A CIRCUIT BREAKER WITH ARC RESTRICTING DEVICE

Abstract: The present invention relates to a circuit breaker com­ prising a pair of contactors (2, 3) each comprising a rigid conductor (201, 301) with a contact (202, 302) secured there­ to, wherein at least one of said contactors (2 or 3) is also provided with an electrically conductive projection (203) secured thereto in proximity to said contact (202 or 302), said contact (202, 302) and said projection (203) having their peripheries surrounded by a high resistivity arc shield (6 or 7) of a resistivity higher than said rigid conductors (201, 301). An arc extinguishing plate assembly (5) is also provided to cool and extinguish an arc drawn across the gap between said contacts (202, 302). With this arrangement, said arc is confined and has its voltage raised by the effects of the arc shield (6,7), and the size of the foot of the arc is limited such that it does not spread to the surface of the conductor (201, 301) in the vicinity of the contact (202, 302). Further, the foot of the arc is caused to shift from the contact (202, 302) to the projection (203), substantially preventing wear of the contact 202, 302) and further extending the length of the arc to more effectively cool and extinguish the arc.

Description: The present invention relates to a circuit breaker according to the preamble of claim 1. Such a circuit breaker is known f.i. from DE-OS-1 765 999. The same is provided with a stationary contactor in form of a metal plate, on which there is attached a main contact of polygonal shape. In order to protect this main contact against arcs of longer duration, the metal plate is covered by a thin sheet of insulating material, which again carries a metal strip, so that in case of a shortcircuit the arc struck between the main contact of the stationary contactor and a corresponding contact of a movable contactor can move upwards from the main contact along the metal strip thereby increasing the lenght of the arc and extinguishing the same. Considering this piror art it is the object of the present invention, to provide a circuit breaker of very simple design which has improved current breaking capabilities. In accordance with the invention this object can be obtained by providing the features as stated with in the characterizing clause of claim 1. Further improvements of the invention are obtained by the features, as stated in the subclaims 2-6. Preferred ways of carrying out the invention are described below with reference to drawings, in which:- Figure 1 (a) is a sectional plan view of a conventional circuit breaker to which the present invention may be applied; Figure 1 (b) is a sectional side view of the item of figure 1(a) taken along phe line b-b in figure 1(a); Figure 2 is a model diagram of the behaviour of an arc drawn across the gap between the contacts of the circuit breaker of figure 1(a); Figure 3(a) is a sectional plan view showing an embodiment of a circuit breaker according to the present invention; Figure 3(b) is a sectional side view of the item of figure 3(a) taken along the line b-b in figure 3(a); Figure 4 is a model diagram showing the behaviour of an arc in the circuit breaker of figure 3(a); Figure 5(a) is an exploded perspective view of a stationary contactor portion employing an embodiment of an arc shield of the invention; Figure 5(b) is an exploded perspective view of a movable contactor portion employing an embodiment of an arc shield of the invention; Figure 6 is a sectional plan view showing another embodiment of a circuit breaker according to this invention; Figure 7 is an exploded perspective view of the stationary contactor portion of the circuit breaker of figure 6; Figure 8 is a sectional plan view showing another embodiment of a circuit breaker according to this invention; Figure 9(a) is an exploded perspective view of a stationary contactor portion employing an embodiment of an arc shield of the invention; Figure 9(b) is an exploded perspective view of a movable contactor portion employing an embodiment of an arc shield of the invention. In the figures, like reference numerals or symbols denote identical or corresponding parts. A conventional circuit breaker to which the present invention can be applied, is explained below on the basis of figures 1(a) and 1(b). An enclosure 1 is made of insulating material, forming the housing for a circuit breaker, which comprises a pair of electrical contactors 2 and 3, which are respectively a stationary contactor and a movable contactor. On an electrical contacting surface of a stationary rigid conductor 201, which forms the main part of the stationary contactor 2, is affixed a stationary-side contact 202, and on an electrical contacting surface of a movable rigid conductor 301, which forms the main part of the movable contactor 3, is affixed a movable-side contact 302, which opens and closes relative to the stationary-side contact 202. An operating mechanism 4 operates to open or close the circuit breaker by moving the movable contactor 3 in or out of contact with the stationary contactor 2. An arc-extinguishing plate assembly 5 is provided in the arc space between the stationary-side contact 202 and the movable-side contact 302, and has cut-out slits 501 in the plates, the slits 501 being open-ended on the side of the stationary-side contact 202 and the movable-side contact 302. The operating mechanism 4 and the arc-extinguishing plate assembly 5 are well known in the art, and are described, for example, in U.S. Patent 3 599130. As appears from this patent, the operating mechanism includes a reset mechanism. An exhaust port 101 is formed un the enclosure 1. In figures 1(a) and (b), when the movable-side contact 302 and the stationary-side contact 202 are in contact, 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 and to the movable rigid contactor 301. When, in this state, an over-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 there-across. The arc voltage rises as the distance of separation of the movable-side contact 302 from the stationary-side contact 202 increases. In addition, at the same time, the arc A is drawn by the magnetic force of attraction in the direction of the arc-extinguishing plate assembly 5, and the arc-extinguishing plates cause the arc to be stretched, thus further raising the arc voltage. In this way, the arc current reaches the current zero point, the arc A is extinguished, and the interruption is completed. 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. The circuit breaker performs the interrupting operation as described above to interrupt over-currents. Explanation is now given with regard to the behaviour of the arc voltage, etc., across the stationary-side and movable-side contacts 202 and 302 of the circuit breaker shown in Figures 1(a) and (b). In general, the arc resistance R (Ω) is given by the following expression: R=ρ I S where ρ: arc resistivity (Ω · cm) I: arc length (cm) S: arc sectional area (cm²) In general, in the short arc A with a high current of at least several kA and an arc length of at most 50 mm, the arc space is occupied by metal particles from the conductor on which the foot of the arc is located. The emission of metal particles from the rigid conductors occurs orthogonally to the surfaces of the rigid conductors, and at the time of the emission, the emitted particles have a temperature close to the boiling point of the metal of the rigid conductors. Further, whether or not they are injected into the arc space, they are injected with electrical energy, rising in temperature and pressure, and taking on conductivity, and they flow out of the arc space at high speed in a direction away from the conductors while expanding in a direction according to the pressure distribution in the arc space. Thus, the arc resistivity ρ and the arc sectional area S in the arc space are determined by the quantity of contact particles produced and the direction of emission thereof. Accordingly, the arc voltage is likewise determined by the behaviour of such contact particles. The behaviour of such electrode particles is now explained in conjunction with figure 2. In figure 2, a pair of conductors 8 and 9 are ordinary conductors in the form of a pair of mutually opposed metallic members, the conductor 8 being an anode, and the conductor 9 being a cathode. Also, the surfaces X of the respective conductors 8 and 9 are opposing surfaces which become contact surfaces when the conductors 8 and 9 come into contact, and the surfaces Y of the respective conductors 8 and 9 indicate the electrically contacting surfaces of the conductors other than the surfaces X, the respective opposing contact surfaces. There is no change in the behaviour of the metal particles given below even when the surfaces X are constructed of the contact members. A contour Z indicated by a dot-and-dash line in the figure indicates the envelope of the arc A struck across the conductors 8 and 9, and further, the metal particles a and metal particles b illustrate in model form the metal particles which are respectively emitted from the surfaces X and Y of the conductors 8 and 9 by vaporization etc., and the directions of emission thereof are respectively the directions of the flow lines indicated by arrows m, m' and n. Such metal particles a and b emitted from the conductors 8 and 9 have their temperature raised by the energy of the arc space, from approximately 3000°C, the boiling point of the metal of the conductors, to a temperature at which the metal particles take on conductivity, i e., at least 8000°C, or to the even higher temperature of approximately 20 000°C, and by the process of the temperature rising, they take energy out of the arc space and lower the temperature of the arc space, the result of which being to increase the arc resistance R. The quantity of energy taken from the arc space by the metal particles a and b increases with the extent of the rise in the temperature of the metal particles, and the degree of rise in temperature is determined by the positions in the arc space and the emission paths of the metal particles a and b emitted from the conductors 8 and 9. Further, the paths of the metal particles a and b emitted from the conductors 8 and 9 are determined by the pressure distribution in the arc space. The pressure in the arc space is determined by the inter-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 density of the current, or in other words, it is determined by the size of the foot of the arc A on the conductors 8 and 9. In general, the metal particles a 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 foot of the arc A on the conductors 8 and 9 is not limited, the metal particles a are blown unidirectionally from one conductor 9 to the other conductor 8 in the form of a vapor jet. When, in this manner, the metal particles a are blown unidirectionally from one conductor 9 toward the other conductor 8, the metal particles a injected into the positive column of the arc A are supplied substantially from only the conductor 9 on one side. Figure 2 illustrates by way of example a case where the metal particles are blown strongly from the cathode to the anode, but blowing in the opposite direction may also occur. The above situation will now be explained. In Figure 2, it is supposed that the blowing, for whatever reason, is unidirectional from the conductor 9 toward the conductor 8. The metal particles a emitted from the surface X being the opposing contact surface of the conductor 9 tend to fly orthogonally to the conductor surface in other words, toward the positive column. At this time, metal particles a emitted from the contact surface X of one conductor 9 are injected into the positive column by pressure produced by the pinch force. Metal particles a emitted from the surface X of the other conductor 8 are pushed by the particle stream in the positive column and are ejected in the direction outside the surface X, instantly escaping from the system without entering the positive column. In this manner, the movements of the metal particles a emitted from the conductor 8 and of the metal particles a emitted from the conductor 9 are different, as indicated by the flow lines of the arrows m and m' in figure 2, because, as stated before, of the difference between the pressures produced by the pinch forces at the conductor surfaces. Thus, the unidirectional blowing from the rigid conductor 9 heats the rigid conductor 8 on the blown side causing the foot (anode spot, cathode spot) of the arc on the surface of the conductor 8 to expand from the front surface X thereof to the other surfaces thereof. In consequence, the current density on the surface of the conductor 8 lowers, and the pressure of the arc lowers, too. Accordingly, the unidirectional blowing from the conductor 9 becomes increasingly strong. The discrepancy in the flight paths of the metal particles a emitted from the respective conductors 8 and 9 thus produced results in a discrepancy in the quantities of energy taken from the arc space. Accordingly, the metal particles a emitted from the surface X of the conductor 9 are able to absorb substantial energy from the positive column, but the metal particles a emitted from the surface X of the conductor 8 are not able to absorb substantial energy, and so they are ejected out of the system without effectively cooling the arc A. Also the metal particles b emitted from the surfaces Y of the conductors 8 and 9 spread, as in the flow lines shown by the arrows n in the figure, and not only do they not take substantial heat from the arc A, but they also increase the arc sectional area S and lower the arc resistance R of the arc A. In this manner, in the instance of blowing from one conductor 9, the efficiency of the cooling of the positive column by the metal particles a deteriorates, and also the metal particles b produced from the surfaces Y of both the conductors 8 and 9, being those surfaces other than the opposing 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 conductor to the other conductor is impedimental to raising the arc voltage and, consequently, it is impossible to enhance the current-limiting performance during breaking. There is the disadvantage that the stationary contactor and the movable contactor generally used in conventional circuit breakers have large surface areas, on the opposing surfaces similar to the conductors of the model of figure 2, and accordingly not only is it impossible to limit the size of the foot of the arc produced, but also they have exposed surfaces such as the side surfaces other than the opposite surfaces, so that, as explained with reference to figure 2, the position and size of the feet (anode spot or cathode spot) of the arc produced on the surfaces of the two conductors cannot be particularly limited, and so with the mechanism explained with regard to figure 2, the unidirectional blowing of the metal particles a from one conductor to the other conductor occurs, and so the arc sectional area increases, and, as stated above, the current-limiting performance during breaking cannot be enhanced. Further, a major drawback of prior contactors is the danger that because of the spread of the foot of the arc to the surfaces Y, the foot of the arc is liable to spread directly to the joining 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 this heat, causing the contact to fall off. The circuit breaker according to the present invention eliminates the abovementioned drawbacks and defects, and comprises in the construction thereof a projection of a material having a conductivity substantially the same as the rigid conductor secured to the rigid conductor, of at least one of a pair of electrical contactors, each contactor comprising a rigid conductor and a contact secured to the rigid conductor, and an arc shield of a high resistivity material of a higher resistivity than the rigid conductor, disposed on the rigid conductor of the aforementioned contactor, in such a manner as to surround the periphery of the contact, and, when the projection is provided, the periphery of the projection. The aforementioned arc shield constitutes an arc restricting device to be discussed hereinbelow. As the above-mentioned high resistivity material for the arc shields, for example, an organic or inorganic insulator, or high resistivity metals such as copper-nickel, copper-manganese, manganin, iron-carbon, iron-nickel, or iron-chromium, etc., may be used. It is also possible to use iron the resistivity of which increases abruptly with a temperature rise. According to Figures 3(a) and 3(b), an enclosure 1 of an insulating material forms the housing for a circuit breaker, and is provided with a gas exhaust port 101. The circuit breaker comprises a pair of electrical contactors 2 and 3, which are respectively a stationary contactor and movable contactor. On an electrical contacting surface of a stationary rigid conductor 201, which forms the main part of the stationary contactor 2, is affixed a stationary-side contact 202, and on an electrical contacting surface of a movable rigid conductor 301, which forms the main part of the movable contactor 3, is affixed a movable-side contact 302. An operating mechanism 4 operates to open or close the circuit breaker by moving the movable contactor 3 in or out of contact with the stationary contactor 2. An arc-extinguishing plate assembly 5 is provided in the arc space between the stationary-side contact 202 and the movable-side contact 302. The arc extinguishing plate assembly 5 has cut-out slits 501 in the plates, the slits being open ended on the side of the stationary-side contact 202 and the movable-side contact 302. Also, to the stationary contactor 2 and the movable contactor 3 are respectively affixed arc shields 6 and 7. As is clear from figure 4(a), the arc shield 6 affixed to the stationary contactor 2 has two through-holes 601 and 602, and through one of such through-holes 601 passes the aforementioned stationary-side contact 202. The arc shield 7 affixed to the movable contactor 3 also has a through-hole 701, through which passes the aforementioned movable-side contact 302. The arc shields 6 and 7 are made of a high resistivity material of a higher resistivity than the abovementioned rigid conductors 201 and 301. With this construction, the respective contacts 202 and 302 of the contactors 2 and 3 have their peripheries surrounded by the respective arc shields 6 and 7, and the portions of the rigid conductors around the contacts are covered by the arc shields 6 and 7. In this embodiment, an electrically conductive projection 203 is provided in proximity to the contact 202 of the stationary contactor, and this projection 203 passes through the other through-hole 602 in the arc shield 6 to project thereabove. In the illustrated embodiment, the height (tp) of the projection 203 is limited in such a way as to not impede the opening and closing of the contacts 202 and 302, but is higher than the height (tc) of the stationary contact 202. That is to say, tc<tp. Next, the operation of the arc shields of the abovementioned embodiment is explained with reference to figure 4 In figure 4 a pair of rigid conductors 8 and 9 is constructed in the same form as those of figure 2, and a pair of arc shields 6 and 7 are respectively mounted on the rigid conductors 8 and 9, with the surfaces X, the opposing surfaces of the rigid conductors 8 and 9, being disposed so as to protrude, and sited in a manner to oppose the electric arc A. Of course, the metal particle behaviour to be described below applies similarly even when the surfaces X are formed from the contact members themselves. That is to say, 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 6 and 7. Accordingly, the peripheral spaces Q which have the relatively high pressures caused by the arc shields 6 and 7 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 confining the fining of the flow lines m, m', o and o' of metal particles a and c emitted from the surfaces X, the opposing surfaces, into the arc space. Therefore, the metal particles a and c emitted from the surfaces X are effectively injected into the arc space. As a result, large quantities of metal particles a and c are effectively injected and take large quantities of energy from the arc space, thus markedly cooling the arc space. Accordingly, the resistivity ρ, i.e. the arc resistance R is significantly raised, as is the arc voltage. Further, when the arc shields 6 and 7 are disposed near and around the contact surfaces of the stationary-side contact and the movable-side contact, namely, the surfaces X, the opposing surfaces shown in Figure 5, the arc A is prevented from moving to the surfaces Y, the other surfaces of the conductor, and also the size of the foot of the arc A is limited. Thus, the emission of the metal particles a and c is concentrated on the surfaces X, and the arc sectional area 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, the rise of the arc resistivity ρ and the rise of the arc resistance R are further improved, and the arc voltage can be further raised. Next, the above described effects are explained with resepct to the embodiment of figures 3(a) and 3(b). When the movable-side contact 302 separates from the stationary-side contact 202, an arc A is struck across the gap between the movable-side contact 302 and the stationary-side contact 202. The arc A, for reasons to be given below, shifts its foot (spot) from the stationary-side contact 202 to the projection 203. That is to say, because of such facts as that the arc voltage between stationary-side contact 202 and the movable-side contact 302 is greatly raised by the effect of the arc shields 6 and 7, as explained above, and the projection 203 is of the same electrical potential as the stationary-side contact 202 and is sited higher than the stationary-side contact in the high temperature, high pressure gas due to the arc A, a dielectric breakdown occurs between the movable-side contact 302 and the projection 203, and the foot of the arc A on the stationary-side contact 202 shifts to the projection 203. Thus, wear of the stationary-side contact 202 is kept to a minimum. Further, the arc shields 6 and 7 surrounding the peripheries of the respective contacts 202 and 302 function as arc restricting devices, so the foot of the arc A does not form at the joining surfaces of the contacts, and, in addition, the foot of the arc A shifts, so Joule heat generation at the contacts is reduced, whereby dislodging of the contact is substantially prevented. Also, the height of the projection 203 (tp) in the present embodiment is greater than the height of the stationary-side contact 202 (tc), and so even with repeated shifting of the arc A through a large number of interruption operations, the projection 203 is not easily worn or reduced. That is to say, any reduction of reliability caused by wear of the projection 203 due to frequent interruptions, is substantially prevented. Naturally, in this case too, the arc A shifted to the projection 203, is subject to the confining effect for the above described reasons, and the current limiting continues. The arc extinguishing plates of the art extinguishing plate assembly 5 may be made either of a magnetic material or a non-magnetic material. That is to say, when they are made of a magnetic material, the arc is effectively cooled, but in a circuit breaker of a large rated current, a problem is created by a temperature rise during rated operation due to eddy currents produced by the magnetic material. On the other hand, when they are constructed of a non-magnetic material, the arc cooling effect is slightly inferior, but there is no problem due to a temperature rise during rated operation. An embodiment of the invention shall be described in relation to figures 5(a) and 5(b), wherein a slit 605 is provided in the arc shield 6 to expose the surface of the stationary rigid conductor 201 between the stationary-side contact 202 and the projection 203, and a slit 705 is provided in the arc shield 7 to expose the surface of the movable rigid conductor 301, extending from a side surface of the movable-side contact 302 in a direction away from the movable-side contact 302, i.e. the direction of travel of the arc A. The exposure of the movable rigid conductor 301 by the slit 705 makes it easier to cause the arc to shift to the projection 203. This point is common to each of the embodiments below. Figure 6 shows another embodiment of the present invention wherein all parts and the construction thereof, with the exception of the projection 203, are substantially similar to the corresponding parts and construction of the embodiment shown in figures 3(a) and 3(b). That is to say, the peripheries of the respective contacts 202 and 302, of the contactors 2 and 3 are respectively surrounded by the arc shields 6 and 7, and so the rigid conductors in those regions are covered by the arc shields 6 and 7. As shown in figure 6 an electrically conductive projection 203 is provided in proximity to the contact 202 of the stationary contactor 2 to the side of the direction in which the arc flows, i.e. the side of the arc extinguishing plates assembly 5, the projection 203 passing through another through-hole 602 to project above the arc shield 6. In this embodiment, the height of the projection (tp) is made to be the same as or lower than the height (tc) of the stationary-side contact 202 of the stationary contactor 2 on which the projection 203 is provided. That is to say, tc≧tp. The basic operation of the circuit breaker of this embodiment is the same as that of the embodiment shown in figure 3(a) and 3(b), and so description thereof is omitted. However, in this embodiment, the height of the projection 203 is lower than or equal to the height of the face of the stationary-side contact 202, and so the length of the arc A increases due to the geometric relationship of the relevant parts, when the foot of the arc A shifts from the stationary-side contact 202 to the projection 203, further raising the arc voltage and thus aiding the arc extinction. Furthermore, with the described form of the projection 203, even if the stationary-side contact 202 or the movable-side contact 302 wears, the projection 203, being lower than or equal to the height of the stationary-side contact 202, will not physically obstruct the contact between the contacts 202 and 302, enabling contact to be reliably made. Also, the arc A that has shifted to the projection 203 is subject to the confining effect discussed in the explanation of figure 4 such that the current limiting effect is, of course, continued. As a means to further increasing the effect of confining the arc A shifted to the projection 203, it is possible to construct the projection 203 with a smaller surface area than the stationary-side contact 202. Figure 8 illustrates an embodiment of the present invention wherein all parts and the construction thereof, with the exception of the projection 203, are substantially similar to the corresponding parts and construction of the embodiment shown in figures 3(a) and 3(b). That is to say, a stationary-side contact 202 is mounted to an end portion of a stationary rigid conductor 201, and a substantially quadrilateral pyramid-shaped electrically conductive projection 203 is provided at the end of the stationary rigid conductor 201 in proximity to the stationary-side contact 202 to the side of the direction in which the arc flows, i.e. the side of the arc extinguishing plate assembly 5. Also, a movable-side contact 302 is mounted to an end portion of the movable rigid conductor 301. As shown in figure 10(a), the stationary-side contact 202 and the projection 203 respectively pass through through-holes 601 and 602 in the arc shield 6, while the movable-side contact 302 passes through a through-hole 701 in the arc shield 7, the arc shields 6 and 7 being fixed respectively to the stationary and movable rigid conductors 201 and 301. The basic operation of the circuit breaker of the embodiment shown in figure 8 is the same as that of the embodiment shown in figure 3(a) and 3(b), and so description thereof is omitted. In this embodiment, a substantially quadrilateral pyramid-shaped electrically conductive projection 203 is mounted to the end of the stationary rigid conductor 201 in proximity to the stationary-side contact 202, so when an arc is drawn across the gap between the contacts 202 and 302, the foot of the arc on the stationary-side contact 202 can be easily shifted to the projection 203. That is to say, due to such facts as that the arc voltage between the stationary-side contact 202 and the movable-side contact 302 is greatly raised by the effect of the arc shields 6 and 7, that the projection 203 is of the same potential as the stationary-side contact 202, and has a pointed tip such that a concentration of the electrical field occurs and the field strength becomes very great, and that the arc is located in a gas that is of high temperature and high ionization due to the arc, a dielectric breakdown occurs between the movable-side contact 302 and the projection 203 and the foot of the arc on the stationary-side contact 202 shifts to the projection 203. Accordingly, wear of the stationary-side contact 202 is reduced, and contact between the arc and the arc extinguishing plate assembly 5 to extinguish the arc is more efficiently achieved. Also, since the areas peripheral to the contacts are covered by the arc shields 6 and 7, the foot of the arc does not shift to the surfaces on which the contacts are mounted, and the rise in the temperature of the contacts is thus reduced, such that the contacts are not caused to fall off. In this embodiment, too, as shown in figure 10(a) a slit 605 is provided in the arc shield 6 in such a manner as to expose the surface of the stationary rigid conductor 201, the slit 605 joining the respective through-holes 601 and 602 provided for the stationary-side contact 202 and the projection 203. Additionally, as shown in figure 10(b), a slit 705 is provided in the movable-side arc shield 7 extending from the movable side contact 302 in the direction in which the arc travels, i.e. towards the arc extinguishing plate assembly 5, this slit 705 thus exposing a portion of the surface of the movable rigid conductor. These slits promote the travel of the arc.

Claims: A circuit breaker with an arc restricting device having a stationary (2) and a movable (3) contactor each comprising a rigid conductor (201, 301) with a contact (202, 302) secured thereto wherein on a least one of said contactors (2) in proximity to said contact (202) there is disposed a second electrically conductive portion (203) to enable the foot of an arc drawn across the gap between said contacts (202, 302) to shift from said contact (202) to said second portion (203) and wherein at least one contactor (2, 3) is provided with an arc shield (6,7) made of a material having a resistivity higher than that of said conductors (201, 301), said arc shield (6, 7) being disposed in such a way as to surround the periphery of said contact (202, 302) characterized in that the second conductive portion is a projection (203) disposed on the conductor (201), that said contacts (203, 302) and said projection (203) are located in a space provided in an arc extinguishing plate assembly (5) for cooling and extinguishing the arc, that the arc shield (6) is provided on the conductor (201) formed with the projection (203) and surrounds said projection (203) and that within the arc shield (6) there is formed a narrow slit (605) exposing a path on the contactor (2) leading from the contact (202) to the projection (203). A circuit breaker as claimed in calim 1, characterized in that the height of said projection (203) positioned in proximity to said contact (202, 302) is greater than the height of said contact (202, 302) to enable the foot of an arc drawn across the gap between said contacts (202, 302) to shift easily from said contact (202, 302) to said projection (203). A circuit breaker as claimed in claim 1, characterized in that the height of said projection (203) positioned in proximity to said contact (202, 302) is lower than the height of said contact (202, 302) such that the length of the arc drawn across the gap between said contacts (202, 302) is increased when the foot of the arc shifts from said contact (202, 302) to said projection (203), thereby assisting the action of extinguishing said arc. A circuit breaker as claimed in claim 1, characterized in that said projection (203) positioned in proximity to said contact (202, 302) to enable the foot of an arc drawn across the gap between said contacts (202, 302) to shift from said contact (202, 302) to said projection (203) is formed as a quadrilateral pyramid with a substantially pointed apex, whereby the foot of said arc is able to shift easily to said projection (203). A circuit breaker as claimed in claim 1, characterized in that the surface area of said projection (203) positioned in proximity to said contact (202, 302) is smaller than the surface area of said contact (202, 302) in proximity, whereby the confining of the arc drawn across the gap between said contacts (202, 302) is assisted. A circuit breaker as claimed in one of the preceeding claims, characterized in that said projection (203) is provided on said stationary rigid conductor (201) of said stationary contactor (2) in proximity to said stationary-side contact (202) on said stationary rigid conductor (201).

Inventors: HISATSUNE, FUMIYUKI, TERACHI, JUNICHI, YAMAGATA, SHINJI, YOSHIYASU, HAJIMU
Applicants: MITSUBISHI DENKI KABUSHIKI KAISHA
Application year: 1982
Main classification: H01H9
IPC codes: H01H9