Trip device of circuit breaker

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a trip device of a circuit breaker to break such a high current as short-circuit current as quickly as possible.

2. Description of the Background Art

There is a circuit breaker which is enclosed in a casing formed of an insulating molding. The circuit breaker is composed of switching contacts, an operating mechanism which opens/closes the switching contacts, a trip device which automatically releases a trip latch mechanism, when overcurrent flows, for working the operating mechanism to open the switching contacts, and an arc-extinguishing device for irresistibly extinguishing arc which is generated when the switching contacts are opened so as to break the current.

Generally, in an electric circuit, if the circuit breaker breaks an enormous abnormal current which occurs due to a short-circuit accident in the electric circuit as immediately as possible to limit the current flowing through the circuit to a small magnitude, the damage to the electric circuit can be made minimum and accordingly the damage to the circuit breaker itself can be reduced. Therefore, the circuit breaker which can more speedily break the short-circuit current can accordingly break a high short-circuit current immediately, so that the rated breaking capacity thereof can be increased.

The electromagnet is applied to a trip device of a conventional circuit breaker which operates upon occurrence of a short-circuit current. The electromagnet operates when the current flowing through a main circuit conductor of the circuit breaker exceeds a predetermined threshold so as to release the trip latch mechanism included in the operating mechanism and thus open the switching contacts.

Such an electromagnet is slow in operation due to inertia of a movable core, and thus it is impossible to break more speedily the short-circuit current when the current exceeds a threshold. In particular, when an enormous abnormal current flows to cause the switching contacts to repel each other due to the electromagnetic force and consequently the switching contacts are opened, the contacts could be brought into contact again unless the trip latch mechanism is immediately released. In such a case, the circuit breaker itself could suffer a great damage.

SUMMARY OF THE INVENTION

One object of the present invention is to provide a trip device of a circuit breaker which can speedily operate in a reliable manner.

According to an aspect of the present invention, a trip device of a circuit breaker operates the circuit breaker that includes switching contacts, an operating mechanism which opens and closes the switching contacts, a trip latch mechanism which works the operating mechanism when released to open the switching contacts, and a housing which encloses at least the switching contacts. The trip device includes a pressure detection space having a wall portion with a repeatedly usable thin plate, an operating rod which protrudes from the pressure detection space when the pressure in the pressure detection space increases, and a return spring which returns the operating rod. The pressure detection space is arranged in the vicinity of the switching contacts, and the operating rod is arranged to release the trip latch mechanism when it protrudes.

In such a structure, when a great abnormal current flows to cause electromagnetic repulsion force and accordingly the switching contacts are opened, arc gas of high temperature and pressure is instantaneously generated and thus the wall portion having the thin plate of the pressure detection space is pressurized. The thin plate then yields to the pressure so that the internal pressure increases to cause the operating rod to protrude and accordingly release the trip latch mechanism. Consequently, the operating mechanism works immediately to complete the tripping operation. During this operation, the arc gas just directly pressurizes the thin plate which surrounds the pressure detection space, and any piece of metallic material that is melted in the vicinity of the switching contacts due to high temperature does not interrupts the movement according to the operating mechanism. In addition, the arc gas itself does not work the trip latch mechanism in order to release it, therefore, the trip latch mechanism and its surroundings are not exposed to the arc gas. After the abnormal current is broken, the arc gas disappears so that the internal pressure of the housing of the switching contacts becomes the atmospheric pressure to return the thin plate to its original shape. As a result, the internal pressure of the pressure detection space returns to its original state, the operating rod is also returned by the return spring, and accordingly, a waiting state to prepare for the next breaking operation starts.

According to another aspect of the invention, the pressure detection space of the trip device of the circuit breaker in the above one aspect of the invention is placed in a cavity which is formed within a wall of the housing, and a through hole is formed at a wall which separates the cavity containing the pressure detection space from the housing enclosing the switching contacts. Any special material or space for arranging the pressure detection space is thus unnecessary and the structure is simplified.

According to still another aspect of the invention, the pressure detection space of the trip device of the circuit breaker in the above one aspect of the invention is composed of a cavity which is formed within a wall of the housing, a through hole which is made at a wall which separates the cavity from the housing, and a thin plate formed to close the through hole.

The wall of the housing itself can be utilized as the pressure detection space, and thus a simplified structure is realized.

According to the another and still another aspects of the invention concerning the trip device of the circuit breaker, the circuit breaker is of a multipole type which has switching contacts in each pole, and a pressure detection space common to different poles adjacent to each other is placed at a wall of the housing which separates the adjacent poles. The structure is thus simplified since the trip device need not be provided at each pole.

In the trip device of the circuit breaker according to any aspect of the invention, a small opening is provided to the pressure detection space so as to allow the outside air to flow. Accordingly, the pressure detection space can easily be returned after pressurization.

The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1

is a cross sectional side view illustrating an ON state of a circuit breaker provided with a trip device of an embodiment of the invention;

FIG. 2

is a cross sectional side view illustrating a tripped state of the circuit breaker shown in

FIG. 1

;

FIG. 3

is a perspective view of the trip device shown in

FIG. 1

which is detached from the circuit breaker;

FIG. 4

is a plan view of the trip device shown in

FIG. 1

which is detached from the circuit breaker;

FIG. 5

is a side view of the trip device shown in

FIG. 1

which is detached from the circuit breaker, illustrating a state in which a pressure detection space of the trip device is not pressurized;

FIG. 6

is a side view of the trip device shown in

FIG. 1

which is detached from the circuit breaker, illustrating a state in which the pressure detection space is pressurized; and

FIG. 7

illustrates an insertion opening for mounting the trip device of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to

FIGS. 1 and 2

illustrating a circuit breaker of three-pole type having a trip device of an embodiment, a casing constituted of a mold base

1

and a mold cover

2

that are made of insulating molding houses a main circuit conducting section including switching contacts, an operating mechanism for operating the switching contacts, a trip device for working the operating mechanism to open the switching contacts when an overcurrent flows, and an arc-extinguishing device for extinguishing arc which is generated when the current is broken by opening of the switching contacts.

The main circuit conducting section includes a connection terminal

3

associated with the power supply, a stationary contact base

5

having power supply connection terminal

3

at one end and a stationary contact

4

at the other end, a movable contact arm

7

having a movable contact

6

at one end which is associated with stationary contact

4

, a flexible conductor

9

connected between the other end of movable contact arm

7

and a bent plate

8

, a heater

11

of an inverted U shape having one end fixed to mold base

1

together with bent plate

8

and the other end connected to one end of a terminal conductor

10

, and a load connection terminal

12

located at the other end of terminal conductor

10

. Those components are provided to each pole.

Movable contact arm

7

is pivotally held by a contact holder

14

with a pin

13

and biased anticlockwise by a contact pressure spring

15

. Contact holder

14

of each pole has its end held by a cross bar

16

of insulating material shared by respective poles. Three poles are simultaneously moved with cross bar

16

around a center of rotation of cross bar

16

as a point of support, by an operation of the operating mechanism common to these poles described later.

The operating mechanism is composed of an operating handle

17

formed of insulating material which is protruded from an opening of mold cover

2

, an operating lever

18

having a shallow U shape cross section to which operating handle

17

is attached, a trip lever

19

having an engaging end

19

a

at one end, a hook

20

having an engaging piece

20

a

associated with engaging end

19

a

, a trip shaft

22

having a claw

21

for stopping rotation of hook

20

by engagement with it, a secured flame

26

which pivotally supports operating lever

18

, trip lever

19

and hook

20

respectively by pins

23

,

24

and

25

and pivotally supports trip shaft

22

, a pair of toggle links

27

and

28

, a pin

29

which couples toggle link

27

with the central upper end of trip lever

19

, a pin

30

which couples toggle links

27

and

28

, and an operating spring

31

placed between the upper end of operating lever

18

and pin

30

. One end of toggle link

28

is coupled with pin

13

.

In this embodiment, the circuit breaker is provided with both a conventional trip device and a trip device of the invention. Each of the trip devices operates when the overcurrent flows so as to rotate trip shaft

22

. The conventional trip device is placed at each pole, and composed of a bimetal

33

attached to heater

11

such that its free end is opposed to a first trip piece

32

which is provided to each pole, an electromagnet formed of a stationary core

34

and a movable core

35

both placed to surround heater

11

, a pin

36

which pivotally supports movable core

35

, and a setting spring

37

which biases movable core

35

clockwise to make it apart from stationary core

34

.

Referring to

FIGS. 3

to

6

, a trip device

38

of the invention includes a pressure detection space constituted of a pressure receiving chamber

40

formed by sticking a pair of symmetrical insulating moldings together, and a piston chamber

41

. The pressure detection space is substantially closed. The insulating molding includes a shallow box-shaped portion having an almost rectangular frame portion

40

a

with some thickness as a side wall and having a thin plate portion

40

b

as a bottom. The insulating molding further includes a semi-cylindrical portion as made by cutting a cylinder along its center axis. The insulating moldings of the pair are opposed to each other and attached at their frame portions

40

a

and walls of the semi-cylindrical portions, producing pressure receiving chamber

40

corresponding to a space similar to a rectangular parallelepiped that is constituted of opposing thin plate portions

40

b

and attached frame portions, and piston chamber

41

formed as a cylinder.

The material and dimension of the insulating moldings are selected such that they have certain elasticity which allows thin plate portion

40

b

of pressure receiving chamber

40

to yield to the pressure of the arc gas generated at each breaking operation and return close to its original state upon depressurization, and they have a property which is not so significantly altered under the influence of a high temperature arc gas.

Piston chamber

41

has a hole

41

a

at its bottom to allow air flow to and from pressure receiving chamber

40

, a hole

41

b at its top for an operating rod

43

with its details given below, and a small hole

41

c

on its side to allow outside air to flow therethrough which is described below. When the insulating moldings of the pair are attached, piston chamber

41

is provided with a piston

42

which freely moves along its inner wall, operating rod

43

which is fixed to piston

42

and projects through an opening of piston chamber

41

, and a return spring

44

which biases piston

42

inward, such that those components are enclosed in piston chamber

41

. For discharging the air inside the piston chamber and for introducing the outside air, a tube

39

is placed at small hole

41

c.

If thin plate portion

40

b

of pressure receiving chamber

40

is pressurized, the internal pressure increases to bias piston

42

against the action force of return spring

44

and accordingly push out operating rod

43

. Operating rod

43

then pushes a second trip piece

47

placed at trip shaft

22

to initiate a tripping operation. At this time, the air inside piston chamber

41

is discharged through tube

39

and thus the air pressure in the piston chamber does not increase. Therefore, piston

42

speedily moves and the tripping operation is initiated immediately. If thin plate portion

40

b

is depressurized, the elasticity of thin plate portion

40

b

as well as the action force of return spring

44

allow pressure receiving chamber

40

and piston chamber

41

to return to their original states. When piston

42

of the piston chamber returns, the outside air is introduced through tube

39

so that the air pressure inside the piston chamber does not decrease and thus the piston is sure to return immediately.

Referring to

FIG. 7

, trip device

38

is inserted through a long and narrow opening

45

formed on the back of mold base

1

to be installed in a cavity formed in an inter-pole wall

46

of mold base

1

that separates a center pole and an end pole on either side. Pressure receiving chamber

40

of trip device

38

thus installed is located on the side of the switching contacts of the circuit breaker, and piston chamber

41

of trip device

38

is located such that operating rod

43

is opposite to the second trip piece

47

placed at trip shaft

22

as shown in

FIGS. 1 and 2

. Further, on both sides of inter-pole wall

46

at which pressure receiving chamber

40

is located, a large hole

48

is formed. Pressure receiving chamber

40

is thus interposed between the center pole and the end pole at the location of hole

48

and accordingly the poles are separated.

The arc-extinguishing device composed of a plurality of magnetic material plates

50

held between opposite insulation plates

49

is provided to each pole. The arc-extinguishing device functions to attract the arc generated upon opening of the switching contacts to magnetic material plates

50

by a magnetic function and accordingly extinguish the arc by a cooling function of magnetic material plates

50

.

An operation of a circuit breaker having such structure is now described below.

FIG. 1

illustrates an ON state of the circuit breaker in which movable contact

6

is in contact with stationary contact

4

(shown by the solid line). In this state, trip lever

19

is biased anticlockwise via toggle link

27

by the function of operating spring

31

, causing engaging end

19

a

to engage with the lower edge of engaging piece

20

a

of the hook

20

to push hook

20

clockwise. This pushing then causes the side surface of the lower right portion of engaging piece

20

a

to engage with claw

21

placed at trip shaft

22

, and accordingly, trip shaft

22

is biased clockwise. These engaging relations are maintained since stopper means (not shown) is provided for preventing trip shaft

22

from further rotating clockwise from the shown position.

Operating handle

17

is biased anticlockwise by the function of operating spring

31

since pin

29

is located on the right side of the acting line of force of operating spring

31

, while operating handle

17

is hindered from rotating by pin

24

of trip lever

19

. Toggle links

27

and

28

are now substantially stretched, contact holder

14

is rotated anticlockwise via pin

13

, and movable contact

6

is in contact with stationary contact

4

. In this state of contact, a sufficient contact pressure is exerted by contact pressure spring

15

.

In the ON state shown in

FIG. 1

, an OFF operation for opening the switching contacts of the circuit breaker is initiated by rotating operating handle

17

clockwise to move the acting line of force of operating spring

31

over a dead point positioned near pin

29

, toggle link pin

30

is then pulled to the light, and toggle links

27

and

28

bend in dogleg form. As a result, contact holder

14

rotates clockwise (not shown) to separate movable contact

6

from stationary contact

4

. An ON operation is done in reverse order.

A tripping operation is next described that is initiated by an operation of the trip device to open the switching contacts.

When a relatively small overcurrent flows through the circuit breaker, heater

11

is overheated to curve bimetal

33

to the left. After a relatively long time has passed, a screw attached to the free end of bimetal

33

pushes the first trip piece

32

to rotate trip shaft

22

anticlockwise. This rotation disengages claw

21

from engaging piece

20

a

to rotate hook

20

clockwise, and accordingly engaging piece

20

a

is disengaged from engaging end

19

a

to rotate trip lever

19

anticlockwise. This rotation of trip lever

19

moves pin

29

to the left side of the acting line of force of operating spring

31

. When pin

29

moves over the dead point, toggle link pin

30

is pulled to the right and toggle links

27

and

28

are bent in a dogleg form, and consequently, the switching contacts are opened as shown in FIG.

2

. It is noted that hook

20

and trip shaft

22

are biased clockwise by a return spring (not shown) having a weak action force. Therefore, they are returned as shown in FIG.

2

.

In the tripped state shown in

FIG. 2

, operating handle

17

is positioned between the ON position and the OFF position. If operating handle

17

is rotated clockwise, a reset operation is realized to establish engagement between engaging end

19

a

and engaging piece

20

a

of the main hook and between engaging piece

20

a

and claw

21

of the trip shaft.

When a relatively high overcurrent such as the one having a value higher than a value set by setting spring

37

flows, a leg of the lower portion of movable core

35

is attracted to stationary core

34

by an electromagnetic attraction force substantially in an instant. Movable core

35

thus rotates anticlockwise, and its arm of the upper portion pushes the first trip piece

32

to rotate trip shaft

22

. As a result, the switching contacts are opened as done by bimetal

33

. Although the operation caused by the electromagnet is mentioned above as done in an instant, there is a considerable delay since a relatively large and heavy movable core is employed in order to set a high current value and generate the force to rotate trip shaft

22

, and therefore the inertia of the movable core is not negligible.

If the overcurrent is like the short circuit current which is quite high compared with the set current value, trip device

38

of the invention operates to rotate trip shaft

22

before movable core

35

starts rotating. Specifically, when such a high current flows, a great electromagnetic repulsion force which exceeds contact pressure by contact pressure spring

15

acts between stationary contact

4

and movable contact

6

. This electromagnetic repulsion force rotates movable contact arm

7

clockwise around pin

13

as shown by the chain line in

FIG. 1

even if the operating mechanism does not work. Consequently, movable contact

6

separates from stationary contact

4

to generate arc of high temperature. This high temperature arc causes partial melting of metal components such as stationary contact

4

, stationary contact base

5

, movable contact

6

, movable contact arm

7

and magnetic material plates

50

, resulting in arc gas containing vaporized metal, and accordingly the pressure around switching contacts increases suddenly. The increased pressure is exerted via hole

48

of inter-pole wall

46

on pressure receiving chamber

40

to pressurize the elastic thin plate portion

40

b

. The volume of pressure receiving chamber

40

thus decreases and accordingly the pressure therein increases. As a result, piston

42

moves upward together with operating rod

43

to push the second trip piece

47

and rotate trip shaft

22

immediately.

After the current is broken, the pressure around switching contacts decreases to reach the atmospheric pressure, thin plate portion

40

b

returns nearly to its original state, and piston

42

and operating rod

43

are also returned to their original states by the function of return spring

44

. Since the opening of tube

39

is located remotely from the region around switching contacts, the air taken into piston chamber

41

is a fresh and low temperature outside air. Therefore, the returning operation of trip device

38

is not interrupted by metal fractions generated when the current is broken. Trip device

38

is thus sure to operate even if an enormous current flows again.

A pair of insulating moldings each having the integrally shaped thin plate portion and frame portion constitutes pressure receiving chamber

40

of trip device

38

of the invention by attachment of the frame portions. Alternatively, thin plates having such an elastic modulus as that of the thin plate portions described above may be attached to both sides of a frame having a certain thickness to produce the pressure receiving chamber. Instead, the cavity in the inter-pole wall

36

may be utilized as the pressure receiving chamber by attaching a thin plate having the elasticity as described above to hole

48

of inter-pole wall

46

, sealing opening

45

for inserting the trip device of the invention, and installing the piston mechanism at inter-pole wall

46

such that the piston mechanism is opposite to the second trip piece

47

. Although the thin plate of the pressure detection space of the invention could be exposed to the high temperature arc gas as discussed above, the thin plate is pressurized with a considerably high pressure and the pressurized time period is short. Therefore, the thin plate of a small elastic modulus may be selected if it has an adequate heat-resistant property.

Although pressure receiving chamber

40

and piston chamber

41

are composed of a pair of integral moldings in this embodiment, they may separately be fabricated and connected by a pipe.

In addition, considering that the pressure of the entire housing of the switching contacts instantaneously increases upon occurrence of the arc, it is not necessarily required to place pressure receiving chamber

40

on the side of the switching contacts.

Although the present invention has been described and illustrated in detail, it is clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation, the spirit and scope of the present invention being limited only by the terms of the appended claims.