GB2465058A

GB2465058A - Mounting bracket for a lightning arrester

Info

Publication number: GB2465058A
Application number: GB0918673A
Authority: GB
Inventors: Kenji Tsuge; Susumu Suzuki
Original assignee: NGK Insulators Ltd
Current assignee: NGK Insulators Ltd
Priority date: 2008-11-04
Filing date: 2009-10-23
Publication date: 2010-05-12
Anticipated expiration: 2029-10-23
Also published as: GB2465058B; HK1138944A1; KR101674206B1; MY150265A; GB0918673D0; TW201019349A; TWI435338B; KR20100050428A; JP2010113817A; JP5149772B2

Abstract

A metallic bracket 5 for supporting a base portion of a lightning arrester is fixed to a yoke 2 of a double insulator strings on the earth side or the line side. A pair of right and left arm portions 14 projecting from an end of the yoke 2 toward the tower arm side is provided in a baseplate 10 of the bracket 5. A backing plate 16 is arranged on a lower face of the yoke 2. The baseplate 10 of the bracket 5 and the backing plate 16 are fastened by a pair of bolts 19 passing through the yoke 2. The arm portions 14 of the baseplate 10 of the bracket 5 and the backing plate 16 are fastened by a pair of bolts 20 passing outside of the yoke 2. The lightning arrester can be correctly and robustly mounted to the insulator chains and can be mounted to an existing power transmission line by the present invention.

Description

TITLE OF THE INVENTION

STRUCTURE FOR MOUNTING LIGHTNING ARRESTER ON INSULATOR

ASSEMBLY

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a lightning arrester mounting structure for mounting a lightning arrester on an insulator assembly for supporting a power transmission line and, more particularly, relates to a structure for mounting a lightning arrester on a double tension insulator assembly consisting of double insulator strings.

Description of the Related Art

Insulator assembly having a length corresponding to system voltage of transmission line insulatively supports a power transmission line to a tower arm; however, a large scale power failure accident is likely to occur when the insulator string is destroyed in lightning strike to the power transmission line.

Consequently, a countermeasure has been implemented since a long time before that an arcing horn is mounted to each of the line side and the earth side of the insulator string and an arc generated by a lightning surge is introduced to the outside of the insulator string to prevent the insulator assembly from being destroyed.

Furthermore, in recent years, a countermeasure has been implemented that a lightning arrester incorporating a zinc oxide element having voltage-current nonlinear characteristics is mounted to an insulator assembly, lightning surge current is immediately flown to the earth side via the lightning arrester in lightning strikes, and a follow current is interrupted and to thereby protect the insulator string and the power transmission line.

Various types of insulator assemblies are available; however, many of the tension insulator assemblies are the double tension insulator strings. This is a structure in which both ends of the double insulator strings in parallel are each connected to a coupling hardware referred to as yoke, the center of the yoke on the earth side is connected to a tower arm by another coupling hardware, and the center of the yoke on the line side is connected to a power transmission line supporting clamp. In the case where a lightning arrester is mounted to such double tension insulator strings, the lightning arrester is mounted at a central position of the double strain insulator strings taking the apparatus stability into account.

Such a lightning arrester needs to be fixed at an upper position with a distance slightly spaced apart from the insulator string. Consequently, as shown in Fig. 3 of Japanese Unexamined Patent Application Publication No. 2003-217790, there has been adopted a conventional structure for mounting a lightning arrester, in which a lightning arrester mounting hardware is fixed to a central portion of a yoke on the grounding side by bolts and a base of the lightning arrester is fixed at an upper portion of the hardware. In this structure, fixation by bolts usingbolt insertionholes formed intheyokeis usual. However, when the voltage class is increased, the lightning arrester becomes large and long accordingly. Therefore, as shown in Fig. 3 of Japanese Unexamined Patent Application Publication No. 2003-217790, fixing force is deficient if the lightning arrester mounting hardware is fixed to the yoke by only two bolts. In such a state, when transverse force is applied to the tip end of the lightning arrester, a misalignment is generated by a difference between a bolt insertion hole and a bolt diameter, a central axis of the lightning arrester is misaligned from the center of the double insulator strings; an electrode at the tip end of the lightning arrester is liable not to be held at a correct position. Furthermore, the fastening force of the bolt is deteriorated due to elapse of time after mounting, and an installation orientation of the lightning arrester with respect to the insulator string changes, and the length of a series gap changes; and therefore, a predetermined lightning protection function is liable not to be secured.

The number of bolts for fastening the lightning arrester mounting hardware to the yoke can be increased to enhance the fixing force. However, a number of the bolt insertion holes cannot be formed due to a problem of the strength depending on the size and shape of the yoke. Besides, in the case where the lightning arrester is installed to the existing power transmission line, additional formation of a new bolt insertion hole in the yoke on a tower is not feasible in reality.

SUIVIMARY OF THE INVENTION

An object of the present invention is to solve the above described conventional problem and to provide a structure for mounting a lightning arrester on an insulator assembly, which enables robust mounting without misalignment with respect to the insulator string even when the lightning arrester becomes large in size and also enables mounting on an existing power transmission line.

According to an aspect of the present invention implemented for solving the aforementioned problems, there is provided a structure for mounting a lightning arrester on an insulator assembly in which a metallic bracket for supporting a base of the lightning arrester is fixed to a yoke which connects an end on the grounding side of a double insulator strings with a tower arm or connects an end on the voltage applying side with a line, wherein a pair of right and left arm portions projecting from the end of the yoke are provided in a baseplate of the bracket attached closely to an upper face of the yoke, a backing plate provided with opposed portions to the arm portions is arranged on a lower face of the yoke, the baseplate of the bracket and the backing plate are mutually fastened by a pair of right and left bolts passing through the yoke, and the arm portions of the baseplate of the bracket and the opposed portions of the backing plate are mutually fastened by a pair of right and left bolts passing outside of the yoke.

It is preferable that the insulator assembly is consist of double tension insulator strings. Further, it is preferable that the bracket is provided with a lightning arrester supporting portion rising obliquely upward from the baseplate. Further, the backing plate may be formed in a two-parted structure.

According to the structure for mounting a lightning arrester on an insulator assembly of the present invention, the baseplate of the metallic bracket for supporting the base of the lightning arrester is fixed to a yoke by a pair of right and left bolts passing through the yoke and a pair of right and left bolts passing outside of the yoke. In this way, the bracket is fixed by at least four bolts arranged in a distributed manner.

Therefore, robust fixing force is secured, and an orientation of a central axis of the lightning arrester is not misaligned even when the lightning arrester is large and long.

Furthermore, according to the structure for mounting a lightning arrester on an insulator assembly of the present invention, two bolt insertion holes only have to be formed in the yoke, and therefore, the strength of the yoke itself is not liable to be lowered. In addition, if the yoke is provided with two bolt insertion holes, no further addition of bolt insertion holes is required; and therefore, an application range to an existing power transmission line can be increased.

Further, according to the structure for mounting a lightning arrester on an insulator assembly of the present invention, the two bolts fasten the baseplate of the bracket and the backing plate mutually on the outside of the yoke.

Therefore, arm portions projecting from the end of the yoke are slightly elastically deformed due to the bolt fastening force.

With this configuration, even when the fastening force of the bolt is deteriorated due to elapse of time after mounting, this elastic deformation compensates for the deterioration of the fastening force of the bolt. Accordingly, even if years elapse, an installation orientation of the lightning arrester with respect to the insulator assembly does not change.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is an overall view showing a double tension insulator strings according to an embodiment of the present invention; Fig. 2 is a front view showing a relevant portion of the present invention; Fig. 3 is a plan view showing a relevant portion of the present invention; Fig. 4 is an exploded perspective view showing a relevant portion of the present invention; Fig. 5 is a schematic cross-sectional view showing a fastening portion; and Fig. 6 is a view showing a modified example of a backing plate.

DETAILED DESCRIPTION OF THE INVENTION

Next, apreferredembodiment of thepresent inventionwill be described in detail on the basis of the drawings.

Fig. 1 isanoverallviewshowingadoubletension insulator stringsaccordingtotheembodimentof the invention. Reference numeral 1 denotes an insulator string, 2 denotes a yoke on the earth side (the tower side) , 3 denotes a yoke on the line side (the power transmission line side), 4 denotes a lightning arrester mounted by a bracket 5 on the yoke 2, and 6 denotes an electrode on the voltage applying side mounted on the yoke 3.

As well known, the yoke 2 on the earth side is connected to a tower arm via another connecting hardware (not shown in the drawing), and an end of the yoke 3 on the line side is fixed to a power transmission line via another connecting hardware (not shown inthe drawing) . Theinsulatorstringl is constituted such that suspension insulators, the number of which corresponds to system voltage of transmission line, are coupled in series.

Furthermore, the lightning arrester 4 has a well-known structure in which a zinc oxide element is coated with a resin envelope with corrugations, and a discharging electrode 7 is connected totheendofthelightningarrester4. Apredetermineddischarge gap G is formed between the discharging electrode 7 and the line side electrode 6; and in lightning strike, lightning surge current is flown to the zinc oxide element of the lightning arrester 4 via the discharge gap G. The zinc oxide element becomes an insulator for commercial voltage. However, the zinc oxide element has voltage-current nonlinear characteristics that it turns into a conductor by rapidly dropping the resistance value against a high voltage resulting from a lightning surge.

Therefore, lightning surge current is immediately flown to the tower side to protect the insulator string 1.

Fig. 2 is a front view showing a relevant portion of the present invention; and Fig. 3 is a plan view thereof.

As shown in Fig. 3, the yoke 2 is a metal plate having a flat isosceles triangle shape, and each of the both ends of the base of the yoke 2 is connected with the respective ends of the insulator strings 1 with connecting hardware 8.

Furthermore, an apex portion of the isosceles sides is connected with a tower arm with connecting hardware (not shown in the drawing) . Incidentally, the yoke 3 on the line side has a similar structure. Both ends of the double insulator string 1 are supported by these yokes 2 and 3, so that the double insulator strings laremaintainedinparalleiwitheachother, andtensile force due to the power transmission line is equally divided into two to be proportionally supported. Two bolt insertion holes 9 are formed in the yoke 2 at right and left symmetrical positions near the base.

The bracket 5 is a member for fixing the lightning arrester 4 to the yoke 2, and includes a tabular baseplate 10 attached closely to an upper face of the yoke 2, a vertical portion 11 rising upward from the baseplate 10, and an inclined lightning arrester supporting portion 12 provided continuously to an upper end of the vertical portion 11, As shown in Fig. 1, the base portion of the lightning arrester 4 is fixed to the lightning arrester supporting portion 12 by a number of bolts, and the lightning arrester 4 is supported in an oblique direction with respect to the insulator string 1.

As shown in Figs. 3 and 4, two bolt insertion holes 13 corresponding to the bolt insertion holes 9 of the yoke 2 described above are formed in the baseplate 10 of the bracket 5. The baseplate 10 of the bracket 5 includes a pair of right and left arm portions 14 projecting from an end of the yoke 2 toward the tower arm side, and bolt insertion holes 15 are formed at opposed portions serving as tip end portions of the arm portions 14.

An intermediate portion of the arm portion 14 is formed in a concave shape so as to be able to pass a connecting hardware for connection with the tower arm. Furthermore, a backing plate 16 provided with opposed portions to the arm portions 14 is arranged on a lower face of the yoke 2. Two bolt insertion holes 17 corresponding to the bolt insertion hole 9 of the yoke 2 and two bolt insertion holes 18 corresponding to the bolt insertion holes 15 of the arm portions 14 are formed also in the backing plate 16. In this embodiment, the backing plate 16 is made of one steel plate.

As shown in Figs. 2 and 3, the baseplate 10 of the bracket is fastened to the yoke 2 by a pair of right and left first bolts 19 passing through the bolt insertion holes 9 of the yoke 2, the bolt insertion holes 13 of the baseplate 10, and the bolt insertion holes 17 of the backing plate 16. Then, the baseplate of the bracket 5 is also fastened to the yoke 2 by a pair of right and left second bolts 20 passing outside of the yoke 2, passing through the bolt insertion holes 15 formed in the armportions 14 of thebaseplate 10, and through the bolt insertion holes 18 of the baseplate 16. Specifically, the first bolts 19 directly fasten the baseplate 10 of the bracket 5 to the yoke 2, and the second bolts 20 indirectly fasten the baseplate 10 of the bracket 5 to the yoke 2 while sandwiching the yoke 2 between the backing plate 16 and the baseplate 10.

Fig. 5 is a schematic cross-sectional view showing these fastening portions in a state where the baseplate 10 of the bracket is fastened to the yoke 2 and the backing plate 16 by the pair of right and left first bolts 19 passing through the yoke 2 and the pair of right and left second bolts 20 passing outside of the yoke 2. The lightning arrester mounting structure of the present embodiment includes such a configuration; and therefore, the following operational advantages can be exhibited.

(1) Since the baseplate 10 of the bracket 5 is fixed to the yoke 2 by four bolts 19 and 20, more robust fixing force is secured than conventional two-bolt system. Therefore, even when the lightning arrester 4 is large and long, a direction of a central axis of the lightning arrester 4 is not misaligned.

(2) Since two bolt insertion holes 9 only have tobe formed in the yoke 2, the strength of the yoke itself is not liable to be lowered. Furthermore, the yoke 2 enables to mount the lightning arrester 4 on an existing power transmission line provided with two bolt insertion holes 9.

(3) Since the second bolts 20 mutually fasten the opposed portions of the baseplate 10 of the bracket 5 and the backing plate 16 on the outside of the yoke 2, the arm portions 14 are elastically deformed from the end of the yoke due to the bolt fastening force and deterioration of the fastening force of the bolt is compensated for by the same amount. Accordingly, even if years elapse, stable fixing force is maintained.

In the above described embodiment, the backing plate 16 is formed in one plate having substantially the same shape as the baseplate 10 as shown in Fig. 6A. However, the backing plate 16 may be formed in a shape where a portion which does not affect the fastening strength is cut away as shown in Fig. 6B.

Furthermore, the backing plate l6rnaybe divided into two, right and left, as shown in Fig. 60; or may be divided into two, front and back, as shown in Fig. 6D. It is to be noted, however, that in the case of Fig. 6D, operational advantage described in the previous paragraph 3) is not obtained. In addition, if the baseplate 10 or the backing plate 16 shown in Fig. 5 is provided with projections so that the projections come into contact with the yoke 2, further stable fixing force is maintained.

Although the present invention is particularly suitable for mounting the lightning arrester on double tension insulator strains, the present invention may also be applied to suspension insulator strains.

Furthermore, in the above embodiment, description has been made on an example of the lightning arrester, which is mounted on the yoke on the grounding side. However, the lightning arrester may be similarly mounted on the yoke on the line side, which supports the power transmission line.

Claims

What is claimed is: 1. A structure for mounting a lightning arrester on an insulator assembly in which a metallic bracket for supporting a base of the lightning arrester is fixed to a yoke which connects an end on the earth side of a double insulator strings with a tower arm or connects an end on the line side with a line, wherein a pair of right and left arm portions projecting from the end of the yoke are provided in a baseplate of the bracket attached closely to an upper face of the yoke, a backing plate provided with opposed portions to the arm portions is arranged on a lower face of the yoke, the baseplate of the bracket and the backing plate are mutually fastened by a pair of right and left bolts passing through the yoke, and the arm portions of the baseplate of the bracket and the opposed portions of the backing plate are mutually fastened by a pair of right and left bolts passing outside of the yoke.
2. The structure for mounting a lightning arrester on an insulator assembly according to claim 1, wherein the insulator assembly is consist of double tension insulator strings.
3. The structure for mounting a lightning arrester on an insulator assembly according to claim 1, wherein the bracket is provided with a lightning arrester supporting portion rising obliquely upward from the baseplate.
4. The structure for mounting a lightning arrester on an insulator assembly according to claim 1, wherein the backing plate is formed in a two-parted structure.
5. A structure for mounting a lightning arrester on an insulator assembly, substantially as herein described with reference to and as shown in the accompanying drawings.
6. In combination, a lightning arrester mounted on an insulator assembly by a structure according to any one of the preceding claims.