SWITCHING DEVICE FOR ELECTRIC POWER SYSTEM

FIELD OF THE INVENTION

The present invention generally relates to a switching device for an electric power system,

and in particular to an outdoor vacuum circuit breaker and an opening spring system

contained therein.

BACKGROUND OF THE INVENTION

A switching device is a key device for an electric power system. A typical switching device,

especially a switching device for a medium- voltage or a high- voltage electric power system,

such as a medium- voltage or a high- voltage vacuum circuit breaker, includes a switching

portion and operating mechanisms. The switching portion includes a current conducting

circuit, an insulation system and a casing. The operating mechanisms include a link lever

system and an operating system, with the operating system controlling the open and close of

the circuit via the link lever system.

Fig. 1 shows a typical switching device for an electric power system, i.e. a vacuum circuit

breaker, generally including: pole rods 1 and a base casing 11. Each of the pole rods 1

includes a vacuum chamber 2, a moveable contact 3, a fixed contact 21, an insulated link rod

4, an upper pole envelop 19, and a lower pole envelop 22. The base casing 11 includes a

supporting bracket 12 for each pole rod, a pin 5 and a sliding- lamina 8 as well as a rail 9 for

each supporting bracket 12, a link lever 6, a driving assembly 7, an opening spring 10. The

driving assembly 7 further includes a magnet 13, a magnetic ring 14, a pipe 15, a coil 16, a

front cap 17, a back cap 18, and an armature 20.

As can be seen in Fig. 1, in a conventional switching device, the insulation is in the form of

an upper pole envelop and a lower pole envelop, with the vacuum chamber 2 and the

insulated link rod 4 enclosed in a closed space formed by the upper pole envelop 19 and the

lower pole envelop 22. Each of the supporting brackets 12 is provided with its major part in

the base 11 and a rail 9 runs in it near the lower end. A pin 5 is provided in a guiding slot of a

corresponding rail 9 and moves up and/or down along the slot. A pin 5 is hinged with one

end of a sliding- lamina 8, and the other end of the sliding- lamina 8 is hinged to one of three

points uniformly provided on the link lever 6. One of the three hinge points one the link

lever 6 is in the different side from the other two with respect to the driving assembly 7. The

portion of the link lever in the driving assembly 7 is coaxially bonded with the armature 20,

and may axially move together with the armature 20 along the cylinder formed by the coil 16

and the magnetic ring 14 etc.

Fig. 1 shows that the switching device is in an open state. Wherein, no current flows in the

coil 16, the armature 20 is subjected to a large static holding force generated by the magnet

13, so that the moveable contact 3 and the fixed contact 21 are in a stably separated state.

When the switching device is to be closed, a current is provided to the coil 16 in a certain

direction to generate a strong magnetic field, so that the resultant force exerted to the

armature 20 is directed to the left. Accordingly, the armature 20 moves together with the link

lever 6 to left. This movement will cause the end of the sliding- lamina 8 hinged to the link

lever 6 move to left, while the other end hinged to the pin 5 (and thus the pin 5) moves up

along the guiding slot of the rail 9 and pushes the supporting bracket 12 to move up, which

in turn pushes the insulated link rod 4 connected with the bracket 12 to move up, thereby

bring the fixed contact 21 in contact with the moveable contact 3 and close the switching

device. At this point, the opening spring 10 is stretched and reset potential energy is stored

therein.

When the switching device is to be opened, a current in reversed direction is provided to the

coil 16 to generate a reverse magnetic field which will compensate the magnetic force

exerted to the armature 20. Therefore, the armature 20 will move to right under the elastic

force of the opening spring 10 and brings the bracket 12 to move down via the

sliding- lamina 8, the rail 9 and the pin 5 thereby separate the movable contact 3 from the

fixed contact 21 to open the switching device.

In the above switching device, the opening spring 10 is arranged beside the link lever 6 and

is substantially parallel to the link lever 6. One end of the opening spring 10 is secured to a

joint 101 provided on the right side of the base 11. The other end of the opening spring 10 is

connected with the link lever 6 at a joint 102 through a pin. In the closed position of the

switching device, the opening spring 10 is stretched. When it is to be opened, the stretching

force of the spring brings the link lever 6 to move to right swiftly. A dumping element 23 is

provided at a position opposite to the link lever 6 on the right side of the base 11. When the

link lever 6 moves to right swiftly and strikes the damping element 23, the kinetic energy of

the link lever 6 is absorbed.

For most switching devices for an electric power system, especially medium- voltage or

high- voltage vacuum CBs, the opening speed can be very high, generally about 1.5m/s and

sometimes up to 2.0m/s. The striking force between the link lever and the dumping element

is accordingly very high. Furthermore, during an opening, the portion of the link lever from

the joint 102 to the right end thereof is subjected to a pressing force. The large pressing force

and the long pressed portion of the link lever intend to cause mechanical deformation to the

link lever 6, thereby degrading mechanical parameters, such as the synchronization among

different phases, the spacing and overrun of the contacts, and shortening the device lifetime.

In addition, the opening spring locates beside the link lever, that is, locates at one side of the

link lever, so the link lever is subjected to a lateral pulling force in addition to an axial force,

which further facilitates the mechanical deformation shortens the device lifetime. The

lifetime of a conventional switching device is within 10,000 open/closes.

In addition, in the above switching device, the installation of the opening spring 10 is

complicated. And the spring is often broken at the joints with the base 11 and the link lever 6,

which increases cost of manufacturing and maintenance.

SUMMARY OF THE INVENTION

In view of the above problems in the conventional switching device, an object of the present

invention is to provide a switching device for an electric power system which eliminates the

disadvantages of the prior art. In the switching device according to the present invention, the

mechanical characteristic is improved, the lifetime of the device is prolonged, the structure

of the device is simplified and the cost of manufacturing and maintenance is lowered.

In one aspect of the present invention, there is provided a switching device for an electric

power system, comprising a conducting part to close or open a circuit and operating

mechanisms to control the close or open operation of the conducting part, said operating

mechanisms comprising a link lever and at least one opening spring, characterized in that:

the link lever engages with one end of the at least one opening spring through the at least one

opening spring, such that the at least one opening spring is compressed when the switching

device is closed, and that the elastic force of the compressed at least one opening spring is

used to open the conducting part when the switching device is to be opened.

According to an embodiment of the present invention, the switching device further

comprises a damping means, such that one end of the link lever strikes on the damping

means during the open operation so as to absorb the kinetic energy of the link lever.

According to an embodiment of the present invention, the link lever is engaged to each of

the at least one opening spring at a location close to the end of the link lever striking on the

damping means, while the other end of the opening spring is secured at a location far from

this striking end and is not engaged with the link lever.

According to an embodiment of the present invention, a pin is provided at the joint of the

link lever and the at least one opening spring, the pin penetrates the link lever

perpendicularly and is secured to the link lever, and the connecting end of the at least one

opening spring with the link lever abuts against said pin.

In another aspect of the present invention, there is provided an operating mechanism for a

switching device, comprising a link lever and at least one opening spring, characterized in

that: the link lever engages with one end of the at least one opening spring through the at

least one opening spring, such that the at least one opening spring is compressed when the

switching device is closed, and that the elastic force of the compressed at least one opening

spring is used to separate the contacts when the switching device is to be opened.

According to an embodiment of the present invention, the switching device further

comprises a damping means, such that one end of the link lever strikes on the damping

means during the open operation so as to absorb the kinetic energy of the link lever.

According to an embodiment of the present invention, the link lever is engaged to each of

the at least one opening spring at a location close to the striking end of the link lever striking

on the damping means, while the other end of the opening spring is secured at a location far

from this striking end and is not engaged with the link lever.

According to an embodiment of the present invention, a pin is provided at the joint of the

link lever and the at least one opening spring, in which the pin penetrates the link lever

perpendicularly and is secured to the link lever, and the engaging end of the at least one

opening spring with the link lever abuts against said pin.

According to a preferred embodiment of the present invention, the switching device is a

three-phase outdoor vacuum circuit breaker.

According to a preferred embodiment of the present invention, the switching device is a

single-phase outdoor vacuum circuit breaker.

BRIEF DESCRIPTION OF THE DRAWINGS

The preferred embodiments of the present invention will be more clearly understood from

the following detailed description taken in conjunction with the accompanying drawings.

The drawings merely illustrate the preferred embodiments of the present invention but not

intend to limit the present invention to the embodiments.

Fig. 1 shows a typical outdoor vacuum circuit breaker in the prior art;

Fig. 2 shows a switching device according to an embodiment of the present invention,

wherein the switching device is provided on an outdoor wire pole; and

Fig. 3 is an enlarged view of the link lever guided opening spring system in the switching

device according to an embodiment of the present invention.

The drawings are not necessarily to scale. And to avoid obscure the inventive steps of the

present invention, some commonly used parts of conventional circuit breakers are omitted.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The present invention will be described with respect to the preferred embodiments.

Fig. 2 shows a three-phase outdoor vacuum circuit breaker for the electric power system

according to an embodiment of the present invention which is installed on a wire pole. As

shown in Fig. 2, the circuit breaker includes: an operation box 1, a mechanism box 2, an

enclosed pole 3, an open/close operating handle 4 and an energizing handle 5 located on a

side of the mechanism box 2. The vacuum circuit breaker is firmly installed on an

installation bracket 6. In the enclosed pole 3, contact elements are provided to control the

open/close of a circuit. The contact elements are in an enclosed vacuum chamber to quench

an arc generated between the contact elements during opening of the circuit. The contact or

separation of the contact elements is driven by driving mechanisms provided in the

mechanism box 2. The driving mechanisms comprise a link lever, a driving crank, and an

opening/closing spring etc. (not shown). The operation of the driving mechanisms is

controlled by operating parts in the operation box 1. The operating parts may comprise an

opening push button and a closing push button for manual operation, and a means for

automatic operation, and may further comprise an energizing mechanism for manually

energizing, an energizing motor for automatically energizing, and an power means (such as a

power spring), etc. Before the circuit breaker is activated, an operator operates the energizing

handle to energize the power means, or the energizing motor energizes the power means.

Once the energizing operation is completed, the operator may operate the close operating

handle to operate the operating parts in the operation box 1, the operating parts in turn

operate, via the driving mechanisms in the mechanism box, the contact elements in the

vacuum chamber to contact with each other so as to close the circuit. The above operation

may also be performed by automatic operating means in the operation box 1. When the

circuit is to be opened, the operator may operate the opening handle to separate the contact

elements so as to interrupt the circuit. Similarly, the operation may also be performed by the

automatic operating means in the operation box 1.

Fig. 3 is a section view of the mechanism box 2 which shows in enlarged view the opening

spring system in the switching device according to an embodiment of the present invention.

As can be seen in Fig. 3, the mechanism box 2 has an integral link lever 21 for linking the

three driving cranks 22 for the three phases respectively. Movement of the link lever 21

makes the three driving cranks 22 move in phase, thus achieving a synchronized open/close

for the three phases. A connecting hole 221 is provided in each crank 22 at a position near

the inflecting corner, through which a pin passes to hinge the crank 22 to the supporting

bracket, such that the crank may rotate around the pin. The lower end 222 of the crank 22 is

hinged to the link lever by a pin, such that the crank and the link lever may rotate with

respect to each other around the pin. The upper end 223 of the crank 22 is hinged to the

insulated link rod by a pin, such that the crank and the insulated link rod may also rotate with

respect to each other around the pin. The link lever 21 penetrates a vertical baffle plate 25

arranged in the mechanism box. The vertical baffle plate 25 is used to support and improve

the strength of the mechanism box. The vertical baffle plate 25 is secured in the mechanism

box 2 and is not movable.

An opening spring 20 is arranged on the link lever 21 such that the link lever 21 penetrates

the opening spring 20, that is, the opening spring 20 is wound around the link lever 21. A

hole 211 is provided at a position near the left end of the link lever 21 and a pin is fixed in

the hole. A rigid pad 212 is provided on right side of the pin. The pad 212 is stopped by the

pin and is not movable to left with respect to the link lever 21. The left end of the opening

spring 20 abuts against the rigid pad 212 and the right end abuts against the vertical baffle

plate 25 directly.

An oil damper 23 is provided on the left side of the mechanism box. During opening, the left

end of the link lever strikes the oil damper and the kinetic energy of the link lever is

absorbed by the oil damper.

Fig. 3 shows a situation in which the circuit breaker is in its closed state and the link lever 21

is hold in a position to the right by the closing mechanism (not shown). Since the link lever

21 moved to right, the opening spring 20 is compressed and the energized. When the

switching device is to be opened, the link lever is released by the closing mechanism and

moves to left swiftly under the drive of the opening elastic force, which drives the crank to

rotate clockwise around the pin 221 so that the upper arm 233 moves downwards and

separates the contacts via the insulated link rod (not shown), thereby interrupt the circuit.

When the link lever 21 moves to bear the leftmost end of the stroke, the left end of the link

lever 21 strikes the oil damper 23 and the kinetic energy is absorbed by the oil damper, so

the link lever gets into a static state quickly.

With the above described structure, those skilled in the art may understand that, firstly,

during an opening process, the portion of the link lever to the right of the hole 211 (which

asserts most of the length of the link lever) is subjected to an axially stretching force, which

never cause mechanical deformation, such as bending, to the link lever. Only the portion of

the link lever to the left of the hole 211 (merely asserts a tiny portion of the length of the link

lever) is subjected to an axially compressing force. Due to the tiny length, there can be

hardly any deformation to this portion. Therefore, the mechanical deformation of the link

lever caused by the opening spring in the prior art is overcome, the performance of the

switching device is improved and the lifetime of the switching device is significantly

prolonged.

Secondly, in the above embodiment, since the link lever is provided through the opening

spring, the link lever is adapted to define the direction of the elastic force exerted by the

opening spring in addition to driving the three phase driving cranks, that is, the link lever 21

is a guide link lever. With such a structure, all applied to the link lever 21 by the opening

spring 20 is axial force without any radial force, which further avoids the mechanical

deformation of the link lever caused by radial force. Accordingly, the performance of the

switching device is improved and the lifetime of the switching device is significantly

prolonged.

In addition, due to the design of the opening spring system with the compressing spring

guided by the link lever, the opening spring 20 can be installed in the system by just abutting

the opening spring between the vertical baffle plate 25 and the pad 212. Therefore, the

construction of the switching device is simplified and the manufacturing cost is reduced.

Meanwhile, in the above structure, the problem that the connection between the spring and

the connecting joint is easy to be broken is avoided and therefore the maintenance cost is

lowered.

It is obvious that the outdoor vacuum circuit breaker according to the present invention is not

limited to the above structure. For example, the link lever 21 may include flange provided at

the corresponding position instead of the hole 211 and the rigid pad 212. The flange should

be large enough to prevent the spring from moving to left. Thus, the object of the present

invention may also be achieved.

Similarly, the right end of the opening spring may abut against a part other than the vertical

baffle plate 25, so as to make the right end of the spring fixed.

Moreover, two opening springs may be provided on the upper and lower sides or the left and

the right sides of the link lever respectively. The right end of each spring abuts against a

fixed part and the left end applies a force to the link lever through a mediate means (such as

a long pin penetrating the link lever perpendicularly to connect the left ends of the springs

with the part of the pin at sides of the link lever). With such a construction, the mechanical

deformation of the link lever caused by the spring system in the prior art is also overcome,

the performance of the switching device is improved and the lifetime of the switching device

is prolonged. Furthermore, the force applied to the link lever by the opening springs is also a

purely axial force without any radial force. Therefore, the mechanical deformation of the link

lever caused by a radial force is further avoided, the performance of the switching device is

improved and the lifetime of the switching device is prolonged.

While the present invention has been described with respect to a three-phase outdoor

vacuum circuit breaker, the present invention is not limited to the above description. Those

skilled in the art may understand that the present invention may be adapted to many other

applications, such as a single phase circuit breaker, an indoor circuit breaker, as well as other

situation where a link lever driven by a spring is used. Therefore, the scope of the present

invention is defined by the accompanying claims other than above description.