Note: Descriptions are shown in the official language in which they were submitted.
~(~ 91/08579 PCl/US90/01220
5~
ARC SPINNER INTERRUPTER
Related Applications
The present application is a ~ontinuation-
In-Part applicati`on of United States Application
- Serial No. 308,145, filed on February 8, 1989.
sackground of the Invention
1. Field of the Invention
_ _ _
The present invention relates generally to
electrical arc interrupter devices and, more particu-
larly, to an arc spinner interrupter having imp~oved
movable contact structure which is cooperable with a
ring electrode to more efficiently extinguish an arc
by decreasing the time required to initiate and
effect spinning of the arc through a cool interrupt-
ing gas.
2. Discussion of the Prior Art
- -
Numerous conventional constructions exist
for providing arc interruption through the use of a
field coil that creates a magnetic field in which an
arc is extinguished. For example, it is known to
provide an arc interruption device in which an arcing
ring is electrically connected in series with a mov-
able contact through a field coil surrounding the
ring, and a fixed contact is disposed internally o~
the ring electrode at a point along the central axis
of the electrode. In this known construction, the
movable contact is mounted for pivotal movement about
an axis extending in a direction perpendicular to and
offset from the central ~ongitudinal axis of the ring
electrode such that the movable contact is mQvable
between a first engaged position radially inward of
W091tO~579 PCT/U~gO/01220
2~7~5~ -2-
1 the ring electrode to a second disengaged po~ition
radially outward of the ring electrode.
When the movable contact of this known de-
vice is pivoted away from the fixed contact, an arc
initially forms between the movable contact and the
fixed contact which is retained between these con-
tacts until the movable contact pi~sses over and
across the ring electrode. Thereafter, the arc is
transferred to the ring electrode and is spun by the
action of magnetic forces created within the ring
electrode by the current flow through the field coil.
This spinning action within the ring electrode even-
tually extinguishes the arc after the arc commutes to
the ring electrode. However, because the arc, is
1~ carried between the movable contact and the fixed
contact during a substantial portion of the travel
time of the movaole contact between the fixed contact
and the ring electrode, an unavoidable delay in the
overall quenching time of the arc occurs. Exemplary
is the mechanism described by Kazushi Fujiwara, et
al. of Yaskawa ~lectric Mfg. Co., Ltd., Xitakyushu,
Japan in a paper presented to the Seco~d Interna-
tional Symposium on Switching Arc Phenomena held at
Lodz, Poland, September 25-27, 1973.
Another known type of arc interrupter con-
struction is disclosed in United States Patent Nos.
4,301,340, 4,301,341, and 4,409,446. In this known
type of construction, a ring electrode is electric-
ally connected in series with a fixed electrode
through a field coil, and a movable contact, pivotal
about an axis intersecting the central axis of the
ring electrode and extending in a direction perpen-
dicular thereto, moves transversely across a circular
pole face of the field coil and inwardly of the axis
thereof when disengaged from the fixed contact which
W~91/0~579 PcT/usso/ol22
-3- 2 ~
1 is disposed either dlrectly on or radially outward of
the ring electrode.
In operation of this second known type of
construction, after the movable contact is removed
from engagement with the fixed contact, the movable
contact moves into close proximity with the ring
electrode such that the arc which ini ially forms
be~ween the movable contact and the fixed contact
commutes to the ring electrode. Thus, a part of the
delay encountered in the previously discussed con-
struction is avoided.
However, in the device disclosed in U.S.
Patent Nos. 4,301,340, 4,301,341, and 4,409,446, it
is critical that the device be constructed with ,the
movable contact positioned very accurately with
respect to the ring electrode in order that the arc
will properly commut~ to the ring electrode once the
movable contac~ pasaes over the ring electrode. Any
variation in the relative spacing of the movable
contact and the ring electrode can have an adver~e
effect on the amount of time required for the device
to extinguish an arc, thus resulting in a device
which operates in an unpredictable manner. In add-
ition, in order to direct the arc into the interior
region of the ring electrode, it is essential in this
second known type of construction, that the movable
contact travel along a path which extends into the
interior of the ring electrode.
In U.S. Patent No. 4,503,302, a third type
of known arc interruption device is illustrated which
is similar to the first mentioned construction above
in that an arcing ring electrode is provided which is
electrically connected in series with a movable con-
tact through a field coil surrounding the ring elec-
trode, and a fixed contact is disposed internally of
WO91/08579 P~T/US90/01220
2~7~ 4-
l the ring electrode. However, in the device shown in
U.S. Patent No . 4,503,302, the movable contact i5
mounted for pivotal movement about an axis extending
in a direction parallel to the central axis of the
ring electrode. Thus, as with the first mentioned
device, the arc remains between the movable contact
and the fixed contast until the movable contact has
moved a substantial distance toward the ring elec-
trode, thus retarding the time required for initia-
tion of arc commutation.
Objects and Summary of the Invention
It is advantageous to provide an arc inter-
ruption device which consistently extinguishes a,rcs
within a relatively narrow time period shortly after
disconnection of the contacts in order to permit the
arc interrupter to be employed in a distribution sys-
tem including other components such as fuse links,
sectionalizers and the like, which rely on the timing
of the arc interruption procedure in their own opera-
tion. Therefore, it is one object of the present in-
vention to provide such a construction.
Another object of the invention is to pro-
vide an arc interrupter which is simple to construct
and which allows somewhat greater tolerance limits
with respect to the spacing of the different parts of
the apparatus as opposed to heretofore known devices
that re~uire very close tolerances.
Further, it is an ob~ect of the present in-
vention to provide an arc interrupter in which an arc
is managed substantially from the time it forms be-
tween the contacts until it has been extinguished in
order to expedite commutation and quenching of the
arc.
wn91tO8579 PCT/US90/01220
-5~ 5~
1 It is also an object of the invention to
provide an arc interrupter in which electrostati-
stress experienced in the vicinity of the angled
portion of a movable contact of the interrupter is
reduced by grading' the field surrounding the angled
portion such that the size of the ring electrode may
be reduced without adversely affecting the ability of
the interrupter to withstand high voltage impulses of
the type commonly experienced when lightning strikes
the electrical distribution lines in communication
with the interrupter.
These advantages, among others are achieved
through the use of an arc interrupter apparatus c~n-
structed in accordance with the present invention.
For example, in its preferred form, an arc interrup-
tion apparatus made pursuant to the invention in-
cludes a fixed electrical contact and a movable elec-
trical contact having an arm that may be selectively
engaged with the fixed contact. An arc interrupting
ring electrode is associated with the contacts and
has opposed ends defining a central longitudinal axis
therebetween while a field coil is provided in sur-
rounding relationship to the ri~g electrode. Means
are provided for electrically connecting the field
coil to the fixed contact so th'at the field coil is
at the same potential as the fixed contact.
The arm of the movable contact includes an
angled portion which projects rom the remaining por~
tion of the arm toward the electrode in a direction
generally parallel to the longitudinal axis of the
electrode. ~hat arm is movable across the electrode
along a path perpendicular to and toward the longi-
tudinal axis thereof when the movable contact is
shifted to interrupt current flow throu~h the con-
tacts. An arc is generated between the movable con-
WO91/08579 PCTtUS90/01220
5~ -6-
1 tact and the fixed contact when the movable contact
in an energized condition is disconnected from the
fixed contact. The arm cooperates with the remaining
portion of the angled portion of the movable contact
to cause first and second electromagnetic forces to
be exerted on the arc upon disconnection of the con-
tacts as the arm approaches the electrode and moves
across the electrode. The first electromagnetic
force acts in a direction toward the ring electrode
so as to encourage commutation of the arc from the
fixe~ contact to the ring with little regard to the
distance of the movable contact from the ring elec-
trode. The second electromagnetic force acts in a
circumferential direction relative to the central
axis of the electrode to enhance spinning and there-
fore extinguishment of the arc.
A means for grading the electrostatic field
surrounding the angled portion of the arm section is
also provided in the interrupter. Preferably, this
means includes a conductor which extends toward the
first axial end of the ring interrupter from the
second axial end along the central longitudinal axis.
The conductor includes an inner axial end that is
separated slightly from the angled portion when the
arm section is moved to a position intersecting the
central longitudinal axis.
3y providing this construction, numerous
advantages are realized. For example, by providing a
uniform gradient in the electrostatic field surround~
ing the angled portion of the arm section, it is pos-
sible for the interrupter to better withstand high
voltage impulses without brea~ing down than would an
interrupter if it were not provided with such grading
means.
~91/08579 PCTiUS90/0122fl
_7- 2~ 5~
i An option to providing grading means in the
interrupter for grading the electrostatic fie}d sur-
rounding the angled portion of the arm section would
be to increase the diameter of the ring electrode
until the gap distance between the angled portion of
the arm section and the ring, when the arm section is
in a position intersecting the central longitudinal
axis, was sufficiently large to prevent arcing when a
high voltage impulse oF a predetermined magnitude was
experienced by the interrupter. However, due to the
size restraints imposed on a recloser that is sealed
within an insulative gas housing, such a solution is
not preferred. Thus, by providing grading in the in-
ventive interrupter, it is possible to reduce, the
diameter of the ring electrode to a size capable of
easily fitting within the conventionally sized space
of a recloser housing.
Another advantage that is realized from the
construction of the present invention resides in the
existence of the conductor of the grading means which
acts to distribute heat developed ~uring normal arc-
ing when the movable contact is separated from the
fixed contact. This distribution of heat occurs when
the arc transfers to the conductor during movement of
the arm section toward a position intersecting the
central longitudinal axis. Once the arc transfers to
the conductor, the angled portion of the arm section
is permitted to cool and the heat generated by the
arc is distributed in the conductor which may have a
larger mass than the angled portion of the arm. In
other words, because the arc does not dwell on the
angled portion of the arm section, the angled portion
does not melt away as quickly as it would if the
grading means conductor were not present in the
interrupter, and the life of the movable contact is
lengthened.
WO 91tO8579 P~/llSgO/01220
2~ ~7~5~
1 Unexpectediy, it has been observed that by
providing the conductor of the grading means in the
interrupter, transfer of the arc from the movable
contact to the conductor sometimes occurs very early
in the interruption process. Speci ically, it is
common during interruption for the i~rc to transfer
from the movable contact to the conductor ~s early as
when the movable contact passes directly over the
ring electrode. Several benefits are realized as a
result of this early arc transfer. For example, by
having early transfer of the arc to the conductor,
elongation of the arc is carried out early in the
interruption process, and the full length of the arc
begins spinning within the electrode earlier in the
interruption process than would occur in the absence
of the conductor. These results enhance the ability
of the apparatus to interrupt the arc quickly and
reliably while providing the other beneits already
discussed.
In a further preferred form of the inven-
tion, the movable contact of the arc interrupter
apparatus is mounted for pivotal movement about a
pivot axis extending in a direction parallel to the
central longitudinal axis of the ring electrode, and
includes a portion disposed generally in a plane per-
pendicular to the central longitudinal axis.
Brief Description of the Drawin~ Figures
A preferred embodiment of the invention i~
described in detail below with reference to the
attached drawing figures, wherein:
Fig. 1 is a plan view of an arc interrupter
made in accordance with the present invention, where-
in the movable contact is connected with the fixed
contact;
~91/08579 PCT/US90/01220
1Fig. 2 is a cross-sectional side view of
the interrupter of Fig. 1;
Fig. 3 is a plan view of the interrupter
with the movable contact shown as being disconnected
5from the fixed contact and moving across the ring
electrode;
Fig. 4 is a cross-sectional side view of
the interrupter of Fig. 3;
Fig. 5 is a plan view of the interrupter
10with the movable contact shown as being within the
circumference of the ring electrode;
Fig. 6 is a cross-sectional side view of
the interrupter of Fig. 5;
Fig. 7 is a plan view of the interrupter
15with the movable contact shown as being positionèd at
the central longitudinal axis;
Fig. 8 is a cross-sectional side view of
the interrupter o Fig. 7;
Fig. 9 is a schematic view illustrat~ng the
20electrostatic ~ield in an interrupter constructed
without a grading rod in place;
Fig. 10 is a schematic view illustrating
the electrostatic field in an interrupter constructed
with a grading rod in accordance ~lith the present
invention; and
25Fig. 11 is a graph illustrating the elec-
trostatic field versus the distance from the movable
contact toward the ring electrode when the movable
contact is located at the central longitudinal axis
for both the interrupter of Fig. 9 and the inter-
rupter of Fig. 10.
.: . . -
~ - , . , . 1
P~ltJS ~ G/O 122~
IPE~/US O 7 OCT i99i
-10^
D_ailed Description of the Preferred Embodiment
An arc interrupter apparatus constructed in accordance with the
present invention for use in electrical switch gear is illustràted in Fig. 1.
Although not shown in the drawing, the apparatus is preferably disposed
within a housing filled with an insulating gas having favorable arc e~tinguish-
ing properties. For example, sulphur hexa~uoride may desirably be employed
as the insulating gas because of the rnany advantages ed by a gas of that
type. ~ulphur hexafluoride is an inert, non-to~c, non lmmable gas that is
an excellent dielectric. In addition, because the gas is electronegative, it is an
excellent arc extinguishing material.
- A pair of bushings preferably extend through the housing in a
sealed manner and are adapted to be connected to the arc interruption
apparatus shown in the figures. One of the bushings is adapted to be
connected to a fixed contact of the apparatus while the other bushing is
connected to a movable contact, so that the current path from a distribution
line or the like incudes the bushing and the fixed contact as well as the
movable contact normally in engagement therewith.
In the apparatus itself, as shown in Fig. 1, the fixed contact 10
and movable contact 12 are mounted, together with a ring electrode 14, on
a support 16 constructed of an insulatfng material such as an acetal or epoxy
resin. The fixed contact 10 includes a generally U-shaped contact element 18
retained on fixed contact arm 20 by any suitable means such as a bolt and nut
arrangement 22. A U-shaped biasing element 24 is sandwiched between the
contact element 18 and the contact arrn 20 and includes two legs extending
along the outer faces of
SU~STlT~ S~lEET
IP~A/US
W~91/08579 PCT/US9~/01220
r,~ ?
1 the legs of the contact element 18. The legs of the
biasing element 24 press inward against the legs of
the contact element 18 in order to bias the legs of
the contact element toward one anothe~r for retaining
the movable contact 12 in engagement with the f~xed
contact 10 during normal current flow through the
apparatus.
An L-shaped stationary arc tip 26 ~Figs. 2
and 4) is provided on the fixed contact 10 which is
also mounted on the contact arm 20 by the holt and
nut assembly 22 and that extends beyond the legs of
the contact element 18 by a predetermined distance.
The stationary arc tip 26 is constructed of a resili-
ent conductive metallic material having suitable arc
resistent properties. The contact arm 20 is mounted
on the support 16 by any suitable means such ZIS by a
further bolt and nut arrangement extending through
the arm 20 and a wall 28 of the support 16.
Although not shown in the drawing, under
some conditions it may be necessary to reinforce the
arc tip by providing additional, thermal resistant
material on the tip. For example, a button of ther-
mally resistant material may be secured to the tip at
the point at which the movable contact separates from
the arc tip during interruption. By providing addi-
tional material at this point, the resistance of the
arc tip to high arc temperature is enhanced.
The movable contact 12 includes an elonga-
ted conductive member 30 having a hole 32 located
interme~iate the ends thereof through which a pivot
pin 34 extends. The movable contact 12 is held in
pressing engagement with a bus 33 by the pivot pin 34
which is spring-loaded to a predetermined force. The
bus 33 connects with one of the bushings. The elon-
gated member 30 includes a first arm section 36 ex-
WO91/08579 PCT/US90/01220 .
-12-
2~:;'7~i~?,
1 tending between the hole 32 and one end 38 of the
member 30 and a second arm section 40 extending from
the hole 32 toward the other end 42 of the member 30.
The first arm section 36 of the member 30 which is
pivotal about the pivot axis defined by the central
axis of the pivot pin 34, can be selectively engaged
with the fixed contact 10 between the legs 18 there-
of. First arm section 36 is preferably of L-shaped
configuration and includes an angled portion 44 which
extends toward the ring electrode 14 from the arm
section 36 in a direction general}y perpendicular to
arm section 36 and parallel to the céntral longitud:i-
nal axis of the ring electrode 14. The angled por-
tion 44 may either be formed of the same piece, of
material as arm section 36 or may be constructed of a
separate piece of material. For example, as shown in
Fig. 4, the angled portion 44 may be constructed of a
~irst hollow cylindrical piece 46 and an arc-~esis-
tant end piece 48, both of which are adapted to be
connected to the arm section 36 by a threaded shaft
or the like extending axially through the angled
portion 44.
The second arm section 40 serves as a lever
through which an actuator 50 may act on the movable
contact 12 to move such contact into and out of en-
gagement with the fixed contact 10. During operation
of the interrupter, as discussed in detail below, the
actuator 50 pivots the elongated member 30 about its
pivot axis along a path extending between the posi-
tion shown in Fig. 1, with the movable and fixed con-
tacts 12, 10 engaged with one another, and the posi-
tion shown in Fig. 7, whereby the movable contact 12
is disposed at the central longitudinal axis of the
ring electrode 14. Although the position at which
the actuator 50 contac-ts the elongated member 30 of
W~9l/08579 PCT/US9~/01220
-13- ~ . d
1 the movable contact i2 is illustrated as being at the
end of the second arm section 40, it i.s noted that an
alternative construction could include an elongated
member which is connected to an actuator at a point
along the first arm section intermediate the hole and
the end of the member at which the angled portion is
disposed.
The support 16 on which the contacts 10, 12
and the ring electrode 14 are mounted is of generally
annular shape including an inner radial surface 52
which extends axially in a direction parallel to the
pivot axis of the movable contact 12. The fixed
contact 10 is mounted on an outer radial surface 54
of the support 16 at a position circumferent.ially
spaced from the position at which the pivot pin 34 of
the movable contact 12 is mounted such that the fixed
contact 10 is separated from the pivot pin 34 of the
movable contact 12 by a distance equal to the dis
tance between the pivot pin 34 and the angled portion
44 of the movable contact 12. By constructing the
apparatus in this manner, the angled portion 44 is
received and retained by the legs of the fixed con-
tact element 18 when the contacts 10, 12 are in en-
gagement with one another. In order to further
facilitate movement of the angled portion 44 into and
out of engagement with the fixed contact element 18 t
the legs of the fixed contact element point in a
direction generally tangent to the path of travel oi:
the angled portion 44 of the movable contact 12.
The arc interrupting ring electrode 14 is
disposed within the opening of the support 16 and
includes opposed axial ends 56, 58 defining a central
longitudinal axis 60 therebetween. The arc inter-
rupting ring electrode 14 is formed of a conductive
material such as copper and is of generally hollow
WO91/08579 PCTtUS90/01220_
-14-
1 cylindrical shape. One end 56 of the ring is closely
surrounded by the insulating material of the support
16 which is flush with one end of the ring electrode
14 and extends radially outward therefrom to a point
beneath the stationary arc tip 26 of the fixed con-
tact 10. As discussed below with reference to the
operation of the apparatus, this insuLating material
disposed between the fixed contact 10 and the ring
electrode 14 serves two beneficial functions. Initi-
ally, as an arc forms between the movable contact 12
and the fixed contact 10 upon separation thereof, a
magnetic force, described below, pushes the arc into
contact with the insulating material thus cooling thè
arc and removing energy therefrom. In addition, when
the arc contacts the insulating material, it somewhat
ablates the material causing gases to be released
which further aids in extinguishing the arc.
A field coil 62 surrounds the ring elec-
trode 14 and is formed by a winding of conductive
strip material, e.g., copper. In the embodiment
illustrated in Fig. 1, the strip material is wrapp~d
from the inside out around the ring electrode in a
clockwise direction. The field coil 62 is in contact
with the ring electrode 14 at the inner radial wind-
ing of the coil 62 and is electrically connected with
the fixed contact 10 by a lead or busbar 64 extending
between the outer winding of the coil 62 and the con--
tact arm 20. Thus, the ring electrode 14 is con-
nected through the field coil 62 to the fixed contact
10 such that the field coil 62 is maintained in an
energized condition while current is flowing between
the movable contact 12 and either the fixed contact
10 or the ring electrode 14. The direction of the
winding of the field coil 62 is important in that the
magnetic force created by current flow through the
W~91/08579 PCT/US90/Ot220
-l5- ~ ~ 7 ~t~
l coil acts in the same direction as the direction in
which the coil 62 wraps around the ring electrode 14.
For example, because the winding extends in a clock-
wise direction in Fig. l, the magnetic force created
by the current flow through the coil 62 also acts in
the clockwise direction on any arc extending inward
from the ring electrode 14 at a right angle to an
inner radial curface 66 thereof. Thus, at each point
along the interior surface 66 of the ring electrode
14, an arc extending radially inward of the surface
is pushed circumferentially along the surface in the
direction of the winding, to cause spinning of the
arc around the interior of the ring electrode 14.
A reinforcing ring 68 is disposed on the
outer circumference of the field coil 62 and is
fitted, along with the ~ield coil into an annular
stepped portion 70 o~ the inner radial surface 52 of
the support 16. The reinforcing ring 68 is prefer-
ably constructed o steel to give mechanical rigidity
to the ring electode 14 and ield coil 62 and pro-
tect the field coil against damage. In addition, the
steel ring 68 retains the coil winding within a
tightly confined area thus enabling the coil winding
to be easily fitted on the support once the winding
has been assembled. The steel ring 68 also serves as
a flux path for the magnetic field outside of the
coil 62.
The operation of the arc interruption
apparatus is depicted in the serial order of the
drawing figures and includes the physical procedure
of pivoting the movable contact 12 out of engagement
with the fixed contact lO.
As shown in Figs. l and 2, during the time
w~len the angled portion 44 of the movable contact 12
remains in engagement with the fixed contact lO, no
W09ltO857~ PCT/US90/~1220
-16-
Z~96~?~
1 arc forms therebetween. However, upon separation of
the movable contact 12 from the stationary arc tip 26
of the fixed contact 10, an arc 72 forms betw~en the
tip 26 and an end 74 of the angled portion 44 of the
movable contact remote from the main elongated seg-
ment 76 of the arm 36, as shown in Figs. 3 and 4.
once an arc 72 has formed bletween the con-
tacts 10, 12 magnetic forces F1 and F2 immediately
act on the arc forcing it to move both in a direction
toward the ring electrode 14 and circumferentially of
the electrode 14 in the direction of the winding of
the field coil 62. For example, in a 15 kV power
distribution system, if a fault current of 4000 amps
is present when the arc interrupter is actuated, the
force F1 would be approximately 0.03 Newtons while
the ~orce F2 would be about 0.93 Newtons. These
forces are generated because o the configuration of
the first arm 36 relative to the arc 72 and may be
calculated by known methods. Because of the con-
figuration of the first arm 36 of the elongated mem-
ber 40, and the orientation of the arm relative to
the arc formed between the arm and the fixed contact,
the forces F1 and F2 act simultaneously to cause the
arc to move in the desired direction.
The force F1 occurs as a result of the con-
figuration of the first arm section 36 of the movable
contact 12 which extends in a direction perpendicu}ar
to the direction in which the arc 72 would travel if
no outside forces acted on the arc. Because of the
angle of the first arm section 36, and the known
behavior of an arc, which acts as a flexible current-
carrying conductor, the arc is moved or bent in a
direction tending to straighten the angle between the
arc and the arm segment 76. This is attributable to
reduction of the interaction of the magnetic fields
~91/08579 pcT/us9o/ot22n
-17~
1 created around the arm segment 76 and the arc by the
flow of the current I1 therethrough. By virtue of
the orientation o~ the arm section 36 relative to the
fixed contact 10 and the ring electrode 14, the arc
72 is moved by the force Fl in the clockwise direc-
tion of the ring electrode 14, which is the same
direction in which the ~orce in the fisld coil 62
acts as discussed below. Therefore, the arc 72 be-
gins to move in the eventual spinning direction
thereof before it has physically commuted to the ring
electrode 14 and before the force of the field coil
62 becomes effective on the arc.
Likewise, since the arc 72 is angled rela-
tive to the angled portion 44 of the arm 36, the arc
wants to straighten out relative to the angled por-
tion 44 under the influence of the force F2 created
as a result of the interaction of the fields gener-
ated by the current I2 through the two conductors.
As a result o~ this force F2, the arc is moved in a
direction toward the ring electrode 14. ~hus, imme-
diately after the arc is formed, it is pushed toward
and into contact with the insulating material of the
support 16 resulting in cooling of the arc prior to
transfer of the arc to the ring electrode 14. In
addition, this second force F2 also pushes the arc
toward the ring electrode 14 in order to force commu-
tation of the arc to the ring electrode at an early
time. The force F2 is substantially larger than the
force F1 because of the separation which exists be-
tween the arc and the elongated segment 76 o~ the arm
section 36 as opposed to the direct contact between
the arc 72 and the angled portion 44.
Although the magnetic field of the coil 62
does not act on the arc during the period of movement
of the movable contact 12 between the fixed contact
WO9lt08579 PCT/US9~/01220
2~7~ ~?~ - 1 8-
1 10 and the ring electrode 14, the arc is advantage-
ously managed from the time it is created, by the
forces F1 and F2 exerted on the arc as a result of
the magnetic fields acting around the first arm sec-
tion 36 of the movable contact 12. One benefit of
such early management includes elongating the arc in
the direction in which the arc will eventually spin
once it commutes to the ring electrode 14. By pro-
viding this early elongation of the arc, the length
of the arc path is increased and the arc material is
dispersed into the insulating gas in the housing,
thus resulting in an expedited quenching of the arc.
In addition, because the arc is forced
against the cool insulating material of the support
16 by the force F2, energy is removed from the arc by
the material even before the arc is able to commute
to the ring electrode 14, and gases are released by
the ablation of the insulating material. These gases
further facilitate extinguishment of the arc. Fur-
thermore, the for¢e F1 urges the arc into contact
with the ring electrode 14 as soon as the movable
contact 12 passes across the electrode ~uch that
early commutation of the arc is promoted.
It is noted that in the preferred embodi-
ment, the stationary arc tip 26 of the fixed contact
10 is radially separated from the ring electrode 14
by a relatively short distance. The advantage
achieved by this construction resides in the presence
of insulating material between the ring electrode 14
and the fixed contact 10 which absorbs energy from
the arc 72 as the arc is pushed into the insulating
material by the force F2. However, the radial spac-
ing between the arc tip 26 and the ring electrode 14
may be varied within a range of spacing distances
without detracting from severa} of the primary advan-
~91/08579 PCT/US90tOI220
--lg-- .
5~
1 tages realized by the present construction.
once the arc 72 has commuted to the ring
electrode 14, as shown in Fig. S, the force F1 is
strongly supplemented by the force Fc of the field
coil 62 which acts within the hollow interior of the
ring electrode in the same direction as Fi. This
force Fc is simi}ar to the forces ~1 and F2 in that
- the force Fc is caused by the interaction between the
fields generated around the arc and coil winding dur-
ing current flow therethrough. secause the arc acts
as a flexible current carrying conductor, the arc, in
attempting to straighten out the current path between
the arc and the coil at each point along the circum-
ference of the coil, moves circumferentially in, the
clockwise direction of the coil as shown in Fig. 5.
However, because of the number of windings in the
coil 62 and by virtue of the direct contact between
the arc 72 and the ring electrode 14, the force Fc
exerted on the arc by the coil 62 is many times
greater than either of the forces F1 and F2.
As shown in Fig. 6, the forcè F2 continues
to act on the arc 72 after commutation of the arc to
the ring electrode 14 as a result of the continued
generally perpendicular relationship between the arc
72 and the angled portion 44 of the arm 36. This
force F2 causes the arc to penetrate the first axial
end 56 of the ring electrode 14 in such a way as t.o
facilitate spinning of the arc by the force Fc.
Thus, no mechanical movement of the movable contact
12 into the interior region defined by the ring
electrode 14 i5 necessary, and it is possible to move
the movable contact 12 along a path extending in a
plane perpendicular to the central longitudinal axis
60 of the ring electrode 14 ln such a way that the
length of the path is longer and thus more advantage-
WO91/08579 PCT/US90/01220
2 ~7 ~ ~ 5?~ -20-
1 ous than the path followed by the movable contact of
known devices wherein the path followed by the mov-
able contact extends physically into the interior
region of the ring electrode.
In Fig. 7, the arm 36 of the movable con-
tact 12 is shown as being disposed with the angled
portion 44 positioned co-linear with the central
longitudinal axi 60 of the ring electrode 14. ~t
this stage of the arc interruption procedure, which
preferably occurs no later than approximately 8
milliseconds after initiation of the fault interrup-
tion operation, it has been found that the arc will
in most instances have already become extinguished.
However, in order to more clearly explain the fo,rces
that act to extinguish the arc, tha arc is illus-
trated as being in existence in the figure.
An understanding of the manner in which the
arc is extinguished first requires comprehension of
the way in which current passes through the arc in-
terrupter apparatus once the arc has commuted to the
ring electrode 14. The current, which is an alter-
nating current, passes through the first arm section
of the movable contact 12 and through the arc 72 into
the ring electrode 14 where it is then conducted
through the winding of the field coil 62. In the
ring electrode 14, the phase of the magnetlc field
passing through the ring is shifted relative to the
phase of the current passing through the arc 72. The
thickness and conductivity of the ring electrode 14
may be varied in order to achieve a desired phase
shift of between approximately 30 and 60 degrees,
such that when the current in the arc 72 approaches
zero during each half cycle, the magnetic field in
the ring 14 is near its peak.
W~1/08579 Pcrtus9o/o122o
-21- ~'7~i5?~
1 Because o~ this phase shift, the arc mate-
rial continues to spin under the influence of the
magnetic field in the ring even when the current
through the arc approaches current zero such that
when the ionized gas created by the arc and making up
the arc material is spun into the ar.c extinguishing
gas within the housing and deionized, the e}ectroneg-
ative nature of the insulating gas quickly deionizes
the arc and restores its dielectric strength, thus
preventing reionization of the gas. The arc is thus
precluded from being re-established.
In order to ensure that no arc forms be-
tween the elongated segment 76 of the arm section 36
and the ring electrode 14, the angled portion 44 of
the arm section 36 is disposed at a distance from the
pivot axis of the movable contact 12 that is approxi-
mately equal to the separation distance betw~en the
pivot axis and the central longitudinal axis 60 .of
the ring electrode 14. Thus, the angled portion 44
Of the first arm section 36 is co-linear with the
central longitudinal axis 60 when the arm section 36
is in the position shown in Fiys. 7 and 8. In addi-
tion, the elongated portion 76 of the arm section 36
is axially displaced from the first axial end 56 of
the electrode 14 by a distance Dl which must create a
dielectric strength greater than the dielectric
strength at D2 between the angled portion 44 and the
ring electrode 14 at the central position of the arm
shown in Fig. 8. In this manner, the dielectric
strength between the ring electrode 14 and the first
arm section 36 is greater than between the ring
electrode 14 and the angled portion 44.
In order to ~lrther strengthen the dielec-
tric strength between .he ring electrode 14 and the
first arm section 36, grading means are provided on
W091/08579 PCT/US9OfO1220
2 ~ 5 ~ ~ -22-
1 the interrupter, as shown in Fig. 8, for grading the
electrostatic field surrounding the angled portion 44
as the arm section 36 approaches the centered posi-
tion shown in Figs. 7 and 8. The grading means in-
cludes a conductor in the form of a hollow copper
grading rod 80 that is positioned within the ring
electrode 14 collinear with the central longitudinal
axis 60. An inner axial end 82 of the grading rod 80
extends preferably to within a quarter inch of the
end piece 48 of the angled portion 44 so that the gap
between the grading rod 80 and the end piece 48 is
minimal when the angled portion 44 is in the position
shown. It is noted that although the grading rod 80
is shown as being hollow, it is possible to construct
the rod of a solid conductor. Further, although it
is preferred to construct the grading rod with a
cross-sectional shape corresponding to the shape of
the angled portion, it is possible to construct the
grading rod with other shapes.
The grading rod 80 is connected at its
opposite end ~not shown) to the bus 33 extending
between one of the bushings and the movable contact
12 so that as the movable contact 12 separates from
the fixed contact 10, the arc 72 sees the angled
portion 44 of the movable contact 12 and the grading
rod 80 as a single conductor. As a result, once the
angled portion of the contact 12 has travelled a
sufficient distance toward the position shown in
Figs. 7 and 8, the arc 72 transfers to the grading
rod 80 rather than dwelling on the end piece 48 of
the angled portion.
Due to the transfer of the arc to the
yrading rod 80 during movement of the angled portion
44 of the movable contact ~2, less heat is created in
the end piece 48 of the angled portion and less wear
W~91/08579 PCT/US90/01220
-23- 2~
l results. This reduction in wear of the end piece
provides a potential additional advantage in that
wear of the end piece normally results in the pre-
sence of an increased metal content in the gas within
the ring electrode which adversely affects the di-
electric strength between the movable contact and the
ring electrode~ Thus, by reducing the amount of
metal in the gas within the ring electrode, it is
believed that a reduction in the dielectric strength
is prevented,
In addition to reducing the amount of wear
experienced by the end piece 48 of the movable con-
tact 12, another advantageous result is achieved by
employing the- grading rod 80 in the interrupter of
the present invention. Turning to Fig. 9, a sche-
matic illustration is provided of the electrostatic
field surrounding the angled portion 44 of the mov-
able contact 12 when the movable contact is located
at the longitudinal axis 60 of the ring electrode 14.
In the figure, a number of equal potential
lines 84-llO are shown which indicate regions of
common potential in the area between the angled
portion 44 and the ring electrode 14. Although the
illustration is two-dimensional, it is noted that
because the configuration of the angled portion 44,
grading rod 80 and ring electrode l4 i~ symmetrical,
the field is substantially identical to that illu-
strated around the entire periphery of the angled
portion.
Turning to Fig. lO, a schematic illustra-
tion is again provided of an electrostatic field
surrounding the angled portion 44 of the movable
contact 12 when in the centered position. However,
in Fig. lO, the grading rod 80 is included in the
apparatus and the effect of the presence of the
WO91/08579 PCT/~S90/01220 ~
2~ 24-
l grading rod on the equal potential lines within the
region between the angled portion and the ring elec-
trode is also shown.
As is known in the art, electrostatic
stress is a force which acts on the eiectrons of
atoms within an electrostatic field and which encour-
ages the electrons to separate from the atoms causing
ionization. In the present case, where such stress
is present in the region surrounding the angled por-
tion 44 of the movable contact 12, the electrostatic
field is such that, upon the interrupter experiencing
a high voltage impulse having a magnitude of, e.g.
llO kV or greater, a breakdown of the dielectric
strength between the movable contact 12 and the ring
electrode 14 occurs and a momentary arc ~orms there--
between. In order to prevent such a breakdown in the
dielectric strength, it is necessary to reduce the
stress in the region surrounding the angled portion
of the movable contact and such a reduction is
achieved by the provision of the grading rod 80
within the ring electrode 14.
As is shown in Fig. 9, the stre6s in the
field surrounding the angled portion 44 of the mov-
able contact 12 is represented by the amount of
crowding of the equal potential lines 84-llO. In
areas where the lines are closely spaced, the stress.
is higher than in regions where the lines are more~
spread out. In other words, the stress level between
any two of the equal potential lines 84-llO may be
expressed as being equal to the voltage potential per
unit length between those two lines in a~y given
direction. As can be seen from a review of Fig 9,
the equal potential lines lO0-llO adjacent the angled
portion of the movable contact are relatively widely
spaced from one another indicating that less stress
~91/08579 PCT/US90/01220
-25- ~ ~ 7 ~ 5~
1 exists in the region adjacent the angled portion 44
~here the grading rod 80 is provided.
A comparison between the stress of the
field existing in the construction of Fig. 9 and the
construction of Fig. 10 is provided in Fig. 11. The
stress is indicated for a specific exemplary embodi-
ment of an interrupter constructed in accordance with
the present invention having a ring e:Lectrode with an
inside diameter of 3 inches. The vertical axis of
Fig. 11 is labeled "FIELD" and is indicated in kV/mm,
and the horizontal axis is labelled "DISTANCE" and is
indicated in inches from the outer surface of the end
piece 48 toward the closest point on the ring elec-
trode 14.
~s can be seen from the figure, the stress
surrounding the angled portion 44 of the movable con-
tact is substantially greater immediately adjacent
the angled portion in the embodiment o Fig. 9, as
indicated by the line 112, where no grading rod is
present, while less stress exists at the same dis-
tance from the angled portion when the grading rod i5
providedj as shown by the line 114 representing the
stress between the end piece and the ring electrode
of Fig. 10. In view of this difference in the stress
adjacent the angled portion with and without the
presence of the grading rod, it can be understood
that the dielectric strength between the angled
portion and the ring electrode may be substantially
increased by the inclusion of the grading rod in the
location shown in Fig. 10. Further, such an increase
in the dielectric strength is achieved without in-
creasing the distance between the angled portion of
the contact 12 and the ring electrode and, thus, it
is not necessary to increase the diameter of the ring
electrode. The line 116 in ~ig. 11 is provided to
wosl/o8579 PCT/US90/01220
Z ~ ~6 ~}~ -26-
l illustrate the negative impulse limit above which
breakdown of the dielectric strength occurs upon
experiencing a high voltage impulse of llO kv in the
exemplary embodiment illustrated. AS can be seen,
the stress adjacent the angled portion exceeds this
limit where no grading rod is present.
Numerous other advantages are realized by
constructing an arc interrupter apparatus in the
manner described above and set forth in the claims.
For example, by providing a construction as des-
cribed, wherein an arc is managed and directed in a
specific manner as set forth commencing with the
instant of formation thereof, it is possible to
extinguish arcs consistently within a shorter ~ime
period than heretofore possible. When such consist-
ent operation can be assured, it is then possible to
more easily design other switch gear components which
rely on the timing of the arc interrupter in their
own operation. Thus, the reliability o not only the
arc interrupter, but also of the e~tire distribution
or switching system is improved by employing an arc
interrupter in accordance with the invention.
In addition, as mentioned above, because
the force F2 acts to push an arc toward the ring
electrode, it is permissible to leave a variable
sized gap between the first axial end of the ring
electrode and the end 74 of the angled portion of the
movable contact without significantly affecting the
timing of the commutation of the arc from the fixed
contact to the ring electrode. Thus, construction
and assembly of the arc interrupter is simplified
while overall consistency in operation of the device
is improved.
W~91/08579 PCT/US90/01220
-27- 2 ~ 3~ 5?,
l It is of course possible to construct an
arc interrupter in accordance with the present in-
vention without departing from the scope of the in-
vention as set forth in the claims. For example,
although the movable contact is shown 'as being pivot-
ally connected to the support in the figures, it is
possible to move the movable contact betw~en engaged
and disengaged positions along any linear or arcuate
path which extends in a direction perpendicular to
the central longitudinal axis of the ring electrode
so long as the orientation of the arm 36 relative to
- the arc remains substantially the same as that illus-
trated in the preferred embodiment, such that two
forces act simultaneously on the arc in two direc-
tions.
