CIRCUIT BREAKER

TECHNICAL FIELD

The present invention relates to a circuit breaker that has an overcurrent protection function and a ground fault protection function and is applicable to a low voltage distribution system.

BACKGROUND ART

As known in this field, circuit breakers applied to a low voltage distribution system are classified into molded case circuit breakers (MCCB) having an overcurrent protection function and earth leakage circuit breakers (ELCB) having an overcurrent protection function and an earth fault protection function.

The molded case circuit breaker has the structure in which functional components, such as a main circuit contact, a switching mechanism, an operation handle, and an overcurrent tripping device are provided in a breaker main case (molded resin case). Meanwhile, the earth leakage circuit breaker has the structure including a zero current transformer that detects an unbalanced current of a main circuit using the main circuit as a primary conductor, an earth leakage detecting circuit (an electronic circuit including an IC) that detects the occurrence of an earth fault from the secondary output level of the zero current transformer, and a trip coil unit that receives an output signal of the earth leakage detecting circuit and trips the switching mechanism of the breaker, in addition to the same functional components for overcurrent protection as those in the molded case circuit breaker. In addition, as power for controlling the earth leakage detecting circuit, an interphase voltage of the main circuit is generally rectified and supplied to the earth leakage detecting circuit.

In addition, the main stream of the domestically-produced general-purpose products of the molded case circuit breaker and the earth leakage circuit breaker is the structure in which the molded case circuit breaker and the earth leakage circuit breaker are provided in main cases with the same size and common components having a protection function are provided in the main cases, in order to improve user convenience.

In the molded case circuit breaker and the earth leakage circuit breaker, the interphase dielectric strength of the main circuit is defined as a standard. In the test, a test voltage (high voltage) is externally applied to measure the dielectric strength of the breaker, with the contact of the main circuit of the breaker being open. In this case, in the earth leakage circuit breaker, the earth leakage detecting circuit composed of an electronic circuit is connected to the control power supply circuit which is branched and connected to the main circuit. Therefore, in order to protect the earth leakage detecting circuit from the test voltage, it is necessary to disconnect the earth leakage detecting circuit from the main circuit during the withstand voltage test. In order to satisfy the requirements, an earth leakage circuit breaker has been proposed which additionally includes a switch (a switch for a dielectric test) for a withstand voltage test which is connected to the switching mechanism of the earth leakage circuit breaker, turns off the switch to disconnect the power supply circuit from the earth leakage detecting circuit during the withstand voltage test, forcibly mechanically trips the switching mechanism of the breaker in conjunction with the operation of the switch to turn off the main circuit contact, and restricts and maintains the breaker in the off state (for example, see Patent Document 1).

CITATION LIST

PATENT DOCUMENT

Patent Document 1: Japanese Patent Application Laid-Open (JP-A) No. 2007-317361

DISCLOSURE OF INVENTION

PROBLEMS TO BE SOLVED BY THE INVENTION

However, for the circuit breaker used in the low voltage power distribution facility, generally, the user selects the molded case circuit breaker or the earth leakage circuit breaker according to conditions, such as the kind of power distribution facility and the kind of load used. However, when newly starting up the power distribution facility, generally, the user uses the earth leakage circuit breaker to check whether a leakage current (earth fault current) is generated from the power distribution circuit and the amount of leakage current and then switches the breaker to the molded case circuit breaker in order to prevent the operation of a load (for example, a motor) from stopping due to the trip of the breaker by a small leakage current. In addition, when the load used in the power distribution facility is changed, in some cases, the molded case circuit breaker, which has been used, is replaced with the earth leakage circuit breaker according to the kind of load.

However, in the related art, the circuit breakers used in the low voltage distribution system are classified into two types, that is, the molded case circuit breakers and the earth leakage circuit breakers. However, a circuit breaker that enables the user to selectively use the overcurrent protection function and the ground fault protection is not disclosed. In Patent Document 1, the switch for a dielectric test is incorporated into the power supply circuit that supplies power to the earth leakage detecting circuit. However, since the switch for a dielectric test is connected to the switching mechanism of the breaker, it is difficult to invalidate the earth leakage protection function and use the molded case circuit breaker.

Therefore, an object of the invention is to provide a new circuit breaker whose protection function is selectively changed by a simple operation such that the user can use the circuit breaker as a molded case circuit breaker or an earth leakage circuit breaker, if needed.

MEANS FOR SOLVING THE PROBLEM

In order to achieve the object, according to an aspect of the invention, there is provided a circuit breaker that has an overcurrent protection function and an earth fault protection function and has a structure including a main circuit contact, a switching mechanism, an overcurrent tripping device, and an earth leakage tripping device including a zero current transformer and an earth leakage detecting circuit which are provided in a breaker main case. The circuit breaker includes a mode switch unit that turns on or off a contact in a power supply circuit supplying power from a main circuit to the earth leakage detecting circuit to selectively set the earth fault protection function to be "valid" or "invalid" (claim 1). The mode switch unit has the following detailed structure.

(1) In the circuit breaker having the above-mentioned structure, the mode switch unit may include a switch body that is provided in the breaker main case and is connected to a feed circuit between the main circuit and the earth leakage detecting circuit and a push-button-type switching portion that turns on and off a switch through an actuator connected to an operation end of the switch body. In addition, an operation end of the push button of the switching portion is provided on a cover of the breaker main case so as to face the outside (claim 2).

(2) In the item (1), the switch body may be an assembly of a switch case which is made of an insulating material and in which polarities are partitioned, a fixed electrode that has a pair of contacts separated from each other and is provided at a lower part of the switch case, a bridge-shaped movable contact that is provided so as to face the fixed electrode, and an operation rod that collectively holds the movable contacts of each polarity and extends to the upper side of the switch case. The switch body may be arranged in a space between the zero current transformer provided in the breaker main case and a side wall of the breaker main case (claim 3).

(3) In the item (1), the actuator may be a tilting lever combined with an urging spring. The actuator may include a pivot shaft portion and lever arms extending from the pivot shaft portion to both sides. One of the lever arms may be connected to the operation rod of the switch body and the other lever arm may be arranged so as to face the leading end of the push button (claim 4). (4) In the item (1), the switching portion may be an assembly of a push button of a push/twist lock type and a cylindrical guide that is provided on the cover of the breaker main case so as to surround the push button and a return spring of the push button. On a circumferential surface of the cylindrical guide, provided is a vertical slit, to which a protrusion formed on the push button is fitted and which guides the push button in an ON/OFF direction, and further provided is an engaging step portion that extends from a lower end of the slit in a circumferential direction, is engaged with the protrusion, and locks and maintains the push button at a lock position (claim 5).

EFFECTS OF THE INVENTION

According to the above-mentioned structure, it is possible to selectively set the earth fault protection function of the circuit breaker to the "valid" mode or the "invalid" mode only by operating the push button of the mode switch unit provided in the circuit breaker. In this way, the user temporarily changes the earth fault protection function of the circuit breaker to be "valid" in order to check whether a leakage current flows through a distribution circuit of an electric power distribution facility and then changes the earth fault protection function to be "invalid" such that the circuit breaker is used as the molded case circuit breaker. Alternatively, the user may return the "invalid" earth fault protection function of the circuit breaker that has been used as the molded case circuit breaker to the "valid" state such that the circuit breaker can be used as the earth leakage circuit breaker.

BRIEF DESCRIPTION OF DRAWINGS

Fig. 1 is a circuit diagram illustrating a circuit breaker according to an embodiment of the invention.

Fig. 2 is an exploded perspective view illustrating the assembly structure of the circuit breaker shown in Fig. 1.

Fig. 3 is a diagram illustrating the structure of a mode switch unit shown in Fig. 1. Fig. 3(a) is an exploded perspective view illustrating the entire mode switch unit and Fig. 3(b) is a perspective view illustrating a cylindrical guide, as viewed from the lower side.

Fig. 4 is a diagram illustrating the internal structure of a switch body shown in Fig. 3. Figs. 4(a) and 4(b) are diagrams illustrating the on and off states of the switch, respectively.

Fig. 5 is a diagram illustrating the operation of the mode switch shown in Fig. 3. Fig. 5(a) is a diagram illustrating the pulled-up state of a push button and Fig. 5(b) is a diagram illustrating the pushed state of the push button.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, exemplary embodiments of the invention will be described with reference to an example shown in Figs. 1 to 5.

First, Fig. 1 is a circuit diagram illustrating a circuit breaker according to the invention. Reference numeral 1 indicates a main circuit corresponding to phases R, S, and T, reference numeral 2 indicates a main circuit contact, reference numeral 3 indicates a switching mechanism of the main circuit contact 2, reference numeral 4 indicates an operation handle, and reference numeral 5 indicates an overcurrent tripping device that detects an overcurrent and a short-circuit current of the main circuit 1 and that trips the switching mechanism 3. In addition, an earth leakage tripping device, which detects an earth fault current of a power distribution path and trips the switching mechanism 3, includes a zero current transformer 6 that detects an unbalanced current using the main circuit 1 corresponding to each of the phases R, S, and T as a primary conductor, an earth leakage detecting circuit (an electronic circuit including an IC) 7 that detects the occurrence of an earth fault from the secondary output level of the zero current transformer 6, and a trip coil unit 8 that receives an output signal from the earth leakage detecting circuit 7 and trips the switching mechanism 3.

The earth leakage detecting circuit 7 receives the interphase voltages of the main circuits 1 of each phase through power lines 9 that are branched and connected to the main circuits 1 of each phase and a rectifying circuit 10 as control power. A mode switch unit 11 according to the invention is connected to the power supply circuit. The detailed structure of the mode switch unit 11 will be described below. In the example shown in Fig. 1, the voltages between the phases R, S, and T of the main circuits are converted into direct currents and the direct currents are supplied to the earth leakage detecting circuit. However, the voltage between the phases R and T may be supplied to the earth leakage detecting circuit 7.

Fig. 2 shows the overall assembly structure of a circuit breaker provided with the mode switch unit 11. In Fig. 2, reference numeral 12 indicates a breaker main case of the circuit breaker which is divided into a case 12a, a cover 12b, and a top cover 12c. In the breaker main case 12, functional components, such as the switching mechanism 3, the operation panel 4, the overcurrent tripping device 5, the zero current transformer 6, the earth leakage detecting circuit 7, the trip coil unit 8, main circuit conductors 13 corresponding to the phases R, S, and T, an arc-extinguishing chamber 14, and a trip crossbar 15 that receives a mechanical output signal of the trip coil unit 8 and trips the switching mechanism 3, are arranged as shown in Fig. 2.

An assembly of the mode switch unit 11 is provided in a space surrounded by an annular core of the zero current transformer 6, the side wall of the case 12a, and a U-shaped main circuit conductor (phase R) 13 which is fitted to the annular core of the zero current transformer. In addition, a push button 16 for turning on or off the switch body of the mode switch unit 11 is attached to the cover 12b so as to face the mode switch unit and an operation window 12c-1 corresponding to the push button 16 is provided in the top cover 12c.

Next, the detailed structure of the mode switch unit 11 and the push button 16 will be described with reference to Fig. 3. The mode switch unit 11 is an assembly of a switch body 17, an actuator 18 connected to an operation end of the switch body 17, and a unit case 19.

The switch body 17 includes a box-shaped switch case (molded resin case) 17a in which polarities are partitioned by partition walls as shown in Fig. 4, fixed electrodes 17b of each polarity that have a pair of left and right contacts separated from each other and are incorporated into a lower part of the switch case 17a, a bridge-shaped movable contact 17c facing the fixed electrodes 17b, and a movable contact holder 17d serving as an operation rod that collectively holds the movable contacts 17c of each polarity and has an operation end drawn out from the switch case 17a to the upper side. A hook-shaped knob portion 17d-1 is formed at the leading end of the contact holder 17d.

In the above-mentioned structure, when the knob portion 17d-1 is pushed in the direction of an arrow A in Fig. 4(a), the movable contact 17c contacts the fixed electrode 17b and the switch is turned on. When the contact holder 17d is pulled up in the direction of an arrow B in Fig. 4(b), the movable contact 17c is separated from the fixed electrode 17b and the switch is turned off.

As shown in Fig. 3, the switch body 17 is fitted and attached to a switch supporting step portion 19a that is provided at the middle position of the unit case 19. Reference numeral 20 indicates six lead lines that are connected to the fixed electrodes 17b of the switch body 17 and extend from the switch case 17a.

An engaging convex portion 19c is formed on the outer circumferential surface of the unit case 19. As shown in Fig. 2, the engaging convex portion 19c is fitted to an engaging groove 12a-1 that is formed by cutting out the upper edge of the side wall of the case 12a, with the mode switch unit 11 mounted on the main case 12 of the breaker. In this way, the unit case is disposed and maintained at a fixed position.

The actuator 18 is a tilting level having a shaft portion 18a serving as a tiling fulcrum and lever arms 18b and 18c that extend from the shaft portion to both sides as a base. In addition, an urging spring 18d (twisted coil spring) is combined with the shaft portion 18a. The shaft portion 18a is rotatably supported by a bearing portion 19b that is provided at the top of the unit case 19. In this way, the actuator 18 is assembled so as to be tiltable. An engaging arm portion 18e to which the knob portion 17d-1 pulled out from the switch body 17 is hooked is formed at the leading end of the lever arm 18b extending from the shaft portion 18a to the right side. In addition, the lever arm 18c extending from the shaft portion 18a to the left side faces the leading end of the push button 16 provided in the case cover 12b, which will be described below. The urging spring 18d provided in the actuator 18 urges the lever arm 18b in the clockwise direction to push the switch body 17 to an ON position in a free state of the actuator.

The push button 16 is a push/twist lock button, is combined with a return spring 21 (compression coil spring), and is fitted to a cylindrical guide 22 that is formed integrally with the cover 12b of the main case 12. At the fitting position, the leading end of the push button 16 faces the lever arm 18c of the actuator 18.

In addition, a groove into which the tip of a screwdriver (tool) is inserted is formed at the head of the push button 16. An engaging protrusion 16a formed at the leading end of a shaft portion which extends from the top to the lower side is engaged with the leading end of the cylindrical guide 22. In this way, the push button 16 is retained. A guide protrusion 16b is formed on the circumferential surface of the top of the push button 16, and a vertical guide slit 22a and an engaging step portion 22b extending from the end of the slit 22a in the circumferential direction are formed on the circumferential surface of the cylindrical guide 22 so as to correspond to the protrusion 16b (see Fig. 3(b)). In this way, the push button 16 is guided in a pressing direction and the push button 16 is locked and maintained at the pressing position by a push/twist operation.

Next, the operation and function of the mode switch unit 11 and the push button 16 will be described with reference to Figs. 5(a) and 5(b). That is, in the initial state of the circuit breaker shipped from a manufacturer, as shown in Fig. 5(a), the push button 16 is pressed to the upper side of the cylindrical guide 22 by the elastic force of the return spring 21. In this state, the actuator 18 of the mode switch unit 11 is tilted in the clockwise direction by the elastic force of the urging spring 18d (see Fig. 3) to push down the movable contact holder 17d (see Fig. 4) of the switch body 17, thereby maintaining the contact in an ON state. In this way, the main circuit 1 and the earth leakage detecting circuit 7 shown in Fig. 1 are connected to each other through the power lines 9. The phase voltage of the main circuit 1 is converted into a DC voltage by the rectifying circuit 10 and is then supplied to the earth leakage detecting circuit 7. Therefore, in this state, the circuit breaker "validates" the earth fault protection function and serves as an earth leakage circuit breaker.

When a tool, such as a screwdriver, is used to push and twist the push button 16 in the direction of the arrow A in Fig. 5(b), the leading end of the push button 16 contacts and presses the actuator 18 of the mode switch unit 11 to drive the lever arm 18c in the counterclockwise direction. In addition, the protrusion 16b provided at the top of the push button 16 is fitted to the engaging step portion 22b formed in the cylindrical guide 22 and is then locked and maintained at the pressing position by the elastic force of the return spring 21. The actuator 18 is pushed by the push button 16 and is restricted and maintained at that position.

In this way, as shown in Fig. 4(b), when the contact holder 17d is pulled up in the direction of the arrow B, the contact is turned off in the switch body 17, and the circuit of the power line 9 shown in Fig. 1 is disconnected. As a result, the earth leakage detecting circuit 7 is disconnected from the main circuit 1 and the function of the earth leakage circuit breaker is removed. The circuit breaker "invalidates" the earth fault protection function and serves as a molded case circuit breaker.

In order to supply a main circuit voltage to the earth leakage detecting circuit 7 to make the circuit breaker function as the earth leakage circuit breaker, the push button 16 is twisted in a direction opposite to the above-mentioned direction outside the breaker case. Then, the protrusion 16b of the push button 16 is separated from the engaging step portion 22b of the cylindrical guide 22 and is then fitted to the guide slit 22a. Then, the push button 16 is pushed up by the elastic force of the return spring 21. Then, the lever arm 18c of the actuator 18 pushed by the push button 16 is tilted in the clockwise direction by the elastic force of the urging spring 18d and the lever arm 18b pushes the movable contact holder 17d of the switch body 17. In this way, the switch returns to the ON state. As a result, the earth leakage detecting circuit 7 is receives the voltage from the main circuit 1 and the circuit breaker functions as the earth leakage circuit breaker.

As can be seen from the above description, it is possible to turn on or off the switch contact of the mode switch unit 11 connected to the power supply circuit between the main circuit 1 and the earth leakage detecting circuit 7 shown in Fig. 1 and set the earth fault protection function of the circuit breaker to be "valid" or "invalid", in cooperative association with the operation of pushing or releasing the push button 16. In this way, the user can use the circuit breaker provided in a power distribution facility as the earth leakage circuit breaker or the molded case circuit breaker, if needed.

In addition, when the withstand voltage test (dielectric test) is performed for the circuit breaker while the circuit breaker is used as the earth leakage circuit breaker, the mode switch unit 11 is turned off to disconnect the earth leakage detecting circuit of the electronic circuit from the main circuit of the circuit breaker such that the earth leakage detecting circuit can be safely protected from a test voltage.

INDUSTRIAL APPLICABILITY

According to the invention, it is possible to provide a new circuit breaker whose protection function can be selectively switched by a simple operation and which can be used as a molded case circuit breaker or an earth leakage circuit breaker by the user, if needed.

DESCRIPTION OF REFERENCE NUMERALS AND SIGNS

1:

MAIN CIRCUIT

2:

MAIN CIRCUIT CONTACT

3:

SWITCHING MECHANISM OF MAIN CIRCUIT CONTACT

5:

OVERCURRENT TRIPPING DEVICE

6:

ZERO CURRENT TRANSFORMER

7:

EARTH LEAKAGE DETECTING CIRCUIT

8:

TRIP COIL UNIT

9:

POWER LINE OF EARTH LEAKAGE DETECTING CIRCUIT

11:

MODE SWITCH UNIT

12:

BREAKER MAIN CASE

16:

PUSH BUTTON

17:

SWITCH BODY

17b:

FIXED ELECTRODE

17c:

MOVABLE CONTACT

17d:

MOVABLE CONTACT HOLDER

18:

ACTUATOR

19:

UNIT CASE

21:

RETURN SPRING

22:

CYLINDRICAL GUIDE