[0001] This invention relates to a circuit breaker and more particularly to a circuit breaker
which offers enhanced current limiting performance during the tripping of the breaker.
[0002] In prior-art circuit breakers, it has been common practice to shift the arc into
an arc extinguisher or to raise the separating speed of the contacts in order to quickly
extinguish an electric arc struck across the gap between a pair of contacts during
the interrupting operation. Such circuit breakers, however, suffer from the disadvantage
that the foot of the arc struck across the gap between the contacts expands to fall
onto the contactor conductors on which the contacts are mounted, and metal particles
produced from the contact surfaces are not effectively injected into the arc space,
so that the arc voltage., which relates to the extinction of the arc, is lowered.
[0003] It is an object of this invention to improve the current limiting performance of
a circuit breaker by controlling the size and position of the foot of an electric
arc struck across a gap between contacts such that the foot of the arc does not expand,
and by effectively injecting the metal particles produced from the contacts into the
arc space, whereby the arc voltage is raised.
[0004] This invention as claimed provides a circuit breaker comprising plate-form arc shields
of a high resistivity material, surrounding the contacts provided on the rigid conductors
of the contactors of a circuit breaker for making and breaking an electric circuit,
and constructed such that the arc shields project substantially from the conductors
in a lateral direction (i.e. the direction laterally traversing the arc).
[0005] Preferred ways of carrying out the invention are described in detail below with reference
to drawings, in which:-
Figure 1(a) is a sectional plan view of a conventional circuit breaker to which this
invention is applicable;
Figure 1(b) is a sectional side view of the circuit breaker of Figure 1(a) taken along
the dot-and-dash line b-b;
Figure 1(c) is a perspective view of an arc-extinguishing plate assembly which is
disposed in the circuit breaker of Figure 1(a):
Figure 2 is a model diagram showing the behaviour of an electric arc which is struck
across the gap between the contacts of the circuit breaker of Figure 1(a);
Figure 3(a) is a sectional plan view of a circuit breaker according to the present
invention;
Figure 3(b) is a sectional side view of the circuit breaker of Figure 3(a) taken along
the dot-and-dash line b-b;
Figure 4 is a model diagram showing the behaviour of an electric arc which is struck
across the gap between the contacts of the circuit breaker shown in Figures 3(a) and
(b);
Figure 5(a) is a plan view of the contact portion of a stationary contactor according
to an embodiment of this invention, in which the plan of the arc shield resembles
the plan of the contact and the planar central point of the arc shield is caused to
coincide with the planar central point of the contact;
Figure 5(b) is a side view of the contactor of Figure 5 (a);
Figure 6(a) is a plan view of a stationary contactor according to an embodiment of
this invention wherein the contact is rectangular and the arc shield is circular in
plan view;
Figure 6(b) is a side view of the contactor of Figure 6 (a);
Figure 7(a) is a plan view of the contact portion of a stationary contactor according
to an embodiment of this invention wherein the contact is circular and the arc shield
is rectangular in plan view;
Figure 7(b) is a side view of the contactor of Figure 7 (a) ;
Figure 8 is a plan view showing the cross-sectional shape of the arc in the embodiment
of Figures 7(a) and (b);
Figure 9(a) is a plan view of the contact portion of a stationary contactor according
to an embodiment of this invention wherein the planar central point of the arc shield
is positioned at a point further from the arc extinguishing plate assembly than the
planar central point of the contact;
Figure 9 (b) is a side view of the contactor of Figure 9(a);
Figure 9(c) is a plan view of the contact portion of a movable contactor which pairs
with the stationary contactor of Figure 9(a);
Figure 9(d) is a side view of the contactor of Figure 9(c);
Figure 10(a) is a plan view of the contact portion of a stationary contactor according
to an embodiment of this invention wherein the arc shield is formed with a concave
surface;
Figure 10(b) is a side view of the contactor of Figure 10(a);
Figure 11(a) is a plan view of the contact portion of a stationary contactor according
to an embodiment of this invention wherein the arc shield is formed with a convex
surface;
Figure 11(b) is a side view of the contactor of Figure 11 (a) ;
Figure 12(a) is a plan view of the contact portion of a stationary contactor according
to an embodiment of this invention wherein the surface confronting the arc is given
an inclination;
Figure 12(b) is a side view of the contactor of Figure 12(a);
Figure 13(a) is a plan view of the contact portion of a stationary contactor according
to an embodiment of this invention wherein the width of the contact narrows towards
the arc extinguishing plate assembly or the gas exhaust ports of the circuit breaker;
and
Figure 13(b) is a side view of the contactor of Figure 13(a).
[0006] In the drawings, identical reference numerals denote similar or corresponding parts.
[0007] Description will now be made of a conventional circuit breaker to which.this invention
is applicable, with reference to Figures 1(a), (b) and (c).
[0008] An enclosure 1 is made of an insulating material, forming the housing for a switching
device, and is provided with an exhaust port 101. A stationary contactor 2 housed
in the enclosure 1 comprises a stationary rigid conductor 201 which is rigidly fixed
to the enclosure 1, and a stationary-side contact 202 which is mounted on one end
of the stationary rigid conductor 201. A movable contactor 3 which is adapted to engage
the stationary contactor 2 comprises a movable rigid conductor 301 which makes or
breaks contact with the stationary rigid conductor 201, and a movable-side contact
302 which is mounted on one end of the movable rigid conductor 301 in opposition to
the stationary-side contact 202. An operating mechanism 4 operates to move the movable
contactor 3 in or out of contact with the stationary contactor 2. An arc-extinguishing
plate assembly 5 functions to extinguish an electric arc A struck upon the separation
of the movable-side contact 302 from the stationary-side contact 202, and it is so
constructed that a plurality of arc-extinguishing plates 501 are supported by frame
plates 502. The arc-extinguishing plates 501 are usually formed of a magnetic material
such as iron.
[0009] Although, for the sake of simplicity of illustration, the arc-extinguishing plates
501 are illustrated in numbers of two and four in Figures 1(b) and 1(c), respectively,
it is to be understood that actually the number of arc-extinguishing plates 501 in
the arc-extinguishing plate assembly 5 may be as high as, for example, ten plates.
[0010] The operating mechanism 4 and the arc-extinguishing plate assembly 5 are well known
in the art, and are described, for example, in US-PS 3,599,130. As is apparent from
this patent, the operating mechanism includes a reset mechanism.
[0011] Assuming now that the movable-side contact 302 and the stationary-side contact 202
are closed, current flows from a power supply side onto a load side along a path from
the stationary rigid conductor 201, to the stationary-side contact 202,to the movable-side
contact 302,to the movable rigid contactor 301. When, in this state, a high current
such as a short-circuit current flows through the circuit, the operating mechanism.4
operates to separate the movable-side contact 302 from the stationary-side contact
202. At this time, an arc A appears across the gap between the stationary-side contact
202 and the movable-side contact 302, and an arc voltage develops thereacross. The
arc voltage rises as the distance of separation of the movable-side contact 302 from
the stationary-side contact 202 increases. In addition, since the arc-extinguishing
plates 501 are made of a magnetic material and have a reluctivity much lower than
that of the surrounding space, a magnetic flux induced by the current of the arc A
is attracted in the direction V (Figure -1(b)) of the arc-extinguishing plates 501.
Accordingly, the arc A is drawn toward the arc-extinguishing plates 5 and is stretched,
whereby the arc voltage rises even further.
[0012] As a means for driving the arc toward the arc-extinguishing plate assembly 5, a method
utilizing an air current is also well known, in addition to the above method utilizing
a magnetic field. More specifically, the arc is driven by the air current which is
created when the air in the enclosure 1 is raised in temperature and pressure by the
energy of the arc A and is discharged through the exhaust port 101. As a means for
driving the arc utilizing a magnetic field, in addition to the above described method
employing arc-extinguishing plates 501, also well known are a method employing a blowout
coil, a blowout magnet, or a permanent magnet; a method utilizing a parallel current
which flows in the reverse direction across the stationary rigid conductor 201 and
the movable rigid conductor 301, etc.
[0013] In the manner described above, the arc current reaches the current zero point to
extinguish the arc A, so that the interruption is completed. Where the power supply
is a D.C. power supply, an arc voltage greater than the supply voltage is generated,
whereby a current limiting action is effected and the current zero point is forcibly
established. With a D.C. power supply, accordingly, a phenomenon similar to that in
the case of the foregoing A.C. current zero point occurs. During the interrupting
operation thus far described, large quantities of energy are generated by the arc
A across the gap between the movable-side contact 302 and the stationary-side contact
202 in a short period of time of the order of several milliseconds. In consequence,
the temperature of the gas within the' enclosure 1 rises abruptly, as does the pressure
thereof, and the high temperature and pressure gas is emitted into the atmosphere
through the exhaust port 101.
[0014] As the circuit breaker performs the interrupting operation as described above, the
operations of the stationary-side contact 202 and the movable-side contact 302 can
be analyzed as follows. In general, the arc resistance R(Ω) is given by the following
expression:
where p: arc resistivity (Ω· cm)
ℓ: arc length (cm)
. S : arc sectional area (cm2)
[0015] In general, in short arc A with a high current of at least several kA and an arc
length ℓ of at most 50 mm, the arc space is occupied by particles of metal from the
rigid conductors on which the arc has its foot. Moreover, the emission of metal particles
from.the rigid conductors occurs orthogonally to the rigid conductor surfaces. At
the time of the emission, the emitted metal particles have a temperature close to
the boiling point of the metal used in the rigid conductors. When injected into the
arc space, the metal particles possess a conductivity due to the electrical energy
of the arc and they are also further raised in temperature by the arc, and flow away
from the rigid conductors at high speed while expanding in a direction conforming
with the pressure distribution in the arc space. The arc resistivity ρ and the arc
sectional area S in the arc space are determined by the quantity of metal particles
produced and the direction of emission thereof. Accordingly, the arc voltage is determined
by the behaviour of such metal particles.
[0016] Figure 2 is a model diagram to illustrate the behaviour of the metal particles. As
shown, a pair of rigid conductors 6 and 7 are ordinary conductors in the form of mutually
opposed metallic cylinders. The rigid conductor 6 is an anode, while the rigid conductor
7 is a cathode. The surfaces X of the respective rigid conductors 6 and 7 are opposing
surfaces which become contact surfaces when the rigid conductors 6 and 7 come into
contact, and the surfaces Y of the respective rigid conductors 6 and 7 are the surfaces
of the rigid conductors other than the opposing contact surfaces X. The description
of the behaviour of the metal particles to be given below also applies similarly to
a case where the surfaces X are formed of the contact members. The contour Z indicated
by a dot-and-dash line in the figure is the envelope of the arc A struck across the
gap between the rigid conductors 6 and 7. Further, metal particles b are typically
representative of the metal particles which are respectively emitted from the surfaces
X and Y of the conductors 6 and 7 by vaporization, etc. The directions of emission
of the metal particles a and b are the directions of the flow lines indicated by arrows
m, m' and n, n', respectively.
[0017] Such metal particles a and b emitted from the rigid conductors 6 and 7 have their
temperature raised by the energy of the arc space from approximately 3,000 C, the
boiling point of the metal of the rigid conductors, to a temperature at which the
metal particles bear conductivity, i.e., at least 8,000°C, or up to an even higher
temperature of approximately 20,000°C. As the temperature rises, the metal particles
take energy out of the arc space and thus lower the temperature of the arc space,
resulting in increased arc resistance R. The quantity of energy taken from the arc
space by the metal particles a and b increases with the rise in the temperature of
the metal'particles. In turn, the rise in the temperature is determined by the positions
and emission paths of the metal particles a and b emitted from the rigid conductors
6 and 7. Further, the paths of the metal particles a and b emitted from the rigid
conductors 6 and 7 are determined by the pressure distribution in the arc space. The
pressure in the arc space is determined by the mutual relationship between the pinch
force of the current itself and the thermal expansion of the metal particles a and
b. The pinch force is a quantity which is substantially determined by the current
density. In other words, it is determined by the size of the foot of the arc A on
the rigid conductors 6 and 7. In general, the metal particles and b may be considered
to fly in the space determined by the pinch force while thermally expanding. It is
also known that, in a case where the size of the foot of the arc A on the rigid conductors
6 and 7 is not limited, the metal particles a are blown unidirectionally from one
rigid conductor 7 to the other rigid conductor 6 in the form of a vapor jet. When
in this manner the metal particles a move unidirectionally from one rigid conductor
7 toward the other rigid conductor 6, the metal particles a to be injected into the
positive column of the arc A are supplied substantially from only the rigid conductor
on one side 7. Figure 2 illustrates by way of example a case where the metal particles
are blown strongly from the cathode to the anode, but they may also be blown in the
opposite direction.
[0018] The above phenomenon will now be described in greater detail. In Figure 2, it is
supposed that the blowing,for whatever reason, is unidirectional from the rigid conductor
7 toward the rigid conductor 6. The metal particles. a starting from the surfaces
X, being the surface of the rigid conductor 7 opposing the rigid conductor 6, tend
to fly orthogonally to the rigid conductor surfaces or, in other words, toward the
positive column of the arc. At this time, a metal particle a which begins its flight
from the contact surface X of one rigid conductor 7 is injected into the positive
column by pressure caused by the pinch force. In contrast, a metal particle a which
begins its flight from the contact surface X of the other rigid conductor 6 is pushed
by the particle stream in the positive column and is ejected outside the contact surface
X, immediately being forced out of the system without entering the positive column.
In this manner, the flights of the metal particle a emitted from the rigid conductor
6 and of the metal particle a emitted from the rigid conductor 7 are different, as
indicated by the flow lines of the arrows m and m' in Figure 2. As stated before,
this is based on the difference between the pressures caused by the pinch forces at
the. rigid conductor surface. Thus, the unidirectional blowing from the rigid conductor
7 heats the rigid conductor 6 on the blown side and expands the foot (anode spot in
some cases, and cathode spot in others) of the arc on the surface of the rigid conductor
6 from the front surface X thereof to the other surface thereof. In consequence, the
current density on the surface of the conductor 6 lowers, as does the pressure of
the arc. Accordingly, the unidirectional blowing from the rigid conductor 7 is increasingly
intensified. The discrepancy in the flight paths of the metal particles a emitted
from the respective rigid conductors 6 and 7 as has thus occurred results in a discrepancy
in the quantities of energy that the particles of both the conductors take from the
arc space. More specifically, a metal particle a blown from the contact surface X
of the rigid conductor 7 is able to absorb substantial energy from the positive column,
whereas a metal particle a blown from the contact surface X of the rigid conductor
6 is not, and so it is ejected out of the system without effectively cooling the arc
A. On the other hand, metal particles b emitted from the surfaces Y of the respective
rigid conductors 6 and 7 spread transversely as indicated by the flow lines of the
arrows n and n' in Figure 2. Therefore, they do not deprive the arc A of substantial
heat. Moreover, they increase the arc sectional area S, resulting in lowered resistance
R of the arc A.
[0019] In this manner, in the instance of blowing from one rigid conductor 7, the efficiency
of the cooling of the positive column by the metal particles a from the other rigid
conductor 6 is reduced. In addition, the metal particles b emitted from the surfaces
Y of both the rigid conductors 6 and 7, being those surfaces other than the opposing
contact surfaces, do not contribute to the cooling of the positive column at all and
may even lower the arc resistance R by increasing the arc sectional area S. Accordingly,
the presence of the unidirectional blowing of the metal particles from one rigid conductor
to the other is impedimental to raising the arc voltage and renders it impossible
to enhance the current-limiting performance during tripping.
[0020] There are, however, several disadvantages in that, in general, the stationary contactor
and the movable contactor used in conventional circuit breakers have large opposing
surface areas, similar to the conductors of the model of Figure 2, making it impossible
to limit the size of the foot of the struck arc. Moreover, the contactors have exposed
surfaces such as peripheral surfaces in addition to the opposing surfaces, so that,
as explained with reference to Figure 2, the position and size of the foot(anode spot
or cathode spot) of the arc appearing on the surfaces of the two conductors cannot
be limited. Furthermore, the unidirectional blowing of the metal particles a from
one contactor to the other occurs, with the result that the arc sectional area increases
as explained with reference to Figure 2, such that the current-limiting performance
during tripping cannot be enhanced, as stated above.
[0021] As appears from the foregoing, in order to enhance the current-limiting performance
of a circuit breaker, the arc voltage has to be raised, and to this end, the metal
particles appearing in the foot of the arc need to be effectively injected into the
positive column from both electrodes. The force which injects the metal particles
into the positive column, is the pressure based on the pinch force arising in the
foot of the arc. The pinch force changes greatly in accordance with the size of the
foot of the arc on the contactors, or with the current density. It is accordingly
possible to control the pinch force. In conventional contactors, the area of the surfaces
X of the conductors is large, which fact effectively prevents a limitation of the
size of the foot of the arc. When the opposing contact surfaces X of both the contactors
are made sufficiently small, the density of current on the contact surfaces X rises
substantially, increasing the pinch force. Accordingly, metal particles are injected
from both sides into the positive column, unlike to the prior-art circuit breaker,
so that the arc voltage becomes higher than in the prior device. With this measure
alone, however, the spread of the foot of the arc to parts other than the contact
surfaces X or to the surfaces Y cannot be restrained, and the current density on the
contact surfaces X decreases by a component corresponding to the spread of the foot
of the arc to the surfaces Y, so that the metal particle injection pressure lowers.
With the contactors of the prior art, accordingly, the cooling effect on the positive
column by the injection of metal particles is not the maximum possible.
[0022] Further, in the contactors of the prior art, the spread of the foot of the arc to
the surface Y leads to the disadvantage that the foot of the arc is liable to spread
directly to the interfacing point between the contact and the conductor which is often
set on the surface Y, and a joint member of a low fusing point may be melted by the
heat of the arc making the contact liable to fall off.
[0023] Now, the invention relates to a circuit breaker which provides good current-limiting
performance in the interruption of excess currents such as accompany electric faults,
and which also has a high arc voltage, and yet in which the problem of the contacts
falling off is eliminated.
[0024] With a circuit breaker according to this invention, the above and other objects can
be achieved by covering and concealing the portions of the rigid, conductors in the
vicinity of the contacts behind arc shields of a high resistivity material with a
higher resistivity than the material forming the rigid conductors (hereinbelow simply
called high resistivity material), leaving a portion of the electrical contact surface
of the contacts of the circuit breaker, whereby the metal particles will be forcibly
injected into the arc space, and wherein the arc shields are of a predetermined form.
As the high resistivily material for the arc shields, organic or inorganic insulators
as well as high resistivity alloys or metals, such as copper-nickel, copper-manganese,
manganin, iron-carbon, iron-nickel and iron-chromium, may be used. It is also possible
to use iron the resistivity of which increases abruptly with temperature.
[0025] Hereinbelow, an embodiment showing the basic construction of this invention is taken
as an example to serve in an explanation of the basic construction of this invention.
[0026] Figures 3(a) and 3(b) are respectively a sectional plan view and a sectional side
view of an embodiment showing the basic construction of this invention. Parts of the
circuit breaker other than the stationary contactor 2 and the movable contactor 3
are constructed similarly to the corresponding parts of the circuit breaker of the
prior art shown in Figures 1(a), 1(b) and 1(c), and so description thereof will not
be repeated. The dimensions to be mentioned.hereinbelow relate to a circuit breaker
in which the rated current is 100 A.
[0027] As shown in Figures 3(a) and 3(b), the stationary contactor 2 is constructed with
a'stationary rigid conductor 201, an arc shield 8 and a stationary-side contact 202.
The plate-form stationary rigid conductor 201 is made of an electrically conductive
material, such as copper, and in the described embodiment it is formed with a width
of 8 mm, while the thickness is 3,2 mm. The lower surface of the stationary rigid
conductor 201 is fastened to the enclosure 1. The stationary-side contact 202 is made
of a silver alloy contact material, and is formed in the shape of a rectangular block
with a square base of 4,5 mm sides and a height of 3,5 mm. The bottom surface of the
stationary-side contact 202 is fastened to the top surface of the stationary rigid
conductor 201 near the fore end thereof. The silver alloy contact material may contain
tungsten carbide (WC) or iridium. The arc shield 8 is made of a high resistivity material
as above described, or an insulating material such as a phenol resin or a ceramic.
It is formed in,a plate form of regular square plan with sides of 12 mm, while the
thickness is 2 mm. Centrally of the arc shield 8 is provided a square through-hole
of sides of approximately 4,5 mm in length, corresponding to the stationary-side contact
202, and the stationary-side contact 202 projects through this hole. In this way,
the arc shield 8 not only covers the upper surface of the stationary rigid conductor
201 in the vicinity of the stationary-side contact 202, but it also substantially
projects horizontally beyond the sides or edges of the stationary rigid conductor
7.
[0028] Further, as shown in Figures 3(a) and 3(b), the movable contactor 3 is constructed
with a movable rigid conductor 301, a movable-side contact 302, and an arc shield
9, each of which is respectively constructed of the same materials as the corresponding
portions of the stationary contactor 2. The movable rigid conductor 301 is formed
in a rod shape of 3,2 mm thickness and 3,2 mm width, and to its lower surface near
the fore end thereof is affixed the upper surface of the movable-side contact 302.
The movable side contact is formed in the shape of a rectangular block with a square
base of 3,2 mm sides, and a height of 3,5mm. The arc shield 9 is formed in a plate
form of regular square plan with sides of 7,5 mm, while the thickness in 2 mm. Centrally
of the arc shield 9 is provided a square through-hole of sides of approximately 3,2
mm length, corresponding to the movable-side contact 302 which projects therethrough.
In a manner similar to the arc shield 8 on the side of the stationary contactor 2,
the arc shield 9 substantially projects horizontally beyond the sides or edges of
the movable rigid conductor 301.
[0029] Assuming now that the movable-side contact 302 and the stationary-side contact 202
are closed, current flows- from a power supply side onto a load side along a path
from the.stationary rigid conductor 201 to the stationary-side contact 202,to the
movable-side contact 302,to the movable rigid conductor 301. When, in this state,
a high current such as a short-circuit current flows through the circuit, the operating
mechanism 4 operates to separate the movable-side contact 302 from the stationary-side
contact 202. At this time, an arc A appears across the gap between the stationary-side
contact 202 and the movable-side contact 302. As explained in detail hereinbelow with
reference to Figure 4, in this arc A the metal particles are reflected by the arc
shields 8 and 9, and the voltage in the arc space is thus made high, with the result
that the arc is effectively cooled and extinguished.
[0030] Figure 4 is a model diagram showing the behaviour of the metal particles in the circuit
breaker of Figures 3(a) and 3(b). The metal particle behaviour to be described may
also be regarded as being substantially identical in an instance where the surfaces
X are constructed of the contact material. In Figure 4, a pair of rigid conductors
6 and 7 are constructed in the same form as those of Figure 2, and the arc shields
8 and 9 respectively project beyond the surfaces X, the. opposing surfaces of the
respective rigid conductors 6 and 7, and are affixed to the respective rigid conductors
6 and 7. With this construction, the pressure values in the spaces Q cannot exceed
the pressure value of the space of the arc A itself. However, much higher values are
exhibited, at least in comparison with the values attained without the arc shields
8 and 9. Accordingly, the peripheral spaces Q which have the relatively high pressures
caused by the arc shields 8 and 9 generate forces that suppress the spread of the
space of the arc A and confine the arc A to a small area. This results in fining and
confining into the arc space of the flow lines m, m', o and o' of metal particles
a and c emitted from the opposing surfaces X. Therefore, the metal particles a and
c emitted from the surfaces X are effectively injected into the arc space.
[0031] As a result, large quantities of effectively injected metal particles a and c take
large quantities of energy from the arc space, and the arc space is markedly cooled.
Accordingly, the resistivity ρ, i.e. the arc resistance R, and hence the arc voltage,
are greatly raised.
[0032] Further, when the arc shields 8 and 9 as shown, for example, in Figures 3(a) and
3(b) are disposed near and around the contact surfaces of the stationary-side contact
202 and the movable-side contact 302, namely the opposing surfaces X shown in Figure
4, the arc A is prevented from moving to the other surfaces Y of the rigid conductors,
and also the size of the foot of the arc A is limited. Thus, the emission of metal
particles a and c is concentrated on the surfaces X, and the arc sectional area S
is contracted, so that the effective injection of the metal particles a and c into
the arc space is further promoted. Accordingly, the cooling of the arc space, and
the rise of the arc resistivity and of the arc resistance R are further improved,
and the arc voltage can be further raised.
[0033] Next, Figures 5(a) and (b) to Figures 12(a) and (b) relate to various embodiments
of a contactor of a circuit breaker according to the present invention. In Figures
5, 6, 7, 10, 11, 12 and 13, the illustration is restricted for_simplicity to the stationary
contactor side as exemplary of the embodiment as a whole. That is to say, the arc
shield or contact on the movable contactor side in each embodied case may be regarded
as being provided similarly and with a similar configuration to the corresponding
stationary contactor side arc shield or contact, and so illustration is omitted.
[0034] Figures 5(a) and (b) illustrate an embodiment wherein the arc shield 8 and the contact
202 have substantially the same form in plan view, and they are respectively affixed
to the rigid conductor 201 of the stationary contactor 2 such that their planar centers
substantially coincide. Figure 5(a) is a plan view of the contact portion of the stationary
contactor 2 of the embodiment, and Figure 5(b) is a side view of the same. In this
embodiment, the plan form of the arc shield 8 affixed to the stationary rigid conductor
201 of the stationary contactor 2 is substantially the same as that of the stationary-side
contact 202, and the planar centers of the arc shield 8
'and the stationary-side contact 202 are arranged so as to substantially coincide.
In the illustrated embodiment the contact and the arc shield each have a shape which
in plan view is substantially trapezoidal. The forming of the contact and the arc
shield such that they have similar plan forms, and positioning them such that their
planar centers coincide, as described above, effectively confines the arc produced
across the gap between the contacts during the tripping operation of the circuit breaker
as shown in Figure 3(b). That is to say, the shape of the arc in the vicinity of the
stationary-side contact 202 and the movable-side contact 302 in cross-section closely
resembles the shape of those contacts 202 and 302. Further, the periphery of the arc
is subject to an equal compressive force from the anode or cathode spots in the vicinity
of the contacts, to the positive column in the center of the arc, by the arc shields
8 and 9 which are similar in plan form to the respective contacts 202 and 302, and
so efficient confining of the arc A is achieved from the moment that the arc is produced.
Thus, the potential inclination of the anode and cathode and the positive column can
be effectively raised from the moment of arc generation, and the arc voltage between
the contacts can be further increased.
[0035] In the embodiment shown in Figures 5(a) and (b), the stationary-side contact 202
and the arc shield 8 are shown as having a trapezoidal shape in plan view, but, of
course, the may have any suitable shape, such as round, rectangular, elliptical, polygonal,
etc. Further, in a case where the rated current is 100 A, the dimensions of the stationary
contactor 2 of Figures 5(a) and 5(b) are fundamentally the same as the corresponding
dimensions in the embodiment of Figures 3(a) and 3(b),but the stationary-side contact
202 is a trapezoid of parallel sides of 3 mm and 6 mm length, and of a height of 5
mm. The height of the contact 202 itself is 3,5 mm, and the lower surface of the contact
202 is affixed to the upper surface of the stationary rigid conductor 201. The arc
shield 8 is 2 mm thick, and is formed as a trapezoid in plan view, with parallel sides
of 9 mm and 20 mm length and a height of 20 mm. Centrally of the arc shield 8 is provided
a through-hole of trapezoidal plan, substantially corresponding in size and shape
to the stationary-side contact 202 which projects therethrough.
[0036] Figures 6(a) and 6(b) illustrate an embodiment wherein the contact 202 is rectangular
in plan and the arc shield 8 is circular in plan. Figure 6(a) is a plan view of the
contact portion of the stationary contactor 2 of the embodiment, and Figure 6(b) is
a side view of the same. At the moment of the tripping operation of the circuit breaker,
the peripheral shape of the arc A produced between the stationary-side contact 202
and the movable-side contact 302 as shown in Figure 3(b), in the vicinity of the rectangular
stationary-side contact 202 and the movable-side contact 302, is rectangular, closely
resembling the shape of the contacts 202 and 302. However, as the arc A advances to
the central point between the contacts, the sectional shape of the arc A is made circular
by the pinch effect of the arc A itself.
[0037] Accordingly, with the arc shields 8 and 9 round in plan, the round portion of the
section of the arc A, i.e. the- outer periphery of the central portion of the arc
positive column, is evenly subjected to a confining force as hereinabove described,
and the potential inclination of the positive column is effectively raised, while
the arc voltage between the contacts is further increased.
[0038] For a circuit breaker of 100 A rating, the dimensions of this embodiment, with the
exception of the arc shields 8 and 9, are the same as the dimensions of corresponding
portions in the embodiment of Figures 3(a) and 3(b). The arc shield 8 is 2 mm thick,
and is circular in plan with a 25 mm diameter, and a rectangular through-hole is provided
centrally thereof with a shape and size substantially corresponding to the stationary-side
contact 202 which projects therethrough.
[0039] Figures 7(a) and 7(b) illustrate an embodiment wherein the contact 202 is circular
in plan and the arc shield 8 is rectangular in plan. Figure 7(a) is a plan view of
the contact portion of the stationary contactor 2 of the embodiment, and Figure 6(b)
is a side view of the same. At the moment of the tripping operation of the circuit
breaker, the peripheral shape of the arc A produced between the stationary-side contact
202 and the movable-side contact 302 as shown in Figure 3(b), in the vicinity of the
circular stationary-side contact 202 and movable-side contact 302, is circular, closely
resembling the shape of the contacts 202 and 302. However, as the arc A advances to
the central point between the contacts, the influence of the shape of the rectangular
plan arc shields 8 and 9 makes itself strongly felt. That is to say,as illustrated
in Figure 4, the distribution in the space Q, in which the pressure rises, corresponds
to the shape of the arc shields 8 and 9, and the sectional shape of the arc A midway
between the contacts accords to that pressure distribution, as shown in Figure 8.
The thus deformed arc A, and particularly those portions of the arc A not within a
cylinder defined between the faces of the opposing contacts 202 and 362, are strongly
affected by the pinch force of the arc A itself, and so the arc A further contracts.
Thus, the potential inclination of the positive column is effectively raised, and
the arc voltage between the contacts is further increased.
[0040] For a circuit breaker of 100 A rating, the dimensions of this embodiment are basically
the same as the corresponding dimensions in the embodiment of Figures 3(a) and 3(b),
except that the stationary-side contact 202 is of circular plan with a 6 mm diameter.
The height of the contact is 3,5 mm. The arc shield 8 is rectangular in plan, being
20 mm wide and 25 mm long, and has a platelike configuration. The arc shield 8 is
2 mm thick. A circular through-hole is provided centrally of the arc shld 8 with a
shape and size substantially corresponding to the stationary-side contact 202 which
projects therethrough.
[0041] Figures 9(a), 9(b), 9(c) and 9(d) illustrate an embodiment wherein the stationary
contactor 2 and the movable contactor 3 have the planar center points of their respective
arc shields 8 and 9 located further from the arc-extinguishing plate assembly than
the respective planar center points of the contacts 202 and 302. Figure 9(a) is a
plan view of the contact portion of a stationary contactor of this embodiment, and
Figure 9(b) is a side view of the same. Figure 9(c) is a plan view of the contact
portion of a movable contactor of this embodiment, and Figure 9(d) is a side view
of the same. In these figures, the - arc shield 8 affixed to the rigid conductor 201
of the stationary contactor 2 has its planar central point located more remote from
the arc-extinguishing plate assembly than the planar central point of the stationary-side
contact 202, and similarly the arc shield 9 on the side of the movable contactor 3
has its planar central point located more remote from the arc-extinguishing plate
assembly than the planar central point of the movable-side contact 302. By virtue
of this disposition, at the moment of the tripping operation of the circuit breaker,the
pressure distribution of the arc A in the space between the stationary-side contact
202 and the movable-side contact 302 is weaker on the side of the exhaust port 101
and stronger on the opposite side. Accordingly, the arc A generated across the gap
between the stationary-side contact 202 and the movable-side contact'302 is distorted
towards the side of the arc-extinguishing plate assembly 5 and the exhaust port 101
in Figure 3(b), and cooling of the arc A by the arc-extinguishing plate assembly 5,
or the exhausting of hot gas from the exhaust port 101 are carried out with good effect.
Thus, the potential inclination of the positive column is effectively raised, and
the arc voltage between the contacts is further increased.
[0042] For a circuit breaker of 100 A rating, the dimensions of this embodiment, apart from
the arc shields 8 and 9, are substantially the same as the corresponding dimensions
of the embodiment of Figures 3(a) and 3(b). The arc shields 8 and 9 are substantially
square plates with a thickness of 2 mm and sides of 25 mm length. In a position disposed
towards the exhaust port, each of the arc shields 8 and 9 is provided with a through-hole
of dimensions.and configuration substantially corresponding to the respective contacts
202 and 302 which respectively project therethrough.
[0043] Figures 10(a) and 10(b) illustrate an embodiment wherein the arc shield 8 is formed
with a concave surface. Figure 10(a) is a plan view of the contact portion of a stationary
contactor of this embodiment, and Figure 10(b) is a side view of the same. In this
embodiment, the surface of the arc shield 8 is concave in form, and so when an arc
A is produced between the stationary-side contact 202 and the movable-side contact
302 at the moment of the tripping operation of the circuit breaker, as shown in Figure
3(b) the arc A is even more strongly confined, and the cross- sectional diameter of
the arc column becomes even smaller than in the case with a flat plate arc shield.
Accordingly, the potential inclination of the anode and cathode and the positive column
are effectively raised from the moment of generation of the arc A, and the arc voltage
between the contacts can be further increased.
[0044] For a circuit breaker of 100 A rating, the dimensions of this embodiment are substantially
the same as the corresponding dimensions of the embodiment of Figures 6(a) and 6(b),
except that the arc shield 8 is provided substantially centrally on the surface which
opposes the arc A, with a spherical concavity with a surface radius of curvature of
approximately 50 mm, and the thickness of the arc shield 8 at its thinnest point,
i.e. in the vicinity of the central point, is approximately 2 mm. The concave depression
is formed substantially concentrically with the arc shield 8, but does not extend
fully to the outer circumference of the latter, leaving a flat circular band of 3
mm width around the concave depression.
[0045] Figures 11(a) and 11(b) illustrate an embodiment wherein the arc shield 8 is formed
with a convex surface. Figure 11(a) is a plan view of the contact portion of a stationary
contactor of this embodiment, and Figure 11(b) is a side view of the same. In this
embodiment, the surface of the arc shield 8 is convex in form, and so the force confining
the arc A at the time of the tripping operation of the circuit breaker, as shown in
Figure 3(b), is inferior in its positive column potential inclination raising power
as compared to the concave arc shield shown in Figures 10(a) and 10(b), but it does
have the advantage that even where repeated switching of the contact causes wear of
the contacts, the arc shields themselves will not make physical contact.
[0046] For a circuit breaker of 100 A rating, the dimensions of this embodiment are substantially
the same as the corresponding dimensions of the embodiment of Figures 6(a) and 6(b),
except that the surface of the arc shield 8 which opposes the arc A is formed with
a spherical convexity of a radius of curvature of approximately 50 mm. The convexity
extends fully to the outer circumference of the circular arc shield 8, and the thickness
of the arc shield 8 at its thickest point, i.e. in the vicinity of its central point,
is approximately 2 mm.
[0047] Figures 12 (a) and 12 (b) illustrate an embodiment wherein the surface of the arc
shield 8 has an inclination. Figure 12(a) is a plan view of the contact portion of
a stationary contactor of this embodiment, and Figure 12(b) is a side view of the
same. In this embodiment, the flat top surface of the arc shield 8 is inclined downwards
in the direction in which the arc A bows towards the arc-extinguishing plate assembly,
and so directionality is imparted to the force that confines the arc A at the time
of the tripping operation of the circuit breaker, as shown in Figure 3(b), and the
arc length, i.e. the length of the current path, tends to increase. In other words,
at the moment of arc generation, the length of the arc grows orthogonally to the contact
surfaces of the stationary-side contact 202 and the movable-side contact 302, and
due to the spaces Q, as shown in Figure 4, produced by the arc shield 8 with an inclined
surface, the length of the arc varies in a direction orthogonal to the arc shield
8. As a result, the length of the arc increases and the arc voltage between the contacts
is further increased..
[0048] In this embodiment, the inclination of the surface of arc shield 8 is downwards in
the direction in which the arc A bows towards the arc-extinguishing plate assembly,
but whatever direction the arc is caused to bow, the inclination may follow it with
similar effects with regard to extending the length of the arc.
[0049] For a circuit breaker of 100 A rating, the dimensions of the embodiment are substantially
the same as the corresponding dimensions of the embodiment of Figures 3(a) and 3(b),
except that the surface of the arc shield 8 which opposes the arc A is formed with
an inclination downwards in the direction of the arc-extinguishing plate assembly
or the exhaust port, whereby the thickness of the arc shield 8 decreases gradually
and evenly from its thickest point, the edge farthest from the arc-extinguishing plate
assembly or exhaust port, where it is substantially 3 mm thick, to its thinnest point,
the edge nearest the arc-extinguishing plate assembly or exhaust port, where it is
substantially 1 mm thick.
[0050] Figures 13(a) and 13(b) illustrate an embodiment wherein the width of the contact
decreases as it approaches the' circuit breaker's arc-extinguishing plate assembly
or gas exhaust port. Figure 13(a) is a plan view of the contact portion of a stationary
contactor of this embodiment, and Figure 13(b) is a side view of the same. In this
embodiment, the arc A generated between the stationary-side contact 202 and the movable-side
contact 302 during the tripping operation of the circuit breaker, as shown in Figure
3(b), is drawn by the arc-extinguishing plate assembly 5 which is made of a magnetic
material, and it moves in the direction of the exhaust port 101 due to the flow of
the arc A, which has a high pressure, and so as the arc A moves, the width of its
foot on the contact narrows. Thus, in addition to the effects of the arc shields 8
and 9 described hereinabove, the arc voltage can be even further raised. In the above
embodiment, the arc shield is circular in form, but as the cross-sectional shape of
the arc column comes to resemble the shape of the stationary-side contact 202 and
the movable-side contact 302, having the shape of the arc shields 8 and 9 resemble
the shape of the stationary-side contact 202 and the movable-side contact 302 further
raises the effectiveness.
[0051] For a circuit breaker of 100 A rating, the dimensions of this embodiment, apart from
the contact 202, are substantially the same as the corresponding dimensions of the
embodiment of Figures 6 (a) and 6(b). The stationary-side contact 202 has a substantially
triangular plan, the base of the triangle being 5 mm and the height of the triangle
being 8 mm. The height of the contact is 3,5 mm, and the contact is affixed on its
lower surface to the upper surface of the stationary rigid conductor 201. The arc
shield 8 is a circular plate in form, 25 mm in diameter and 2 mm thick, and is provided
at its central portion with a through-hole of a size and configuration,substantially
the same as the stationary-side contact 202 which projects therethrough.
1. A circuit breaker comprising a pair of contactors (2, 3) comprising rigid conductors
(201, 301) with contacts (202, 302) formed with a predetermined shape fastened thereto,
said contactors (2, 3) functioning to open and close an electric circuit, and arc
shields (8, 9) formed with a predetermined shape disposed on said contactors (2, 3),
surrounding said contacts (202, 302) and covering and concealing therebehind said
rigid conductors (201, 301) in the vicinity of said contacts (202, 302), and which
substantially project beyond said rigid conductors (201, 301) in a direction traversing
an arc struck across the gap between said pair of contacts (202, 302), and which has
a resistivity higher than that of said rigid conductors (201, 301) of said contactors
(2, 3).
2. A circuit breaker as claimed in claim 1, wherein said predetermined form of said
arc shields (8, 9) fixed to said rigid conductors (201, 301) is substantially similar
in plan to said predetermined form of said contacts (202, 302), and said arc shields
(8, 9) are affixed to said rigid conductors (201, 301) such that their planar centers
substantially coincide respectively with the planar centers of said contacts (202,
302).
3. A circuit breaker as claimed in claim 1, wherein said predetermined forms of said
arc shields (8, 9) and said contacts (202, 302) are substantially different.
4. A circuit breaker as claimed in claim 1, wherein said contacts (202, 302) are rectangular
in plan and said arc shields (8, 9) are circular in plan, and said arc shields (8,
9) are affixed to said rigid conductors (201, 301) such that their planar centers
substantially coincide respectively with the planar centers of said contacts (202,
302).
5. A circuit breaker as claimed in claim 1, wherein said contacts (202, 302) are circular
in plan and said arc shields (8, 9) are rectangular in plan, and said arc shields
(8, 9) are affixed to said rigid conductors (201, 301) such that their planar centers
substantially coincide respectively with the planar centers of said contacts (202,
302).
6. A circuit breaker as claimed in claim 1, wherein said arc shields (8, 9) are affixed
to said rigid conductors (201, 301) such that their planar centers are respectively
disposed away from the planar centers of said contacts (202, 302) in a predetermined
direction.
7. A circuit breaker as claimed in claim 1, wherein the surfaces of said arc shields
(8, 9) surrounding said contacts (202, 302) are provided with a concavity.
8. A circuit breaker as claimed in claim 1, wherein the surfaces of said arc shields
(8, 9) surrounding said contacts (202, 302) are provided with a convexity.
9. A circuit breaker as claimed in claim.1, wherein the surfaces of said arc shields
(8, 9) surrounding said contacts (202, 302) are provided with an inclination in a
predetermined direction.
10. A circuit breaker as claimed in claim 1, wherein the width of said contacts (202,
302) gradually narrows in a predetermined direction.