged at 
an outer edge portion of the outer bottom portion. 
In the first aspect of the invention, a depression portion is constructed 
by means of the inner side wall portion, the outer side wall portion and 
the bottom portion. Then, the corona control ring is secured to for 
example an upper end of a phase-to-phase spacer in such a manner that the 
depression portion faces upward to reduce an electric field at the end 
portion of the phase-to-phase spacer, so that corona generation is 
suppressed. 
Moreover, the water discharge holes, each having a racetrack shape, are 
arranged in the bottom portion. If rain falls, water does not pool in the 
depression portion and is discharged through the water discharge holes. 
Therefore, it is possible to eliminate the drawback wherein water pools in 
the depression portion and is discharged collectively through the water 
discharge holes each having a small diameter and the water discharged from 
the water discharge holes becomes a projection shape at which an electric 
field concentrates. As a result, it is possible to suppress corona 
discharge. 
In the second aspect of the invention, no inner side wall portion is 
arranged and the outer bottom portion has a width smaller than that of the 
bottom portion as compared with the first aspect of the invention. 
Therefore, no depression portion is formed and thus various problems due 
to corona discharge can be eliminated.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Hereinafter, a first embodiment of the present invention will be explained 
with reference to the drawings. At first, a phase-to-phase spacer 11, to 
which a corona control ring 1 is installed, is explained. As shown in FIG. 
3, the phase-to-phase spacer 11 has an insulation rod 12 made of FRP 
(fiber reinforced plastic) at its center portion. An insulation coating 
layer 13 made of rubber is molded around an outer surface of the 
insulation rod 12. A plurality of insulation sheds 13a are integrally 
formed with the insulation coating layer 13. Metal fittings 14 to connect 
conductors and phase-to-phase spacers are secured to an upper end portion 
and a lower end portion of the insulation rod 12 respectively. The corona 
control rings 1 are arranged around the metal fittings 14. 
The-phase-to-phase spacer 11 having the construction mentioned above is 
secured between the upper and the lower conductors (not shown) by means of 
the metal fittings 14. 
Next, the corona control ring 1 will be explained. As shown in FIGS. 1 to 
3, a corona control ring main body 2 made of aluminum or aluminum alloy is 
formed into a tubular shape by casting, and has an upper opening. 
Moreover, the corona control ring main body 2 has a cut out portion 3 and 
has a "C" shape as a whole. Since the cut out portion 3 is provided, the 
corona control ring 1 can be installed and detached to the phase-to-phase 
spacer 11 even if the phase-to-phase spacer 11 is secured to the 
conductors beforehand. 
A depression portion 4 is arranged at an upper surface of the corona 
control ring main body 2. The depression portion 4 is arranged from one 
open end portion 2a to the other open end portion 2b except that a base 
portion of a securing portion 8 mentioned below is formed. Herein, the 
open end portion means an end portion of the corona control ring main body 
2 adjacent the cut out portion 3. Since the depression portion 4 is 
provided, the weight of the corona control ring 1 can be made light, and a 
thickness of the corona control ring 1 can be made substantially uniform. 
In the embodiment mentioned above, since the depression portion 4 is 
provided, the corona control ring main body 2 is constructed by a bottom 
portion 5, and an inner side wall portion 6 and an outer side wall portion 
7 respectively arranged at an inner edge portion and an outer edge portion 
of the bottom portion 5. Outer surfaces arranged from the bottom portion 5 
to the inner side wall portion 6 or the outer side wall portion 7 have a 
curved shape. Open ends of the inner side wall portion 6 and the outer 
side wall portion 7 are respectively bent outwardly and inwardly, and are 
continuously connected to the opposed open ends of the outer side wall 
portion 7 and the inner side wall portion 6 respectively to form open end 
portions 2a and 2b. The open end portion 2a (2b) of the corona control 
ring main body 2 has a projection shape and one open end portion 2a is 
opposed to the other open end portion 2b. 
The securing portion 8 is formed integrally with the corona control ring 
main body 2 such that it extends from the outer side wall portion 7 to a 
center portion of the corona control ring main body 2 through the 
depression portion 4. The securing portion 8 has a binding portion 8a at 
its tip portion, and a binding depression portion 8b is formed in the 
securing portion 8 at its center portion. A binding plate 9 coupled with 
the securing portion 8 has a binding depression portion 9a at its center 
portion. The binding plate 9 is secured to the securing portion 8 by means 
of screws and nuts such that the binding depression portions 8b and 9a are 
opposed. 
In the corona control ring 1 mentioned above, water discharge holes 10 are 
arranged in the bottom portion 5. That is, one water discharge hole 10 is 
formed from one open end portion 2a to the base portion of the securing 
portion 8 in the bottom portion 5. The other water discharge hole 10 is 
formed from the other open end portion 2b to the base portion of the 
securing portion 8. In this manner, two water discharge holes 10 having a 
racetrack shape are arranged along an extended direction of the corona 
control ring main body 2. As shown in FIG. 2, since the water discharge 
holes 10 are arranged in the bottom portion 5, there remains only an inner 
bottom portion 5b and an outer bottom portion 5a of the bottom portion 5 
having a substantially one-fourth circle shape. Therefore, the bottom 
portion 5 can be constructed in an extremely weight reduced manner as 
compared with the conventional corona control ring shown in FIGS. 7 and 8. 
As shown in FIG. 3, the corona control rings 1 having the construction 
mentioned above are secured to an upper end and the lower end of the 
phase-to-phase spacer 11 such that the metal fittings 14 are arranged 
between the binding depression portions 8b and 9a of the securing portions 
8 and are fixed by means of screws. In this case, the upper corona ring 1 
is secured to the upper metal fitting 14 such that the depression portion 
4 is opened upward i.e. in an upward direction in the figures. Moreover, 
the lower corona ring 1 is secured to the lower metal fitting 14 such that 
the depression portion 4 is opened downward. The corona rings 1 mentioned 
above can decrease a concentration of an electric field near the upper end 
portion and the lower end portion and can suppress the generation of 
corona discharge. 
Since the upper corona ring 1 mentioned above has the depression portion 4 
opened upward, water pools in the depression portion 4 if rain falls. 
However, in the corona ring 1 mentioned above, the water discharge hole 10 
arranged in the bottom portion 5 has a larger open area substantially 
equal to the bottom portion 5. Therefore, the water discharge hole 10 
according to the invention has a higher water discharging efficiency than 
that of the known water discharge hole 27 having a small diameter. In this 
case, water remaining at the outer bottom portion 5a and the inner wall 
portion 5b each having a small area and water adhered to the inner side 
wall portion 6 and the outer side wall portion 7 and moved downward can be 
discharged through the water discharge hole 10 without pooling in the 
depression portion 4. Moreover, a part of the rain falls directly through 
the opening of the depression portion 4 and the water discharge hole 10 
without touching the side wall portions 6 and 7. 
As mentioned above, according to the embodiment mentioned above, since the 
water discharge hole 10 having a large open area is arranged in the bottom 
portion 5, water is not maintained in the depression portion 4 and can be 
discharged through the water discharge hole 10 if a rain fall is hard. 
Therefore, it is possible to eliminate a collective water fall of the 
water maintained in the depression portion 4, and thus it is possible to 
suppress the generation of a projection portion of the water discharge 
hole 10, at which an electric concentrates. As a result, it is possible to 
increase an operation voltage at which noise due to corona generation 
reaches a limit level. That is, it is possible to eliminate jamming for 
television, radio and other signals. Further, since the corona generation 
voltage can be increased, it is also possible to suppress radiation 
generation. As mentioned above, various problems due to corona discharge 
can be prevented. 
Moreover, since the water discharge hole 10 has a large opening area in the 
bottom portion 5, the water maintained in the depression hole 4 can be 
completely discharged. Therefore, it is possible to eliminate corrosion of 
the corona control ring main body 2 due to the pooled water. Further, it 
is possible to make a total weight of the corona ring 1 light. 
In the embodiment mentioned above, the corona control rings 1 arranged at 
the upper end portion and the lower end portion of the phase-to-phase 
spacer 11 have the same construction because of easy preparation work, 
easy securing and light weight of the phase-to-phase spacer 11. However, 
the lower corona control ring 1 has no disadvantages with respect to water 
pooling in the depression portion 4 mentioned above. Therefore, the lower 
corona ring 1 may have a different construction i.e. have no water 
discharge holes 10. 
Hereinafter, a second embodiment of the present invention will be explained 
with reference to the drawings. In the second embodiment mentioned below, 
portions similar to those of the first embodiment are denoted by the same 
reference numerals as those of the first embodiment. 
As shown in FIGS. 6 and 7, a corona control ring main body 16 of a corona 
control ring 15 according to the second embodiment comprises only the 
outer bottom portion 5a and the outer side wall portion 7 extending from 
the edge of the outer bottom portion 5a. Therefore, the corona control 
ring main body 15 has a cross sectional shape of substantially one-fourth 
of a circle. Then, open ends of the outer side wall portions 7 are bent 
inwardly to form open end portions 16a and 16b each having a circular 
projection shape. The open end portions 16a and 16b are opposed to each 
other at the cut out portion 3. 
In the second embodiment mentioned above, since the corona control ring 
main body 16 has only the outer bottom portion 5a and the outer side wall 
portion 7, no depression portion 4 of the first embodiment is formed. 
Therefore, the generation of the projection portion due to water pooling 
in the depression portion 4 can be preferably prevented, and thus it is 
possible to suppress the generation of corona discharge even if rain fall 
is hard. 
The present invention is not limited to the embodiments mentioned above, 
but various modifications mentioned below are possible. 
(1) In the first embodiment, the water discharge hole 10 having a racetrack 
shape is divided into two pieces at a base of the securing portion 8 as a 
boundary, but it is possible to divide two water discharge holes 10 
respectively into two pieces as shown in FIG. 5. In this manner, a number 
of water discharge holes 10 can be used. If the number of water discharge 
holes 10 is increased, the bottom portions remaining between the water 
discharge holes 10 function to reinforce the corona control ring 4 and 
thus a decrease of the mechanical strength can be prevented. Moreover, the 
water discharge holes 10 having the racetrack shape and the water 
discharge holes 27 having a small diameter may be used together. 
(2) In the first embodiment, a part of the corona control ring main body 2 
having a circular shape is cut out at the cut out portion 30 but it is 
possible to eliminate the cut out portion 3 as shown in FIG. 4. In this 
case, the securing portion 8 is connected between the inner side wall 
portions 6 like a bridge and the binding portion 8a is formed at a center 
of the securing portion 8. In this manner, if no cut out portion 3 is 
provided, it is possible to suppress the generation of the corona 
discharge between the open end portions 2a and 2b. It should be noted 
that, even in the corona control rings 2a and 2b, the cut out portion 3 
may be closed as mentioned above. 
As mentioned above, according to the invention, since the water discharge 
holes having a racetrack shape are arranged in the bottom portion of the 
corona control ring main body, water pooled in the depression portion of 
the corona control ring main body can be discharged rapidly and 
completely, and thus corona discharge can be preferably prevented even if 
rain fall is hard. Therefore, various problems due to corona discharge can 
be eliminated.