Note: Descriptions are shown in the official language in which they were submitted.
~119219
Th~ invention relates to switchgear in which an arc
is formed between electrodes, namely, to electromagnetic switch-
gear using a magnetic blast which provides for the lengthening
of the arc when the arc column is acted upon by the force
resulting from electromagnetic interaction between the arc
current and a magnetic field. In particular, the invention
relates to eleetromagnetic arc extinction apparatus used in
switchgear.
The apparatus of t~e invention is suitable for use
on any desirable alternating or direct current circuits and
can find use in high-voltag~ heavy-current switchgear including
circuit breakers, fuses and electroexplosion trips.
A quenching arc occurring in switchgear can be
extinguished by recovering the arc voltage up to that existing
across the eontacts of the circuit being switched.
It is known that the breaking arc voltage is given by
U = E 11 ~ ~ UN, where E is the intensity of the electric field
in the arc column, la is the length of the arc, and ~ UN is
the sum of the voltage drops at the electrodes. There are
therefore three ~ethods by which the arc voltage can be increased:
increasing the number of voltage drops at the
-2
B 7~
lll9Z~9
electrodes; increasing the intensity of the electric field in
B the arc column; and lengthening the quenching arc.
During the switching of alternating-current circuits,
the arc can be extiguished (the electric strength of the in-
terelectrode gap can be restored) at current zero in an al-
ternatin~-current circuit. This feature can be used effecti-
vely in the case of vacuum-type circuit breakers which are
bein~ develop~d on a wide ba~is at the present time.
Increasing the number of voltage drops at the electrodes
is basically applicable to low-voltage switchgear. In this
case t the quenching arc is split into a number o~ series-con-
nected smaller arcs each of which ha~ its own voltage drop at
the anode and cathode. Since the sum of these voltage drops
does not usually exceed several tens o~ voltsthis method is
used as an auxiliary one in the case of high-voltage switch-
gear.
At present, the method o~ increasing the intensity of
the electric field in the arc column is basically ~uitable
~or high-voltage applications where U exceeds 10 to 20 kV.
The method can find use in a.c. oil, small oil volume, air-
-blast and S~6-filled circuit breakers. For the~e voltages,
a.c. circuit breakers rated for higher parameters act as d.c.
circuit breakers.
In these apparatus, the intensity of the electric field in
the arc column is increased in a manner that the arc column
is subjected to longitudinal, lateral or radial/longitudinal
blast using the working gas (compressed air or sulphur hexa-
.
: :
.
.
~119Zl9
fluoride gas) or the products obtained during the decomposi-
tion of the working liquid (oil). In this case, the inten~ity
E is e~ual to hundreds or thousands of V/cm, the spacing bet-
~een the electrodes amounts to several ten~ of centimeter, the
arc le~gth 11 reaches one to two meters, and a maximum turn-
-off voltage for one pair of electrodes reaches a ~alue of
100 to 300 kV. However, the disadvantage of the apparatus is
that they have a low switching time, ~ , which is usually
equal to 0.2 to 0.06 s. In the latest embodiments, attempts
are made to attai~ 0.02 s swi~ching time by using sulphur
he,~afluoride gas.
Another disad~antages of the described apparatus are con-
cerned with large dimensions and weight and with sophisticated
design and laborious maintenance. Indeed, oil is fire-hazar-
dous, air must be compressed, and S~6 gas requires that the
construction be hermeticalb sealed.
B The lengtheniDg of the 4DeD~bi*~ arc basically applies to
electromagnetic switchgear in which case an arc is caused to
move under the action of the force ~ resulted from electromag-
netic interaction between the arc current and a magnetic field,
; that movement being performed over di~erging (horn-shaped)
electrodes and accompanied b~ a lengthening of the arc. The
ma~netic field is formed by external sources suoh a~ arc-
-quenching coils or the magnetic field of the arc current it-
self is employed.
Electromagnetic switchgear offers simple d~sign feature~
and good reliability, allows for multip~e switching of circuits,
does not require special work~ng medium and pro~ides for a
r
~ 4 ~
2i9
higher operational speed that is increased with an increase of
the current being interrupted, which makes this switchgear current-
limiting during the interruption of short-circuit currents.
Finally, with electromagnetic switchgear a.c. and d.c. uses are
possible.
The switching time T of electromagnetic switchgear
is determined by the distance _ covered by the arc column when
it is moved in a direction of t~e driving force F, and is also
determined by the velocity Va which is dependent upon the force
F and upon the conditions under which the arc column is moved.
Therefore, T = a/Va. In the case of a straight arc, its length
may exceed the value of a several times at most. For example,
1 = ~a if the arc is semicircular. ~ith la~U/E, a relationship
between the switching time T and the turn-off voltage U in the
case of electromagnetic switchgear is given by ~=U/kEVa where
k = la/a is the proportionality coefficient to relate the arc
length and the path covered by the arc column, this coefficient
being dependent upon the arc shape. In the case of a freely
moving arc, the intensity E is dependent upon the arc velocity
and current and is usually equal to 10 to 100 V/cm. ~ith U = 10
kV at Va%50 m/s, E~30 V/cm and k = ~, the switching time T be-
comes equal to 0.02 s, which gives the overall size of the arc
extinction apparatus equal to 2a x 2 m.
To reduce the overall size of the arc extinction
apparatus and provide for better operating conditions and good
arrangement of its components, electromagnetic switchgear is us-
ually provided with an arc cham~er which is a slit-shaped struc-
ture.
~ - 5 -
~'
~119219
formed from plates made of electrically insulating material.
The arc chamber operates to form the arc and to determine the
direction of its movement, provides for an increase the inten-
sity ofthe electric field in the arc column by compressing and
cooling the latter, and makes it possible to utilize magnetic
circuits that help enhance magnetic blast. When a labyrinth
(zig-zaglike) slit is used the ~uenching arc can be lengthened
additionally. However, the length of the arc can be increased
using a labyrinth arc chamber only several times since the force
F responsible for the movement of the arc column is decreased
in this case with the result that switchgear is given a lower
response.
To interrupt currents that are smaller in comparison
to rated current magnitude and that therefore result in a decrease
in the effectiveness of magnetic blast, electromagnetic circuit
breakers are usually provided wi~h a self-blast air system.
Labyrinth arc chambers made it possible to develop
electromagnetic circuitbreaker-s rated, for example, for 10 to
20 kV and having the overall size of 1 m approximate-y and the
switching time not exceeding 0.06 s. However, electromagnetic
circuit breakers cannot find use at the present for switching
higher voltages since their dimensions would become too large in
this case along ~ith a decreased switching time which is an im-
portant parameter of a circuit breaker.
The range of working voltages handled by electro-
magnetic circuit breakers can be increased by employing a spiral
or helix-shaped breaking arc, the helix having a small value of
the pitch ~.
r~ 6
~,~
1119219
Known in the art is a circuit breaker utili~ing a helix-
B shaped ~le~ch~*~ arc (cf. J. Miyachi, H.Naganawa, Spiral Arc
in SF6 Facilitating DC Interruption, III International Confe-
rence on Gas Dischsrges, Lo,ndon, 1974, p. 521). In this circuit
breaker, a free straight arc is ~ormed between electrodes closed
by a wire a~ter the latter is exploded electrically or after
the parting of the electrodes in an axial direction. The arc
surrounded by a ma~netic field applied in a longitudinal direc-
tion relati~e to the electrodes axi-~ takes the for~ of a helix
that expa~d~ in a radial direction and the voltage across the
electrodes tends to rise in this case. ~owever, the helix featu-
res a nonregular form due to the presence of a large number of
random distortions o~ very diversified shapes and dimensions.
~his results in a condition where certain portions or turns of
the arc column are caused to converge and a brealEdo~n there-
fors ta'~es place with the result that a sudden decrease in thè
voltage across the electrodes occurs, while the portions of
the arc column brought together are shunted and disintn-
grated. This phenomenon basically applies to small-scale dis-
tortions of the arc column which tend to de~elop at a greater
rate.
This arc is therefore difficult to ubilize; a ratio bet-
ween the arc length and the electrode spacing amounts to 10
to 12 with the arc diameter of 4 to 6 cm and the helix pitch
o~ 3 cm approximately.
There is an arc extinction apparatus for switchgear
(cf. German Patent ~o. 330,268, cl. 23c 355, 1919), which
apparatus comprises two electrodes adspted to produce a
lll9Z:l9
quenching arc in the the from o~ a helix that expands in a
raclial direction.
In the described apparatus, the electrodes are mounted on
a cylinder member made of an electrically insulating material
and are bent to take the form o~ a heli~. ~o protect the elec-
trode turns from breakdown, the cylinder member has a heli~-
-shaped partition made of an electrically insulating material
and having the value of the pitch of its helix equal to the
electrode helix pitch.
The e~pansion of the arc in a radial direction is attained
due to the force of electromagnetic interaction between the
tanOential component o~ the arc current and the longitudinally
oriented ma~netic field formed by an arc-que~ching coil disposed
within the cylinder member.
When the electrodes are caused to move in opposite direc-
tlons the parting of the electrodes takes place and~a qusn^hi~
arc is struck. The electromagnetic interaction between the ra-
dial component of the arc current at the areas adjacent the
electrodes and a longitudinally oriented magnetic field causes
the "winding" of the arc on to the helix-shaped electrodes ~ith
the result that the arc assumes the form of a helix.
The ~u~ching arc expands in a radial direction and moves
away from the surface of the cylinder member at a location
where the helix partition does not give in~luence on the from
of the arc column and on the direction in which the latter is
moved and does not resist the occurrence of a breakdown bet-
ween the adjacent turns of the helix arc. As a result, the arc
can be lengthened within specific limits only and the working
~,
lll9Z19
voltage at which the switchgear operates reliably amounts to a
value of several kV, the proper overall size of the apparatus
not exceeding 1 m in thïs case.
The described apparatus is therefore disadvantageous
in that the working voltage is low due to a small length of the
helix-shaped arc so produced, which is equal to one or more
turns. In addition, the electrodes must follow a helix path
and must have a helix shape, which results in complex design
features of the associated switchgear.
~n object of the invention is to provide an electro-
magnetic arc extinction apparatus for switchgear, which apparatus
can provide for an increase in the working voltage at the given
overall dimensions of the switchgear so that its switching time
is maintained at a preset level or increased.
Another object of the invention is to provide a
relatively simple electromagnetic arc extinction apparatus for
switchgear operating at the working voltage exceeding 10 kV.
Still another o~ject of the invention is to provide
an electromagnetic arc extinction apparatus for switchgear,
which apparatus can be used in different switching devices
s-uch as circuit ~reakers, fuses and electroexplosion trips.
Accordingly, the present invention provides an
electromagnetic arc extïnction apparatus for switch~ear,
comprising: an arc chamber formed of electrically insulating
material and defining a helical cavity having a pitch which is
at least 10 times smaller than the diameter of the arc chamber
measured over the cross-section t~ereof, an axial channel in
sa;d arc chamber communicating throughout its extent with the
helical cavity, and two electrodes disposed in alignment in said
axial channel such that, in the presence of a magnetic field, an
arc struck between said two electrodes will be expanded out-
wardly into said helical cavity thereby to extend the length of
B
lll~Zl9
the arc.
Advantageously, the electromagnetic arc extinction
apparatus has an arc chamber whose cavity narrows in a radial
direction.
Preferably, the electromagnetic arc extinction
apparatus has an arc chamber that comprises strengthening members
disposed in its cavity and rigidly attached to its walls, with
the result that the apparatus is robust and has good mechanical
strength and vibration stability.
Advantageously, the electromagnetic arc extinction
apparatus has an arc cham~er that includes elements made of an
electrically conducting material and adapted to shift the ends
of the arc in a radial direction, said elements being disposed
on respective end faces of the arc chamber and electrically
connected to respective electrodes which are located on
corresponding end faces of the arc chamber, said elements being
used to provide for greater service life of the electrodes.
Preferably, the electromagnetic arc extinction apparatus
has a first electrode allowed to be moved in the axial channel
of an arc chamber, the first electrode having a rod made of an
electrically inqulating material, adapted to resist the oacur-
~.
--10--
B
Z~g
rence of a breakdown in the axial channel, and affixed to that
end of the firstelectrodewhich faces a second electrode having
an axial hole that accomodates the rod, the length of the latter
being selected to be equal at least to the spacing between the
two electrodes with the first electrode held in its extreme
position.
Advantageously, the electromagnetic arc extinction
apparatus has an arc chamber that narrows towards that its end
face on which said first electrode is located and is allowed to
be moved in the axial channel of said arc chamber.
Preferably, the electromagnetic arc extinction appa-
ratus comprises a fusible element in the form of a wire that con-
nects two electrodes, andalso comprises an arc chamber, said
fusible element being disposed in the axial channel of the arc
chamber, the diameter of the wire being selected to be equal to
that of the axial channel.
Advantageously, the electromagnetic arc extinction
apparatus for switchgear comprises a fusible element in the form
of a wire that connects two electrodes, and also comprises an
arc chamber having an insert made of an electrically insulating
material, the insert being disposed in the axial channel of the
arc chamber and having its diameter equal to that of the axial
channel, and the fusible element being arranged in the form of
a helix and disposed on the insert in the cavity of the arc chamber.
The apparatus of the invention provides for a helix-
shaped arc whose helix has a small pitch. This ensures a higher
compactness of spatial arrangement of the arc and small
- 11 -
",, ~:
~g219
overall dimensions of the apparatus of the invention ~hich is
capable of switching high voltages reaching hundreds of kYs and
more and is suitable ~or a.c. and d.c. applications. ~he path
covered by the arc column during its movement in a radial di-
rection, caused by electromagnetic interaction between the arc
current and a magnetic field, is maintained during the switch-
ing process at a low magnitude reachin~ 1 m approximately, with
the result that the switching time is high and the apparatus can
be operated as a currentlimiting one during the interruption
of shoxt-circuit currents.
A small pitch of the helix of the arc provides for effect-
iYe use of the magnetic field of the arc current itself, which
ensures higher switching time of the apparatus of the inven-
tion and simpler design of the associated switchgear since the-
re is no need in some cases for arc-quenching coils and magne-
tic circuits.
~ he apparatus of the invention provides for high-voltage
heavy-curre~t electromagnetic circuit breakers uhich are compa-
rsble with the present-day competitors l~noY~ in the art such as
oil, small oil volume, air-blast and SF6-filled circuit breakers
rated ~or the voltages of tens and hundreds of ~ and more and
for currents of hundreds and thousands of A and more. The elec-
tromag~etio circuit breakers provide for multiple switching o~
the controlled circuits and for higher switching time (for
example, halfwave current interruption is attained in the case
of a.c. circuits). ~hese circuit breakex~ also offer good re-
liability and convenient maintenance.
- 12 -
,
.
.
1119219
In the case of fuse gear, the apparatus of the in-
vention makes it possible to construct simple, inexpensive and
high-speed protective devices of the overall dimensions whieh can
handle working voltages of hundreds of kV and can be operated
on a.c:. and d.e. circuits; such devices are not known in the
prior art.
In addition, the apparatus of the invention can pro-
vide for the construction of high-voltage heavy-current trips
which fund use in some special eases sueh as the switching of in-
10 - duetion-type aeeumulators.
The invention will now be described in more detail,
by way of example only, with reference to the accompanying draw-
ings, in whieh:-
Figure 1 is a cut-away perspective view of an electro-
magnetie are extinetion apparatus for switehgear, aecording to
the invention;
Figure 2 is a longitudinal seetion view of an embodi-
ment of the are ehamber of the eleetromagnetie are extinetion
apparatus, the cavity of the are ehamber having its seetion nar-
rowing in a radial direetion, according to the invention;
~ Figure 3 i5 a longitudinal seetion view of another
; embodiment of the are ehamber of the eleetromagnetic are extine-
tion appatatus, the cavity of the are ehamber having a zig-zag
like seetion, aeeording to the invention;
Figure 4 is a longitudinal seetion view of the are
chamber of the ~leetromagnetie are extinetion apparatus,
having fixation members;
- 13 -
~7~?"'
~19Z19
Figure 5 is a section taken along the line V-V of Fig.
4, according to the invention;
Figure ~ is a longitudinal section view of the
electromagnetic arc extinction apparatus having end face discs,
according to the invention;
Figure 7 is- a longitudinal section view of an embod-
iment of the electromagnetic arc extinction apparatus, including
a rod made of an electrically insulating material ana disposed
in the axial channel of the arc chamber, according to the
invention;
- Figure 8 shows an electromagnetic arc extinction
apparatus for fuse gear, according to the invention;
Figure g shows an electromagnetic arc extinction
apparatus for fuse gear and electroexplosion trip, according
to the invention.
The electromagnetic arc extinction apparatus for
switchgear, according to the invention, is described as an arc
extinction apparatus intended for a circuit breaker. The
apparatus is intended for connection to the power contacts of a
2~ circuit breaker which serve to carry the current during a time
interval ~etween two successive switchings.
The apparatus of the invention comprises an arc chamber
1 (Fig. 1~ including a helical cavity and an axial channel 2.
The latter accommodates two electrodes 3,4. The diameter of
the electrodes 3,4
3~
-14-
B
....
ill9;~19
ls determined by the magnitude of the working current and is
equal to the diameter of the axial channel 2. The electrodes
3,4 are usually made of copper, copper/tungsten alloys and the
like. The apparatus of the invention also comprises conventional
arc-quenching coils (not shown) which are connected, for example,
in series with the apparatus. These arc-quenching coils produce
the magnetic field B (shown by a respective arrow in the figure)
within the arc chamber 1 during the switching process. In the
given embodiment, the magnetic field B is oriented in a direc-
tion coincident with the axis of the arc chamber 1 and the elec-
trodes 4,3 and is, therefore, a longitudinal one.
The arc chamber 1 causes a breaking arc 5 having a
helical shape to move in a radial direction. In Fig. ~, r is
the instantaneous radius of the arc 5 and F is the radial com-
ponent of the force of electromagnetic interaction between the
arc 5 and the magnetic field B, respective arrows being used to
show the directions in which the column of the arc 5 is acted
upon by that force. The arc chamber 1 is formed by a screwlike
body which is a helical blade 6 having a pitch ~ and defining
between adjacent turns thereof, the helical cavity having width
. The helical cavity serves as an arc-quenching slit structure
of the apparatus. The width of the slit structure and the magni-
tudes of the current of the arc 5 and of the magnetic field B
determine the parameters of the arc 5 as follows: The current
density; the size and shape of the arc column and the intensity
of the electric field thereof; and the velocity of the arc column.
The
- 15 -
:1119Z19
width of the helical cavity of the arc chamber 1 is usually
selected to be equal to 2 to lOmm.
It is common practice to select the value of the pitch
of the helical cavity of the arc cham~er 1 as small as possible.
It is dependent upon the material, fabrication techniques, operating
conditions and service life of the arc chamber 1 and, more speci-
fically, upon a maximum permissible thickness of the helical
blade 6 which equals to ~ ). The helical blade 6 or the arc
chamber 1 can be manufactured from different electrically insula-
ting materials such as arc-resistant and gas-generating ones.
For example, cast plastics including polysulfone, polycarbonate
and lavsan can be used for the purpose.
In the given embodiment, the heat load applied to
the walls of the arc chamber 1 is less than the thermal load that
affects the walls of the known electromagnetic labyrinth-type
arc chambers due to the fact that in the former case the arc column
moves with a greater velocity ( this phenomenon will be explained
hereinafter). In addition, the helical blade 6 of the arc chamber
1 is subjected tb a relatively small mechanical load since the
arc 5 acts upon it from two sides. As a result, the material
of the helical blade 6 may possess properties that are inferior
to those of the material from which the known electromagnetic
labyrinth-type arc chambers are made.
The arc chamber 1 can be manufactured by casting
or stamping. It is possible to construct a cheap sectional
variant of the chamber comprised of the elements of the helical
blade which connect one another.
- 16 -
~119Z19
The absolute values of the diameter D and length L
of the arc chamber 1 are determined by the working voltage and
switching time of the associated switchgear (see calculation
examples given below). The ratio between the diameter D of
che chamber 1 and the pitch of the helical cavity must be not
less than 10 in order to obtain a sufficient lengthening of the
arc 5 which is 102 to 103 times the ~ength L of the chamber l,
which determine the maximum separation between the electrodes
3,4.
The helical cavity of the arc chamber 1 (Fig. 1)
is rectangular in cross-section in the radial direction. It is
good practice, however, to make the cavity narrow in a radial
direction in order to obtain a variation of the intensity of the
electrical field of the arc column as the current decreases
during the switching process. Figure 2 shows an arc chamber 7
whose helical cavity has a trapezoidal section.
Figure 3 shows an arc chamber 8 whose helical cavity
has a zig-zag like section extending in a radial direction.
According to this embodiment, the arc chamber 8 may also have its
helical cavity with a variable pitch ~, which makes it possible
to vary the velocity of the arc column. This embodiment is
advantageous in that the axial channel 2 (Fig. l) can be protected
from light radiation emitted by the arc 5, that tends to expand
in a radial direction, with the result that the electrical strength
of the medium contained in the axial channel 2 is restored at
a higher rate. In addition, the zig-zag like section of the
- helix cavity of the arc chamber 8
` 30
- 17 -
- ~ L
lll9Z19
(Fig. 3) allows the sound effect occurring during the switching
proces,s to be reduced.
To provide for mechanical strength, robustness and
vibration stability of the apparatus of the invention, it com-
prises strengthening members 9, io (Figs. 4,5) which are disposed
within the helical cavity of an arc chamber 11 (Fig. 4) and are
rigidly coupled with the walls of the chamber, said walls being
formed by a helix blade 12. The arc chamber 11 has an axial
channel 13 which accomodates electrodes 14, 15.
The strengthening members 9,10 (Fig. 5) are arranged
in two rows in circumferential relation to the arc chamber 11.
One of the two rows includes the strengthening members 9 made
as cylindrical inserts, while the other row includes the strengh-
ening members 10 made as ribs.
The position and dimensions of the strengthening
members 9,10 are dependent upon the materials and fabrication
processes used for the manufacture of the members and the arc
chamber 11 and must be s~ch that an arc 16 (Fig. 5) is allowed
to pass freely around the members. The position of the column
of the arc 16 is shown for two- successive points in time occupied
by the arc in the course of its movement in a radial direction:
a is the point in time when the arc passes around the members 9
and b is the point in time when the arc approaches the members 10.
- 18 -
~19219
The strengthening members 9,10 can be fabricated
from metal. In this case, they additionally act as an arc-quen-
ching grid with the result that the parameters of the arc chamb~r
11 are improved. In this embodiment, the strengthening member
9,10 must be electrically insulated one from another.
In addition, the strengthening members can provide
a means for coupling separate parts of a sectional arc chamber
with an appreciable assembly accuracy.
To allow the ends of the arc to be moved in a radial
direction, additional horn-shaped electrodes are introduced in
the arc chamber. These electrodes, made of an electrically
conducting material, are oriented in a radial direction at the
beginning and end of the helical cavity; the electrodes must
be electrically connected to respective main electrodes.
Figure 6 shows an embodiment of the apparatus of the
invention which comprises elements17,18 made of an electrically
conducting material and allowing for the movement of the support
spots of the arc in a radial direction. The elements 17,18
are implemented as metallic discs having axial holes and disposed
on the end faces of the arc chamber 19. The elements 17,18
are electrically connected to respective electrodes 20,21 which
are located at corresponding end faces in an axial channel 22.
The elements 17,18 can be fabricated, for example, from copper.
Figure 6 shows how the arc 23 expands in a radial
direction as its ends move o~er the elements 17,18.
~. -- 19 --
~.,
1~92~g
~igure 7 shows an electromagnetic arc extinction appara-
tus for a high-~oltage heavy-current circuit breaker. In the
given embodiment, an immovable electrode 24 is implemented,
for example, as a tubing that has its inner diameter equal to
the diameter of a movable electrode 25. There is a rod 26 ma-
de of an electrically insulating material and coupled, for
example, by thread connection with the movable electrode 25.
~he diameter of the rod 26 is equal to the diameter of
the movable electrode 25 and has its length equal at least to
the spacing between the electrodes ~4, 25 with the electrode
25 held in it~ extreme position.
~he rod 26 provides ~or a condition where no breakdown
occurs between the electrodes 24, 25 which are bein~ dra~n
apart during the switching process, a feature ensuring reliab-
le operation of an arc chamber 27.
A preferred material for the rod 26 is an arc-resistant
and gas-~enerating one. Since the shape of the rod 26 is simple,
~arious materials such as ceramics, boron nitride and asbestos-
-cement can be used for the purpose. It ic~ feasible to make the
electrode 24, for example, from one or more current-collecting
ja~s.
B Note that the position of a quenchin6 arc 28 in the figu-
re corresponds to a certain point in time during which the ap-
paratus oY the invention is operated.
It is pre~erable to select that outline of the arc chamber
27 which corresponds to the form of the quenching arc 28, caused
to expand in a radial direction, which form being attained at
the moment when the switching process is terminated. According
-- _
, ~, -
.
,
,
1~9Z19
to one of the embodiments, the arc chamber 27 narrows to-
wards the end face at which the movable electrode 25 is lo-
cated.
Let us calculate the overall and working dimensions of a
circuit breaker which can handle a voltage U of 100 kV and
which is operated in conjunction with the apparatus of the
invention. Assume that the circuit breaker o~fers a s~itch-
ing time of 10 ms, which provides for a half-wave interrupt-
ion in the case of an a.c. circuit being switched. With an
average velocity Va of the arc column equal to 50 to 100 m/s
approximately, the permissible height of the slit and, therefo-
re, the diameter D of the apparatus of the invention is given
by
D ~ 2V2Z = 1 to 2 m
With an avérage intensity E of the electric field in the
column of the breaking arc being moved equal to 20 to 30 VtcmJ
the desired arc length la is given by la = EU~?O to 100 m, a
twofold margin for the turned-off voltage U being selected to
take into account an overvoltage condition.
To provide for proper design of the apparatus of the in-
vention, let the pitch ~ of the helix blade be equal to 1 cm
approximately and the length L of the arc chamber be equal to
its diameter D. This gives
le --~
; D - L = ~ a ~ ~ 0.48 to 0.55 m
- - 21 -
~ . .
'
ll~9Z19
Therefore, the arc chamber h~;ing the dimensions D c o.55 m
and L ~ 0.55 m is capable o~ switching a.c. and d.c. circuits
at a voltage U of 100 kV (with a two~old voltage margin) and
a switching time ~ c 0.01 s. With the apparatus of the i~ven-
tion, there is no need for the following components of modern
100-kV circuit breakers: a reservoir accommodating 6 to 12 tons
of oil in an oil circuit breaker, that weighs itself 8 to 15
tons; a reservoir accommodating 0.5 to 1.5 tons o~ oil in a
small volume oil circuit breaker, that ~eighs itself 4 to 8
tons; a receiver with a compressor rated for 2 to 6 ~a in a
compressed-air circuit brea~er, that weighs itsel~ 5 to 8
tons; and a hermetically sealed casing rated for 0.3 to 0.6 ~æa
and filled with an expensive SF6 gas, in a self-blast S~6 cir-
cuit breaker, that weighs itself 5 to 8 tons. Note that these
modern circuit breakers can provide for a switching time of
0.06 to 0.1 s i~ the case of a.c. applications only.
~ igure 8 sho~s an electromagnetic arc extinction apparat-
us for a high-voltage fuse. The apparatus comprises an arc
; chamber 29 made of an electrically insulating material. Immo-
vable electrodes 30, 31 are located in axial relationship to
the arc chamber 29 at it~ end faces and are connected by a fu-
sible element 32 implemented as a wire made, for example, of
copper. ~he fusible element 32 is disposed in the axial channel
o~ the arc chamber 29, ths diameter of the ~usible element 32
being equal to the diameter o~ the axial channel.
It is known that ~uses are basically intended to protect
the associated circuits ~rom short circuit and must there~ore
; o~fer a shorter switching time. In addition, fuses must be
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appreciably simple and cheap. ~odern high-voltage fuses offer
normal operation at voltage levels not exceeding 30 to 50 kV.
The basic component of a fuse is a fusible element that
connect-q immovable electrodes serving in this case as po~er
leads. The ratio between the arc length at the e~d o~ the
switching pxocess and the length of the ~usible element is one
of the most critical parameters that influence the design and
operation of a fuse.
The high-voltage fuse of ~ig. 8 has a maximum permissible
value of the above-mentioned ratio due to the fact that a
straight fusible element 32 is used which has its length equal
to the length of the arc chamber 29.
For example, an arc chamber of a 100-kv fuse (with a
twofold voltage margin) has a quenching time of 3 ms at
~= 1 cm, E = 25 V~cm and Va = 50 m/s. In this case, the para-
meters ~.L and ratio la/L are determined as follows:
D = 2Va ~= 0.3 m, L =~ = 0.9 m, and la/L = 90.
These dimensions ensure proper technical implementation
of an arc ch~mber for a 100-kV fuse.
~ igure 9 shows another embodiment of the apparatus of
the invention intended for a fuse and an electroexplosion
trip, which embodiment comprises an arc chamber 33 whose axial
channel accommodates a cylindrical insert 34. The diameter of
the latter is equal to the diameter of the axial channel of
the arc chamber 33. Wound on the insert 34 is a fusible ele-
~ ment 35 having a pitch equal to the pitch of the ~ cavity
;~ of the arc chamber 33. The insert 34 is made o~ an electrically
insulating material identical, for example, with that of the
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.,
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1~19219
arc chamber 33. T'he end faces o~ the insert 34 ha~e respective
metallic discs 36,37 which provide for electric contact bet-
ween the fusible element 35 and immovable electrodes 38,39
o~ a ~use or electroexplosion trip.
In the given embodiment, the insert 34 can be replaced
after the fusible element 35 has been blown. It is feasible,
i~ the case of fuse application, to allow the insert 34 to be
moved alon~ the axis of the arc cha~ber 33 after the fuse
blowing so as to indicate that the circuit is turned off. A
new insert 34 with a new fusible element 35 is inserted in
the arc chamber 33 and is ~ixed in a manner that a due space
B alignment between the fusible element 35 and the ~ ca~ity
of the arc chamber 33 is attained.
~ he arc chamber intended for fuse application can be
made a multiturn one and the insert can be provided with se-
veral fusible elements equal in number to the number o~ the
turns of the helix cavity of the arc chamber. If a ~usible ele-
me~t is blown, the next one can be connected in the curcuit
by rotating the insert or the arc chamber together with the
insert by a certain angle.
~ he embodiments of the present invention can be used in
conjunction with the kno~n method~ dealing with arc extinction
and employed in electromagnetic switching devices so as to
impro~e the parameters o~ the latter.
The working medium in the circuit breaker housing can be
changed; for examplet the latter is filled with the SF6 ~as.
The pressure within the housing can be ~aried; ~or example,
the pressure is increased or decreased, or the housing is
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lll~Zl9
evacuated, the two latter cases being concerned with an increasein the switching time of the circuit breaker.
The arc voltage can be increased by virtue of arc-
quenching and deionizing grids implemented as the sets of insula-
ted plates arranged at the outlet of the arc-quenching slit in a
direction of movement of the arc column.
Like conventional electromagnetic arc chambers, the
arc chamber of the invention may have its helical cavity arranged
in a zig-zag like (labyrinth) fashion along the quenching arc,
namely, in a tangential direction, which provides f~r an additional
increase of 1.5 to 3 times in the arc length without considerable
increase in the overall dimensions of the arc chambers.
It is known that electromagnetic arc extinction de-
vices cannot work effectively in the case of circuit breaker appli-
cations when small currents are interrupted (which means that gas
switching must be effected at a small load). To eliminate this
drawback, the arc chamber of the present invention can be provided,
like conventional electromagnetic arc chambers, with a gas
`~: blast which is directed into the helical cavity with the result
that a small-current quenching arc is lengthened.
Such a gas blast, for example, an air blast, can be
delivered through the axial holes made in the movable and immo-
vable e`lectrodes as well as~;n the rod of an electrically insula-
ting material, connected with the movable electrode, and can be
led into the helical cavity of the arc chamber through evenly
distributed radial holes. The blast can also be delivered through
the body of the helical blade and led into the cavity
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lll9Zi9
through respective holes in the base of the blade in the vicini-
ty of the axial channel of tne arc chamber~
The circuit breaker provided with the apparatus of the
invention operates in the following manner. After an interrupt
control signal is generated, the power contacts of the circuit
breaker are separated with the result that the circuit current
passes through the electrodes 3,4(Fig. 1) of the apparatus of
the invention.
The arc 5 formed in the axial channel 2 of the arc
10 - chamber after the parting of the electrodes 3,4 is surrounded
by the longitudinal magnetic field B produced by magnetic-blast
coils (not shown). Under these conditions and at specific values
of the associated parameters, the arc column changes to a helix-
like shape (cf. an article by E.I. Asinovsky, A.A. Afanasyev,
E.P.Pakhomov, entitled "Helix Instability of Arc in Longitudinal
Magnetic Field" Proceedings of the Academy of Sciences of the
USSR, 231, No. 2, 1976). Thus, there results a radial component
of the force F of electromagnetic interaction between the arc
current and the magnetic field due to the occurrence of the tan-
gential component of the current of the quenching arc 5. Thatradial component of the force F causes the helical quenching
arc to be drawn into the helical cavity of the arc chamber 1 and
expand in a raaial direction.
In the presence of the longitudinal magnetic field,
the radial components of the current of the quenching arc 5,
existing at the areas adjacent the electrodes, cause a rotation
of respective portions of the arc 5 in opposite directions under
the action of the tangential compo-
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~119Zi9
nents of the force F. The arc 5 is therefore wound on the elec-
trodes 3,4 in the form of a helix determined by the helical cavity
of the arc chamber 1. As a result the rate of rise of the longi-
tudinal s~ze of the quenching arc 5, which expands in a radial
direction, is always greater than the rate of parting of the
electrodes 3,4.
After the arc S reaches the length which allows for the
recovery of a voltage across the contacts of the circuit breaker
e~ual to the voltage across the contacts of the circuit being switch-
ed, the current drops to zero. At this point in time, the break-
ing process is terminated.
The making process is effected in a reverse order as
follows: first, the electrodes 3,4, of the apparatus of the in-
vention are closed, and then, the power contacts (not shown) of
the circuit breaker.
The apparatus of the invention provides for a condition
where the arc 5 expands in a radial direction on a stable basis
so that no considerable leading or lagging of separate turns of
the arc takes place. This is due to the fact that the currents
through the adjacent turns act upon one another, i.e., the attrac-
tion of parallel currents takes place. In this case, the helix
blade 6 of the arc chamber 1 is not subjected practically to
mechanical stress since the arc column 5 acts upon it from two sides,
~ote that an unbalanced condition of the longitudinal component of
the force ~ of interaction of the turns of the arc 5 produce a
force that is always directed to the centre of the arc chamber 1.
A first approximation of the characteristics of the appa-
ratus of the invention is given by the following equations. One
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1119Z19
of them describes the arc volta~e U(t) - ~r ~t)l(t)E/~, and the other
describes the rate of recovery o~ the arc voltage aU/~t = ~(t)EVa/~,
where r(t) and l(t) are the current radius and the longitudinal size
of the arc 5, respectively.
According to the invention, the inductance of the arc
5 itself must be taken into conslderation.
Referring to Figs. 4,5, there is shown an arc 16 which
expands in a radial direction and approaches the fixation members
9 (the position a in Fig. 5) where it is distorted and passes
around the members. At this point in time there results a break-
down betweenthe approaching portions of the arc column 16a behind
the obstacles passed àround, namely, the fixation members 9,
with the result that a new helix arc 16b is formed which is
practically an undisturbed one.
Figure 6 shows the arc chamber 19 provided with respec-
tive metallic discs 17,18 on its end faces. In this case, the
arc 23 tends to expand in a radial direction as well as in a longi-
tudinal direction (as it is "wound" on the electrodes 20,21).
When the arc 23 approaches the chamber end faces it then appears
at the discs 17, 18 and changes to a barrelshaped form which may
further become practically cylindrical. Like the case with horn-
shaped electrodes, thls allows for a reduction of the erosion of
the electrodes 20,21.
The apparatus of the invention shown in Fig. 7 is operated
in a distinct manner during the first operational step. Here, the
rod 26, adjacent the movable electrode 25 and caused to be moved
therewith, is ~ntroduced into the axial channel of the
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1119 Zl~ ~ r
arc chamber 27 during the parting o~ the electrodes 24,25. The
resulting arc 28 is drawn i~mediately into the he~ix cavity of
the arc chamber 27 which connects the separated electrodes 24,25.
As a result, the arc 28 is caused t~ assume a helical form corres-
ponding to that of the cavity of the arc chamber 27. The rod 26
therefore allows for im~nediate production of a helical shaped
arc 28 with the result that the intermediate steps of forming
and introducing the arc into the helical cavity of the arc chamber
are not included in the switching process.
As previously described, the arc 28 so produced tends
to expand in a radial direction under the action of the force
F and is wound on the electrodes 24,25, following the path of the
helix cavity of the arc chamber 27. Thus, the arc 28 acts upon
the rod 26 for a short time interval, which provides for favour-
able operating conditions of the rod.
Since the arc 28 has a small pitch ~, it is practically
a heavy-current plasma solenoid which produces an additional
longitudinal magnetic field B, thereby providing for due operation
of the arc chamber 29. This means that the magnetic field of the
current of the arc 28 is utilized on a very effective basis. In
the example described above, the interruption of a current of 2 and
20 kA with the help of a lOOkV apparatus is accompanied by the
occurrence of a longitudinal magnetic field obtainable from 55
current turns of the quenching arc, said field amounting to 0.2
and 2 T, respectively, as measured at the axis of the arc chamber.
The apparatus of the invention therefore makes it possible to sim-
plify the design
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lllgZi9
of the associated switchgear due to the fact that magnetic-
-blast coils and magnetic circuits are not necessary in many
ca,ses.
There are specific cases concerned with the use of the
apparatus of the invention in conjunction with fuses and
electroexplosion trips. The embodiment of the invention shown
in ~ig. 8 is operated in conjunction with a fuse as follows.
After th~ ~usible element 32 has been blown, a breaking arc
is so formed and the resulting arc column tends to expand at
a higher rate during the initial period of the arc formatio~
since plasma conductivity is considerably less than metal con-
ductivity. ~he arc column can e~pand only towards the ~*}~
cavity of the arc chamber with the result that a helix-shaped
quonching arc is produced already during that period.
The helix-shaped ~e~R~ arc then expands in a radial
direction and is given a considerable lengthening. Under these
conditions, the longitudinal size of the arc is held equal to
the length of the arc chamber. This provides for an additional
increase in the rate of the arc lengthening so that the rate
of recovery of the ~oltage across-the contacts of the swit-
chgear is increased too.
After the fusible element 35 (~ig. 9) has been blown, the
breaking arc immediately assumes a helix-like shape ha~ing a
preset radius and pitch. In addition, the current being in-
terrupted creates its o~n longitudinal magnetic field during
the blowing of the fusible element 35. As a result, a greater
switch'ing time is attained~
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