JPS6226712A - Pole mounting construction of arresting insulator for aerialtransmission line - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] Object of the Invention (Industrial Application Field) The present invention relates to a pole mounting structure for a lightning arrester device for an overhead power transmission line.
More specifically, the present invention relates to a pole mounting structure for a lightning arrester device for an overhead power transmission line, which is provided with power transmission line suspension insulators on both left and right sides, and a lightning arrester is installed between both suspension insulators.

(Conventional technology) Generally, overhead power transmission lines are installed on steel towers to quickly discharge abnormally high voltage caused by lightning strikes to the ground using lightning protection insulators to prevent ground faults and improve system reliability. A lightning arrester device is used.

As this conventional example, as shown in FIG. 7, an insulator chain 86 is suspended from the steel tower 1 via an insulator mounting bracket 85,
The electric wire 30 is connected to the lower end of the insulator chain 86 via a clamp 87.
In addition, the upper cap metal fitting 88 has a supporting metal fitting 8.
An arcing horn 91 is fixed to the lower end of the lightning arrester 90, and an arcing horn 93 is fixed to the cap fitting 92 at the lower end of the insulator chain 86. There was something that was opposite.

On the other hand, conventionally, as shown in FIG. 8, an insulator chain 86 is suspended from the tip of the steel tower 1, and a lightning arrester 94 is directly connected between the tower 1 and the electric wire 30 supported at the lower part 81 of the insulator chain 86. There was a system that was built diagonally and used air gap heat, a system similar to lightning arresters at power generation and substations.

(Problem to be Solved by the Invention) However, in the former conventional device shown in FIG. Therefore, it was difficult to maintain a stable shape during erection, and installation work was time-consuming.

In a lightning arrester device with such a configuration, if the lightning arrester element has a low discharge withstand capacity, a low level of pollution resistance, and the lightning arrester is relatively smaller and lighter than the suspended insulator, it may be installed directly to the suspended insulator. The influence of the single lightning arrester on the behavior of the entire insulator device was negligible. However, as the range of application has expanded, lightning arrester insulators have become larger due to demands for increased discharge withstand capacity, implementation of safety measures, and improved antifouling properties, and the drawbacks of this pole mounting method have become impossible to ignore.

In other words, there is insufficient clearance due to static balance when there is no wind, abnormal vibration due to lateral vibration in the direction of the track or perpendicular direction under strong winds, and inertia due to the dead weight of the lightning arrester and vibrations on the end fittings of the suspended insulator. These include insufficient strength due to bending loads, and an increase in width under the rim due to installing the lightning arrester in a nearly horizontal position to ensure the insulating strength and air gap area of the lightning arrester.

In addition, in the latter conventional device shown in Fig. 8, when there is no wind or vibration, the load shared by the lightning arrester is only its own weight, but when the wire is vibrated due to strong winds, falling ice or snow, etc., the burden is generated on the wire. Most of the horizontal load is borne by the lightning arrester, and the lightning arrester is required to have the same strength and reliability as a suspended insulator, resulting in a problem of increased size and weight.

The tower arms also needed to have a special structure to withstand this load. Furthermore, since the wire is supported at two points, the suspension insulator and the lightning arrester, and the vertical load is shared and the horizontal load is borne, special lamps are required, resulting in a complicated structure that reduces reliability and price. There was a problem with the surface.

The first object of the present invention is to solve the above-mentioned problems, increase the stability of the entire device, reduce the clearance, and make it more compact. We have developed a pole mounting structure for lightning arrester devices for overhead power transmission lines that can significantly reduce the repetitive bending load that acts on the lightning arrester even when shaken, and further improve reliability by preventing collisions between the suspension insulator and the lightning arrester. It is about providing.

In addition to the first object, the second object of the present invention is to significantly reduce the repetitive bending load that acts on the lightning arrester even when the transmission line swings in a direction perpendicular to the line direction, and to reduce the load on the suspended insulator. It is an object of the present invention to provide a pole mounting structure for a lightning arrester device for an overhead power transmission line, which can prevent the occurrence of imbalance and further improve reliability.

Structure of the Invention (Means for Solving the Problems) In order to achieve the first object, the first invention rotatably connects a connecting yoke to the steel tower via a hanging metal fitting, and The upper ends of a pair of left and right suspension insulators are rotatably connected to both ends of the yoke, and a spacing member is installed between the lower ends of both suspension insulators. The electric wire is supported, and the upper and lower parts of the lightning arrester are connected at one point between the connecting yoke and the spacing member, respectively, and the connecting yoke, the hanging insulator, the spacing member, and the lightning arrester are connected to the connecting yoke. are arranged symmetrically with respect to a perpendicular line passing through the center of rotation of the lightning arrester, and furthermore, at least the upper connecting fitting part of the upper and lower connecting fitting parts of the lightning arrester is arranged in the longitudinal direction with respect to the connecting yoke or the spacing member.
In other words, it is possible to rotate it in a direction substantially perpendicular to the direction of the power transmission line.

Further, in order to achieve the second object, a second invention provides, in addition to the means of the first invention, at least an upper connecting point of the upper and lower connecting points of the lightning arrester to a connecting yoke or a spacing member. On the other hand, we have adopted a method that allows it to rotate in the left-right direction, that is, in the direction of the power transmission line.

(Function) In the first invention, since the entire nine lightning arrester insulators are symmetrical with respect to the perpendicular line passing through the rotation center of the connecting yoke, not only the entire device is stabilized, but also one of the two suspension insulators can be suspended. When a suspension insulator is separated, the separated suspension insulator may collide with the lightning arrester, but since the connecting yoke and the spacing member are connected by the lightning arrester, the shock caused by the collision is small and the lightning arrester is Damage is prevented. As a result, the disconnected suspension insulator does not collide with the normal suspension insulator, and therefore, the normal suspension insulator is prevented from breaking off, and the power transmission line is prevented from falling to the ground.

In addition, even if the lightning arrester sways in a direction perpendicular to the line direction of the power transmission line due to wind pressure, etc., the upper end connection of the lightning arrester has one point, and the connecting metal part can rotate in the same direction, so it will not affect the lightning arrester. The repeated bending loads caused by this are significantly reduced.

Since the lightning arrester is supported at both ends, collision between the lightning arrester and the suspended insulator is prevented.

In addition to the effects of the first invention, the second invention is such that even if the lightning arrester sways in the direction of the transmission line due to wind pressure, etc., the upper end connecting part of the lightning arrester can rotate in the same direction. No repeated bending loads are applied. Since the lightning arrester is supported at both ends at the center of rotation of the suspension point, no unbalanced load is generated on the suspension insulator.

If the insulator device swings in the direction of the track or in a direction perpendicular to the same in a strong wind, the relative position of the connecting cork and the spacing member may change. Even under this condition, since both ends of the lightning arrester are connected at one point, excessive stress concentration does not occur in the lightning arrester.

(Example) Hereinafter, an example embodying the present invention will be described based on FIGS. 1 to 5.

As shown in Fig. 2, a hanging metal fitting 2 with an inverted U-shape on the front is fixed to the steel tower 1 with bolts 3, and another hanging metal fitting 2 with an upside-down U-shape on the side is fixed to the steel tower 1. A lower bracket 4 is hung so as to be rotatable in the left-right (track) direction and front-rear (perpendicular to the track direction) direction, and a connecting yoke 6 is connected between the lower ends of the hanging bracket 4 by a connecting pin 5 in the left-right direction. It is hung so that it can rotate.

Roughly speaking, the overhead insulator device for overhead power transmission lines of this embodiment includes a pair of suspension insulators as suspension insulators supported at both left and right ends of the connection yoke 6 and formed in the same structure. 7.7, the spacing rod 22 installed between the lower ends of the suspension insulator chain 7.7, and the connecting yoke 6.
and a pair of left and right clamps 28, 28 for supporting the power transmission line 30 at two points at both ends of the spacing rod 22. It is composed of.

A reinforcing rib 22a is provided on the lower side of the spacing rod 22 over substantially the entire length thereof, as shown in FIG. 5(a). In place of this reinforcing rib 22a,
), reinforcing ribs 22b to 22C of various shapes may be attached.

Therefore, to explain the double suspension insulator chain 7.7, a first connecting link 9 is connected to both left and right ends of the connecting yoke 6 by connecting pins 8 so as to be rotatable in the left and right direction. The second connecting link 1 is connected by the connecting pin 10.
1 are connected so as to be rotatable in the front and rear directions. Further, a third connecting link 13 is connected to the second connecting link 11 by a connecting pin 12 so as to be rotatable in the left and right direction. Furthermore, the upper end of a suspension insulator chain 15 configured by connecting a large number of suspension insulators in series is connected to the lower end of the third connecting link 13 via a connecting pin 14 so as to be rotatable in the left-right direction. . A fourth connecting link 1G is connected to the lower end of the insulator chain 15 so as to be rotatable in the left-right direction, and a connecting plate 18 is connected to the link 16 so as to be rotatable in the left-right direction by a connecting pin 17. Plate 18 and the third connecting link 1
3 has arcing horns 19 and 20 on the power supply side and the ground side.
is fixed in a cantilever manner by bolts 21.

A spacing rod 22 is installed by a connecting pin 23 between a pair of connecting plates 18.18 located at the lower ends of both suspended insulator chains 7.7.

As is clear from FIG. 2, the two suspended insulator chains 7, 7 are installed in a substantially inverted V-shape as a whole.

Further, the connecting yoke 6, both suspended insulators 7.7, and the spacing rod 22 are symmetrically formed with respect to the perpendicular line H--H passing through the connecting pin 5, and are formed generally into a trapezoidal shape as a whole.

A fifth connecting link 26 is connected to the pair of connecting plates 18.18 so as to be rotatable in the left and right direction by a connecting pin 27, and both links 26.26 are each provided with a clamp 28.2.
8 are rotatably connected by connecting pins 29, 29, and the power transmission line 30 is held at two places by both clamps 28, 28. The power transmission line 30 is covered with an armor rod 31, and the clamp 28 and the power transmission line 3o are fastened with a nut 32 so that they cannot move relative to each other.

A connecting link 33 is connected to a pin 34 in the center of the connecting yoke 6.
A supporting metal fitting 40 is connected to the lower end of the connecting link 33 so as to be rotatable in the left-right direction, and a supporting metal fitting 40 is connected to the lower end of the connecting link 33 so as to be rotatable in the horizontal direction. Hanging ears 49, which will be described later, provided at the upper and end portions are suspended so as to be rotatable in the front-back direction. This lightning insulator 36
is located on the perpendicular line H-H passing through the connecting pin 5.

On the other hand, a mounting plate 37 is fixed upwardly at the upper center of the spacing rod 22, and at the center of the mounting plate 37,
The connecting link 38 is rotatably connected in the left-right direction by a pin 39, and a support metal fitting 40 is connected to the pin 41 between the connecting link 38 and a hanging ear 49 (described later) provided at the lower end of the lightning arrester 36.
It is loosely connected so that it can be rotated in the front-rear direction and left-right direction, and no tension is applied thereto. A plurality of through holes 38a for engaging the pins 41 are vertically provided through the connecting link 38, forming a vertical length adjustment mechanism. In addition, dimensional tolerances between the suspension insulator chains 7, 7 and the lightning arrester 36 are accommodated. In addition, the mounting plate 37
and a pressure relief path forming cover 58 (described later) of the lightning arrester 36 are electrically connected by a lead wire 42 for noise prevention. The upper end of this lead wire 42 is welded to the pressure relief path forming cover 58, and the metal fitting 43 at the lower end is fastened to the mounting plate 37 with bolts 44.

Next, the structure of the lightning arrester 36 will be explained with reference to FIGS. 3 and 4.

Cylindrical flange fittings 46 and 47 are fitted and fixed to the upper and lower outer circumferential surfaces of the porcelain insulator tube 45 by cementing 48. A pin 35 is attached to the outer peripheral surface of both the upper and lower flange fittings 46.47 for the connecting link 33.40.
．． The hanging ears 49 and 49 connected by 41 are 180 degrees apart from each other.
It is integrally formed with a certain degree of precision.

On the end faces of the insulator pipe 45 and the flange fittings 46 and 47,
The terminal plates 5o and sx are fixed by a plurality of bolts 52 (eight in this embodiment, but only one is shown). Seal members 53 and 53 are interposed between the end faces of the insulator tube 45 and the terminal plates 50 and 51, respectively.

Pressure relief passages 50a and 51a are provided through the terminal plates 50 and 51 to communicate the space inside the insulator tube 45 with the atmosphere.

The pressure relief passage 50 is located at the end of the terminal plate 50.51.
rupture discs 54 and 54 are brought into contact so as to cover a and 51a,
A pressure ring 55.55 is brought into contact with the surface of the rupture disc 54.54 and fixed by the bolt 52. Seal members 56 and 57 are interposed concentrically at two locations between the end faces of the terminal plates 50 and 51 and the rupture discs 54 and 54, respectively, so that the space within the insulator tube 45 is maintained in a sealed state.

The pressing ring 55. is attached to the end surface of the terminal plate 50.51.
The opening edges of the pressure relief path forming covers 58.58 are brought into contact with each other so as to surround the vicinity of the outer periphery of the pressure relief path forming covers 58.5.
8 is fixed to the terminal Fi50.51 by a plurality of ports 59. On the outside of the cover 58, 58 are pressure relief ports 58a, 58 that are inclined toward each other and correspond to each other.
a is formed. The pressure relief ports 58a, 58a are arranged in the left-right direction, that is, in the direction orthogonal to the line direction of the power transmission line 30.
And it is oriented in the opposite direction to the steel tower 1.

On the other hand, on the outer circumferential surface of the flange metal fittings 46 and 47, a third.
As shown in Figure 4, arcing ring arms 60a, 60a
is attached, and a substantially annular arcing ring 60.60 is attached to the end thereof so as to surround the insulator tube 45 with a margin.
is horizontally supported in a cantilever manner, and a portion thereof is cut out at a position corresponding to the pressure relief ports 58a, 58a, as shown in FIG.

Next, to explain the internal lightning protection structure of the insulator tube 45, the inside of the insulator tube 45 is made of reinforced plastic (F
A tension-resistant insulating cylinder 61 made of material such as RP) is accommodated,
Inner flange fittings 62 and 62 are fitted and fixed airtightly to the outer periphery of both upper and lower ends of the insulating cylinder 61 with an adhesive 63.

The end faces of both flange fittings 62.62 and the terminal plate 50.5
Mounting tubes 64 and 65 are interposed between the two holes and are fixed by a plurality of poles 66 and 67. And the upper mounting fif? i64 to the terminal plate 5 by the port 66
0, and the tension-resistant insulating cylinder 61 is suspended and held in a predetermined position.

On the other hand, pressure relief passages 62a, 62a are transparently provided in the lid of the flange fitting 62.62, and the flange fitting 62.62 and the mounting tube 64 are arranged so as to seal the passages 62a, 62a.
．． 65, rupture discs 68, 68 are interposed. Seal members 69, 69 are interposed between the flange fittings 62, 62 and the rupture discs 68, 68, and between the rupture discs 68, 68 and the mounting tubes 64, 65, respectively. Further, a sealing member 70 is also interposed between the terminal plate 50 and the mounting tube 64.

An engagement recess 65a is formed in the lower end surface of the lower mounting vI65, into which an engagement protrusion 51b protruding from the upper surface of the terminal plate 51 is fitted so as to be relatively movable in the vertical direction.
By absorbing the relative movement in the vertical direction due to the difference in thermal expansion between the tension insulating tube 61 and the tension insulating tube 61, damage to the tensile insulating tube 61 is prevented. Moreover, the engagement recess 65a and the engagement protrusion 51b
A sealing member 71 is interposed between the two. moreover,
A drop-off prevention bolt 72 is attached to the terminal plate 51 and attached to the mounting tube 6.
5:, ++;, η, and is screwed onto the flange fitting 62, allowing relative movement between the insulator tube 45 and the +tj/I-clad insulating tube 61, and also preventing the insulator tube from falling when the insulator tube 45 is broken. That's what I do.

Further, a recess 51C is formed on the upper surface of the terminal plate 51, and a spring 7 having a shunt 78 is absorbed in the recess 51c, and its upper end is pressed against the lower surface of the mounting tube 65, thereby establishing electrical continuity. It is measured.

A lightning arrester element 73 made of a material mainly composed of zinc oxide and having nonlinear voltage-current characteristics is accommodated in the tension-resistant insulating cylinder 61. The lightning arrester element 73 has an annular tightening member 75.75 engaged with contact fittings 74.74 that are in contact with both upper and lower ends, and a tightening rod 76 formed of FRP is attached to this tightening member.
A plurality of them are stacked with a NAND 77 inserted through them.

As shown in FIG. 3, an element 73 is pressed between the recess 55b of the flange fitting 55 and the contact fitting 74 to ensure good contact between the elements and to prevent mutual displacement of the elements by external impact. A spring 81 having a shunt 80 is housed therein.

Next, the operation of the lightning arrester device for overhead power transmission lines constructed as described above will be explained.

Now, when an abnormal voltage occurs on an overhead power transmission line due to an unexpected large-scale lightning strike, this voltage passes through the clamp 28, the fifth connecting link 26, the connecting plate 18, the spacing rod 22, the mounting plate 37, and the lead wire 42, and then the lightning After passing through the insulator 36, the hanging ears 49 of the flange fitting 46, the support fitting 40,
It flows to the steel tower 1 via the connecting link 33, the connecting yoke 6, and the hanging fittings 4 and 2, and is grounded.

When the abnormal current flows through the lightning arrester element 73 of the lightning arrester 36 and the lightning arrester element 73 is destroyed, an extremely high temperature arc is generated due to the following current. For this reason,
The pressure inside the tension-resistant insulation cylinder 61 increases, and the rupture discs 68.54 burst one after another, causing the pressure relief passages 50a, 51 of the terminal plates 50.51 to rupture.
A super high temperature arc flows into the pressure relief path forming cover 58.58, and is further discharged to the outside from the pressure relief ports 58a, 58a.
Transition between 0 and 0.

Now, in the embodiment of the present invention, the suspension insulator chains 7 and 7 are attached in a substantially inverted V shape to the connection yoke 6 rotatably suspended from the steel tower 1, and A spacing rod 22 is installed and fixed between the lower ends of the rods 2 and 7.
The power transmission line 30 is held at two places at both ends of the connecting yoke 6, and the upper end of the lightning arrester 33 is fixed at one point in the center of the connecting yoke 6. Since each of the above-mentioned members is configured symmetrically with respect to the perpendicular line H-H passing through 5, even if the power transmission line 30 is shaken in the line direction due to wind, etc., it will not sway abnormally, and the insulator connected load can be reduced. In addition to suppressing the promotion of imbalance,
Collision between the lightning arrester and the suspension insulator chain becomes less likely to occur. In addition, even if the insulator device attempts to sway in a direction perpendicular to the line direction, the weight of the insulator acts on it, suppressing the amount of sway and preventing abnormal movement, reducing the clearance between the energized side and the tower body. Collisions between the lightning arrester and the suspension insulator chain are also less likely to occur.

Furthermore, in the event that either one of the pair of suspended insulator chains 7.7 is separated, one of the clamps 28 is moved downward by the weight of the power transmission line 30, but the amount of movement is not that thick (and Since the other clamp 28 also does not deviate much from its original position, the separated suspension insulator chain 7 is rotated toward the lightning arrester 33 around the connecting pin 8 solely by its own weight.

However, this rotational force is weak, and the shock caused by the collision against the lightning arrester 33 is small, so that the lightning arrester 33 is not destroyed. As a result, the suspended insulator chain 7 was separated from the lightning arrester 33.
Although the lightning arrester may be slightly damaged by colliding with the lightning arrester,
The power transmission line 3 is reliably prevented from destroying the normal suspension insulator chain 7.
0 can be prevented from falling to the ground.

In particular, in the embodiment of the present invention, the connecting points of the upper and lower parts of the lightning arrester 36 are arranged in the front-rear direction with respect to the connecting yoke 6 and the spacing loft 22, that is, in the line direction of the power transmission line, and in the left-right direction, that is, approximately perpendicular to the line direction. Since the lightning arrester 36 can be rotated in the direction, even if the power transmission line sways in the line direction or in a direction perpendicular to the line direction due to wind pressure or the like, the repetitive bending load acting on the lightning arrester 36 can be eliminated and reliability can be improved.

Note that the present invention can also be embodied in the following embodiments.

(1) As shown in FIG. 6, the lightning arrester 36 is interposed between a pair of parallel left and right suspension insulator chains 7.7. In the case of this embodiment, even if one suspension insulator chain 7 is severed,
The impact at that time was on lightning arrester 36 and normal suspension insulator 7.
Therefore, the lightning arrester 36 is not damaged.

(2) In each of the embodiments described above, the lightning arrester 36 is made unrotatable in the left-right direction, that is, in the track direction, and is mounted so that it can be rotated in the front-back direction, that is, in the direction perpendicular to the track direction.

The embodiment described in this section (2) is an embodiment of the first invention.

(3) For example, rupture F168 or pressure relief path forming cover 5
8. Any type of lightning arrester may be used, such as a type that does not include 8.58.

(4) In place of the suspension insulator chain 15, one or more long-stem insulators (as shown) may be used.

Effects of the Invention As detailed above, the first invention can improve the stability of the entire lightning arrester device for power transmission lines, and even if a hanging insulator should break, a normal hanging insulator will not be destroyed. It is possible to prevent the power transmission line from falling to the ground, and even if the power transmission line sways in a direction perpendicular to the line direction due to wind pressure, etc., the repetitive bending load on the connection part of the lightning arrester can be eliminated, and the lightning arrester This has the effect of preventing collisions between the suspension insulator and the suspended insulator, and improving reliability.

In addition to the effects of the first invention, the second invention can eliminate the repeated bending load applied to the lightning arrester and the unbalance of the suspended insulator load even if the power transmission line sways in the direction of the line due to wind pressure, etc., thereby improving reliability. This has the effect of further improving the

[Brief explanation of the drawing]

Fig. 1 is a perspective view of a road body in which a lightning arrester device for power transmission lines is mounted on poles, showing an embodiment of the present invention, Fig. 2 is a front view showing an enlarged view of the lightning insulator device, and Fig. 3 is a view of FIG. 4 is an enlarged half sectional view taken along the line AA of FIG. 2, FIG. 4 is an enlarged sectional view J1i taken along the line B-B of FIG. FIG. 6 is a front view showing another example of the present invention, and FIGS. 7 and 8 are front views showing conventional examples, respectively. 6...Connection yoke, 7...Suspension insulator chain, 22...
Spacing maintenance rondo, 26... Fourth connecting link, 28...
・Clamp, 36... Lightning arrester.

Claims (1)

[Claims] 1. A connecting yoke is rotatably connected to the steel tower via a hanging metal fitting, and the upper ends of a pair of left and right suspension insulators are rotatably attached to both ends of the connecting yoke. A spacing member is installed between the lower ends of both suspension insulators, a power transmission line is supported at the bottom of the spacing member, and a lightning arrester is installed between the connecting yoke and the spacing member. The upper and lower parts of the lightning arrester are connected at one point, and the connecting yoke, the hanging insulator, the spacing member, and the lightning arrester are arranged symmetrically with respect to a perpendicular line passing through the center of rotation of the connecting yoke. An overhead structure characterized in that at least the upper connecting fitting part of the upper and lower connecting fitting parts is rotatable in the front-back direction with respect to the connecting yoke or the spacing member, that is, in the direction substantially perpendicular to the line direction of the power transmission line. Pole mounting structure for lightning protection insulators for power transmission lines. 2. The overhead transport system according to claim 1, wherein the connecting fitting part between the lightning arrester and the connecting yoke or the spacing member has a length adjustment mechanism for absorbing dimensional tolerances between the suspension insulator and the lightning arrester. Pole mounting structure for lightning arrester device for electric wires. 3. A connecting yoke is rotatably connected to the steel tower via a hanging metal fitting, and the upper ends of a pair of left and right suspension insulators are rotatably connected to both ends of the connecting yoke, and both suspensions are connected rotatably to the steel tower. A spacing member is installed between the lower ends of the insulators, a power transmission line is supported at the lower part of the spacing member, and the upper and lower parts of the lightning arrester are installed between the connection yoke and the spacing member, respectively. The connecting yoke, hanging insulator, spacing member, and lightning arrester are connected at one point, and the connecting yoke, hanging insulator, spacing member, and lightning arrester are arranged symmetrically with respect to a perpendicular line passing through the center of rotation of the connecting yoke. At least the upper connecting fitting part of the part is rotatable with respect to the connecting yoke or the spacing member in the front-rear direction, that is, in the direction of the power transmission line, and in the left-right direction, that is, in the direction substantially perpendicular to the line direction. Features a pillar mounting structure for lightning arrester devices for overhead power transmission lines.