JPS5910006B2 - High pressure vacuum circuit breaker - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a high-voltage vacuum circuit breaker, and more specifically to a circuit breaker of this type that has an exceptionally high voltage withstand capability even after the contacts have become rough due to the influence of arcing.

There are the following prior patents related to this invention.

That is, U.S. Pat. No. 3,210,505 and U.S. Pat. No. 3,211,866.
No. 3261 954, No. 3283101,
No. 3555223 and West German Patent No. 124877
No. 5.

The circuit breaker of this invention has relatively movable contacts which are actuated to close the circuit breaker and separated to open the circuit breaker.

In the high voltage applications discussed in this section, it is common for pre-contact arcing to occur during the final stages of closing, before the contacts engage each other.

That is, as the contacts approach in this final stage, the high voltage between them causes a breakdown (i.e., a pre-contact arc) between the contacts that are still apart, followed by an arc that continues until the contacts actually engage. This arc tends to roughen the contacts, not only due to corrosive effects, but also to the point of creating welds between the contacts that must be broken during subsequent opening operations.

This roughening typically reduces the voltage withstanding capability of the circuit breaker when it is in the open position.

The object of the invention is to provide a circuit breaker capable of withstanding exceptionally high voltages when fully open, despite contact roughening caused by previous arcing and other associated effects. It is to compose.

In one form of practicing the invention, two annular shield electrodes are provided surrounding the rod to which the contacts are mounted.

Each shield electrode electrically connects to an associated rod.

The shield electrodes are mounted at spaced apart positions and have opposing front surfaces.

When the circuit breaker is fully open, its contacts are retracted from the front of the shielded area in a region of relatively low field strength.

Since the contacts are thus shielded by the shielding electrode from areas of high electric field strength, the possibility of initiation of dielectric breakdown between the contacts is significantly reduced.

Initially, the shield electrode has a smooth front surface and the breakdown voltage between these surfaces is high.

However, the effect of the arc is to roughen these surfaces, severely impairing the ability of the circuit breaker to withstand the high pressures that can be applied to the gaps between these surfaces.

One way to protect the surfaces of the electrodes from damage due to arcing or arcing effects is to locate these surfaces in areas relatively remote from the arcing region of the contact.

However, this separation makes the shielding effect of the electrodes on this contact area less effective.

It is therefore another object of the present invention to locate the shielding electrode relatively close to the arcing area of the contacts when the circuit breaker is fully open, so that an effective shielding action can be obtained. , the contact and the shielding electrode are configured so that the risk of the shielding electrode becoming rough due to the arc or the influence of the arc is relatively small.

One form of the invention provides for both contacts to move during closing and opening operations.

When the circuit breaker is fully open, the contacts are in the previously described shielding position retracted from the front of the shielding electrode.

However, during closing, the two contacts are pushed from their fully open shielded positions into the gap between the two shield electrodes, and are brought into contact with each other when the contacts are approximately midway between the two shield electrodes. match.

During this closing operation, if a pre-contact arc occurs when the two contacts approach each other, it will always occur between the contacts, and the resulting arc will usually be localized to the contacts only, and the shielding then relatively distant. excluded from the electrodes.

In order that the invention may be better understood, reference will now be made to the drawings.

Referring to FIG. 1, the illustrated vacuum circuit breaker has a high vacuum hermetic envelope 10. As shown in FIG.

The jacket has a cylindrical casing 11 made of insulating material and a pair of metal end caps 12, 13 at each end of the casing.

A suitable seal 14 is provided between the end cap and the casing;
Create a vacuum-resistant joint between these parts.

Typical pressure within the envelope is less than 10-4 Torr.

In the central region of the casing, the insulating inner surface of the casing 11 is protected by a suitable metal shield 15 so that the metal vapor generated by the arc does not condense thereon.

This shield is suitably supported on the casing 11,
Preferably, it is electrically isolated from both end caps 12,13.

The shield 15 acts in a known manner to intercept the vapor generated by the arc before it reaches the casing 11.

Two relatively movable contacts 17,1 in the vacuum envelope 10
8 is provided.

In FIG. 1, these contacts are shown in solid lines in the fully open position.

A contact 17 is suitably secured to the inner end of a conductive contact rod 17a which passes freely through the lower end cap 12.

By sealingly fixing both ends of the flexible bellows 20 to the end cover 12 and the contact rod 17a, the contact rod 17a and the end cover 1
2 will be sealed.

The bellows 20 allows the contact rod 17a to be removed without damaging the vacuum inside the jacket.
can move vertically.

A contact rod 18a through which the contact 18 freely passes through the upper end cover 13
is fixed to the inner edge of the

A flexible shell 21 provides a vacuum-tight seal around the contact rod 18, allowing it to be moved longitudinally without compromising the vacuum within the envelope.

The end cap 12 is kept at the same potential as the contact 17 by a flexible electrical connection 16, and the end cap 13 is kept at the same potential as the contact 17 by a flexible electrical connection 19.
Therefore, it is maintained at the same potential as the contact 18.

A fixed sleeve bearing 24, which is supported on the end cap 12 on the outside of the jacket, guides the contact rod 17a in a substantially straight vertical movement.

A corresponding sleeve bearing 26 guides the other contact rod 18a to move substantially linearly in the vertical direction.

Contacts 17.18 when the contacts are in the fully open position of Figure 1
For electrostatic shielding, the invention provides a pair of stationary, generally annular shielding electrodes 30,32.

Each shield electrode surrounds an associated contact and contact rod in a radially spaced manner and is electrically connected to and at approximately the same potential as the associated contact.

In order to support the shielding electrode 30, the metal tube 35 is connected to the contact rod 17a.
A bowl-shaped metal shield 37 supports the tube 35 on the lower end cap 12 .

The lower end of the bowl-shaped shield 37 is brazed to the end cap 12 and the upper end to the tube 35.

The upper end of tube 35 is suitably coupled to the lower end of shield electrode 30.

Structures 35, 37 electrically connect the shielding electrode 30 to the lower end cap 12 and thus to the contact rod 17a.

The other shield electrode 32 is supported on and electrically connected to the upper end cap 13 by metal structures 35a, 37a corresponding to structures 35, 37.

By driving the two contacts 17, 18 from the position of the solid line in FIG. 1 to the position of the dashed line in FIG.
The circuit breaker is closed.

Each contact has a contact surface 4 at its inner end opposite the other contact.
has 0.

When the contact surfaces 40 engage each other, the circuit breaker is fully closed and the contact surfaces are within the reference plane 42.

This reference plane 42 extends perpendicular to the longitudinal axis of the bar and is approximately midway between the front faces 50 of the shield electrodes 30,32.

After the closing operation has been performed as described above, the circuit breaker is opened at a desired time by returning the two contacts 17, 18 from the closed position shown by the broken line to the fully open position shown by the solid line.

A suitable linkage for effecting the same and opposite movement of the two contacts 17, 18 relative to the reference plane 42 is shown in FIG.

This linkage consists of two parts 60, 60a and a vertically movable actuating rod 62 which pivotally connects these parts.

Portion 60 corresponds to linkage 110 described in US Pat. No. 3,594,525.

It has two bell cranks 63, 64, each mounted on a fixed pivot, and interconnected by a wiping mechanism 65.

One arm of the bell crank 63 is pivotally connected to the contact rod 17a, and the other arm is pivotally connected to one end of the wiping mechanism 65.

One arm of the other bell crank 64 is a wiping mechanism 65.
It is connected to the other end, and the other arm is pivotally connected to the actuating rod 62 .

When the operating rod 62 is moved downward, the two cranks 63
, 64 rotate clockwise about their respective pivots to drive the contact rod 17a through an upward closing stroke.

The wiping mechanism 65 is shown schematically because it can be of any conventional and suitable type, as shown, for example, in FIG. 5 of U.S. Pat. No. 3,025,173.

One purpose of the wiping mechanism is to cause the driven part to overtravel slightly after the contacts are engaged at the end of the closing stroke.

The other portion 60a of the linkage is also substantially the same as portion 60 and will therefore not be described in detail.

The same reference numerals are used for corresponding parts of the two linkages, and the subscript a is used for the part of the linkage 60a.
is attached.

The crank 63a is upside down relative to the crank 63, so when the operating rod is moved downward, the contact rod 18
It can be seen that a moves downward.

Therefore, when the actuating rod 62 moves in one direction, the contact rods 17a and 18a move in the opposite direction.

Each portion of the linkage is balanced so that the contact rods move at substantially the same speed and over substantially the same travel.

In one example in which this circuit breaker is used in a circuit, high voltage exists between contacts 17 and 18 when the circuit breaker is completely open and during closing operation, but when the circuit breaker is open, the contacts There is no voltage between G).

In this application, the high voltage that exists between the contacts during the closing operation can cause dielectric breakdown or pre-contact arcing to occur during the final stages of the closing operation as the contacts approach each other.

This breakdown is followed by an arc between the contacts, which continues until the contacts engage each other, thus shorting the arc.

This arc not only erodes the contacts, but also
When the parts melted by the arc engage, there is a tendency to roughen the surface of the contacts, which may lead to fusion of the contacts.

When the contacts are pulled apart in the subsequent opening operation, the welded part is damaged.
This causes further surface roughening.

In most high pressure equipment, this roughening results in 17 and 18
When the parts shown in Figure 1 are separated and a high voltage is applied between them, the dielectric breakdown voltage between these parts tends to decrease.

However, in this invention, when the circuit breaker is completely open,
By placing the contacts in a region with low electric field strength,
Because they are effectively shielded from areas of high electric field strength, a high breakdown voltage can be maintained between the contacts 17, 18 even when such surface roughening occurs.

This will be explained in more detail below.

When the circuit breaker is fully opened as shown in FIG. 1, the equipotential lines of the electrostatic field near the shielding electrode 30 are as shown by broken lines 39a and 39b in FIG. Become.

Line 39a represents approximately the 95th factor and line 39b represents approximately the 90th factor of the voltage present in the gap between the electrodes.

Therefore, it can be seen that because the contact point 17 is retracted from the front surface 50 of the shielding electrode 30, it is located in a region where the strength of the electrostatic field is extremely small.

Similarly, the equipotential lines of the electric field near the other shield electrode 32 have a corresponding shape, and the contact 18 when completely open is similarly in the 0Q region of low electric field strength.

As described above, due to the low electric field strength near the contact surface 40, dielectric breakdown begins at the contact point, even though the contact surface has been roughened due to the arc and the influence of the arc, as described above. Fear is greatly reduced.

Shield electrode 30. In order to utilize 32 effectively and maintain high breakdown voltages, it is important to keep its surfaces in areas of strong electric fields, particularly front surface 50, relatively smooth.

To help keep the surface smooth, the pre-contact arc during closing is localized to the contacts 17 and 18, and the shield electrode 30
．． It is highly desirable not to start at 32 or come into contact with these shield electrodes.

It is also desirable that metal droplets created by the arcing before contact between contacts 17, 1B not be deposited on the shield electrode.

One way to protect the shield electrode from these effects is to place the shield electrode in an area relatively distant from the contacts.

However, this separation reduces the shielding effect that the shielding electrode has on the contacts.

For example, if the diameter of the shield electrode 30 is increased and moved further away from the contact 17, the equipotential lines of the electrostatic field as shown at 39a will fall deeper into the central region of the shield electrode 30, and the contact surface 40 The area immediately adjacent to is the area where the electric field strength is higher.

In this invention, both contacts are displaced longitudinally from their shielded, fully open position during the closing operation, so that the contact engagement occurs in the central region of the gap between the shielding electrodes. , effective shielding can be achieved using shielding electrodes closely surrounding contacts 17,18.

In this regard, when the contact surface 40 is engaged at the end of the closing motion,
Note that it is on or immediately adjacent to the central reference senmen 42.

Typically, a pre-contact arc occurs between surfaces 40 when they are near a central reference plane 42.

Since the illustrated circuit breaker is specifically for high voltage applications, the gap between the electrodes 30, 32 is unusually long for a vacuum circuit breaker, e.g. about 2 inches, so that the central reference point on which the contacts engage is The plane is about 1 inch from each shield electrode.

This relatively large distance substantially reduces the risk that a pre-contact arc that occurs as the closing contacts approach reference plane 42 will originate from or contact the shield electrode.

The fact that the pre-contact arc is generated vertically away from both shield electrodes keeps the pre-contact arc away from the electrodes and prevents the risk of molten metal droplets generated by the arc from the contact sticking to the electrodes. It also plays an important role in making it smaller.

Most of this metal flies generally radially outward from the arcing region, but the longitudinal offset of the shield electrodes 30, 32 from the arcing region results in the shield electrodes being out of the path of such droplets.

This would not be the case if the arcing region was even partially within the confines of either annular shield electrode.

In order to reduce the amount of metal splatter produced by pre-contact arcing and to ensure exceptionally short gap lengths during pre-contact arcing, one embodiment of the invention utilizes U.S. Pat. 3,143,373, the contacts are made of aluminum or aluminum-based materials.

IJ IJ aluminum has an exceptionally good dielectric strength and is exceptionally resistant to roughening due to arcing or the effects of arcing.

Preferably, the shield electrode is made of a hard, highly ductile ferrous material such as that described in US Pat. No. 3,769,538.

These materials also have excellent dielectric strength in a vacuum.

Stainless steel also shields the electrode 30. It is a suitable material for 32.

Generally, soft metals such as copper and aluminum are avoided for electrodes 30.32.

This is because the dielectric strength is inferior to the above-mentioned steel.

Although this invention has been described with particular reference to applications in circuit breakers that are opened under no voltage conditions and therefore do not form an arc when opened, it is to be understood that the invention is not limited to such applications in a broader sense. Not until now.

The present invention can also be advantageously used in applications where an arc is generated when the circuit is opened.

This is because such an arc is conventionally extinguished after the contact has traveled a small portion of its opening stroke, and the contact surface 40 enters a shielded position within the surrounding shield electrodes 30, 32. This is because the arc will be extinguished long before.

Therefore, the metal droplets generated by this arc fly radially outward as usual and do not hit the shield electrode.

Because the arcing region between the contact surfaces 40 is vertically offset from the shielding electrode, and normally the arcing occurs at the contacts 17, 1B.
Since there is little or no magnetic effect on the arc on surface 40 that would tend to transfer it from the electrode 30, 32 to the electrode 30, 32, there is little risk that the open arc will transfer to the shield electrode.

As an additional feature of the present invention, the shielding electrode 3
The bowl-shaped metal support 37 used for 0 provides a means of reducing the electric field strength in the vicinity of the seal 14.

This bowl-shaped support 37 extends immediately past the insulating inner wall of the cylindrical casing 11, past the seal 14, and for a considerable distance towards the central reference plane 42, so that it is not in the vicinity of the seal. The approximate shape of the electric field in each case is 70
The intensity is relatively low, as represented by the approximately 80% and 90% equipotential lines shown at a and 70b.

This shielding effect on the seal advantageously suppresses the known tendency for electric fields to concentrate at glass-to-metal interfaces such as those present in seal 14.

A bowl-shaped support 37a has the same shielding effect on the seal 14 at the upper end of the cylindrical casing 11.

While specific embodiments of the invention have been illustrated and described, it will be apparent to those skilled in the art that various modifications may be made within the scope of the invention.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of a vacuum circuit breaker according to one type of the invention, with the fully open position of the circuit breaker contacts shown in solid lines and the fully closed position shown in broken lines. FIG. 2 is a schematic illustration of the circuit breaker and its appropriate operating linkage, and FIG. 3 is an enlarged view of a portion of FIG. 1, showing a portion of the electric field. Explanation of main symbols, 10: Outer cover, 11: Casing, 12
, 13: End dream, 17, 18: Movable contact, 17a, 18a
: contact rod, 20, 21: bellows, 30, 32: shielding electrode, 50: its front surface.

Claims (1)

[Claims] 1. A high vacuum envelope having spaced apart electrically conductive ends and electrically insulating means between the ends and insulating the ends from each other, a pair of circuit breaker contacts, and a circuit breaker within the jacket surrounding the contacts. in a high-pressure vacuum circuit breaker having an electrically isolated metal shield supported on said ends, with two movable contact rods passing through said ends and longitudinally of the rods relative to the associated ends. movable, each contact rod supporting one circuit breaker contact;
The longitudinal length of the contact rods is such that the sealing means provides a seal between each contact rod and its associated end and drives the contacts into a closed position and away from each other to open the circuit breaker. a movable, generally annular shield electrode surrounding and electrically connected to each contact rod, the shield electrode being mounted at a fixed position within the envelope; The opposing front faces of the shielding electrodes are longitudinally spaced apart from each other and are on either side of the contact point of said two contacts during circuit breaker closing, said contact rods having associated contacts therewith during circuit breaker opening operation. The front face of the shield electrode is movable to a retracted opening position, and the shield electrode is arranged in a manner sufficient to ensure that arcing during circuit breaker opening operation is typically localized to the contacts and expelled from the shield electrode. a distance apart from the contact location of the two contacts, and the position of each of the contacts at the time of occurrence of the pre-contact arc during circuit breaker closing operation typically confines the pre-contact arc to the contacts. A high-voltage vacuum circuit breaker characterized in that it is located sufficiently ahead of the front surface of the shielding electrode so that arcs are excluded from the shielding electrode.