JPH0510781B2 - - Google Patents

Description

[Detailed description of the invention]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vacuum interrupter, and more particularly to a so-called vertical magnetic field type vacuum interrupter that is equipped with means for generating an axial magnetic field (longitudinal magnetic field) parallel to an arc. Conventional technology A vertical magnetic field type vacuum interrupter is
By applying a vertical magnetic field parallel to the arc, the arc is dispersed on the electrode surface, preventing its local concentration, and thereby preventing excessive melting of the electrode, thereby improving current cutting ability. A vertical magnetic field is generated by introducing a pair of electrode rods into a vacuum container so that they can approach and separate from each other, and by fixing an electrode consisting of an arc diffusion part and a contact part to the inner end of each electrode rod. A coil as a means may be provided outside the vacuum container as described in Japanese Patent Publication No. 42-13045, or as described in Japanese Patent Publication No. 53-41793,
Japanese Patent Publication No. 54-22813 or Japanese Patent Publication No. 56-
As described in Japanese Utility Model Publication No. 130037, etc., it is possible to provide the back of each electrode in a vacuum container, or furthermore, as described in Japanese Utility Model Application Publication No. 56-57443, etc., a pair of electrodes in a vacuum container can be provided. It is constructed by providing for the outer periphery. Incidentally, the electrode material of the vacuum interrupter is required to have the following properties () to (). (i) High current cutting ability (ii) High withstand voltage (iii) Low consumption (iv) Low current cutting value (v) Low contact resistance (vi) High welding strength Small However, it is not possible to satisfy all the properties with a single material, and certainly not with pure metals, and now depending on the application of the vacuum interrupter, it is especially necessary to sacrifice some of the other properties. Materials that satisfy the following characteristics are selected. However, in the electrodes of conventional vertical magnetic field type vacuum interrupters, the arc diffusion part is made of copper (Cu).
In order to suppress the eddy current generated due to the linkage of the longitudinal magnetic field in this arc diffusion part,
As described in Japanese Patent Application Laid-Open No. 50-52562, a plurality of radial slits are provided. However, due to the low tensile strength of Cu, approximately 20 Kgf/mm ² , and the fact that it has multiple slits, the arc diffusion section is susceptible to shocks during charging and extinguishing, as well as the electromagnetic force of large current arcs. In order to prevent deformation due to impacts and the like caused by this, the axial dimension (thickness) and weight have increased. In addition, the arc and electric field concentrate at the edge of the slit, reducing the current shearing ability and dielectric strength, especially the dielectric strength after shearing (dynamic dielectric strength), and causing a large amount of wear on the arc diffusion area. There is a problem. On the other hand, the contact part was designed for high current and low voltage.
It is made of a Cu-Bi alloy (for example, Cu-0.5Bi alloy), which is Cu containing a small amount of bismuth (Bi), as described in Japanese Patent Publication No. 12131, etc., or it is used for small current and high voltage applications. It is formed of a Cu--W alloy (for example, a 20Cu-80W alloy) in which Cu contains tungsten W, as described in Japanese Patent No. 36121 and the like. However, in order to cope with the rise in current and voltage accompanying the recent expansion of power systems, there is a demand for electrodes that have excellent current shedding ability and dielectric strength. OBJECT OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and is a longitudinal magnetic field system that is small, lightweight, durable, and equipped with electrodes that can be used to cut large currents and high voltages. The purpose is to provide a vacuum interrupter. Structure of the Invention In order to achieve the above object, the present invention introduces a pair of electrode rods into a vacuum container so that they can approach and separate from each other, and an arc diffusion part and a contact part are provided at the inner end of each electrode rod. Fix the electrodes consisting of
In a vacuum interrupter comprising a coil for applying an axial magnetic field parallel to the arc to the outside of the vacuum vessel or inside the vacuum vessel, the arc diffusion portion of each electrode is made of 30 to 70% by weight of magnetic stainless steel. In addition to being formed from a composite metal,
Contact area: 20-70% copper, 5-70% chromium,
and a composite metal consisting of 5 to 70% by weight of molybdenum. Embodiments Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a longitudinal cross-sectional view of a vacuum interrupter showing an embodiment of the present invention, and this vacuum interrupter is arranged in a vacuum container 1 on its axis, and a pair of electrode rods 2, 2 are placed relatively close to each other. A pair of electrodes 3, 3 in the shape of a cap-shaped disk are mechanically fixed to the inner end of each electrode rod 2 with an insulating spacer interposed, and each electrode rod 2 and electrode 3 are connected to each other as electrodes. A coil 4 is disposed on the back of the electrode rod 3 and generates a vertical magnetic field by changing the axial current (vertical direction in FIG. 1) flowing through the electrode rod 2 into a loop current centered around the electrode rod 2.
4 and is electrically connected to each other. That is, the vacuum container 1 is a thin annular sealing fitting made of Fe-Ni-Co alloy or Fe-Ni alloy, etc., with two cylindrical insulating tubes 5, 5 made of glass or ceramics fixed at both ends. 6, 6, . . . are joined together to form a single insulating cylinder, and both open ends thereof are closed by disc-shaped metal end plates 7, 7 through the other sealing fittings 6, 6, and high vacuum inside (for example, pressure below 5×10 ^-5 Torr)
It is formed by exhausting the air. And vacuum container 1
Inside, each electrode rod 2 has a respective metal end plate 7.
It is introduced from the center of the vacuum container 1 so that it can be relatively approached and separated while maintaining airtightness. In addition, one (upper in FIG. 1) electrode rod 2
is airtightly inserted into one metal end plate 7, and the other electrode rod 2 is inserted into the other metal end plate 7 as an axis while maintaining the airtightness of the vacuum vessel 1 via a metal bellows 8. It is inserted so that it can move freely in the direction. Further, in FIG. 1, 9 and 10 are a shaft shield and a bellows shield, 11 is a main shield, and 12 is an auxiliary shield. At the inner end of each electrode rod 2, as shown in FIGS. 2 and 3, there is a disc-shaped disc made of a material with high conductivity such as Cu and having a diameter suitably larger than the diameter of the electrode rod 2. a mounting base 4a; two arms 4b extending outward in a radial direction (left-right direction in FIG. 2) from opposing positions on the outer periphery of the mounting base 4a;
A 1/2 shunt type coil 4 consisting of an arc portion 4c curved in an arc shape in the same direction with the mounting base 4a as the center from the end of each arm 4b is attached to the mounting base 4.
It is fixed by brazing through a recess 13 formed on one (lower side in FIG. 2) of the surface of the a. The coil 4 includes a ring-shaped attachment portion 14a that is fitted onto the outer circumference of the inner end of the electrode rod 2 by brazing.
A plurality of support arms 14b extend radially outward from the outer periphery of the attachment portion 14a, and each support arm 14b
It is reinforced by being brazed to a coil reinforcing body 14 consisting of a ring-shaped support part 14c connecting the ends of the coil reinforcing body 14. The coil reinforcing body 14 is made of a material with high mechanical strength and low electrical conductivity, such as stainless steel. A circular recess 15 is provided on the other surface of the mounting base 4a of the coil 4, and the recess 15 is made of a material with high mechanical strength and low conductivity, such as stainless steel or Inconel. An insulating spacer 16 formed in a cylindrical shape is fixed by brazing via a small diameter flange 16a formed at one end thereof. The large-diameter flange 16b formed at the other end of the insulating spacer 16 is fitted with a circular plate-shaped mounting having a diameter appropriately larger than that of the large-diameter flange 16b and having a through hole approximately the same diameter as the inner diameter of the insulating spacer 16. A base 17a, two arms 17b extending radially outward from opposing positions on the outer periphery of the mounting base 17a, and a radius of curvature approximately equal to the arcuate portion 4c of the coil 4 from the end of each arm 17b. The auxiliary coil 1 consists of a circular arc portion 17c curved in an arc shape with an appropriate length in the same direction opposite to this, and is made of a material with high conductivity such as copper.
7 is fixed by brazing via an engagement step 18 provided on one (lower side in FIG. 2) surface of the mounting base 17a. The auxiliary coil 17 and the coil 4 are each circular arc portion 17c of the auxiliary coil 17.
One end is fixed to a recess 19 provided at the end of the coil 4, and the other end is electrically connected via an axial current-carrying pin 20 inserted into a through hole 21 provided at the end of each arcuate portion 4c of the coil 4. has been done. The electrode 3, which is formed to have approximately the same diameter as the coil 4, is attached to the auxiliary coil 17 by brazing to the mounting base 17a through a recess 22 provided at the center of the back surface.
It is joined to each arm 17b and arc portion 17c via the back surface by brazing. Electrode 3 is on the opposing surface (upper surface in FIG. 2)
The arc diffusion part 3a is formed in the shape of a cap-shaped disk with a circular recess 23 in the center and gradually becomes thinner as it approaches the periphery, and has a flat circular contact surface on the opposing surface and becomes gradually thinner as it approaches the periphery. The arc diffusion part 3 is formed in a cap-shaped disk shape and
Contact portion 3 fixed to recess 23 of a by brazing
b, and is provided in the shape of a cap-shaped disk as a whole. The arc diffusion portion 3a of the electrode 3 is formed of a composite metal of 30 to 70% by weight of magnetic stainless steel and 30 to 70% by weight of Cu. Examples of magnetic stainless steel include ferrite stainless steel and martensitic stainless steel. As ferritic stainless steel, SUS405, 429, 430, 430F, 434
As martensitic stainless steel,
Examples include SUS403, 410, 416, 420, 431, 440C. This composite metal has an electrical conductivity of 3 to 30% (IACS%) when ferritic stainless steel is used, and a conductivity of 4 to 30% when martensitic stainless steel is used. It is something that you have. Moreover, the tensile strength and hardness are 30 Kgf/mm ² or more and 100 to 180 Hv (1 Kg) in both cases. In addition, the contact portion 3b contains 20 to 70% by weight of Cu, 5 to 70% by weight of chromium (Cr), and molybdenum (Mo).
It is formed from 5 to 70% by weight of composite metal.
Furthermore, this composite metal has a conductivity of 20-60% and
It has a hardness of 120-180Hv (1Kg). On the other hand, the composite metal forming the arc diffusion portion 3a and the composite metal forming the contact portion 3b are manufactured in substantially the same manner. Next, various manufacturing methods will be explained using a composite metal forming the contact portion 3b as an example. (1) For example, mix a predetermined amount of -100 mesh Cr powder and -100 mesh Mo powder, place this mixed powder in a container made of a material that does not react with Cr, Mo, and Cu (e.g., alumina), and place it on top of the container. Place the Cu block in a vacuum (5x
10 ^-5 Toor), first heat at 10,000℃ for 10 minutes to degas and form a porous base material consisting of Cr and Mo.
Cu by heating at 1100℃ for 10 minutes at a temperature above ℃)
This is done by infiltrating a porous base material. (2) Powder Cr and Mo, mix them in a predetermined amount, place this mixed powder in a container made of alumina, etc., and place it in a non-oxidizing atmosphere (for example, in a vacuum, hydrogen gas, nitrogen gas, or Argon gas, etc.) at a temperature below the melting point of each metal (for example, below the melting point of Cu if the Cu material is placed on the powder in advance, or Cr if the Cu material is not placed on the powder in advance). (below the melting point of
~60 minutes) to form a porous base material, and then heated and held above the melting point of Cu in the above atmosphere (for example, at 1100°C for about 5 to 20 minutes) to infiltrate Cu into this base material. Combine them as one. (3) Powder Cu, Cr, and Mo metals, mix them in predetermined amounts, press-mold this mixed powder to form a mixed element body, and then place this mixed element body in a non-oxidizing atmosphere. Cu
below the melting point of Cu (e.g. 1000℃) or above the melting point of Cu and below the melting point of other metals (e.g. 1100℃)
This is done by holding the metal powder at a temperature of (about 5 to 60 minutes) and bonding each metal powder particle together. . Here, the particle size of the metal powder is not limited to -100 mesh (149 μm or less), but may be -60 mesh (250 μm or less). However, when the particle size is larger than 60 meshes, it becomes necessary to increase the heating temperature or lengthen the heating time as the diffusion distance increases when diffusion bonding each metal powder particle, which reduces productivity. This will result in a decline. On the other hand, as the upper limit of the particle size decreases, uniform mixing (uniform dispersion of each metal powder particle) becomes difficult, and it is easy to oxidize, making handling troublesome and requiring pretreatment before use. Since there are problems such as the amount of particles required, there is naturally a limit, and the upper limit of the particle size is selected based on various conditions. Further, in both of the above-mentioned manufacturing methods (2) and (3), a vacuum atmosphere is preferable as a non-oxidizing atmosphere since it has the advantage that degassing can be performed simultaneously during heating and holding. However, even when manufactured in a non-oxidizing atmosphere other than a vacuum atmosphere, there is no difference in performance as an electrode for a vacuum interrupter. Next, -A component composition (ferritic stainless steel SUS434
50% by weight and Cu50% by weight) and -A component composition (martensitic stainless steel SUS410
The structural states of each composite metal (Cu 50% by weight and Cu 50% by weight) are shown in Figures 4A to D and Figure 5A, respectively.
It looked like the X-ray photograph shown in ~D. That is, the X-ray photographs in Figures 4A and 5A are secondary electron images, and the X-ray photographs in each Figure B are characteristic X-ray images showing the dispersion state of iron (Fe), with island-like The white parts scattered around are Fe. The X-ray photographs in each figure C are characteristic X-ray images showing the dispersion state of chromium (Cr), and the gray parts scattered like islands are Cr. Furthermore, the X-ray photographs in each figure D are characteristic X-ray images showing the dispersion state of Cu, with the white portion being Cu. Therefore, SUS434 particles are bonded to each other to form a porous base material, and Cu is infiltrated into the pores (voids) of this base material to form a strongly bonded composite metal. I know that there is. In addition,
The same applies to SUS410 particles. Furthermore, -A component composition (Cu50 weight%, Cr10 weight% and Mo40 weight%) and -B component composition (Cu50 weight%, Cr25 weight%) produced by manufacturing method (1)
and Mo25% by weight) and -C component composition (Cu50% by weight, Cr40% by weight and Mo10% by weight)
The structural state of each composite metal is shown in Fig. 6A~
D, X shown in FIGS. 7A-D and 8A-D
It looked like a line photo. That is, FIG. 6A, FIG. 7A, and FIG. 8A.
The X-ray photographs in Figure B are secondary electron images, and the X-ray photographs in each figure B are characteristic X-ray images showing a Cr dispersion state, and the white parts scattered like islands are Cr. Moreover, the X-ray photographs in each figure C are characteristic X-ray images showing the dispersion state of Mo, and the white parts scattered like islands are Mo. Furthermore, the X-ray photographs in each figure D are characteristic X-ray images showing the dispersion state of Cu, with the white portion being Cu. Therefore, Cr and Mo particles diffusely bond with each other to form a porous base material, and Cu is infiltrated into the pores (voids) of this base material to form a strongly bonded composite metal. It can be seen that this is the case. On the other hand, -A forming the arc diffusion part 3a,
The test results of various properties of the composite metals having the component compositions -B, -C, -A, -B and -C and the composite metals having the component compositions -A, -B and -C forming the contact portion 3b are as follows: , became as follows. Here, -B component composition is SUS434
70% by weight and 30% by weight of Cu, and the -C component composition is 30% by weight of SUS434 and 70% by weight of Cu. Moreover, the -B component composition is 70% by weight of SUS410 and 30% by weight of Cu, and the -C component composition is 30% by weight of SUS410 and 70% by weight of Cu.
The composite metals having the component compositions -B, -C, -B and -C were produced in the same manner as the composite metal having the -A component composition. (1) Electrical conductivity (IACS%) Arc diffusion part -A component composition 5 to 15% -B component composition 3 to 8% -C component composition 10 to 30% -A component composition 5 to 15% -B component composition 4 to 8% -C component composition 10~30% Contact part -A component composition 40~50% -B component composition 40~50% -C component composition 40~50% (2) Tensile strength Arc diffusion part 30Kgf/mm ² or more ( 3) Hardness Arc diffusion part 100 to 180Hv (1Kg) Contact part 120 to 180Hv (1Kg) In addition, the arc diffusion part 3a is formed of a composite metal of -A component composition into a hat-shaped disk shape with a diameter of 100m/m, The contact portion 3b is made of a composite metal having a -A component composition and is formed into a cap-shaped disk shape with a diameter of 60 m/m to form the electrode 3 shown in FIG. The results of various performance verifications conducted on the vacuum interrupter shown in Figure 1 are as follows. (1) Current shedding capacity The shedding condition is rated voltage 1.2KV (restart voltage
2.1KVJEC-181), it was possible to cut a current of 63KA (rms) at a cutting speed of 1.2 to 1.5 m/s. In addition, the rated voltage is 84KV (restart voltage 143KV,
JEC-181), 52KA (r.
ms) was able to be cut off. In addition, the arc diffusion part 3a is -B, -C,
When using a composite metal having the respective component compositions of -A, -B and -C, the contact portion 3b is made of -B and -C.
The current shearing ability of each composite metal of each component composition and the comparative products tested under the same conditions were as shown in Table 1, which also shows the number of times of shearing durability. Here, the comparative product whose arc diffusion part is made of Cu is:
The arc diffusion part has 6 slits,
Those that are electrically connected to the back side of the arc diffusion part and the end of the arc part of the coil via a current-carrying pin without using an auxiliary coil (for example,
22813).

【table】

[Table] (2) Dielectric strength When the gap was maintained at 30m/m and a shock wave withstand voltage test was performed, the result was ±400KV (variation ±
It showed a dielectric strength of 10KV). In addition, similar tests were conducted after multiple cycles of high current (63 KA) and after interruption, but there was no change in dielectric strength. Furthermore, a similar test was conducted after a small advance current (80A) was interrupted, but the dielectric strength hardly changed. In addition, the dielectric strength of the combination of the arc diffusion part 3a and the contact part 3b made of the composite metal of each component composition is the same as that of the composite metal of the -A component composition and -
It showed the same value as the combination with the composite metal of component A composition. Table 2 shows the results of shock wave withstand voltage tests for the product of the present invention (a combination of -A component composition and -A component composition) and the conventional product.

[Table] (3) Welding resistance After applying a current of 25KA (rms) for 3 seconds under a pressure of 130Kg (IEC short-time current standard), 200Kg
The contact resistance could be removed without any problem with a static removal force of 2 to 8% after that. In addition, under a pressure of 1000Kg, 50KA (rm
There was no problem in tripping after applying the current (s. In addition, the arc diffusion part 3a is -B, -C,
Similar results were obtained when the composite metals had the respective compositions of -A, -B and -C, and when the contact portion 3b was made of the composite metals having the compositions of the -B and -C components. (4) Ability to withstand small delayed currents (inductive loads)
The current cutoff value obtained by applying a current of 30A is 3.9A on average (standard deviation σn ⁼ 0.96, number of samples n ⁼
100). In addition, when the contact part 3b has a -B component composition, an average of 3.7A (σn=1.26, n=100), and when a -C component composition, an average of 3.9A (σn=1.5, n=
100). Moreover, the arc diffusion part 3a is -
Similar values were also obtained when each component composition was B, -C, -A, -B, and -C. (5) Leading small current (capacitive load) resistance voltage: 84KV×1.25/√3, 80A leading small current test (JEC-181) was conducted 10,000 times, but no re-ignition occurred. It was hot. In addition, the arc diffusion part 3a is -B, -C,
Similar results were obtained when the composite metals had the respective compositions of -A, -B and -C, and when the contact portion 3b was made of the composite metals having the compositions of the -B and -C components. By the way, the composition of the composite metal forming the arc diffusion part 3a is 30 to 70% by weight of magnetic stainless steel.
In the case where the composition was outside the range of 30 to 70% by weight of Cu, satisfactory properties could not be obtained. That is, when the amount of magnetic stainless steel was less than 30% by weight, the electrical conductivity increased and the generation of eddy current became significant. In addition, the strength decreased, the durability deteriorated, and the thickness had to be increased. On the other hand, when the content exceeded 70% by weight, the shearing performance decreased significantly. Further, the component composition of the composite metal forming the contact portion 3b is Cu20~70% by weight, Cr5~70% by weight, Mo5~
Even in cases outside the 70% by weight composition range, satisfactory properties could not be obtained. That is, if Cu is less than 20% by weight,
The electrical conductivity decreased and the contact resistance significantly increased, while when it exceeded 70% by weight, the welding force and shear value increased significantly and the dielectric strength decreased significantly. Furthermore, when Cr content is less than 5% by weight, the dielectric strength decreases significantly;
When it exceeded 20%, the electrical conductivity and mechanical strength were significantly reduced. Further, when Mo was less than 5% by weight, the dielectric strength was significantly lowered, while when it was more than 70% by weight, the mechanical strength was significantly lowered and the cleavage value became significantly larger. In addition, in the above-mentioned embodiment, a case was described in which the coil 4 is a 1/2 shunt type, but the coil 4 is not limited to this. For example, the coil 4 is of a 1 turn, a 1/3 shunt type, or a 1/4 It is also good as a branch type. Further, the electrical connection between the electrode 3 and the coil 4 is not limited to the case where the auxiliary coil 17 bonded to the back of the electrode 3 is used. One end of the electrode may be directly connected to the center of the back surface of the electrode. Furthermore, the coil 4 is not limited to the case where the coil 4 is provided on the back of the electrode 3;
Of course, the coil may be arranged so as to surround the pair of electrodes, or the coil may be arranged outside the vacuum vessel as described in Japanese Patent Publication No. 13045/1983. Effects of the Invention As described above, according to the present invention, the arc diffusion part is formed of a composite metal composed of 30 to 70% by weight of magnetic stainless steel, 30 to 70% by weight of Cu, and 30 to 70% by weight of Cu, and the contact part is formed of a composite metal of 20 to 70% by weight of Cu. 70% by weight, 5 to 70% by weight of Cr, and 5 to 70% by weight of Mo.
The arc diffusion part is made of Cu, and multiple slits are provided in this arc diffusion part to suppress the generation of eddy current, and the contact part is made of Cu-0.5Bi alloy or 20Cu-
Compared to the conventional one made of 80W alloy, it has various effects described below. (1) By improving the tensile strength of the arc diffusion part, the thickness and weight of the electrode can be significantly reduced, and the durability of the electrode can be greatly improved. (2) Since the arc diffusion part and the contact part have low conductivity, it is possible to significantly reduce the occurrence of eddy current, and since there is no need to provide slits, mechanical strength such as tensile strength is improved, and the above ( The effect of 1) can be further promoted. (3) The arc diffusion part and the contact part are made of a composite metal with high hardness and uniformly dispersed components, and the arc diffusion part has no slits, which prevents excessive melting of the arc diffusion part and the contact part. As a result, it is possible to significantly reduce wear and tear on both parts, improve insulation recovery characteristics, and almost eliminate a decrease in dielectric strength after multiple turns or breakage. Furthermore, the current cutoff value can be reduced. (4) In particular, both current shedding capacity and dielectric strength can be significantly improved compared to conventional ones.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal sectional view showing one embodiment of the vacuum interrupter of the present invention, FIGS. 2 and 3 are longitudinal sectional views and exploded perspective views of the electrodes in FIG. 1, respectively, and FIGS. 4A, B, and C. , D and Figure 5 A, B,
C and D are X-ray photographs showing the structural states of different compositions of the composite metal forming the arc diffusion part, respectively.
Figures A, B, C, D, Figure 7 A, B, C, D, and Figure 8 A, B, C, D are X-ray photographs showing the structural states of different compositions of the composite metals forming the contact area, respectively. It is. 1... Vacuum container, 2... Electrode rod, 3... Electrode,
3a...Arc diffusion part, 3b...Contact part, 4...
coil.

Claims (1)

[Claims] 1. A pair of electrode rods is introduced into a vacuum container so that they can approach and separate from each other, and an electrode consisting of an arc diffusion part and a contact part is fixed to the inner end of each electrode rod. , in a vacuum interrupter comprising a coil for applying an axial magnetic field parallel to the arc to the outside of the vacuum vessel or inside the vacuum vessel, the arc diffusion portion of each of the electrodes is made of 30 to 70% by weight of magnetic stainless steel. and a composite metal consisting of 30 to 70% copper by weight, and the contact part is made of 20 to 70% copper.
A vacuum interrupter characterized in that it is formed of a composite metal consisting of 70% by weight, 5 to 70% by weight of chromium, and 5 to 70% by weight of molybdenum. 2. The vacuum interrupter according to claim 1, wherein the magnetic stainless steel is ferritic stainless steel. 3. The vacuum interrupter according to claim 1, wherein the magnetic stainless steel is martensitic stainless steel.