A plunging member of a safety shutter assembly of an air circuit breaker (ACB)
Patent Information
- Application Number
- PCT/IN2026/050289
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- Priority Date
- 2025-02-21
- Filing Date
- 2026-02-19
- Publication Date
- 2026-08-27
Smart Images
Figure IN2026050289_27082026_PF_FP_ABST
Abstract
Description
[0001] A PLUNGING MEMBER OF A SAFETY SHUTTER ASSEMBLY OF AN AIR CIRCUIT BREAKER (ACB)
[0002] TECHNICAL FIELD
[0003] The present invention generally relates to the field of circuit breakers. Particularly, the present invention relates to a plunging member of a safety shutter assembly for an Air Circuit Breaker (ACB), specifically for a withdrawable type ACB.
[0004] BACKGROUND
[0005] This section is intended to provide information relating to the field of the invention and thus, any approach or functionality described below should not be assumed to be qualified as prior art merely by its inclusion in this section.
[0006] A circuit breaker is an electro-mechanical switching device capable of carrying and interrupting flow of current in an electrical circuit. The circuit breaker is commonly also known as an over current protective device. Under normal circuit conditions, the circuit breaker CLOSES the electrical circuit, and thereby allows the flow of the current from a line side (i.e., power supply side) to a load side (i.e., output load connection side) and breaks the electrical circuit under abnormal circuit conditions i.e., fault conditions. In simple words, the circuit breaker is an equipment which can OPEN or CLOSE the electrical circuit, under all conditions viz. no load, full load, and fault conditions. Low voltage circuit breakers are commonly known to be deployed for low voltage applications, for example 1000 Volts or lower.
[0007] Various examples of low voltage circuit breakers are known, for example, a Miniature Circuit Breaker (MCB), a Molded Case Circuit Breaker (MCCB), a Residual Current Circuit Breaker (RCCB), an Air Circuit Breaker (ACB), and the like. Notably, the ACB is used in applications of withstanding current rating ranging between 65 kA (kiloampere) to 100 kA, nominal current ranging between 800 A (Ampere) to 10 kA, and voltage rating below 450V. The ACB is commonly known to be deployed in distribution panels, particularly, upstream the other over-current protective devices such as, the MCB, the MCCB, and the like.
[0008] The Air Circuit Breaker (ACB), as its name suggests, employs ‘air’ as a dielectric medium for quenching and / or extinguishing arc formed therein, in the event of a fault condition. The fault condition includes, but is not limited to, an over-current fault condition, a short-circuit fault condition, and the like. Further, in the event of the short-circuit fault condition, contrary to thefunctioning of the MCB, MCCB, and other similar circuit breakers, the ACB is capable of ‘withstanding’ a fault current for a maximum time span of 1 second. The ACB is largely classified into two broad categories, namely, a fixed-type Air Circuit Breaker (ACB) and a withdrawable-type Air Circuit Breaker (ACB). Essentially, the withdrawable-type ACB comprises a fixed cradle unit and a withdrawable drawer unit, wherein the withdrawable drawer unit is capable of being slidably withdrawn from the fixed cradle unit. General details of the ACB, irrespective of its type, are provided hereunder for ease of understanding of a reader.
[0009] A typical ACB, particularly the withdrawable-type ACB is capable of being operated amongst three states, namely, an ON state, an OFF state, and a TRIP state. The ACB comprises a frame member, a plurality of pole assemblies housed and supported within the frame member, an operating mechanism installed onto the plurality of pole assemblies, and a control panel unit adapted to fittingly attach with the frame member. The frame member protects various components of the ACB against any extraneous matter and also safeguards users from coming into contact with a current path established within the ACB during its operation.
[0010] In the typical ACB, the plurality of pole assemblies are operated together amongst the ON state, the OFF state, and the TRIP state, by means of the operating mechanism. Particularly, the operating mechanism of the ACB employs a charging spring arrangement capable of being adjusted between a CHARGED state and a DISCHARGED state. As is commonly known, the ACB can be manipulated to the ON state only if the said charging spring arrangement is in the CHARGED state, and the charging spring arrangement is automatically adjusted to the DISCHARGED state, once the ACB is in the ON state. To adjust the charging spring arrangement back to the CHARGED state, a charging lever member is provided in the control panel unit.
[0011] In the withdrawable-type ACB, the withdrawable drawer unit is adapted to rack-in into the fixed cradle unit, and rack-out from the fixed cradle unit. The withdrawable drawer unit comprises a first set of current carrying terminals, and the fixed cradle unit comprises a second set of current carrying terminals. A safety shutter assembly and a shutter plate arrangement is employed to selectively permit and restrict access to the current carrying terminals of the fixed cradle unit. The withdrawable drawer unit is capable of being manipulated amongst a CONNECTED position, a TEST position, and a DISCONNECTED position. The safety shutter assembly is adapted to actuate the shutter plate arrangement to allow access to the current carrying terminals when the withdrawable drawer unit is manipulated from the TEST position to the CONNECTED position, and when the withdrawable drawer unit is manipulated from the CONNECTED position to theTEST position, the safety shutter assembly is deactivated to restrict access of the current carrying terminals.
[0012] In the conventional ACB comprising the safety shutter assembly and the shutter plate arrangement, the shutter plate arrangement was not completely opened to allow access to the second set of current carrying terminals when the withdrawable drawer unit was manipulated from the TEST position to the CONNECTED position, resulting in an improper connection of the first and second set of current carrying terminals.
[0013] Accordingly, in light of the aforementioned drawbacks and several other limitations inherent in the existing art, there is a well-felt need to provide a reliable and rapidly opening-safety shutter assembly and the shutter plate arrangement for the ACB, which is capable of reducing the mechanical delay and is also capable of being easily assembled, which the present disclosure aims to address.
[0014] SUMMARY OF THE INVENTION
[0015] This section is intended to introduce certain aspects of the disclosed system in a simplified form and is not intended to identify the key advantages or features of the present disclosure.
[0016] The present disclosure relates to a plunging member of a safety shutter assembly of an Air Circuit Breaker (ACB), such that the ACB comprises a fixed cradle unit, and a withdrawable drawer unit. The fixed cradle unit comprises a pair of shutter plates slidably installed thereto, and the safety shutter assembly fixedly installed thereon. The safety shutter assembly comprises a housing, a pair of tongs each being pivotally installed within the housing and defining a first side engaging with a portion of the pair of shutter plates, a second side, and a spring member. The plunging member defines an actuating top positioned on a first side of the pair of tongs, and is adapted to receive an actuating force from the withdrawable drawer unit when attempted to be arranged with the fixed cradle unit. A shaft extends from the actuating top on the first side of the pair of tongs and is positioned against the second side of the pair of tongs. Further, the plunging member comprises a plunger base positioned on an opposite side of the pair of tongs, and adapted to be resiliently positioned within the housing against the spring member, wherein, during a forward stroke of the plunging member upon the actuating top receiving the actuating force from the withdrawable drawer unit, the shaft engages with the second side of the pair of tongs, to pivotally move the pair of tongs in a first direction, wherein, during a return stroke of the plunging member upon the actuating top released from the actuating force, the plunger base engages with the second side of the pair of tongs, to pivotally move the pair of tongs in a second direction.According to an aspect of the present disclosure the pair of shutter plates comprises a first shutter plate and a second shutter plate, and the pair of tongs comprises a first tong and a second tong, such that the first side of the first tong engages within the first shutter plate, while the first side of the second tong engages within the second shutter plate.
[0017] According to another aspect of the present disclosure the plunging member is manipulated between a first position and a second position, by the withdrawable drawer unit, through the actuating top, such that in the first position, the plunger base presses against the spring member compressing the spring member, and in the second position, the spring member decompresses, pushing the plunger base in an opposite direction, which causes sliding of the safety shutter plates towards each other in the first position, thereby aligning the plurality of slits of the safety shutter plates, thereby opening the through passage, and in the second position, the safety shutter plates slide away from each other, thereby misaligning the plurality of slits of the safety shutter plates, thereby closing the through passage.
[0018] According to yet another aspect of the present disclosure the first position corresponds to a racked-in position of the withdrawable drawer unit of the ACB, and the second position corresponding to a racked-out position of the withdrawable drawer unit.
[0019] According to yet another aspect of the present disclosure the shutter assembly further comprises a top cover member, and a bottom cover member, such that the top cover member, and the bottom cover member, houses the pair of tongs, the spring member, and the plunging member.
[0020] According to yet another aspect of the present disclosure the top cover member comprises a pair of protruded slots and a plurality of mating locks, such that the pair of protruded slots are configured to accommodate the bottom cover member, and the plurality of mating locks snap fits with the bottom cover member to join the top cover member with the bottom cover member.
[0021] According to yet another aspect of the present disclosure, the bottom cover member comprises a pair of stud members, a pair of stopper members, and a plurality of mating holes, such that the pair of stud members are a tubular protrusion, adapted to pivotally support the pair of tongs, and are configured to mate with the pair of protruded slots, the pair of stopper members are spaced apart, to form a cavity, which enables the plunging member to slide therebetween, and further accommodates the spring member therein.
[0022] According to yet another aspect of the present disclosure, the pair of stopper members are adapted to form a stopping point to arrest the movement of the plunging member beyond the stoppingpoint, and the plurality of mating holes are provided on a side portion of the bottom cover member, and the plurality of mating locks abut with the plurality of mating holes thereby forming a snap fit between the top cover member and the bottom cover member.
[0023] According to yet another aspect of the present disclosure, the pair of tongs are provided with an opening through which the pair of stud members passes thereby allowing a to-and-fro movement of the pair of tongs.
[0024] According to yet another aspect of the present disclosure the pair of safety shutter plates comprises the plurality of slits, and a plurality of notches, such that the plurality of notches are configured on a bottom end of the pair of safety shutter plates such that when the pair of tongs align with the plurality of notches, pivotal movement of the pair of tongs results in sliding movement of the pair of safety shutter plates.
[0025] According to yet another aspect of the present disclosure, in the first direction, the first tong and the second tong of the pair of tongs, move towards each other, and in the second direction the first tong and the second tong of the pair of tongs, move away from each other.
[0026] According to yet another aspect of the present disclosure, upon manipulation of the plunging member to the first position, during the rack-in operation of the withdrawable drawer unit corresponding to the racked-in position of the withdrawable drawer unit, the plunging member is pushed inside the cavity, and the plunger base compresses the spring member, and the shaft manipulates the pair of tongs, such that pair of tongs are actuated and pushed towards each other, and due to the alignment of the pair of tongs with the plurality of notches, the safety shutter plates slide towards each other such that plurality of slits of each of the pair of safety shutter plates align with each other to open the through passage.
[0027] According to yet another aspect of the present disclosure, upon manipulation of the plunging member in the second position, during rack-out operation of withdrawable drawer unit, corresponding to a racked-out position of the withdrawable drawer unit, the spring member decompresses, pushing the plunger base out of the cavity, and the shaft manipulates the pair of tongs, such that pair of tongs are pushed away from each other, and due to misalignment of the pair of tongs with the plurality of notches, the safety shutter plates slide away from each other, causing the plurality of slits of each of the pair of safety shutter plates to misalign with each other thereby closing the through passage.
[0028] BRIEF DESCRIPTION OF DRAWINGSIn order to explain the technical solution in the embodiments of the present application more clearly, the drawings used in the description of the embodiments will be briefly introduced below. It is obvious that the drawings in the following description are only some embodiments of the application. Forthose skilled in the art, without any creative work, other drawings can be obtained based on these drawings.
[0029] Figure 1 illustrates a front perspective view of an Air Circuit Breaker (ACB), in accordance with the concepts of the present disclosure.
[0030] Figure 2 illustrates a rear perspective view of the ACB, in accordance with the concepts of the present disclosure.
[0031] Figure 3 illustrates a side sectional view of a withdrawable drawer unit of the ACB of Figure 1, in accordance with the concepts of the present disclosure.
[0032] Figure 4 illustrates a side sectional view of a fixed cradle unit of the ACB of Figure 1, in accordance with the concepts of the present disclosure.
[0033] Figure 5 illustrates a side sectional view of the ACB of Figure 1, in a DISCONNECTED position, in accordance with the concepts of the present disclosure.
[0034] Figure 6 illustrates a side sectional view of the ACB of Figure 1, in a TEST position, in accordance with the concepts of the present disclosure.
[0035] Figure 7 illustrates a side sectional view of the ACB of Figure 1, in a CONNECTED position, in accordance with the concepts of the present disclosure.
[0036] Figure 8 illustrates a side sectional view of an arrangement of an operating mechanism and a plurality of pole assemblies of the ACB of Figure 1, in an ON position corresponding to a CLOSED state of the ACB, in accordance with the concepts of the present disclosure.
[0037] Figure 9 illustrates a side sectional view of the arrangement of Figure 8, in an OFF / TRIP position corresponding to an OPEN state of the ACB of Figure 1, in accordance with the concepts of the present disclosure.
[0038] Figure 10 illustrates a top view of the withdrawable drawer unit in the DISCONNECTED position, in accordance with the concepts of the present disclosure.Figure 11 illustrates a top view of the withdrawable drawer unit in the TEST position, in accordance with the concepts of the present disclosure.
[0039] Figure 12 illustrates a front view of the fixed cradle unit, in accordance with the concepts of the present disclosure.
[0040] Figure 13 illustrates a perspective view of a relative arrangement between a pair of shutter plates and a safety shutter assembly in a first position of the pair of shutter plates, in accordance with the concepts of the present disclosure.
[0041] Figure 14 illustrates a perspective view of the relative arrangement between the pair of shutter plates and the safety shutter assembly in a second position of the pair of shutter plates, in accordance with the concepts of the present disclosure.
[0042] Figure 15 illustrates an exploded perspective view of relative arrangement between the safety shutter assembly and the pair of shutter plates, in accordance with the concepts of the present disclosure.
[0043] Figure 16 illustrates an assembled perspective view of the safety shutter assembly, in accordance with the concepts of the present disclosure.
[0044] Figure 17 illustrates a sectional top view of the safety shutter assembly depicting a plunging member of the safety shutter assembly in an extended state, in accordance with the concepts of the present disclosure.
[0045] Figure 18 illustrates a sectional top view of the safety shutter assembly depicting a plunging member of the safety shutter assembly in a retracted state, in accordance with the concepts of the present disclosure.
[0046] Figure 19 illustrates an exploded perspective view of the safety shutter assembly of Figure 16, in accordance with the concepts of the present disclosure.
[0047] Figure 20 illustrates a perspective view of a bottom cover member of the safety shutter assembly, in accordance with the concepts of the present disclosure.
[0048] Figure 21 illustrates a perspective view of a top cover member of the safety shutter assembly, in accordance with the concepts of the present disclosure.Figure 22 illustrates a perspective view of the pair of safety shutter plates of the ACB, in accordance with the concepts of the present disclosure.
[0049] Figure 23 illustrates a top view of the relative arrangement between the safety shutter assembly and the pair of shutter plates depicting sliding movement thereof in the extended state and the retracted state of a plunging member of the safety shutter assembly, in accordance with the concepts of the present disclosure.
[0050] DETAILED DESCRIPTION
[0051] In the following description, for the purposes of explanation, various specific details are set forth in order to provide a thorough understanding of embodiments of the present invention. It will be apparent, however, that embodiments of the present invention may be practiced without these specific details. Several features described hereafter can each be used independently of one another or with any combination of other features. An individual feature may not address any of the problems discussed above or might address only one of the problems discussed above. Some of the problems discussed above might not be fully addressed by any of the features described herein. Exemplified embodiments of the present invention are described below, as illustrated in various drawings in which like reference numerals refer to the same parts throughout the different drawings.
[0052] Figure 1 illustrates a front perspective view of an Air Circuit Breaker (ACB)
[0100] , in accordance with the concepts of the present disclosure. Figure 2 illustrates a rear perspective view of the ACB
[0100] , in accordance with the concepts of the present disclosure. Figure 3 illustrates a side sectional view of a withdrawable drawer unit
[0116] of the ACB
[0100] of Figure 1, in accordance with the concepts of the present disclosure. Figure 4 illustrates a side sectional view of a fixed cradle unit
[0114] of the ACB of Figure 1, in accordance with the concepts of the present disclosure. Figure 5 illustrates a side sectional view of the ACB
[0100] of Figure 1, in a disconnected position, in accordance with the concepts of the present disclosure. Figure 6 illustrates a side sectional view of the ACB
[0100] of Figure 1, in a test position, in accordance with the concepts of the present disclosure. Figure 7 illustrates a side sectional view of the ACB
[0100] of Figure 1, in a connected position, in accordance with the concepts of the present disclosure. Figure 8 illustrates a side sectional view of an operating mechanism
[0102] of the ACB
[0100] of Figure 1, in an ON position corresponding to a CLOSED state of the ACB, in accordance with the concepts of the present disclosure. Figure 9 illustrates a side sectional view of the arrangement of Figure 8, in an OFF / TRIP position corresponding to an OPEN state of the ACB
[0100] of Figure 1, in accordancewith the concepts of the present disclosure. Figure 10 illustrates a top view of the withdrawable drawer unit in the DISCONNECTED position, in accordance with the concepts of the present disclosure. Figure 11 illustrates a top view of the withdrawable drawer unit in the TEST position, in accordance with the concepts of the present disclosure. Figure 12 illustrates a front view of the fixed cradle unit, in accordance with the concepts of the present disclosure. Figures 1 to 12 are to be viewed in conjunction with each other, in order to appreciate the scope of the present invention. For ease of reference and understanding, different embodiments relating to the structure and arrangement of the air circuit breaker is elucidated hereunder, with reference to the aforementioned accompanying drawings.
[0053] The ACB
[0100] is capable of being operated amongst three states, namely, an ON state, an OFF state, and a TRIP state. The ACB
[0100] comprises a frame member (not shown), the plurality of pole assemblies
[0104] housed and supported within the frame member, the operating mechanism
[0102] installed onto the plurality of pole assemblies
[0104] , and a control panel unit
[0108] adapted to fittingly attach with the frame member, to protect various components of the ACB
[0100] against any extraneous matter and also safeguard users from coming into contact with a current path established within the ACB
[0100] during its operation.
[0054] In the ACB
[0100] , the plurality of pole assemblies
[0104] is operated together between the ON state and the OFF / TRIP state, by means of the operating mechanism
[0102] , Particularly, the operating mechanism
[0102] of the ACB
[0100] employs a charging spring arrangement (not shown) capable of being adjusted / manipulated between a CHARGED state and a DISCHARGED state. As is commonly known, the ACB
[0100] can be switched to the ON state only if the said charging spring arrangement is in the CHARGED STATE, and the charging spring arrangement is automatically adjusted to a DISCHARGED state, once the ACB
[0100] is in the ON state. To adjust the charging spring arrangement back to the CHARGED state, a charging lever member
[0106] is provided in the control panel unit
[0108] , In the ‘ON’ position, the ACB
[0100] allows a flow of current from a line side (i.e., input supply side) to a load side (i.e., output side), whereas, in each of the ‘OFF’ position and the ‘TRIP’ position, the ACB
[0100] restricts the flow of current therethrough. The ACB can be broadly classified into two categories, namely, a fixed-type ACB
[0100] and a withdrawable-type ACB
[0100] ,
[0055] Referring to figure 12, the withdrawable-type ACB
[0100] is a two-part circuit breaker comprising a fixed cradle unit
[0114] and a withdrawable drawer unit
[0116] , wherein the withdrawable drawer unit
[0116] is detachably installed within the fixed cradle unit
[0114] , preferably, in a slidable manner, either vertically or horizontally. The fixed cradle unit
[0114] employs a terminal device
[0118] connected to the line side, while the withdrawable drawer unit
[0116] comprises various components and / or units described hereinabove. Further, the fixed cradle unit
[0114] comprises a pair of shutter plates
[0700] slidably installed thereto, and a safety shutter assembly
[0400] fixedly installed thereon. Particularly, fixed cradle unit
[0114] comprises at least one projection [114a], such that the at least one projection [114a] is adapted to slidably lock the pair of shutter plates
[0700] with the fixed cradle unit
[0114] once assembled therewith. Further, the fixed cradle unit
[0114] comprises a cavity [114b], such that the cavity [114b] is adapted to fixedly support therein the safety shutter assembly
[0400] , The withdrawable drawer unit
[0116] is operable relative to the fixed cradle unit
[0114] amongst the DISCONNECTED position, the TEST position, the CONNECTED position, and an EJECTED position.
[0056] The frame member is a housing structure that provides a mounting base and support structure for holding and supporting each of the plurality of pole assemblies
[0104] therein. In particular, the frame member defines pole holding cavities (not shown) to mount and support each of the plurality of pole assemblies
[0104] therein. Notably, each of the plurality of pole assemblies
[0104] are fixedly attached within the pole holding cavities defined by the frame member. An attachment means for attaching the plurality of pole assemblies
[0104] within the pole holding cavities defined by the frame member includes, but is not limited to, a bolt attachment means, a screw attachment means, a rivet attachment means, an adhesive attachment means, a fit attachment means, a weld attachment means, and the like. The structure and arrangement of the control panel unit
[0108] will be elucidated hereafter.
[0057] The control panel unit
[0108] is fittingly mounted on the frame member, to cover various components of the ACB
[0100] housed within the frame member. The control panel unit
[0108] has various portions to define electrical parameters related to ACB
[0100] , The control panel unit
[0108] also has various visual indicators for indicating the real-time status of at least one of the charging spring arrangement, the plurality of pole assemblies
[0104] , and other such similar arrangements and / or units.
[0058] Referring to figures 5 to 7, each of the plurality of pole assemblies
[0104] includes a pole housing
[0120] , a stationary contact unit
[0122] , a moving contact unit
[0124] , and an arc chute unit
[0126] , More particularly, a number of the plurality of pole assemblies
[0104] , in combination, define a number of electrical connection poles of the ACB
[0100] , The stationary contact unit
[0122] is an electric contact plate-like structure that may be positioned within a defined portion in the casing unit
[0120] , The stationary contact unit
[0122] is provided to connect to electrical wires from the lineside. In particular, in complete assembly of the ACB
[0100] , the electrical wires from the line side are usually connected to the stationary contact unit
[0122] ,
[0059] On the other hand, the moving contact unit
[0124] is a moving structure that engages / di sengages with the stationary contact unit
[0122] , to allow / restrict the flow of electric current therethrough. The moving contact unit
[0124] is rotatably positioned within a defined portion in the pole housing
[0120] , and is further connected to electrical wires on the load side. In particular, in complete assembly of the ACB
[0100] , the electrical wires from the line side are usually connected to the stationary contact unit
[0122] , Further, the moving contact unit
[0124] is pivotally adjusted while being positioned within the pole housing
[0120] , to make and release a contact relative to the stationary contact unit
[0122] , in order to allow and restrict the flow of electric current therebetween, respectively. Notably, the moving contact unit
[0124] ‘makes’ a contact relative to the stationary contact unit
[0122] to allow the flow of electric current (the ‘ON’ position), while the rotary contact unit ‘releases’ a contact relative to the stationary contact unit
[0122] , to restrict the flow of electric current (the ‘OFF’ or ‘TRIP’ position).
[0060] Referring to figures 8 and 9, the moving contact unit
[0124] is commonly known to comprise a moving contact carrier [124a], a plurality of contact fingers [124b] adapted to be affixed within the moving contact carrier [124a], and a carrier frame (not shown) adapted to pivotally connect the moving contact unit
[0124] relative to a pole shaft [102a] of the operating mechanism
[0102] , Notably, the plurality of contact fingers [124b] is known to be made up of a combination of two elements, for example, silver and copper. Such a structure enables each of the plurality of contact fingers [124b] to function as a pair of contacts, namely, a main contact and an arcing contact. Essentially, the plurality of contact fingers [124b] are affixed relative to the moving contact carrier [124a] in a resiliently pivotal manner, such that upon tripping, as soon as the moving contact unit
[0124] disengages from the stationary contact unit
[0122] , the arcing contact rapidly engages with the same, preferably, in a tip-to-toe manner, thereby safeguarding the ACB
[0100] against nuisance arcing.
[0061] The arc chute unit
[0126] is positioned within the arc chute unit portion [120a] of the pole housing
[0120] and comprises of a two-wall shaped arc chute holder member [126a] and an arc chute member [126b], The arc chute holder member [126a] and the arc chute member [126b] are arranged together to vent out gases generated by an arc caused due to engagement / disengagement of the moving contact unit
[0124] relative to the stationary contact unit
[0122] through a vent channel defined by the arc chute holder member.Figure 10 illustrates a top view of the withdrawable drawer unit in the DISCONNECTED position, in accordance with the concepts of the present disclosure. The safety shutter assembly
[0400] comprises a housing, top cover member
[0402] , a bottom cover member
[0404] , a pair of tongs
[0406] , a spring member
[0408] , and a plunging member
[0410] , The top cover member
[0402] and the bottom cover member
[0404] houses the pair of tongs
[0406] , the spring member
[0408] , and the plunging member
[0410] , The pair of tongs
[0406] are pivotally housed within the housing, and define a first tong [406c] and a second tong [406d] which each engage with a portion of the pair of the shutter plates
[0700] , The pair of tongs
[0406] are configured to actuate the pair of shutter plates
[0700] ,
[0062] Referring to Figure 21, The top cover member
[0402] comprises a pair of protruded slots
[0502] and a plurality of mating locks
[0504] , The pair of protruded slots are configured for accommodating the bottom cover member
[0404] , The plurality of mating locks
[0504] snap fits with the bottom cover member
[0404] for connecting the top cover member
[0402] with the bottom cover member
[0404] ,
[0063] Referring to Figure 20, the bottom cover member
[0404] comprises a pair of stud members
[0602] , a pair of stopper members
[0604] , and a plurality of mating holes
[0606] , The pair of stud members
[0602] are a tubular protrusion or a pin for pivotally supporting the pair of tongs
[0406] , The pair of tongs
[0406] are provided with an opening through which the pair of stud members
[0602] passes thereby allowing a to-and-fro movement of the pair of tongs
[0406] , The pair of tongs
[0406] comprises a first tong [406c] and a second tong [406d], The pair of stud members
[0602] are also configured to match with the pair of protruded slots
[0502] , The pair of stopper members
[0604] are spaced apart, to form a cavity
[0412] , which enables the plunging member
[0410] to slide therebetween, and further accommodates the spring member
[0408] therein.
[0064] Referring to figures 15 to 19, the plunging member
[0410] defines an actuating top [410c], a shaft [410b], and a plunger base [410a], The actuating top [410c] is positioned on a first side of the pair of tongs
[0406] , such that the actuating top [410c] is adapted to receive an actuating force from the withdrawable drawer unit
[0116] when attempted to be arranged with the fixed cradle unit
[0114] , The shaft [410b] extends from the actuating top [410c] on the first side [406a] of the pair of tongs
[0406] , and is positioned against a second side [406b] of the pair of tongs
[0406] , The plunger base [410a] is positioned on an opposite side of the pair of tongs
[0406] , and is adapted to be resiliently positioned within the housing against the spring member
[0408] , During a forward stroke of the plunging member
[0410] the actuating top [410c] receives the actuating force from the withdrawable drawer unit
[0116] , and the shaft [410b] engages with the second side [406b] of the pair of tongs
[0406] , to pivotally move the pair of tongs
[0406] in a first direction, such that the firsttong [406c] and the second tong [406d] of the pair of tongs
[0406] , move towards each other. During a return stroke of the plunging member
[0410] the actuating top [410c] gets released from the actuating force, and the plunger base [410a] engages with the second side [406b] of the pair of tongs
[0406] , to pivotally move the pair of tongs
[0406] in a second direction, such that the first tong [406c] and the second tong [406d] of the pair of tongs
[0406] , move away from each other.
[0065] The pair of stopper member
[0604] are provided within the bottom cover member
[0404] , The spring member
[0408] may be accommodated within the pair of stopper members
[0604] , The pair of stopper members
[0604] acts as a stopping point for stopping the movement of the plunging member
[0410] beyond the stopping point. The plunging member
[0410] may move in a linear manner within the cavity of the top cover member
[0402] and the bottom cover member
[0404] , In one example, the plunging member
[0410] may be fully inserted into the cavity on being actuated, this may be called the forward stroke of the plunging member
[0410] , The plunging member
[0410] may be connected with the spring member
[0408] and functions in conjunction with each other.
[0066] Due to the connection of the plunging member
[0410] with the spring member
[0408] , the plunging member
[0410] on being actuated is pushed down the cavity
[0412] , and on release of the actuating force snaps back to its original position due to the spring force caused by the compression of the spring member
[0408] , The plurality of mating holes
[0606] may be provided on a side portion of the bottom cover member
[0404] , the plurality of mating locks
[0504] abuts with the plurality of mating holes
[0606] thereby forming a snap fit between the top cover member
[0402] and the bottom cover member
[0404] , It may be noted that the connection of the top cover member
[0402] to the bottom cover member
[0404] is only exemplary in nature and may be made in other manners as may be understood to a person skilled in the art in light of the present disclosure, and such connection shall not be construed to be limiting to the example provided herein.
[0067] As provided above, the to-and-fro movement of the pair of tongs
[0406] is actuated by the movement of the plunging member
[0410] , In one scenario, when the plunging member
[0410] on being actuated is pushed down the cavity of the safety shutter assembly
[0400] , the plunging member
[0410] pushes the pair of tongs
[0406] towards each other. In another scenario, when the plunging member
[0410] ceases to be actuated and snaps back to its original position, the plunging member
[0410] pushes the pair of tongs
[0406] in opposite direction. In one example, the plunging member pushes one side of the L-shaped pair of tongs
[0406] and then pulls the one side of the pair of tongs
[0406] leading to movement of the pair of tongs
[0406] , The movement of the pair of tongs
[0406] leads to actuation of the pair of safety shutter plates.Referring to figures 13 to 15 and 22, The pair of safety shutter plates
[0700] are a pair of flat plates comprising a first shutter plate [700a] and a second shutter plate [700b], The first side [406a] of the first tong [406c] engages within the first shutter plate [700a], while the first side [406a] of the second tong [406d] engages with the second shutter plate [700b], The pair of safety shutter plates
[0700] comprises a plurality of slits
[0702] , and a plurality of notches
[0704] , The plurality of slits
[0702] may be an opening or a cutout shaped according to the current carrying terminals such as provided in the withdrawable drawer unit. The plurality of slits
[0702] allows the current carrying terminals of the withdrawable drawer unit
[0116] to be aligned and connected with the current carrying terminals of the fixed cradle unit
[0114] , The plurality of slits
[0702] may be configured on each of the pair of safety shutter plates
[0700] such that at least a pair of slits are provided adj acently on a safety shutter plate from the pair of safety shutter plates
[0700] , In one example, the plurality of slits
[0702] may be provided on each of the pair of shutter plates
[0700] such that when the pair of shutter plates
[0700] are arranged together, the plurality of slits of each of the pair of shutter plates
[0700] are opposite to each other. The plurality of slits
[0702] of the pair of safety shutter plates
[0700] are arranged in a crisscross manner, such that during the movement of the pair of safety shutter plates
[0700] , the plurality of slits
[0702] creates a shutter mechanism thereby opening and closing a through passage created by the arrangement of the pair of safety shutter plates
[0700] , The through passage allows the current carrying terminals of the withdrawable drawer unit
[0116] to pass through such through passage of the pair of safety shutter plates
[0700] thereby allowing connection of the current carrying terminals of the withdrawable drawer unit
[0116] and the fixed cradle unit
[0114] , In an example, the pair of safety shutter plates
[0700] are slidably adjustable relatively in an opposite direction to each other, enabling a shutter mechanism due to the positioning of the plurality of slits
[0702] and the linear adjustment of each of the pair of safety shutter plates
[0700] ,
[0068] The plurality of notches
[0704] may be configured on the bottom end of the pair of safety shutter plates
[0700] such that when the pair of tongs
[0406] are aligned with the plurality of notches
[0704] respectively, then the movement of the pair of tongs
[0406] results in the movement of the pair of safety shutter plates
[0700] , When the pair of tongs
[0406] of the safety shutter assembly
[0400] is actuated and pushed towards each other, then due to the alignment of the pair of tongs
[0406] with the plurality of notches
[0704] , the safety shutter plates
[0700] may either slide towards each other or away from each other causing the plurality of slits
[0702] of each of the pair of safety shutter plates
[0700] to align with each other and opening the through passage. Similarly, on actuation and movement of the pair of tongs
[0406] , in opposite direction, the safety shutter plates
[0700] also slidethereby causing the plurality of slits
[0702] of each of the pair of safety shutter plates
[0700] to misalign with each other thereby closing the through passage.
[0069] In one exemplary embodiment, there may be one or more safety shutter assembly
[0400] being installed with the pair of safety shutter plates
[0700] , For example, a plurality of safety shutter assemblies
[0400] may be provided along with the pair of safety shutter plates
[0700] corresponding to the plurality of notches
[0704] provided in the pair of safety shutter plates
[0700] , The provision of the plurality of safety shutter assemblies
[0400] facilitates the movement of the pair of safety shutter plate
[0700] enabling the shutter mechanism. Due to provision of multiple safety shutter plates and the provision of the plurality of safety shutter assemblies
[0400] , the rapid opening feature is facilitated, which have several advantages in terms of safety, reduced costs, etc.
[0070] During the movement of the plunging member
[0410] when pushed inside the cavity
[0412] of the safety shutter assembly
[0400] , the plunger base [410a] is pushed into the cavity
[0412] and the shaft of plunging member
[0410] pushes the pair of tongs
[0406] towards each other. On removal of the actuating force by the withdrawable drawer unit
[0116] , due to the spring force generated by compression of the spring member
[0408] , the plunger base [410a] is pushed away from the cavity
[0412] and the plunger base [410a] pushes the pair of tongs
[0406] away from each other. In one example, when the pair of tongs
[0406] are shaped in L-shape configuration, the plunger base [410a] and the shaft [410b] pushes one portion of the pair of tongs
[0406] from either side to enable the movement of the pair of tongs
[0406] , In one embodiment, the shaft [410b] is of a predetermined length, based on the dimensions of each of the current carrying terminals of the ACB
[0100] , The provision of the predetermined length of the shaft [410b] of the plunging member
[0410] facilitates the pair of safety shutter plates
[0700] to remain open until the current carrying terminals of the withdrawable drawer unit are away from the pair of safety shutter plates
[0700] to avoid damaging the current carrying terminals.
[0071] The safety shutter assembly
[0400] on the fixed cradle unit
[0114] is configured to engage with the withdrawable drawer unit
[0116] , Specifically, the plunging member
[0410] may engage with the withdrawable drawer unit
[0116] , As provided above, the withdrawable drawer unit may be installed slidably into the fixed cradle unit
[0114] , and in such event, the withdrawable drawer unit
[0114] may be in three positions namely the CONNECTED position, the TEST position, and the DISCONNECTED position.
[0072] Referring to figure 23, the safety shutter assembly
[0400] for the ACB
[0100] is in a second position i.e. in a disengaged state. The disengaged state of the safety shutter assembly
[0400] is a state inwhich the withdrawable drawer unit
[0116] is in the disconnected position or the TEST position, and the plunging member
[0410] is the disengaged state. The safety shutter assembly
[0400] similarly may also be in a first position i.e. in an engaged state when the withdrawable drawer unit
[0114] is in the CONNECTED position and the plunging member
[0410] is in the engaged state. Essentially, the disengaged state and the engaged state of the safety shutter assembly
[0400] is corresponding to the disengaged state and the engaged state of the plunging member
[0410] , The engaged state and disengaged state of the safety shutter assembly
[0400] may change based on the position of the withdrawable drawer unit
[0116] with respect to the fixed cradle unit
[0114] ,
[0073] When the withdrawable drawer unit
[0116] is slidably installed in the fixed cradle unit
[0114] , the withdrawable drawer unit
[0116] transitions from the DISCONNECTED position to the TEST position, and then to the CONNECTED position. This transition has four phases, i.e., a first phase, a second phase, a third phase, and a fourth phase. The first phase is a phase in which the withdrawable drawer unit
[0116] transitions from the DISCONNECTED position to the TEST position. The second phase is a phase in which the withdrawable drawer unit
[0116] transitions from the TEST position to the CONNECTED position. The third phase is a phase in which the withdrawable drawer unit
[0116] transitions from the CONNECTED position to the TEST position. The fourth phase is a phase in which the withdrawable drawer unit
[0116] transitions from the TEST position to the DISCONNECTED position. Each of these phases will be explained in detail in the foregoing description. The configuration of the safety shutter assembly
[0400] enables the safety shutter assembly
[0400] to function in such a manner and enables all of the above-mentioned phases.
[0074] The first phase as provided above is the phase in which the withdrawable drawer unit
[0116] transitions between the DISCONNECTED state to the TEST state. In this the withdrawable drawer unit
[0116] on being slidably inserted into the fixed cradle unit
[0114] , forms a predetermined gap between the withdrawable drawer unit
[0116] and the safety shutter assembly
[0400] , In such a state, the withdrawable drawer unit
[0116] does not actuate the plunging member
[0410] of the safety shutter assembly
[0400] , This position is when the withdrawable drawer unit
[0116] is partially installed in the fixed cradle unit
[0114] , In such a phase, the safety shutter assembly
[0400] remains in the disengaged state. The plurality of slits
[0702] of the safety shutter plates
[0700] remains closed in the current state acting as an insulating barrier between the current carrying terminals.
[0075] The second phase as provided above is the phase in which the withdrawable drawer unit
[0116] transitions from the TEST position to the CONNECTED position corresponding to a first position, i.e. a rack-in position of the withdrawable drawer unit
[0116] , In this phase, the plunging member
[0410] of the safety shutter assembly
[0400] is actuated by the withdrawable drawer unit
[0116] ,thereby pushing the plunging member
[0410] into the cavity
[0012] of the safety shutter assembly
[0400] , The plunger base [410a] compresses the spring member
[0408] , and the shaft [410b] manipulates the pair of tongs
[0406] , such that pair of tongs
[0406] are actuated and pushed towards each other, and due to the alignment of the pair of tongs
[0406] with the plurality of notches
[0704] , the safety shutter plates
[0700] slide towards each other such that plurality of slits
[0702] of each of the pair of safety shutter plates
[0700] align with each other to open the through passage. Due to this, the current carrying terminals of the withdrawable drawer unit
[0116] safely passed through the plurality of slits
[0702] for further connection to the current carrying terminals of the fixed cradle unit
[0114] , Once the movement of the withdrawable drawer unit
[0116] is complete, the current carrying terminals of the withdrawable drawer unit
[0116] is connected with the current carrying terminals of the fixed cradle unit
[0114] , thereby achieving the connected position, allowing the operation of the ACB
[0100] , In this phase, the predetermine gap between the withdrawable drawer unit
[0116] and the fixed cradle unit
[0114] decreases.
[0076] The third phase as provided above is a phase in which the withdrawable drawer unit
[0116] transitions from the CONNECTED position to the TEST position, corresponding to a second position, i.e. a rack-out position of the withdrawable drawer unit
[0116] . In this phase, due to the movement of the withdrawable drawer unit
[0116] towards the outside the fixed cradle unit
[0114] i.e. away from the fixed cradle unit
[0114] , the force acting upon the plunging member
[0410] of the safety shutter assembly
[0400] by the withdrawable drawer unit
[0116] is removed, causing decompressing of the spring member
[0408] thereby, pushing the plunger base [410a] in an opposite direction, which causes sliding of the safety shutter plates
[0700] away from each other, thereby misaligning the plurality of slits
[0702] of the safety shutter plates
[0700] , thereby closing the through passage. Due to the movement of the plunging member
[0410] in this phase, the safety shutter plates
[0700] slides thereby causing the plurality of slits
[0702] of the safety shutter plates to misalign and close the through passage. Due to this, the current carrying terminals of the withdrawable drawer unit safely passed through the plurality of slits
[0702] for disconnection from the current carrying terminals of the fixed cradle unit
[0114] , Once the movement of the withdrawable drawer unit is complete, the current carrying terminals of the withdrawable drawer unit
[0116] is disconnected with the current carrying terminals of the fixed cradle unit
[0114] , thereby achieving the test position, allowing the operation of the ACB
[0100] to end. In this phase, the predetermine gap between the withdrawable drawer unit and the fixed cradle unit increases.
[0077] The fourth phase as provided above is a phase in which the withdrawable drawer unit
[0116] transitions from the TEST position to the DISCONNECTED position. In this phase, the withdrawable drawer unit
[0116] is slidably taken out from the fixed cradle unit
[0114] , In such aphase, the safety shutter assembly
[0400] remains in the disengaged state. The plurality of slits
[0702] of the safety shutter plates
[0700] remains closed in the current state acting as an insulating barrier between the current carrying terminals.
[0078] In simpler words, when the withdrawable drawer unit
[0116] travel occurs and the safety shutter plates
[0700] is opened, the pair of tongs
[0406] abut with the plunging member
[0410] , and are consequently locked thereto. This enables the shutter plates
[0700] to remain in its OPEN state.
[0079] Various advantages of the presently disclosed plunging member
[0410] of the safety shutter assembly
[0400] of the ACB
[0100] exist. The plunging member
[0410] provides a rapid opening safety shutter assembly
[0400] which increases the safety of the ACB
[0100] , Further, creepage between the current carrying terminals is increased. Furthermore, due to the rapid opening of the pair of shutter plates
[0700] , no delays occur during the rack-in operation of the ACB
[0100]
[0080] While the preferred embodiments of the present invention have been described hereinabove, it should be understood that various changes, adaptations, and modifications may be made therein without departing from the concepts of the present invention. It will be obvious to a person skilled in the art that the present invention may be embodied in other specific forms without departing from its spirit or essential characteristics. The described embodiments are to be considered in all respects only as illustrative and not restrictive.
[0081] LIST OF COMPONENTS
[0082] 100 - Air circuit breaker
[0083] 102 - Operating mechanism
[0084] 102a - Pole shaft
[0085] 104 - Pole assembly
[0086] 106 - Charging lever member
[0087] 108 - Control panel unit
[0088] 110 - Bus bar units
[0089] 114 - Fixed cradle unit
[0090] 114a - Projection114b - Cavity
[0091] 116 - Withdrawable drawer unit 118 - Terminal device
[0092] 120 - Pole housing
[0093] 120a - Arc chute unit portion 122 - Stationary contact unit 124 - Moving contact unit
[0094] 124a - Moving contact carrier 124b - Plurality of contact fingers 126 - Arc chute unit
[0095] 126a - Arc chute holder member 126b - Arc chute member
[0096] 400 - Safety Shutter Assembly 402 - Top Cover Member
[0097] 404 - Bottom Cover Member 406 - Pair of Tongs
[0098] 406a - First side
[0099] 406b - Second side
[0100] 406c - First tong
[0101] 406d - Second tong
[0102] 408 - Spring Member
[0103] 410 - Plunging Member410a - Plunger base
[0104] 410b - Shaft
[0105] 410c - Actuating top
[0106] 412 - Cavity
[0107] 502 - Pair of Protruded Slots 504 - Plurality of Mating Locks 602 - Pair of Stud Members 604 - Pair of Stopper Members 606 - Plurality of Mating Holes 700 - Pair of shutter plates 700a - First shutter plate 700b - Second shutter plate 702 - Plurality of Slits
[0108] 704 - Plurality of Notches
Claims
We Claim:
1. A plunging member [410] of a safety shutter assembly [400] of an air circuit breaker (ACB)[100], such that the ACB [100] comprises a fixed cradle unit [114], and a withdrawable drawer unit [116], such that the fixed cradle unit [114] comprises a pair of shutter plates [700] slidably installed thereto, and the safety shutter assembly [400] fixedly installed thereon, the safety shutter assembly [400] comprising a housing, a pair of tongs [406] each being pivotally installed within the housing and defining a first side [406a] engaging with a portion of the pair of shutter plates [700], a second side [406b], and a spring member [408], the plunging member [410] defines:an actuating top [410c] positioned on a first side [406a] of the pair of tongs [406], and adapted to receive an actuating force from the withdrawable drawer unit [116] when attempted to be arranged with the fixed cradle unit [114];a shaft [410b] extending from the actuating top [410c] on the first side [406a] of the pair of tongs [406], and positioned against a second side [406b] of the pair of tongs [406]; anda plunger base [410a] positioned on an opposite side of the pair of tongs [406], and adapted to be resiliently positioned within the housing against the spring member [408], wherein, during a forward stroke of the plunging member [410] upon the actuating top [410c] receiving the actuating force from the withdrawable drawer unit [116], the shaft [410b] engages with the second side [406b] of the pair of tongs [406], to pivotally move the pair of tongs [406] in a first direction,wherein, during a return stroke of the plunging member [410] upon the actuating top [410c] released from the actuating force, the plunger base [410a] engages with the second side [406b] of the pair of tongs [406], to pivotally move the pair of tongs [406] in a second direction.
2. The plunging member [410] as claimed in claim 1, wherein the pair of shutter plates [700] comprises a first shutter plate [700a] and a second shutter plate [700b], and the pair of tongs [406] comprises a first tong [406c] and a second tong [406d], such that the first side [406a] of the first tong [406c] engages within the first shutter plate [700a], while the first side [406a] of the second tong [406d] engages within the second shutter plate [700b],3. The plunging member [410] as claimed in claim 1, is manipulated between a first position and a second position, by the withdrawable drawer unit [116], through the actuating top[410c], such that in the first position, the plunger base [410a] presses against the spring member [408], compressing the spring member [408], and in the second position, the spring member [408] decompresses, pushing the plunger base [410a] in an opposite direction, which causes sliding of the safety shutter plates [700] towards each other in the first position, thereby aligning the plurality of slits [702] of the safety shutter plates [700], thereby opening the through passage, and in the second position, the safety shutter plates [700] slide away from each other, thereby misaligning the plurality of slits [702] of the safety shutter plates [700], thereby closing the through passage.
4. The plunging member [410] as claimed in claims 1 and 3, wherein the first position corresponds to a racked-in position of the withdrawable drawer unit [116] of the ACB [100], and the second position corresponding to a racked-out position of the withdrawable drawer unit [116],5. The plunging member [410] as claimed in claim 1, wherein the shutter assembly [400] further comprises a top cover member [402], and a bottom cover member [404], such that the top cover member [402], and the bottom cover member [404], houses the pair of tongs [406], the spring member [408], and the plunging member [410],6. The plunging member [410] as claimed in claim 4, wherein the top cover member [402] comprises a pair of protruded slots [502] and a plurality of mating locks [504], such that the pair of protruded slots [502] are configured to accommodate the bottom cover member [404], and the plurality of mating locks [504] snap fits with the bottom cover member [404] to join the top cover member [402] with the bottom cover member [404],7. The plunging member [410] as claimed in claims 1 to 5, wherein the bottom cover member [404] comprises a pair of stud members [602], a pair of stopper members [604], and a plurality of mating holes [606], such that the pair of stud members [602] are a tubular protrusion, adapted to pivotally support the pair of tongs [406], and are configured to mate with the pair of protruded slots [502], the pair of stopper members [604] are spaced apart, to form a cavity [412], which enables the plunging member [410] to slide therebetween, and further accommodates the spring member [408] therein.
8. The plunging member [410] as claimed in claims 1 to 6, wherein the pair of stopper members [604] are adapted to form a stopping point to arrest the movement of the plunging member [410] beyond the stopping point, and the plurality of mating holes [606] are provided on a side portion of the bottom cover member [404], and the plurality of mating locks [504] abut with the plurality of mating holes [606] thereby forming a snap fit between the top cover member [402] and the bottom cover member [404],9. The plunging member [410] as claimed in claims 1 to 7, wherein, the pair of tongs [406] are provided with an opening through which the pair of stud members [602] passes thereby allowing a to-and-fro movement of the pair of tongs [406],10. The plunging member [410] as claimed in claim 2, wherein the pair of safety shutter plates [700] comprises the plurality of slits [702], and a plurality of notches [704], such that the plurality of notches [704] are configured on a bottom end of the pair of safety shutter plates [700] such that when the pair of tongs [406] align with the plurality of notches [704], pivotal movement of the pair of tongs [406] results in sliding movement of the pair of safety shutter plates [700],11. The plunging member [410] as claimed in claims 1 to 10, in the first direction, the first tong [406c] and the second tong [406d] of the pair of tongs [406], move towards each other, and in the second direction the first tong [406c] and the second tong [406d] of the pair of tongs [406], move away from each other.
12. The plunging member [410] as claimed in claims 1 to 11, wherein upon manipulation of the plunging member [410] to the first position, during the rack-in operation of the withdrawable drawer unit [116] corresponding to the racked-in position of the withdrawable drawer unit [116], the plunging member [410] is pushed inside the cavity [412], and the plunger base [410a] compresses the spring member [408], and the shaft [410b] manipulates the pair of tongs [406], such that pair of tongs [406] are actuated and pushed towards each other, and due to the alignment of the pair of tongs [406] with the plurality of notches [704], the safety shutter plates [700] slide towards each other such that plurality of slits [702] of each of the pair of safety shutter plates [700] align with each other to open the through passage.
13. The plunging member [410] as claimed in claims 1 to 11, wherein upon manipulation of the plunging member [410] in the second position, during rack-out operation of withdrawable drawer unit [116], corresponding to a racked-out position of the withdrawable drawer unit [116], the spring member [408] decompresses, pushing the plunger base [410a] out of the cavity [412], and the shaft [410b] manipulates the pair of tongs [406], such that pair of tongs [406] are pushed away from each other, and due to misalignment of the pair of tongs [406] with the plurality of notches [704], the safety shutter plates [700] slide away from each other, causing the plurality of slits [702] of each of the pair of safety shutter plates [700] to misalign with each other thereby closing the through passage.