Note: Descriptions are shown in the official language in which they were submitted.
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OPENING AND CL08ING MEC~ANISM FOR A ~EDIUM OR HIGH VOLTAGE
~ECTRICA~ SWITCH
BACKGROUND OF THE INVENTION
The invention relates to a medium or high voltage electrical
switch or circuit breaker.
In state-of-the-art manner, for example according to the Patent
US-A-4,529,853, a switch of this kind notably comprise~ :
- a main circuit provided with at least one stationary main
contact and at least one movable main contact pivotally mounted
around a spindle;
- an auxiliary circuit, which may be called shunting circuit,
arranged in parallel to the main circuit and provided with a
stationary auxiliary contact and a movable auxiliary contact
pivotally mounted on the same spindle;
- a drive mechanism designed to drive the movable main contact
and movable auxiliary contact simultaneously in rotation around
the spindle in question.
The shortcoming of such a switch lies in the fact that there is
a rigid direct coupling in rotation between the movable main
contact and the movable auxiliary contact.
The ob;ect of the invention is to overcome this shortcoming.
SUMMARY OF THE INVENTION
According to the invention, the drive mechanism includes a
variable angular offset mechanism able to vary the relative
angular positions of the movable auxiliary contact and the
movable main contact when operations of the switch take place.
According to a first embodiment, the angular offset mechanism is
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adapted to allow two pseudo-stable relative angular positions, a
first angular position activated at the end of opening travel of
the switch and for which, when the subsequent Glosing operation
takes place, closing of the auxiliary contacts precedes closing
of the main contacts, and a second angular position activated at
the end of closing travel of the switch and for which, when the
subsequent opening operation takes place, opening of the main
contacts takes place at appreciably thP same time as opening of
the auxiliary contacts.
To achieve this, the movable auxiliary contact is arranged
between two plates articulated around said spindle, securedly
united in rotation with said movable main contact and urged
towards one another by means of spring means; a ball-bearing
locking mechanism with two positions is inserted between said
plates and the movable auxiliary contact, the first angular
position being activated by means of a first stop, and the
second angular position being activated by means of a second
stop formed by the movable auxiliary contact.
According to a second embodiment, the angular offset mechanism
is adapted to allow continuous variations of the angular offset
when operations of the switch take place, so that when a closing
operation takes place, closing of the auxiliary contacts
precedes closing of the main contacts and when an opening
operation takes place, opening of the main contacts precedes
opening of the auxiliary contacts.
To achieve this, the angular offset mechanism comprises two
connecting rod-crank mechanisms driven simultaneously by a
common motor shaft, a first connecting rod-crank mechanism
associated with the movable main contact and a second connecting
rod-crank mechanism associated with the movable auxiliary
contact.
Preferably, the switch according to the first or second
embodiment comprises in addition a second auxiliary circuit, for
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example a vacuum switch, arranged in parallel with said main
circuit and said auxiliary circuit, and provided with arcing
contacts.
The invention applies notably to switches and circuit breakers
in which the main circuit and auxiliary circuit are immersed in
an insulating gas of high dielectric strength, such as sulphur
hexafluoride (SF6), the second auxiliary circuit being formed by
a vacuum switch which is also immersed in the insulating gas.
BRIEF DESCRIPTION OF THE DRAWINGS
Other advantages and features will become more clearly apparent
from the following description of various illustrative
embodiments of the invention, given as non-restrictive examples
only and represented in the accompanying drawings, in which :
- Figure 1 is a schematic side view of a first embodiment of the
invention,
- Figure 2 is a schematic front view of the main circuit and
auxiliary circuit of the first embodiment according to figure 1,
- Figures 3 to 6 illustrate operation of the first embodiment
according to figures 1 and 2, the switch being respectively in
the open position (figure 3), then in the course of closing
(figure 4), then in the closed position (figure 5), and finally
in the course of opening (figure 6),
- Figure 7 illustrates a possible diagram as far as the opening :
and closing sequences of the switch according to the first
embodiment are concerned, .
- Figure 8 is a schematic side view of a second embodiment of
the invention,
- Figures 9 to 11 illustrate operation of the second embodiment
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according to figure 8, the switch being respectively in the open
position (figure 9), in the course of closing or opening (figure
10), and finally in the closed position (figure 11),
- Figure 12 illustrates a possible diagram as far as the opening
and closing sequences of the switch according to the second
embodiment are concerned.
DESCRIPTION OF THE PREFERRED EMBODIMENT
With reference to figures 1 and 2, illustrating a first
embodiment, the enclosure 4, either sealed or not, of the switch
is filled with air or a dielectric gas such as sulphur hexa-
fluoride (SF6) and comprises a current input terminal strip 1
and a current output terminal strip 2. The input terminal strip
1 is divided into three conducting branches la, lb and lc. The
two branches la and lb respectively bear at their ends two
stationary main contacts 30a and 30b, whereas the branch lc
bears at its end a stationary auxiliary contact 35.
The stationary main contacts 3Oa and 3Ob are designed to
cooperate with movable main contacts 20a and 20b pivotally
mounted around a spindle 3; the stationary auxiliary contact 3S
cooperates with a movable auxiliary contact 25, also pivotally
mounted around the spindle 3.
The spindle 3 is supported by two fixed conducting branches 2a
and 2b which are joined together at the level of the output
terminal strip 2.
The movable auxiliary contact 25 is electrically connected to
the branches 2a and 2b, and therefore to the output terminal 2,
by means of an electrical connection 4.
The auxiliary circuit formed by the auxiliary contacts 25, 35 is
therefore arranged in parallel to the main circuit formed by the
main contacts 2Oa, 2Ob, 3Oa and 3Ob.
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A drive rod 6, parallel to the spindle 3, passes through the
movable main contacts 2Oa and 2Ob and is connected to a crank 9
mounted with rotation around the spindle 10 by means of a
connecting rod 7 articulated on the spindle 8.
In figure 2, two plates 28a and 28b located on each side of the
movable auxiliary contact 25, and also pivotally mounted around
the spindle 3 and having the drive rod passing through them and
being urged towards one another by means of a spring 27 located
on a spindle 29, each bear two hemispherical housings 26a and
26b. A ball-bearing 26 housed in a drilling in the movable
auxiliary contact 25 is held in one or the other pair of
housings 26a or 26b.
The assembly formed by the movable auxiliary contact 25, the two
plates 28a and 28b, housings 26a and 26b, spring 27 and ball-
bearing 26, forms a ball-bearing locking mechanism with two
pseudo-stable positions, enabling variations to be made of the
relative angular positions between the movable main contacts
20a, 20b on the one hand and the movable auxiliary contact on
the other hand.
In addition, according to a preferred embodiment, a third
electrical circuit comprising a state-of-the-art vacuum switch
15, connected on the one hand to the terminal strip 1 by the
electrical connection 16, and on the other hand to the terminal
strip 2 by the electrical connection 19, is arranged in parallel
to the main and auxiliary circuits. The movable rod 14 of the
vacuum switch 15 is connected to the crank 9 by a connecting rod
ll equipped with a spring 12. U.S. Patent US-A-5,155,315 which
describes the mechanism associated with the vacuum switch should
be advantageously referred to.
Operation of the mechanism will now be described in detail with
reference to figures 3 and 6.
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In the open position of the switch (Figure 3), the tongue 25a is
up against a fixed stop 5 and the ball-bearing 26 i5 positioned
in the housings 26a of the two plates 28a and 28b. In other
words, the movable auxiliary contact 25 is in advance of the
movable main contacts 2Oa and 2Ob.
With a view to closing of the switch (Figure 4), the crank 9 is
made to rotate around the spindle 10. The crank 9 drives the
connecting rod 7, the drive rod 6 and thereby the two movable
main contacts 20a and 20b and the two plates 28a and 28b. The
latter in turn drive the movable auxiliary contact 25 via the
ball-bearing locking mechanism.
In a first stage, the movable auxiliary contact 25 comes into
contact with the stationary auxiliary contact 15, the main
contacts still being open.
Then in a second stage (Figure 5), $he point 25b of the
auxiliary contact 25 knocks against a stop 35a of the stationary
auxiliary contact 35, which has the effect of making the ball-
bearing locking mechanism rock to the position 26b; at the same
time, the movable main contacts 20a and 20b close on the
stationary main contacts 30a and 30b.
In this second stage, it will therefore be noticed that the
ball-bearing locking mechanism activated at the end of closing
travel has enabled the angular offset between the movable main
contacts 20a and 20b and the movable auxiliary contact 25a to be
modified. This offset has in fact become very small, so that
when subsequent opening of the switch takes place (Figure 6),
opening of the main and auxiliary contacts will take place at
appreciably the same time. Preferably opening of the main
contacts will take place slightly before opening of the
auxiliary contact.
At the end of opening travel, the tongue 25a knocks against the
stop 5 (Figure 3), which has the effect of making the ball-
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bearing locking mechanism rock to the initial position 26a, andtherefore in fact of varying the angular offset so that when
subsequent closing takes place, closing of the auxiliary
contacts again precedes closing of the main contacts.
If, according to the preferred embodiment, the switch is
equipped with the third electrical circuit comprising the vacuum
switch 15, driving of the crank 9 simultaneously brings about
opening and closing of the vacuum switch 15. The crank 9 and
connecting rod 11 form a toggle mechanism, so that closig of the
contacts 15a and 15b of the vacuum switch 15 takes place only in
the course of the opening and closing operations of the switch
(Figures 4 and 6). In the stable open or closed positions, the
contacts 15a and 1sb of the vacuum switch 15 remain open
(Figures 3 and 5).
Figure 7 gives for illustrative purposes a diagram of opening
and closing of the three electrical circuits (main, auxiliary,
vacuum switch) versus time. In the stable open position (O), the
three circuits are naturally open. When the closing operation is
triggered, the auxiliary circuit first closes, followed by
closing of the vacuum switch, and only then closing of the main
circuit, and finally, at the end of travel of the crank g,
reopening of the vacuum switch.
Consequently in the stable closed position (F), the main and
auxiliary circuits are closed, whereas the vacuum switch is
open. When the opening operation is triggered, the vacuum switch
first closes, and then after a certain time the main circuit
opens immediately followed by opening of the auxiliary circuit,
and finally opening of the vacuum switch, returning to the
stable open position (O).
The advantage of such a sequence lies in the fact that when the
switch closes, closing of the auxiliary circuit takes place
before closing of the vacuum switch, prestriking therefore takes
place at the level of the auxiliary circuit, thus eliminating
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well-known phenomena of multiple restriking associated with
vacuum switches which generate voltage surges harmful for
certain applications, for example medium voltage motors.
This moreover enables the erosion on the main contacts and the
force required for closing of the main contacts to be reduced.
The auxiliary contacts can be made from arc resistant material,
with a possible compensation against their wear.
The preferred embodiment described above is particularly well-
suited to a medium voltage or extra-high voltage switch, in
which the sealed enclosure 1 is filled with a dielectric gas
such as SF6; the vacuum switch 15 will then be immersed in this
dielectric gas as has already been proposed in French Patent FR-
A-2,655,766.
Figures 8 to 12 illustrate a second embodiment of the invention;
their reference numbers are the same as those of the first
embodiment for the components common to both embodiments.
We can find notably the enclosure 4, input terminal strip 1 and
output terminal strip 2, stationary main contact 3Oa, stationary
auxiliary contact 3S, movable main contact 20a and movable
auxiliary contact 25, the latter two being pivotally mounted
around the spindle 3. The auxiliary circuit is arranged in
parallel to the main circuit.
The drive rod 6 passes through the movable main contact 20a and
is connected to the crank 9 by means of a connecting rod 7
articulated on the spindle 8.
A second drive rod 6a passes through the movable auxiliary
contact 25 and is connected to the crank 9 by means of a second
connecting rod 7a articulated on the spindle 8a. The two
connecting rod-crank systems 7 and 7a being distinct and
different, it becomes possible to introduce a continuous
variation of the angular offset between the movable main contact
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20a and the movable auxiliary contact 25 when rotation of the
crank 9 takes place. In the open position of the switch (Figure
9) the movable main contact 20a is appreciably in phase with the
movable auxiliary contact 25. In the course of closing or
opening (Figure 10), the movable auxiliary contact 25 is
respectively ahead of or behind the movable main contact 2Oa.
The opening cycle (O) and closing cycle (F) of the switch
represented in figure 12 are consequently symmetrical.
Figure 11 shows the switch in the closed position.
According to a preferred embodiment, a third electrical circuit
comprising a vacuum switch 15 is arranged in parallel to the
main and auxiliary circuits.
If the vacuum switch 15 is added, controlled in the same way as
in the first embodiment, the opening and closing diagram (Figure
12) remains perfectly symmetrical. When closing takes place, the
vacuum switch circuit will close first, followed by closing of
the auxiliary circuit, then closing of the main circuit, and
finally the vacuum switch circuit will open again.
Inversely when opening takes place, the vacuum switch circuit
will close first, followed by opening of the main circuit, then
opening of the auxiliary circuit, and finally the vacuum switch
circuit will open again.
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