GB2117973A - Circuit protecting sensor - Google Patents

Abstract

A circuit protecting sensor (10) comprises a cylinder (12) divided into two cylinder members (13, 14) with a common magnetic head (15) interposed between them. One of the members (13) contains a viscous fluid sealed therein and an oil plunger (16) and the other member (14) contains an operating plunger (19) projecting partly out of the cylinder. The plungers are biased by respective springs (17, 30) normally away from the magnetic head (15). When a short-circuit current is detected by a coil (24) wound on the cylinder (12), the operating plunger (19) is immediately attracted by the magnetic head (15) independently of the oil plunger (16) prior to its attraction to the magnetic head. When a relatively small overcurrent is detected by the coil (24) the operating plunger (19) is not attracted to the head (15) until the oil plunger (16) reaches the head, thereby achieving a time delay. <IMAGE>

Description

SPECIFICATION Circuit protecting sensor This invention relates to a circuit protecting sensor which operates in response to a detection of short-circuit current or overcurrent higher than a rated current and, more particularly, to an abnormal current sensor which operates to protect associated circuits immediately when a shortcircuit current is detected but with a time delaying action when an overcurrent slightly higher than the rated current is detected.

The circuit protecting sensor of the kind referred to can be incorporated in, for example, a circuit breaker that breaks a circuit to which the breaker is applied when an electric current over a rated current by a predetermined value flows in the circuit. As has been disclosed in, for example, U.S.Patent No. 3,329,913 and Japanese Patent Publication No. 18258/1966, such circuit breaker generally comprises a fixed contactor having a fixed contact, a movable contactor carrying a movable contact contactable with a fixed contact, a manually contact opening and closing mechanism including a trip means which responds to any abnormal current for forcibly separating the movable contactor from the fixed contactor, and an arc suppressing means arranged adjacent the fixed and movable contacts, and the circuit protecting sensor is provided in the breaker in the form of an electromagnetic device operating in response to a short-circuit current or overcurrent to electromagnetically attract an associated armature linked to the trip means of the contact opening and closing the mechanism.

When the short-circuit current or overcurrent continues to flow through a detecting coil of the protecting sensor, the armature is attracted to the magnetic pole of the sensor, the movable contactor is caused to be separated from the fixed contactor to open the contacts, and the circuit is broken with respect to an input current source, while an arc produced when the contacts are rapidly opened is driven toward the arc suppressing means to be thereby divided minutely, cooled and suppressed.

It has been expected that, when applied to such circuit breaker or the like, the sensor will operate with a time delaying action when such current slightly higher than the rated current as, for example, a current more than 11 5% of the rated current is detected but, on the other hand, will operate immediately without the time delaying action when a short-circuit current is detected.

However, in such circuit protecting sensors as the well known electromagnetic devices, the one of so-called oil dash-pot type having a time delaying action has been defective in that the operating time upon detection of the short-circuit current is relatively long and, in the case where a circuit element low in the withstand current such as a semiconductor element is included in the circuit of the circuit breaker to which the sensor is applied, the element is caused to be damaged during the delayed operation. In order to solve such problems, there has been suggested a protecting sensor which operates only when a short-circuit current is detected without any time delay, but this has still been defective in that the sensor responds also to, for example, rush current and lacks universal usage.

A primary object of the present invention is, therefore, to provide a circuit protecting sensor which involves a sufficient time delaying action to operate gradually when an electric current slightly larger than a rated current is detected but, on the other hand, immediately operates within a very short time when a short-circuit current is detected.

Another object of the present invention is to provide a circuit protecting sensor showing an operating time reduced to a large extent so that, when applied to a circuit breaker, the time required for opening the contacts can be shortened and thereby the current limiting effect can be remarkably improved.

Still another object of the present invention is to provide a circuit protecting sensor which elevates the current limiting effect as applied to the circuit breaker, so that any application of the short-circuit current to the circuit in which the circuit breaking is to be achieved can be minimized and any element low in the withstand current even if such element is included in the circuit.

Other objects and advantages of the present invention will become apparent from the following description of the invention detailed with reference to the preferred embodiments shown in the accompanying drawings, in which: FIGURE 1 is a perspective view of an embodiment of the circuit protecting sensor according to the present invention in nonoperating state; FIG. 2 is a vertically sectioned view of the sensor of FIG. 1; FIG. 3 is a top plan view of a circuit breaker shown as an example of application of the protecting sensor of the present invention with its movable and fixed contacts opened; FIG. 4 is a side elevation of the circuit breaker of FIG. 3 with one of the two-halve casings removed for showing its interior; FIG. 5 is an elevation similar to FIG. 4 but with a reduced scale and with certain parts sectioned along line V-V in FIG. 3;; FIG. 6 is an elevation similar to FIG. 5 but with the movable and fixed contacts closed and with most of the casing omitted; FIG. 7 is an elevation similar to FIG. 6 but showing a state at which an overcurrent begins to flow through a detecting coil of the sensor; FIG. 8 is an elevation similar to FIG. 6 but showing the state at which the sensor is perfectly operated by the overcurrent to open the contacts; FIG. 9 is an elevation similar to FIG. 6 but showing the state where a short-circuit current flows through the sensor applied to the same and the contacts are thereby opened; FIG. 10 is a diagram showing relations of the time of passing a current through the sensor shown in FIGS. 1 and 2 to the operating time as compared with those of conventional products;; FIG. 11 is a diagram showing arc suppressing characteristics of the same sensor as in FIG. 10 as applied to a circuit breaker; FIG. 12 is an axially sectioned view showing substantially in a similar manner to FIG. 2 another embodiment of the sensor according to the present invention in the state of non-operation; FIG. 13 is a sectioned view similar to FIG. 12 of the sensor shown therein but in the state when an overcurrent flows through a detecting coil of the sensor; and FIG. 14 is a sectioned view similar to FIG. 12 of the sensor shown therein but in the state when a short-circuit current flows through the detecting coil of the sensor, While the present invention shall now be explained in the following with reference to the embodiments and examples of application shown in the drawings, it will be understood that the present invention is not to be limited only to them but is to include all modifications, alterations and equivalent arrangements possible within the scope of appended claims.

Referring to FIGS. 1 and 2, in an aspect of the present invention, a circuit protecting sensor 10 is provided with both functions of operating highly immediately when a short-circuit current is detected and of operating in response, with a time delaying action, to a detection of an overcurrent larger by a predetermined value than a rated current, by disposing two plungers in a common cylinder having a magnetic head 1 5 in the middle so as to have the magnetic head 1 5 held between them.

More specifically, the circuit protecting sensor 10 of the present invention comprises a yoke 11 of a magnetic member substantially rectangular in section and a cylinder 12 extending between the upper and lower side portions of the yoke 11 as fixed thereto, while the cylinder 12 comprises a lower cylinder body 13 opened at the upper end and made of such non-magnetic material as preferably brass, and an upper cylinder body 14 opened at both ends and made of such nonmagnetic material as preferably a plastic to have a diameter slightly larger than the lower cylinder body 13, and a magentic head 1 5 is fitted to the respective openings of the lower and upper cylinder bodies 13 and 14 so as to couple them with each other.Within the lower cylinder body 13, such viscous fluid as preferably a silicone oil is enclosed as sealed, and an oil plunger 1 6 made of a magentic material and a coil spring 1 7 normally resiliently biasing the oil plunger 1 6 toward the inner surface of the bottom of the lower cylinder 13 are contained. Further, the lower cylinder body 1 3 is fixed to a lower side portion 1 8 of the yoke 11 as projected downward at the bottom end through the center of the lower side portion 1 8 so as to dispose the upper end of the oil plunger 16 substantially at the level of the lower side portion 18 of the yoke as being biased downward by the spring 17.

Further, within the upper cylinder body 14, an operating plunger 1 9 of a magnetic material is contained, a rod part 21 with which a head part 20 is integrally formed at the head end is fixed to the upper end of the plunger 19, the head part 20 is always projected outward and the rod part 21 is so provided as to also partly extend out of a constricted upper end part of the upper cylinder body 14 which is fitted at the upper end fixedly in a circular hole having a flange part 23 of the upper side portion 22 of the yoke 11.

A detecting coil 24 is wound on the cylinder 12 substantially over the entire length in the axial direction of the cylinder and is led out of the yoke at both ends 25 and 26 to be connectable to the circuit an overcurrent and short-circuit current in which are to be detected so that, when the sensor is applied, for example, to a later described circuit breaker, one end 25 may be led out through one side portion 27 of the yoke 11 and connected to a lead wire 28 as seen in FIG. 4. In addition, a flange part 29 is formed on the rod part 21 of the plunger 19, and a coil spring 30 is arranged compressively between the flange part 29 and the upper end part of the upper cylinder body 14 to normally hold the operating plunger 1 9 in its uppermost or maximum extruded position.

Further, the operation of the circuit protecting sensor 10 of the present invention shall be explained in conjunction with the operation of the circuit breaker to which the inventive sensor is applied. Referring to FIGS. 3 to 9, the head part 20 of the operating plunger 1 9 of the sensor 10 is operatively connected with the trip means of the circuit breaker, an end 25 of the detecting coil 24 is connected with a movable contactor through the lead wire 28 and the other coil end 26 is connected with a terminal member of the circuit breaker. Now, if a handle 31 of a manual contact opening and closing mechanism of the circuit breaker is rotated counterclockwise as seen in FIG.

6 about a supporting shaft 32 as the centre from the position in FIG. 4 or 5, a U-shaped link 38 engaged at one leg part 33 to the handle 31 and at the other leg part 34 to a link arm 35 and loosely fitted in a sliding window 37 of a bearing frame 36 which is formed integrally with the yoke 11 and pivotably supporting the link arm 35 is positioned substantially vertical and, at this time, the base end part of the link arm 35 comes into an engagement with a latch piece 39, the link arm 35 is inclined downward at the other tip end part, whereby a movable contact 42 of a movable contactor 41 connected through a supporting shaft 40 to the link arm 35 is brought into contact with a fixed contact 47 of a fixed contactor 46 fixed in a casing 43 as held by holding bases 44 and 45 of the casing 43.

The latch piece 39 is so provided as to be simultaneously rotatable about a supporting shaft 49 as the center with an operatively connecting arm 48 of the trip means engaged directly with the head part 20 of the sensor 10 in counterclockwise direction in the drawings to be disengaged with the link arm 35 when the operating plunger 19 moves downward as described later. Such coil spring 50 as shown by dotted lines in FIG. 4 is fitted around the supporting shaft 49 to normally rotate the connecting arm 48 counterclockwise in the drawings, whereby the coil spring 30 shown in FIGS. 1 and 2 as fitted around the rod part 21 of the operating plunger 19 in the sensor 10 can be omitted.

When, in the state where the fixed contact 47 and movable contact 42 are thus closed, such overcurrent as, for example, of more than 11 5% of a rated current flows through the detecting coil 24 of the sensor 10, the magnetic head 1 5 is excited through the detecting coil 24, the oil plunger 1 6 is attracted by the excited magnetic head 1 5 relatively gradually against the coil spring 1 7 and the viscosity of the oil sealed in the lower cylinder body 13 and thereby a time delaying action is achieved so that, even if such overcurrent flowing for a relatively short time as a starting current is detected, the oil plunger 1 6 will not be caused to be attracted to the magnetic head.Further, when the oil plunger 1 6 is attracted to the magnetic head 1 5, the permeance of the magnetic circuit through the yoke 11 will increase and the operating plunger 1 9 normally biased into the uppermost position through the connecting arm 48 by the coil spring 50 will be relatively quickly attracted to the magnetic head 1 5 as shown in FIG. 8.

With the downward movement of this operating plunger 19, the connecting arm 48 and latch piece 39 operating integrally with the arm will rotate about the supporting shaft 49 as the centre, the latch piece 39 separates from the link arm 35 and the movable contactor 41 is quickly separated from the fixed contactor 46 by the tension of a return spring 52 hung between the movable contactor 41 connected to the link arm 35 and a tip end 51 of the frame 36. If an arrangement is made so that a downward projection 54 of the link arm 35 will be kicked by a foot part 53 of the operatively connecting arm 48 with the rotation of the arm at this time, the response to the detecting operation of the sensor 10 can be optimumly increased.

When a short-circuit current of, for example, more than 200 to 300% of the rated current flows through the detecting coil 24, on the other hand, in the foregoing state of the contacts closed, a strong magnetic fieid is generated in the detecting coil 24 and the operating plunger 1 9 within the upper cylinder 14 is immediately quickly attracted to the magnetic head 1 5 as shown in FIG. 9 without waiting form the oil plunger 1 6 of the lower cylinder 13 to be attracted to the magnetic head 15.

With the downward movement of this operating plunger 19, the connecting arm 48 and latch piece 39 operating integrally with the arm are caused to rotate about the supporting shaft 48 as the centre and, the same as described above, the movable contactor 41 is quickly separated from the fixed contactor 46. The arc produced when the contacts are quickly opened will be divided, cooled and suppressed in an arc suppressing means 60 arranged between upper and lower arc running plates 55 and 56 and comprising deion grids 59 respectively fixed at regular intervais to a side plate 57 and back plate 58.Further, it will be easily understood by those skilled in the art that, in the above described circuit breaker, the circuit protecting sensor is positioned by means of a base part 61 made within the casing 43, the detecting coil 24 is connected at one end to a terminal member 62, the fixed contactor 46 is connected to another terminal member 64 through a connecting part 63 so that a detected current can be passed therethrough.

The operation characteristics of the above described circuit protecting sensor according to the present invention shall be explained in the foliowing with reference to FIG. 10. It is found that, in the case of the sensor 10 of the present invention, as shown by the curve X, the sensor operates comparatively slowly with an overcurrent up to about twice as large as the rated current but, on the other hand, with such current as greatly exceeding twice as large as the rated current, it can be operated with an operating time less than 0.01 second and further, with a large current exceeding 10 times as large as the rated current, the operating time will be much less than 0.01 second so as to be close to 0.01 second.On the other hand, in the case of a conventional circuit protecting sensor having a time delaying action, normally as shown by the characteristic curve A, the operating time will require more than 1 second even when a short-circuit current three times as large as the rated current flows. Further, even in a conventional protecting sensor having a time delaying action made high in the speed by improving, for example, the magnetic characteristics, as shown by the curve B, an improvement can be seen up to a current about twice as large as the rated current but, with a short-circuit current exceeding three times as large as the rated current, the operating time has required almost one second.Therefore, it has not been able to apply the sensor to such case that an element low in the withstand current such as a semiconductor element is included in the circuit to be protected by means of the circuit breaker. On the other hand, in a conventional protecting sensor intended to be used mostly for instantaneous response, no time delaying action is provided and the operating time can be made short as shown by the curve C but, even if a current less than about 1.25 times as large as the rated current flows for about 0.1 second, the sensor operates so it will be likely to operate even in response, for example, to the starting electric power of the circuit associated with the sensor and only a poor universality can be obtained for the usage, and even with a current exceeding 10 times as large as the rated current an operating time of about 0.01 second is required, resulting in that the instantaneous response has still been poor.

In addition,the operation characteristics of the circuit breaker provided with the protecting sensor according to the present invention can be improved to a large extent so that the peak value of the arc voltage can be reached within a very short time, whereby the current limiting effect is remarkably improved. Therefore, it is found that, when the protecting sensor according to the present invention is set in an ordinary conventional circuit breaker which requires an arc suppressing time of substantially 12 m.sec.

without any arc suppressing means as shown by the curve "a" of a chain line in FIG. 11 and substantially about 6 m.sec. with an arc suppressing means as shown in the curve "b" of a dotted line in the drawing, the suppressing time can be improved to be substantially remarkably less than 5 m.sec. as shown by the curve "x" of a solid line.

According to another aspect of the present invention, there is suggested another embodiment wherein the operating plunger comprises a first plunger operating responsive to the overcurrent and a second plunger responsive to the shortcircuit current. Referring to FIG. 12, the members respectively corresponding to those used in the embodiment of FIGS. 1 and 2 are denoted by adding 100 to their respective reference numerals.

In an operating plunger 119 of a protecting sensor 110 of this embodiment, a second plunger 11 9b is inserted coaxially through a first plunger 11 9a which operates responsive to the short-circuit current and movably in the axial direction of the first plunger 11 9a. Further, an attracting head part 120a positioned within a cylinder 112 is fixed to one end of the second plunger 11 9b and an operating head part 1 20b positioned outside the cylinder 112 is fixed to the other end of a nonmagnetic spacer 11 9c is arranged between opposing end faces of the first and second plungers 11 9a and 119b.Further, a coil spring 1 30b arranged between a flange part 129 provided on a rod part 121b of the second plunger 11 9b and an end of the cylinder 112 or a yoke 111 acts to resiliently bias the second plunger 11 9b and first plunger 11 9a axially outward with respect to the cylinder 112. A second coil spring 1 30a partly surrounding the both plungers 11 9a and 11 9b and arranged between an intermediate magnetic head 11 5 and the first plunger 11 9a is arranged within a cylinder body 114 housing therein the first and second plungers 11 9a and 119b.

When the overcurrent flows in this embodiment through a detecting coil 124 around the cylinder 112, as shown in FIG. 13, an oil plunger 116 opposing the operating plunger 119 is attracted to the intermediate head 11 5 and, thereafter, only the second plunger 11 19b is attracted to the head 115. On the other hand, when the short-circuit current flows, as shown in FIG. 14, the first and second plungers 11 9a and 11 9b are both attracted immediately to the head 11 5 against the coil spring 1 30b and independent of the attracted movement of the oil plunger 11 6.

Therefore, the provision of the second plunger operating independently responsive to the overcurrent in the operating plunger makes it possible to control an interrupting pickup current and to adapt the sensor sufficiently to any overflowing current in the case of candescent lamps and any motor starting current.

In this embodiment of FIGS. 12 to 14, other arrangements and operations than those referred to in the foregoing are substantially the same as in the embodiment of FIGS. 1 and 2 and detailed references thereto are omitted here.

In the circuit protecting sensor of the present invention formed as described above, there can be realized such effects that a sufficient time delaying effect can be achieved, a remarkably instantaneous response can be well attained so that, as applied, for example, to the circuit breaker, the current limiting action can be greatly improved, it can be adopted without any obstruction in a circuit including an element low in the withstand current, thus sufficiently universal usages can be well attained, the mass of the plunger responsive specifically to the short-circuit current can be reduced when a single operating plunger is employed so as to improve the instantaneous response.

Claims (9)

1. A circuit protecting sensor for protecting an associated circuit from an overcurrent or shortcircuit current, comprising a cylinder divided into two cylinder bodies by an interposed magnetic head, a yoke in which said cylinder is fitted with one of said cylinder bodies projected partly out of said yoke, a detecting coil wound around the cylinder, a fluid plunger contained together with a viscous fluid in said partly projecting cylinder body and subjected to a spring-load acting in the direction separating the body from said magnetic head, and an operating plunger contained in the other cylinder body as projecting partly at an end out of the cylinder and subjected to a spring-load acting in the direction separating from the magnetic head.

2. A sensor according to claim 1, wherein said magnetic head is fitted to respective opposing end openings of said cylinder bodies so as to couple them together.

3. A sensor according to claim 1 or claim 2, wherein said spring-load for said fluid plunger is provided by means of a coil spring contained in said one cylinder body, and said spring-load for said operating plunger is provided by means of a coil spring arranged between a flange provided on said projected end of said operating plunger and an end of said other cylinder body.

4. A sensor according to any preceding claim, wherein a head part to be coupled to a device to which said sensor is applied is fixed to said projected end of said operating plunger.

5. A sensor according to claim 1 or claim 2, wherein said operating plunger comprises a first plunger operating in response to an overcurrent and a second plunger inserted through said first plunger movably in the axial direction of said cylinder and operating in response to a shortcircuit cylinder, and respective said first and second plungers are subjected to said spring-load.

6. A sensor according to claim 5, wherein said spring-load for said first plunger is provided by means of a coil spring arranged between said magnetic head and the first plunger within said other cylinder body.

7. A sensor according to claim 5 or claim 6, wherein a head part positioned within said other cylinder body and attractable to said magnetic head is provided at one end of said second plunger, and an operating head part positioned outside the other cylinder body is provided at the other end.

8. A sensor according to claim 7, wherein said operating head part is provided at an end of said second plunger forming said extended end of said operating plunger for connecting the plunger with a device to which the sensor is to be applied.

9. A sensor according to any one of claims 5 to 8, wherein said spring-load acting on said one of the plungers is provided by means of coil spring contained in said one cylinder body, and wherein the spring-load for said second plunger of the other plunger is provided by means of a coil spring arranged between a flange attacHed to an end of the second plunger forming the outer end of the said other plunger and the end of the associated cylinder body remote from the magnetic head.

1 0. A circuit protecting sensor substantially as described herein with reference to the drawings.

9. A sensor according to any one of claims 5 to 8, wherein said spring-load for said fluid plunger is provided by means of a coil spring contained within said one of said cylinder bodies, and said spring-load for said second plunger of said operating plunger is provided by means of a coil spring arranged between a flange attached to an end of the second plunger forming said projecting end of the operating plunger and an end of said other cylinder body.

10. A circuit protecting sensor substantially as described herein with reference to the drawings.

New claims or amendments to claims filed on 29th March 1983.

Superseded claims 1-10.

New or amended claims

1. A circuit protecting sensor for protecting an associated circuit from an overcurrent or shortcircuit current, wherein a cylinder is provided with a magnetic head and a detecting coil wound around the cylinder, the cylinder being divided into two cylinder bodies and secured to and partly projected from a yoke, a respective plunger displaceable toward the magnetic head in response to one of the different level currents is located in each of said cylinder bodies, the displacing of the plunger in one of the cylinder bodies being subjected to a retarding force effected by means of a viscous fluid and springload, and the cylinder is provided with an actuating member capable of driving an associated external device in response to the displacement of the other plunger, wherein the two divided cylinder bodies are coupled to form the cylinder with the magnetic head fixed between the cylinder bodies, the two plungers are accessible to the magnetic head in opposite directions, the actuating member is coupled to said other plunger, and a spring-load is arranged to act on the said other plunger and actuating member in a direction separating them from the magnetic head.

2. A sensor according to claim 1, wherein the magnetic head is fitted to respective opposing end openings of said cylinder bodies so as to couple them together.

3. A sensor according to claim 1 or claim 2, wherein said spring-load acting on said one of the plungers is provided by means of a coil contained in said one cylinder body, and wherein the springload for the other plunger is provided by means of a coil spring arranged between a flange provided on the outer end of said other plunger and the end of the associated cylinder body remote from the magnetic head.

4. A sensor according to any preceding claim, wherein a head part adapted to be coupled to a device to which said sensor is applied is fixed to the outer end of said other plunger.

5. A sensor according to claim 1 or claim 2, wherein the said other plunger comprises a first plunger operating in response to an overcurrent and a second plunger inserted through said first plunger movably in the axial direction of said cylinder and operating in response to a shortcircuit cylinder, both said first and second plungers being subjected to said spring-load.

6. A sensor according to claim 5, wherein said spring-load for said first plunger is provided by means of a coil spring arranged between the magnetic head and the first plunger within said other cylinder body.

7. A sensor according to claim 5 or claim 6, wherein a head part positioned within said other cylinder body and attractable to said magnetic head is provided at one end of said second plunger, and an operating head part positioned outside the other cylinder body is provided at the other end.

8. A sensor according to claim 7, wherein said operating head part is provided at an end of said second plunger forming an extended end of said other plunger for connecting the plunger with a device to which the sensor is to be applied.