NL2016852B1

NL2016852B1 - Pressure-operated load switch

Info

Publication number: NL2016852B1
Application number: NL2016852A
Authority: NL
Inventors: Wu Guocheng; Hu Weifeng
Original assignee: Zhuhai Comking Electric Co Ltd
Priority date: 2015-12-14
Filing date: 2016-05-30
Publication date: 2019-09-16
Also published as: CN105390328A; NL2016852A

Abstract

The invention discloses a pressure-operated load switch, which includes a load switch mechanism and a grounding switch mechanism. The pressure-operated load 5 switch may realize a function of opening and closing the grounding switch mechanism under the condition that there is short-circuit current or failure current in a circuit, so that the shortcoming that a maintainer may overhaul the load switch mechanism only by closing the grounding switch mechanism under the condition of cutting off power is overcome.

Description

Technical field of the invention

The invention relates to the field of electrical equipment, and in particular to a pressure-operated load switch.

Background of the invention

A pressure-operated load switch and combined electrical apparatus, a three-phase alternating current 10kV and 50Hz indoor high-voltage switching device, is widely applied to area network construction and transformation projects, industrial and mining enterprises, high-rise buildings, public facilities and the like, may be used as a loop network power supply or terminal, and plays an role in electric energy distribution, control and protection. A pressure-operated load switch in a conventional art adopts a round copper bar as a grounding switch, a fixed contact adopts copper clips, and the load switch is closed when the copper bar is clamped by the two copper clips of the fixed contact; and however, such a copper clip manner may provide only low contact pressure, and opening and closing operation is implemented completely by manpower, so that a live opening and closing function of the grounding switch may not be realized. There is another pressure-operated load switch, its combined apparatus is assembled with a grounding switch mechanism with an opening and closing capability, and the pressure-operated load switch is linked with a grounding switch through a crank arm and a connecting rod, so that there exists tedious mounting, unreliable performance and interlocking adjustment difficulty.

Summary of the invention

In view of this, the invention provides a pressure-operated load switch with an improved structure.

A pressure-operated load switch of the invention is structured by the following technical solution, the pressure-operated load switch including a load switch mechanism and a grounding switch mechanism, wherein the load switch mechanism includes a frame and three phases of electric connecting components, and the three phases of electric connecting components are all fixedly connected with the frame; the grounding switch mechanism is grounded through a wire, and includes a grounding switch bracket, an operating shaft and three phases of grounding components arranged on the operating shaft in a sleeving manner; the grounding switch bracket is fixedly connected with the frame; and the operating shaft transversely penetrates through the grounding switch bracket, and may rotate in through holes of the grounding switch bracket, positions of the three phases of grounding components and the three phases of electric connecting components correspond one to one, and the operating shaft may drive the three phases of grounding components and the three phases of electric connecting components to contact or be separated in a rotating process.

Preferably, the pressure-operated load switch further includes an interlocking mechanism connected between the load switch mechanism and the grounding switch mechanism; and the interlocking mechanism may prevent one of the load switch mechanism and the grounding switch mechanism from being closed.

Preferably, the grounding switch mechanism further includes a connecting rod, and the connecting rod penetrates through the three phases of grounding components to connect the three phases of grounding components in series.

Preferably, each electric connecting component includes an upper support part, a moving contact pedestal, a switch master busbar and a fixed contact; the frame, the upper support parts, the moving contact pedestals, the switch master busbars and the fixed contacts are fixedly connected in sequence; each grounding component includes a grounding switch, connecting plates, driving plates, an upper pressure spring seat, a pressure spring, a lower pressure spring seat, connecting plate limiting pins, an upper pressure spring seat fixing pin and a lower pressure spring seat fixing pin; each grounding switch includes two blades, and a distance between the two blades is smaller than a width of each fixed contact; each connecting plate is arranged on the operating shaft in the sleeving manner, and is fixedly connected with the corresponding two blades; the driving plates are arranged on the operating shaft in the sleeving manner, and are arranged on the two sides of connecting plates; two ends of the pressure springs are fixed on the upper pressure spring seats and the lower pressure spring seats respectively, the upper pressure spring seats are fixedly connected with the driving plates through the upper pressure spring seat fixing pins, and the lower pressure spring seats are movably connected with the grounding switch bracket through the lower pressure spring seat fixing pins; and the operating shaft drives the driving plates and the connecting plates to rotate when rotating, the driving plates compress the pressure springs in a rotating process, the pressure springs may continue driving the operating shaft to rotate after being compressed under the action of restoring force, and the connecting plates drive the grounding switches and the fixed contacts to contact or be separated.

Preferably, each grounding component further includes Belleville springs; and the Belleville springs penetrate through the two blades of the grounding switch for fixed connection therewith.

Preferably, first curved limiting grooves are formed in lower ends of the connecting plates; and inwards-sunken circular arcs are formed at two ends of the first limiting grooves, and radiuses of the circular arcs at the two ends are the same as radiuses of the connecting plate limiting pins.

Preferably, second curved limiting grooves are formed in lower ends of the driving plates; and each second limiting groove is formed by three sections of circular arcs, inwards-sunken circular arcs are formed at two ends, an outwards-raised circular arc is formed in middle, and radiuses of the circular arcs at the two ends are the same as radiuses of the upper pressure spring seat fixing pins.

Preferably, the load switch mechanism further includes a load switch operating shaft, and the interlocking mechanism includes an interlocking piece, guide bolts, an upper interlocking plate and a lower interlocking plate; the interlocking piece is a waist-shaped piece, two ends are shaped into outwards-raised semicircles, and the semicircles at the two ends are coaxial; the guide bolts horizontally penetrate through waist-shaped holes in a body of the interlocking piece and the frame, and are fixed between the interlocking piece and the frame through nuts; the upper interlocking plate is coaxially fixed on the load switch operating shaft, and a first inwards-sunken cambered limiting hole with a radius the same as that of the semicircle at the upper end of the interlocking piece is formed in its circular edge; and the lower interlocking plate is coaxially fixed on the grounding switch operating shaft, and a second inwards-sunken limiting hole with a radius the same as that of the semicircle at the lower end of the interlocking piece is formed in its circular edge.

The invention has beneficial effects as follows:

1: the pressure-operated load switch of the invention may realize a function of opening and closing the grounding switch mechanism under the condition that there is short-circuit current and failure current in a circuit, so that the shortcoming that a maintainer may overhaul the load switch mechanism only by closing the grounding switch mechanism under the condition of cutting off power is overcome;

2: the three-phase grounding switch mechanism is connected in series through the connecting rod, so that operation synchronism of the grounding switches in opening and closing processes of the grounding switches and the fixed contacts is ensured, and an arcing phenomenon is avoided;

3: the pressure springs and the Belleville springs adopted in each phase of the grounding switch mechanism and interference contact between the two blades of each grounding switch and the fixed contacts increase contact pressure between the grounding switches and the fixed contacts, so that burning contact of the fixed contacts or the arcing phenomenon caused by insufficient contact force and vibration between the grounding switches and the fixed contacts under a heavy current condition is avoided; and

4: by the interlocking mechanism, a five-prevention protection requirement of electrical equipment is met.

Brief description of the drawings

Fig. 1 is a front view of a pressure-operated load switch according to embodiment 1;

Fig. 2 is a bottom view of a grounding switch mechanism of a pressure-operated load switch according to embodiment 1;

Fig. 3 is a top view of a grounding switch mechanism of a pressure-operated load switch according to embodiment 1;

Fig. 4 is a side view of a grounding switch mechanism of a pressure-operated load switch in a closed state according to embodiment 1;

Fig. 5 is a section view of a grounding switch mechanism of a pressure-operated load switch in an open state according to embodiment 1;

Fig. 6 is a section view of a grounding switch mechanism of a pressure-operated load switch in a closed state according to embodiment 1;

Fig. 7 is a section view of a grounding switch mechanism of a pressure-operated load switch in a closing switching point state according to embodiment 1;

Fig. 8 is a section view of a grounding switch mechanism of a pressure-operated load switch in an opening switching point state according to embodiment 1;

Fig. 9 is a state diagram of an interlocking mechanism in a closed state of a grounding switch mechanism of a pressure-operated load switch according to embodiment 1; and

Fig. 10 is a state diagram of an interlocking mechanism in an open state of a load switch mechanism of a pressure-operated load switch according to embodiment

1.

Detailed description of the embodiments

In order to make the technical solution and technical effect of the invention clearer, a specific implementation mode of the invention will be described below with reference to the drawings and an embodiment in detail.

Embodiment 1:

As shown in Fig. 1 to Fig. 10, a pressure-operated load switch in the invention includes a load switch mechanism 1, a grounding switch mechanism 2, an interlocking mechanism 3 and an operating handle (not shown in the figures).

The load switch mechanism 1 includes a frame 11, three phases of electric connecting components 12 and a load switch operating shaft 13. The three phases of electric connecting components 12 are connected with three phases of power of a power grid respectively, the three phases of electric connecting components 12 are all fixedly connected with the frame 11, and each phase of electric connecting component 12 includes an upper support part 12-1, a moving contact seat 12-2, a switch master busbar 12-3 and a fixed contact 12-4. The upper support parts 12-1 are horizontally fixed with the frame 11 by nuts; the moving contact seats 12-2 are perpendicularly fixed on the upper support parts 12-1; and the switch master busbars 12-3 are horizontally fixed with the moving contact seats 12-2 by nuts, and perpendicularly extend downwards. The fixed contacts 12-4 are horizontally fixed on inner lateral surfaces of the switch master busbars 12-3 of each phase. The load switch operating shaft 13 is horizontally fixed on the frame 11.

The grounding switch mechanism 2 includes a grounding switch bracket 21, a grounding switch operating shaft 22, three phases of grounding components 23 and a connecting rod 24; the grounding switch operating shaft 22 may drive the three phases of grounding components 23 and the three phases of electric connecting components 12 to contact and be separated in a rotating process. Positions of each phase of grounding component 23 and each phase of electric connecting component 12 correspond one to one, and each phase of grounding component 23 includes a grounding switch 23-1, Belleville springs 23-2, connecting plates 23-3, driving plates 23-4, an upper pressure spring seat 23-5, a pressure spring 23-6, a lower pressure spring seat 23-7, connecting plate limiting pins 23-8, an upper pressure spring seat fixing pin 23-9 and a lower pressure spring seat fixing pin 23-10.

The grounding switch bracket 21 is fixed below the frame 11, and includes a transverse plate 21-1, first vertical plates 21-2 and second vertical plates 21-3. The transverse plate 21-1 is horizontally arranged, the first vertical plates 21-2 are arranged at two ends of the transverse plate 21-1 and perpendicularly fixed therewith, and the second vertical plates 21-3 are perpendicularly fixed on the transverse plate 21-1 between the two first vertical plates 21-2 in pairs at intervals. The grounding switch bracket 21 is connected to the ground through a wire (not shown) connected with it.

The grounding switch operating shaft 22 is cylindrical, and an operating handle limiting groove 22-1 penetrating through two ends is axially formed in a lateral surface. A section of the operating handle limiting groove 22-1 in the embodiment is a sector passing through a circle centre, and may also be another noncircular shape, such as a square or a polygon. The grounding switch operating shaft 22 penetrates through the first vertical plates 21-2 and the second vertical plates 21-3 in parallel with the transverse plate 21-1, and may rotate in through holes of the first vertical plates 21-2 and the second vertical plates 21-3. When the operating handle rotates to further drive the grounding switch operating shaft 22 to rotate, since a rib on the operating handle is meshed with the operating handle limiting groove 22-1, the operating handle limiting groove 22-1 may limit the operating handle to avoid relative rotation of the operating handle and the grounding switch operating shaft 22.

The connecting plates 23-3 are arranged on the grounding switch operating shaft 22 between the second vertical plates 21-3 of each pair in a sleeving manner. A first curved limiting groove 23-3-1 is formed in an upper end of each connecting plate 23-3, inwards-sunken circular arcs are formed at two ends of each first limiting groove 23-3-1, and radiuses of the circular arcs at the two ends are the same as radiuses of the connecting plate limiting pins 23-8.

Each grounding switch 23-1 includes two blades 23-1-1, and the two blades 23-1-1 are fixed with the corresponding connecting plates 23-3 through a nut and a bolt; and the two blades 23-1-1 are provided with Belleville spring fixing holes, a Belleville spring 23-2 is arranged on an outer side of each of the blades 23-1-1, and the Belleville springs 23-2 penetrate through the Belleville spring fixing holes and are fixed through nuts. A distance between each pair of grounding switches 23-1 is smaller than a width of each fixed contact 12-4.

Two ends of the pressure springs 23-6 are fixed on the upper pressure spring seats 23-5 and the lower pressure spring seats 23-7 respectively. Lower parts of the connecting plates 23-3 are arranged in through grooves in middle of the upper pressure spring seats 23-5, and are fixedly connected with the upper pressure spring seats 23-5 through the upper pressure spring seat fixing pins 23-9. The lower pressure spring seats 23-7 are arranged between the second vertical plates 21-3 of each pair, each lower pressure spring seat fixing pin 23-10 penetrates through the corresponding lower pressure spring seat 23-7 and the corresponding two vertical plates 21-3 to movably connect the lower pressure spring seat 23-7 with the second vertical plates 21-3, and the lower pressure spring seat 23-7 may rotate around the lower pressure spring seat fixing pin 23-10 between the two second vertical plates 21-3.

The driving plates 23-4 are arranged between the connecting plates 23-3 and the adjacent second vertical plates 21-3. Second curved driving grooves 23-4-1 are formed in lower ends of the driving plates 23-4, each second driving groove 23-4-1 is formed by connecting three sections of circular arcs, inwards-sunken circular arcs are formed at two ends, an outwards-raised circular arc is formed at middle, and radiuses of the circular arcs at the two ends are the same as radiuses of the upper pressure spring seat fixing pins 23-9.

The connecting rod 24 is cylindrical, is arranged in parallel with the grounding switch operating shaft 22, transversely penetrates through overlapped parts of the connecting plates 23-3 and the grounding switches 23-1, and is fixed with the grounding switches 23-1.

The interlocking mechanism 3 includes an interlocking piece 31, guide bolts 32, an upper interlocking plate 33 and a lower interlocking plate 34. The interlocking piece 31 is a waist-shaped piece, two ends are shaped into outwards-raised semicircles, and the semicircles at the tow ends are coaxial; and the guide bolts 32 horizontally penetrate through waist-shaped holes in a body of the interlocking piece 31 and the frame 11, and are fixed between the interlocking piece 31 and the frame 11 through nuts. The upper interlocking plate 33 is coaxially fixed on the load switch operating shaft 13, and a first inwards-sunken cambered limiting hole 33-1 with a radius the same as that of the semicircle at the upper end of the interlocking piece 31 is formed in its circular edge; and the lower interlocking plate 34 is coaxially fixed on the grounding switch operating shaft 22, and a second inwards-sunken cambered limiting hole 34-1 with a radius the same as that of the semicircle at the lower end of the interlocking piece 31 is formed in its circular edge.

An opening and closing working principle of the grounding switch mechanism of the pressure-operated load switch is as follows:

during closing, the operating handle is arranged on the grounding switch operating shaft 22 in the sleeving manner, the operating handle is rotated clockwise (direction P in Fig. 5) to drive the driving plates 23-4 and connecting plates 23-3 arranged on the grounding switch operating shaft 22 in the sleeving manner to rotate clockwise, the inwards-sunken circular arcs on right sides of the lower ends of the driving plates 23-4 drive the upper pressure spring seat fixing pins 23-9 to rotate clockwise, the pressure springs 23-6 are compressed in a clockwise rotating process of the upper pressure spring seats 23-5, the upper pressure spring seat fixing pins 23-9 break limiting of left edges of the inwards-sunken circular arcs on right sides of the second driving grooves 23-4-1 when axle centers of the upper pressure spring fixing seats 23-9 rotate to the same straight line where an axle center of the grounding switch operating handle 22 and axle centers of the lower pressure spring seat fixing pins 23-10 are located, and upper ends of the pressure springs 23-6 outwards extend under the action of restoring force to drive the grounding switch operating shaft 22 to continue rotating clockwise until the upper pressure spring seat fixing pins 23-9 are limited by left edges of the inwards-sunken circular arcs on left sides of the second driving grooves 23-4-1; and meanwhile, the connecting plates 23-3 also rotate clockwise along with the grounding switch operating shaft 22, the two blades of each grounding switch 23-1 clamp the fixed contacts 12-4 in a process of rotating clockwise along with the connecting plates 23-3, the fixed contacts 12-4 form interference contact with the grounding switches 23-1 because the widths of the fixed contacts 12-4 are more than the distance between the two blades, and pressure provided by the Belleville springs 23-3 the left and right blades increases contact force between the grounding switches 23-1 and the fixed contacts 12-4 to make them closely contact to avoid burning damage of the fixed contacts 12-4 or an arcing phenomenon caused by insufficient contact force and vibration between the grounding switches 23-1 and the fixed contacts 12-4 under a heavy current condition. The switch master busbars 12-3, the fixed contacts 12-4, the grounding switches 23-1, the grounding switch bracket 21, the wire and the ground form a charge loop, and charges of the load switch mechanism 1 flow to the ground through the loop. A closing process of the pressure-operated load switch is shown in Fig. 5—>Fig. 7—>Fig.

6.

During opening of the grounding switch, the operating handle is rotated counterclockwise, and a working process of each part is a reverse process during closing, and will not be elaborated herein; and the opening process is shown in Fig. 6^Fig. 8^Fig. 5.

As shown in Fig. 9, in the closing process of the grounding switch, the lower interlocking plate 34 fixed with the grounding switch operating shaft 22 also rotates clockwise at the same time of clockwise rotation of the grounding switch operating shaft 22, the second limiting hole 34-1 rotates clockwise until limiting of the interlocking piece 31 is released, the semicircular arc at the lower end of the interlocking piece 31 is driven by the clockwise rotating circular arc of the lower interlocking plate 34 to move upwards until the semicircular arc at the upper end of the interlocking piece 31 falls into the first limiting hole 33-1 of the upper interlocking plate 33, and the load switch operating shaft 13 is limited by the interlocking piece 31, and may not rotate. Therefore, a “five-prevention” protection requirement that “closing of a circuit breaker or a load switch during closing of a grounding switch is forbidden” in the field of electrical equipment is met.

As shown in Fig. 10, similarly, when the load switch operating shaft 13 is rotated clockwise, the upper interlocking plate 33 simultaneously rotates clockwise, the first limiting hole 33-1 rotates clockwise until limiting of the interlocking piece 31 is released, the semicircular arc at the upper end of the interlocking piece 31 is driven by the clockwise rotating semicircular arc of the upper interlocking plate 33 to move downwards until the semicircular arc at the lower end of the interlocking piece 31 falls into the second limiting hole 34-1 of the lower interlocking plate 34, and the grounding switch operating shaft 22 is limited by the interlocking piece 31, and may not rotate. Therefore, a “five-prevention” protection requirement that “closing of a grounding switch during closing of a load switch is forbidden” in the field of electrical equipment is met.

The guide bolts 32 allow the interlocking piece 31 to move up and down only.

From the abovementioned working process, it can be seen that the grounding switch mechanism 2 is grounded through the wire, the load switch mechanism 1 is grounded when the grounding switches 23-1 and the fixed contacts 12-4 contact, and the pressure-operated load switch in the embodiment may realize a function of opening and closing the grounding switch mechanism 2 under the condition that there is short-circuit current and failure current in a circuit, so that the shortcoming that a maintainer may overhaul the load switch mechanism 1 only by closing the 5 grounding switch mechanism 2 under the condition of cutting off power is overcome;

and moreover, the connecting rod 24 connects the three phases of grounding switches 23-1 in series, so that operation synchronism of the grounding switches 23-1 in opening and closing processes of the grounding switches 23-1 is ensured, and an arcing phenomenon is avoided.

The above is only the preferred embodiment of the invention and not intended to limit the invention, and for those skilled in the art, the invention may have various modifications and variations. Any modifications, equivalent replacements, improvements and the like made within the spirit and principle of the invention shall fall within the scope of protection of the invention.

Claims

Conclusions:

A pressurized load switch comprising a load switch mechanism (1) and an earthing switch mechanism (2), the load switch mechanism (1) including a frame (11) and three phases of electrical connection components (12), the three electrical connection components (12) all fixedly connected to the frame (11), in which the grounding switch mechanism (2) is grounded via a wire and a grounding switch bracket (21), a control shaft (22) and three phases of grounding components (23) mounted on the control shaft (22) as in a cover; the grounding switch bracket (21) is rigidly connected to the frame (11); and the control shaft (22) transversely pierces the grounding switch bracket (21); and can rotate in holes of the grounding switch clamp (21), the positions of the three phases of grounding components (23) and the three phases of electrical connection components (12) corresponding one to the other and the operating axis (22) the three can contact or separate phases of grounding components (23) and the three phases of electrical connection components (12) in a turning process.

The pressurized load switch according to claim 1, further comprising a coupling mechanism (3) between the load switch mechanism (1) and the earthing switch mechanism (2), wherein the coupling mechanism (3) can prevent one of the load switch mechanism (1) and the earthing switch mechanism (2) is closed.

The pressurized load switch according to claim 1 or 2, wherein the grounding switch mechanism (2) further comprises a connecting rod (24) and the connecting rod (24) extends through the three phases of grounding components (23) around the three phases of grounding components ( 23) to connect in series.

The pressurized load switch according to claim 1, wherein each electrical connection component (12) comprises a superimposed support member (12-1), a moving contact seat (12-2), a switch master busbar (12-3) and a fixed contact (12-4) ), wherein the frame (11), the upper support members (12-1), the moving contact seats (12-2), the switch master bus bars (12-3) and the fixed contacts (12-4) are fixedly connected to each other, wherein each grounding component (23) a grounding switch (23-1), connecting plates (23-3), drive plates (23-4), an upper compression spring seat (23-5), a compression spring (23-6), a lower compression spring seat (23 -7), limit pins (23-8) for the connecting plates, a locking pin (23-9) for the upper compression spring seat and a locking pin (23-10) for the lower compression spring seat, each earthing switch (23-1) having two blades (23 -1-1) and the distance between the two blades is narrower than a width of each fixed contact (12-4);

each connecting plate (23-3) is mounted on the operating shaft (22) as in a sleeve and fixedly connected to the corresponding two blades (23-1-1);

the drive plates (23-4) are mounted on the operating shaft (22) as in a sleeve and are arranged on two sides of the connecting plates (23-3);

two ends of the compression springs are attached to the upper compression spring seat (23-5) and the lower compression spring seat (23-7) respectively, the upper compression spring seats (23-5) being fixedly connected to the drive plates (23-4) by means of the locking pins (23-9) for the upper compression spring seats and the lower compression spring seats (23-7) are movably connected to the grounding switch bracket (21) by means of the locking pins (23-10) for the lower compression spring seats;

the control shaft (22) drives the drive plates (23-4) and the connecting plates (23-3) to rotate and while rotating the drive plates (23-4) press the compression springs (23-6) in a turning process, the compression springs (23 -6) being able, after being depressed, to further rotate the actuating shaft (22) by a spring action and the connecting plates (23-3) driving the earth switches (23-1) and the fixed contacts to make contact or to break.

The pressurized load switch according to claim 4, wherein each grounding component (23) further comprises Belleville springs (23-2) and the Belleville springs (23-2) extend through the two blades of the grounding switch (23-1) to be firmly connected.

The pressurized load switch according to claim 4, wherein first curved boundary grooves (23-3-1) are formed in lower ends of the connecting plates (23-3); and recessed circular arcs are formed at two ends of the first boundary grooves (23-3-1) and the radius of curvature of the circular arcs at the two ends are the same as curvature radiuses of the boundary pins (23-8) for the connecting plates.

The pressurized load switch according to claim 4, wherein second curved drive grooves (23-4-1) are formed in lower ends of the drive plates (23-4), and each second curved drive groove (23-4-1) is formed by three sections of circular arcs, with inwardly recessed circular arcs formed at two ends and an outwardly raised circular arc formed at the center and the curvature rays of the circular arcs at the two ends being the same as curvature rays of the locking pins (23-9) for the upper compression spring seats.

The pressurized load switch according to claim 2, wherein the load switch mechanism (1) further comprises a load switch operating shaft (13) and the coupling mechanism (3) a coupling part (31), guide bolts (32), an upper coupling plate (33) and a lower includes coupling plate (34);

the coupling part (31) is a waist-shaped part, two ends formed as outwardly projecting semi-circular arcs, the semi-circular arcs being coaxial;

the guide bolts (32) protrude horizontally through waist-shaped holes in a body of the coupling part (31) and the frame (11) and are fixed between the coupling part (31) and the frame (11) by means of screws;

the upper coupling plate (33) is coaxially fixed on the load switch operating shaft (13) and a first recessed slightly curved hole (33-1) with a radius of curvature which is the same as that of the semicircular arc at the upper end of the coupling part (31) is at its circular edge;

the lower coupling plate (34) is coaxially secured on the grounding switch operating shaft (22) and a second inwardly recessed limit hole (34-1) with a radius of curvature which is the same as that of the semicircular arc at the lower end of the coupling part (31) is formed on its circular edge.