DE3325264A1 - ELECTRODE CONTACTS FOR POWER INTERRUPT - Google Patents

Description

9153-RD-14OO1

GENERAL ELECTRIC COMPANY

Electrode contacts for power line interruption

The invention relates to electrical contacts and electrical Contact materials for use in power circuit breakers, in particular on directionally solidified materials for use in such contacts.

In heavy current transmission systems it is often necessary or desirable interrupt the flow of current. This function is often performed by contacts that are separated in an evacuated housing. This construction takes advantage of the desirable dielectric properties of vacuum conditions, vacuum as well as other interrupting ones However, the flow of current does not stop immediately after the contacts have been separated. Rather, the contact separation ignites an arc which, in the special case of vacuum interrupters, is maintained by a hot plasma that is passed through local heating, evaporation and ionization of contact metal arises. In an AC power system, the contact separation is generally random in time with respect to the sinusoidal Change in system current and voltage. After the arc is formed, the system current will flow for most of the time remaining half-cycle of the current in which the arc is ignited,

Further. If the arc current approaches a sine zero crossing, incline the processes that sustain the discharge lead to instability, which suddenly causes the arc to collapse. At this point The magnitude of the current can typically range from a fraction of an ampere to a few tens of amps as a function from the contact material as well as a variety of other conditions.

Because this jump to a current zero state in such a short time

- 8th

Time (down to about 10 s) occurs, parasitic inductive Effects give rise to high voltage surges, especially when the jump to the zero current from a relatively high Current value takes place. As is well known in the electrical art, the generated voltage surge is determined by the relationship E = -L dl / dt. It can be seen that a rapid jump to zero-current state can easily lead to understandably high voltage surge values gives. It is therefore desirable to create plasma arcs that develop a high degree of arc stability. This means, In AC systems, it is generally desirable to create conditions that will allow the plasma arc to persist for so long as possible, but not longer than the occurrence of the next zero-current point after contact separation. So done the jump to a current zero value after the extinction of an arc from a relatively low arc current value. This makes the Generation of undesirably high voltage surge values minimal.

The increase in the arc stability at lower values of the arc current is an important consideration in selecting a contact material for use in vacuum line interruption devices. Usually, high arc stability is achieved by choosing metals that have low boiling points. One such a choice represents a considerable compromise by including such low-boiling metals as a class of relatively poor dielectric Show strength under vacuum conditions.

Other experimenters in the field have observed that certain Alloys develop properties that are common to everyone

their components are superior in terms of arch stability. For example, copper developed in a special circuit a current draw value of about 5 A, while tungsten itself exhibits a current draw value of 10-20 A under similar conditions. However, it has been found that a copper-tungsten alloy may exhibit a smaller current draw value than other such values. That is, certain alloys exhibit properties that those of each of their components are superior in terms of arc stability at the low current values of interest here.

The electrical contacts are in many line breaker forms mounted on conductive support parts. Such a structure is often necessary because of economic considerations it is generally undesirable to use the entire electrode assembly made from the more expensive contact material. Furthermore, the support parts serve as a convenient heat sink and heat conductor for dissipating Heat from electrical contact. Thus, an extremely desirable property of any electrical contact material is that it has a high degree of thermal conductivity, especially in a direction from the electrode contact surface to the body of the Carrier part or the electrode carrier. Furthermore, in addition to having a thermal path, it is also highly desirable to have a Distance of low electrical resistance between the electrical contact surface and the body of the carrier part that the contact is mounted to create. In this regard, however, it should be noted that the addition of a metal is too another, for which the solubility of one component in the other is a few percent or more, the electrical conductivity belittles. The heat conduction properties and a small amount of energy scattering in the bulk of the contact material are particularly important in a vacuum because the heat generated at the contact interface is mainly conducted by the electrode carriers is distributed through it. For contacts working in air or another atmosphere, there is additional cooling by convention on the contact side surfaces. There are also other differences when compared to the operation of contacts in air with operation in a vacuum. In particular, the choice of

Contact material for use in air is severely limited by the problem of oxidation and consequently high contact resistance. This is especially true for contact materials that use copper. So, in general, is the selection of materials for use in vacuum devices significantly different from the selection for use in devices where the contacts are exposed to air are.

Such have been efforts in the past to form mixtures made of metal components for electrode contacts have generally not been fully successful, mainly due to undesirable growth the electrical resistivity of materials with mutual solubility. So it seems desirable that contact materials exist as a matrix of different materials in elemental form. In certain matrices, however, they have become higher Boiling metals in particular proved desirable by having characteristically higher dielectric strength in vacuo demonstrate. Furthermore, the stability of vacuum arcs is known to be due to the interfaces on the electrode surface between mutually insoluble components increased. It has been found in the past, for example, that a tungsten matrix that is bonded with copper impregnated, has greater arc stability than either tungsten or copper, used in its pure form.

It is also pointed out here that experimenters in other fields in the past have used the technique of directional freezing of materials applied in a number of different processes and materials. However, these processes are not has been widely used for the manufacture of vacuum contact materials. But K. Chrost and S. Wojciechowski from the Institute of Transformers, Electrical Machines and Apparatus at the Technical University of Lodz, Lodz, Poland Directionally solidified Ag-Cu mixtures for electrical contacts in a publication entitled "Properties of Directionally Solidified Silver-Copper Contact Materials "in Proceedings of the 9th International Conference on Electric Contact Phenomena, p. 259-264, 1978. Also, other experimenters have

the construction of fibrous material made from extruded Wire, suggested. For example, H. H. Kocher and D. Stöckel have used such heterogeneous fiber composite contact materials in a publication entitled "Material Transformer of Composite Contact Materials". However, no directional solidification is discussed. Also, no agents are discussed that include copper in vanadium. In a publication entitled "Behavior at Closing or Opening of Silver-Metallic-Oxide Materials in Electric Power Engineering "by M. Poniatowski, K.-H. Schröder and E. P. Schulz in Proceedings of the 8th International Conference on Electric Contact Phenomena, pp. 353-358, 1976, is an extruded silver / silver oxide material with SnO2 inclusions on a vertical plane Contact surface oriented fiber structure shown. A similar silver / silver oxide composite is in a publication with the title "Replacement of Silver / Cadmium Oxide by Silver / Tin Oxide in Low Voltage Switching Devices" by Manfred Poniatowski, Ernst-Dieter Schulz and Axel Wirths in Proceedings of the 8th International Conference on Electric Contact Phenomena, pp. 359-364, 1976 disclosed. However, none of these publications is on the directional solidification of materials such as copper, Vanadium and other such materials. Furthermore, copper and vanadium mixtures are previously used in the manufacture of electrical Contact materials have not been used.

U.S. Patent 3,514,557 teaches that it is desirable to have a non-refractory one Metal, such as copper, in a vanadium boride (VB2) / refractory compound matrix. Directed, dendritic or fibrous structuring of the material is not mentioned and the teachings of this patent appear aimed solely at cases where metalloids, such as boron or silicon, are used to make a refractory composite be used in place of elemental material.

It should also be pointed out that in several cases of interest it is also desirable to remove the bow from his steer current position to other positions or other electrodes. Such transition phenomena are also

j NAUK. - " ^:

has not been achieved through the use of processes or materials of directional solidification, as is the case in manufacturing electrical contacts are applied.

According to a preferred embodiment of the invention comprises a electrical contact for use in electrical power circuit interruption devices a block of conductive material having at least one contact surface; the material includes a directionally solidified mixture of at least two mutually insoluble metal components. According to a preferred embodiment According to the invention, the electrode contact material comprises a mixture of copper and vanadium having between about 1 and about 92 Weight percent vanadium. Such electrical contacts are used in electrode assemblies in two different ways. at In one embodiment of the invention, the orientation of the solidification is generally parallel to the contact surface on which the bow hits. This embodiment is particularly desirable in those situations where arching motion or relocation is to be achieved. In addition, the electrode contact according to the invention can be used in an electrode unit in which the direction of solidification is generally perpendicular to the surface on which the plasma arc is incident. It is precisely this latter embodiment that is the most effective for heat transfer and electrical resistance properties.

The invention also encompasses the use of directionally solidified contact materials in vacuum interrupters. Especially a preferred one Contact form comprises a multicomponent mixture formed using at least two mutually insoluble metal components. Next can also be a material that is a mixture comprised of copper and vanadium, can be used as an electrical contact with or without directional solidification.

Thus, it is an object of the invention to provide an electrical contact which has high arc stability at low arc current values shows; there should be directed solidified electrical contacts and

Materials are created for it that improve the thermal and electrical contact properties, especially in a vacuum; aside from that Directionally solidified electrode contacts and materials are to be created for them to prevent the displacement of the plasma arc reinforce from one position to another; electrical contacts and contact material should also be created, especially for vacuum circuit breakers that use a mixture of copper and vanadium, not only as a mixture, but also in directionally solidified form include; and finally, electrode assemblies should arise that use the electrical contacts and Ma- «, materials according to the invention.

What is considered essential to the invention is in the final Part of the description specially executed and clearly claimed. The invention, however, is both organizational as well as method of practice along with further objects and advantages, best with reference to the following description to be understood in conjunction with the figures; of these is

Fig. 1 is a current / time diagram showing a current interruption period illustrates;

FIG. 2 is a diagram similar to FIG. 1, more particularly illustrating various low current arc stability conditions;

Fig. 3 is a cross-sectional side elevation of an electrode unit with electrode material according to the invention;

Fig. 4 is a top plan view of one of the electrode units shown in Fig. 3;

Fig. 5 is a sectional side view of an embodiment the invention which further illustrates the use of directionally solidified electrode contact material;

Fig. 6 is a side sectional view of an electrode insert

is called similar to Fig. 5, which directed a different orientation for the illustrates solidified material;

Figure 7 is a photomicrograph of a copper-vanadium electrode contact material in longitudinal section, and

Fig. 8 is similar to Fig. 7 except that a cross-sectional view of the material is shown.

The diagram shown in Figure 1 illustrates a full period of an electrically interrupted current waveform. In the diagram shown, the curve has a periodicity T. For the case of conventional US mains current frequencies, T is 16.6 ms. In order to electrically break a circuit having the sinusoidal waveform described, it is conventional practice to begin disconnecting electrical circuit breaker contacts at a random time, e.g., t-. In almost all cases, however, a plasma arc develops between the separated electrical contacts, creating a persistent current path through the ionized plasma material, which primarily comprises vaporized metallic material from the surface of the electrical contacts. The current continues to rise up to a maximum value and then falls sinusoidally until a time when the current reaches a value range at which the current suddenly and unpredictably falls to zero _{at a time t 2.} At the critical current value, the current drops very quickly. As discussed above, this high rate of change in current is responsible for generating large voltage surges. It is therefore generally desirable to keep the threshold current value from which this rapid surge occurs as low as possible. The timing and current value associated with this current drop are a consequence of the lack of arc stability at low current values. This sudden power failure is known as a power failure. Chopping currents are mainly determined by the electrode contact material used. Under ideal conditions, the arc would _{extinguish at a time t 3} corresponding to a point T / 2 s after the preceding zero point.

The phenomenon of the current interruption is examined in more detail in FIG. 2, which shows an enlargement of part of the diagram illustrated in FIG. 1 immediately before time t ₃ . In particular, there are shown three possible arc extinction transitions at times t _2a , t _2b and t _2c . If the current stall occurs at time t ₂ , the arc is described as being relatively unstable. However, if the current stall occurs at a time t-, the arc is described as being relatively stable. In general, high arc stability at these low current levels is a desirable feature of electrical circuit breaker devices and, in particular, is a fundamental advantage of the invention.

Fig. 3 illustrates another advantage that comes with the inventive, directionally solidified electrode contact material is to be achieved. In particular, have conductive electrode carrier parts 12 embedded in them annular electrode contact rings 10. In detail, an arc 13 is shown, which between Contacts 10 flips over. The electrode structural unit shown in FIG. 3 is similar to the constructions currently used in conventional vacuum circuit breaker devices. In particular, it is generally desirable in such devices to avoid the transition of the arc from a To promote the area between the electrode contacts 10 to the conductive carrier part 12. The ring-shaped electrode contact is according to the invention 10 made of composite materials which have solidified directed in the radial direction, as shown by the horizontal dashed lines of the contact 10 indicated. In particular, such solidification facilitates the transition of the arc 13 from an area between Contacts 10 to an area between the larger, more separated, current-carrying structures 12. The structure 12 is illustrated in further detail in Fig. 4, which shows that it has a substantially disk-shaped structure comprises annular electrode contact 10 attached thereon. Furthermore, the conductive carrier part 12 preferably has slots or spiral indentations 14 to promote the arc rotation. Such a structure is suitable for electrical vacuum switching

circuit breaker shapes conventional.

FIGS. 5 and 6 illustrate further electrode units made with the directionally solidified materials according to the invention can be used. In particular, in FIG. 5 the conductive carrier part 16 acts not only as an electrically conductive element, but rather also as a heat sink. However, the electrode contact 20 is the main surface that the arc hits. It's the contact 20, which determines the degree of arc stability in the interrupter. In detail shows, as indicated by vertical dashed lines, the contact 20 directional solidification in a direction substantially perpendicular to the surface that the Arc hits. The embodiment according to the invention shown in FIG. 5 thus offers three significant advantages over this the commonly used electrode contacts. First, the directional solidification provides in the direction shown increased thermal conductivity between the arc surface 21 and the conductive support member 16. Second, creates the Directional solidification in the direction shown increases electrical conductivity between the arc-forming surface 21 and the carrier part 16. This arises from the presence of numerous conductive channels in the contact 20. Third, it is obtained the directional solidification provided in the contact 20, the arc stability by maintaining the interface structure between elemental metals. Furthermore, the electrode material shows excellent dielectric strength. Thus illustrated Fig. 5 shows a preferred embodiment of the invention.

In those applications where arc migration or movement is desired, a directionally solidified material can be used to make this hike easier. Such a material and structure is illustrated in Figure 6 in which a contact 30 is used will. Contact 30 shows directional solidification in a direction practically parallel to the arcing surface Since arcs tend to move more easily towards the expanded component, this is directional solidification thus useful in controlling the movement of the sheet to the

5264

-X-

Electrode contact surfaces, i.e. the arcing surfaces. This aspect of the invention is also illustrated in Figure 3 above, after which it is generally desirable to use the plasma arc to impart a radial outward movement.

In general, the electrode material according to the invention comprises a mixture of at least two mutually insoluble metal components, that are rigidly directed. One material that has been found to be particularly useful is a mixture of copper and Vanadium, wherein the vanadium is present in an amount between about 1 and about 92 weight percent. The directionally solidified copper-vanadium material according to the invention is described in more detail below and shown in FIGS. Other Mutually insoluble materials which can be directionally solidified according to the invention include aluminum and antimony, silver and Copper, copper and bismuth, copper and lead, copper and lithium, aluminum and beryllium, silver and nickel and aluminum, aluminum and chromium, aluminum and titanium and aluminum and vanadium. The following Table I shows a non-exclusive list of Materials and composition ranges useful in the present invention.

Table I. materials

Ag-Ni Al-Be Al-Bi Al-Cr Al-Sb Al-Ti Cu-Bi Cu-Li Cu-Pb Cu-V

Range (wt%)

1-98 Ni

1 - 98 al

(any composition range) 80-99 Al 1-82 Sb 63- 99 Al (any composition range)

1 - 92 V

The process of directional solidification itself is on the metallurgical level Area well known. However, it has not yet been used for the purpose of amplifying the arc movement in vacuum contact machines.

materials have been applied. Furthermore, it has not yet reached that associated with arc stability at low arc current values Problem has been applied. In directional solidification, a blank is made from the desired mixture through a hot one Zone out in which the material is melted locally and again solidifies when the blank is passed through the hot zone in a step process. The alignment of the resulting structure appears to be based on the affinity of like atoms for each other during re-solidification. For the purposes of the invention includes the electrode material for use in the process of directional solidification has two or more components, one of which is in is essentially insoluble in the remaining constituents, this constituent preferably being a metal of relatively high electrical Conductivity is. Again it was found that in particular Copper and vanadium have the desired insolubilities, boiling points and electrical conductivities. It was also found that they are very well suited to directed solidification. But it was also found that an electrode contact with Copper and vanadium exhibit superior arc stability properties even under non-directional solidified conditions.

The ease of delivery of the copper-vanadium mixture of the directional Solidification is illustrated in greater detail in FIGS. 7 and 8, both of which are scanning electron microscope images of FIG Represent copper vanadium. Fig. 7 illustrates a longitudinal section a directionally solidified copper-vanadium mixture. Fig. 8 is identical to Fig. 7 except that it is a cross-sectional view of the copper-vanadium mixture is illustrated. In the representation shown, the copper shows itself to be the lighter one of the two existing materials. Each of the scanning electron micrographs shown in FIGS. 7 and 8 was taken with the made of the same specimen, and the view is that of surfaces which have been metallographically polished. Furthermore, in FIG. 7 also see a series of white spots that are actually artifacts of the imaging process. Similar spots are also seen to a lesser extent in FIG. These, too, are artifacts of the imaging process. With every microscope image is

a length scale of 150 pm is also shown for comparison purposes. It can be seen from Figures 7 and 8 that the copper is in the form of a plurality of columnar layers extending from a surface to the other in a vanadium matrix. It can thus be seen that the phenomenon of directed solidification is evident , extends all through the material and not just a surface phenomenon is. So are the directionally solidified according to the invention Materials, apart from being interfaces between constituent materials on the electrode surface for stabilization of the arc, equipped with a further property that fibers or dendritic columns of a Components, such as copper, are united along the contact axis of symmetry and thus the electrical and thermal conduction from the contact surface support financially. The material used in Figures 7 and 8 is a 50% vanadium / 50% copper mixture (on a weight basis) Furthermore, the microscope photographs of FIGS. 7 and 8 were taken from surfaces which are essentially perpendicular to one another are.

It can thus be seen from the above that the electrode material according to the invention increases the arc stability at low current values, increased thermal conductivity between arc-forming Surface and the conductive carrier part and also he • s provides increased electrical conductivity in the same direction. Furthermore, it should also be appreciated that the invention the use of directionally solidified electrode contact materials in a variety of electrical circuit breaker devices allows where the arc migration is deliberated through Choice of the direction of solidification can be very favored. Finally, it can also be seen that the invention's performance increased by vacuum arc circuit breakers.

While the invention is more preferred here in detail by way of certain Embodiments has been described, modifications and changes can be made by those skilled in the art. Therefore All such modifications and changes that come within the scope of the invention are intended to be covered by the claims.

Blank page

Claims (9)

1 River Road Schenectady, N.Y./U.S.A. Claims 1. An electrical contact for use in a vacuum interrupter apparatus with a block of conductive material having at least one contact surface, wherein the material is a directionally solidified mixture, selected from the group consisting of the following pairs of mutually insoluble metal components comprises; Copper and vanadium with about 1 to about 92% vanadium, Copper and bismuth, Copper and lithium, Copper and lead, Aluminum and titanium with about 63 to about 99% aluminum, Aluminum and antimony with about 1 to about 82% antimony, Aluminum and chromium with about 80 to about 99% aluminum, Aluminum and beryllium with about 1 to about 98% aluminum, Aluminum and bismuth and Silver and nickel with about 1 to about 98% nickel, the percentages being percentages by weight. 2. An electrode contact according to claim 1, the electrode of which is a includes circular disc. 3. An electrode contact according to claim 1, the electrode of which is a Ring includes. 4. The electrode contact according to claim 1, the electrode of which is a flat plate includes. 5. Electrode unit with a conductive support part and the electrode according to claim 1, on a surface of the support part attached. 6. Electrode unit according to claim 5, in the directional solidification is generally perpendicular to the surface. 7. Electrode unit according to claim 5, the directional solidification of which is substantially parallel to the surface. 8. electrode contact for use in high voltage circuit breaker devices; comprising a solidified mixture of copper and vanadium, the vanadium between about 1 and makes up about 92% by weight of the electrode contacts. 9. Material, particularly useful in electrical contact, with a solidified mixture of copper and vanadium, wherein the vanadium is between about 1 and about 92 weight percent.