UNDERVOLTAGE TRIP DEVICE OF CIRCUIT BREAKER AND OVERVOLTAGE AND UNDERVOLTAGE TRIP DEVICE

BACKGROUND

The present invention relates to an undervoltage trip device used in a circuit breaker for a commercial power supply.

An undervoltage trip device is configured to stop the supply of power from a commercial power supply when voltage becomes lower than a predetermined voltage.

Fig. 10 shows an example of a conventional undervoltage trip device. A rectification circuit 1 performs full-wave rectification on the voltage of a commercial power supply AC to generate full-wave rectified voltage Vrec. Excitation current Ic, which corresponds to the full-wave rectified voltage Vrec, is supplied to the coil 3, which is wound around an electromagnet core 2. A sensitivity adjustment element 4 connects the commercial power supply AC to the rectification circuit 1. The sensitivity adjustment element 4 is a capacitor or a resistor. A capacitor having a large capacitance and serving as a delay time setting element 5 is connected between the two terminals of the coil 3.

A movable plunger 6 is urged away from the core 2 by a spring 7. When the coil 3 is supplied with current, the movable plunger 6 is magnetically attracted to the core 2. A breaker device 8 functions to stop the supply of power VL to a load device when the urging force of the spring 7 separates the movable plunger 6 from the core 2.

Referring to Fig. 11, the movable plunger 6 is continuously attracted to the core 2 against the urging force of the spring 7 when the voltage of the commercial power supply AC has a substantially normal level and the excitation current Ic flowing to the coil 3 is greater than or equal to a threshold It. Under this situation, the load device is supplied with the power VL.

The movable plunger 6 is separated from the core 2 due to the urging force of the spring 7 when the voltage of the commercial power supply AC decreases and the excitation current Ic becomes lower than the threshold It. In this case, the breaker device 8 functions to stop the supply of power VL to the load device.

The sensitivity adjustment element 4 is arranged to adjust a threshold voltage of the commercial power supply AC that separates the movable plunger 6 from the core 2. The delay time setting element 5 is arranged to set a delay time from when the excitation current Ic output from the rectification circuit 1 becomes lower than the threshold It to when the breaker device 8 functions to separate the movable plunger 6 from the core 2.

Japanese Laid-Open Patent Publication Nos. 2003-308775 and 2005-135690 each disclose an undervoltage trip device similar to that described above. Japanese Laid-Open Patent Publication No. 61-124222 discloses an undervoltage trip device that supplies the coil with excitation current only under a fault condition.

SUMMARY

In a conventional undervoltage trip device, the magnetic characteristics of the core 2 and the plunger 6 and the shape and condition of attraction surfaces of the core and the plunger affect the threshold voltage of the commercial power supply AC that separates the movable plunger 6 from the core 2. To set the desired sensitivity for the undervoltage trip device in relation with changes in the voltage of the commercial power supply AC, high accuracy would be needed to manufacture the core 2 and the movable plunger 6. The manufacturing process of the core and the plunger includes, for example, annealing magnetic members for forming the core and the plunger, polishing the attraction surfaces of the core and the plunger, and controlling a gap between the attraction surfaces. Such high accuracy manufacturing process increases the cost of the core and the movable plunger.

Further, it is complicated and difficult to adjust the sensitivity of the undervoltage trip device in relation to changes in the voltage of the commercial power supply AC with the sensitivity adjustment element 4. In addition, a capacitor having a large capacitance would be needed for the delay time setting element 5 to produce desired delays. Such a capacitor would enlarge the trip device and increase component costs.

It is an object of the present invention to provide an undervoltage trip device that has stabilized voltage sensitivity and a sufficient delaying capability, and allows for reductions in size and cost.

One aspect of the present invention is an undervoltage trip device for a circuit breaker. The undervoltage trip device includes an undervoltage detection unit configured to compare a voltage corresponding to a voltage of a power supply with a first threshold voltage and output an undervoltage detection signal. A delay unit is configured to output an excitation current interruption signal when the undervoltage detection signal is continuously output over a predetermined time or longer. A switch circuit is configured to interrupt an excitation current of a coil in accordance with the excitation current interruption signal. An interruption mechanism is configured to interrupt the supply of power from the power supply to a load device when the excitation current to the coil is interrupted. The undervoltage detection unit includes a first comparator configured to compare a comparison voltage, which changes when the voltage of the commercial power supply changes, with the first threshold voltage, which is settable to the first comparator. The delay unit includes a capacitor, a charge circuit connected to the capacitor to charge the capacitor when the undervoltage detection signal is received, a discharge circuit that discharges the capacitor when the undervoltage detection signal is not output from the undervoltage detection unit, and a second comparator configured to compare the voltage level of the capacitor with a predetermined second threshold voltage, which is settable to the second comparator, to output the excitation current interruption signal.

The one aspect of the present invention provides an undervoltage trip device that has stabilized voltage sensitivity and a sufficient delaying capability, and allows for reductions in size and cost.

Preferably, the undervoltage detection unit is configured to integrate the voltage of the commercial power supply to calculate an effective value, and compare the effective value with the first threshold voltage to output an undervoltage detection signal.

Preferably, the undervoltage detection unit is configured to integrate the voltage of the commercial power supply to calculate an average voltage value, and compare the average voltage value with the first threshold voltage to output an undervoltage detection signal.

In one embodiment, the switch circuit includes a transistor which is deactivated to interrupt the excitation current in response to the excitation current interruption signal.

In one embodiment, the first threshold voltage of the first comparator and the second threshold voltage of the second comparator are separately settable.

A further aspect of the present invention is an overvoltage-undervoltage trip device for a
circuit breaker. The overvoltage-undervoltage trip device includes a delay time setting undervoltage detection unit configured to compare a voltage corresponding to a voltage of a power supply with a first threshold voltage to generate an undervoltage detection signal and, when the undervoltage detection signal is continuously output over a predetermined time or longer, output an excitation current interruption signal. A delay time setting overvoltage detection unit is configured to compare the voltage corresponding to the voltage of the commercial power supply with a predetermined third threshold voltage to generate an overvoltage detection signal and, when the overvoltage detection signal is continuously output over a predetermined time or longer, output the excitation current interruption signal. A switch circuit is configured to interrupt an excitation current that is supplied to a coil in accordance with the excitation current interruption signal. An interruption mechanism is configured to interrupt the supply of power to a load device •when the excitation current to the coil is interrupted. The delay time setting undervoltage detection unit includes an undervoltage detection unit that includes a first comparator configured to compare a comparison voltage, which changes when the voltage of the commercial power supply changes, with the first threshold voltage, which is settable to the first comparator, to generate the undervoltage detection signal, and a delay unit that receives the undervoltage detection signal from the undervoltage detection unit. The delay unit includes a charge circuit that charges a capacitor when the undervoltage detection signal is received, a discharge circuit that discharges the capacitor when the undervoltage detection signal is not received, and a second comparator configured to compare the voltage level of the capacitor with a predetermined second threshold voltage, which is settable to the second comparator, to output the excitation current interruption signal.

In one embodiment, the first threshold voltage is set to be higher than the comparison voltage when the excitation current decreases and the interruption mechanism thereby stops functioning, and the third threshold voltage is set to be lower than the comparison voltage when the delay time setting overvoltage detection unit and the delay time setting undervoltage detection unit become non-functional.

In one embodiment, the first threshold voltage is equal to or slightly higher than an attractable lower limit voltage and higher than a functional lower limit voltage of the delay time setting overvoltage detection unit and the delay time setting undervoltage detection unit, wherein the attractable lower limit voltage corresponds to a minimum magnetic attraction force generated by the coil to continue supplying power to a load device.

Preferably, the first threshold voltage of the first comparator and the second threshold voltage of the second comparator are separately settable.

As will be appreciated, other aspects, embodiments, and/or configurations of the disclosure are possible utilizing, alone or in combination, one or more of the features set forth above or described in detail below.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention, together with objects and advantages thereof, may best be understood by reference to the following description of the presently preferred embodiments together with the accompanying drawings in which:

Fig. 1 is a block diagram of an undervoltage trip device in a first embodiment;

Fig. 2 is a circuit diagram of an undervoltage detection unit and a delay unit;

Fig. 3 is a timing chart illustrating the operation of the lower voltage detection unit and the delay unit;

Fig. 4 is a circuit diagram of a switch circuit;

Fig. 5 is a block diagram of an overvoltage-undervoltage trip device in a second embodiment;

Fig. 6 is a timing chart illustrating the operation of the trip device shown in Fig. 5;

Fig. 7 is a circuit diagram of a delay time setting overvoltage detection unit;

Fig. 8 is a schematic diagram illustrating the setting of a threshold voltage;

Fig. 9 is a circuit diagram of a switch circuit in another example;

Fig. 10 is a circuit diagram of a conventional undervoltage trip device; and

Fig. 11 is a timing chart illustrating the operation of the undervoltage trip device shown in Fig. 10.

DESCRIPTION OF EMBODIMENTS

A first embodiment of an undervoltage trip device will now be described.

In the undervoltage trip device shown in Fig. 1, a rectification circuit 11 is connected to a commercial power supply AC. The rectification circuit 11 performs full-wave rectification on the voltage of the commercial power supply AC and outputs a full-wave rectified voltage Vrec.

A coil 12 is wound around an electromagnet core 14 and connected between the rectification circuit 11 and the switch circuit 13. The full-wave rectified voltage Vrec is supplied to one end of the coil 12. A capacitor CI, which is connected parallel to the coil 12, slightly smoothens the full-wave rectified voltage Vrec from the rectification circuit 11 to generate excitation current Ic, which is supplied to the coil 12.

A movable plunger 15 is located proximal to the core 14. When the coil 12 is supplied with the excitation current Ic, the movable plunger 15 is magnetically attracted to the core 14. A spring 16 urges the movable plunger 15 away from the core 14. When the urging force of the spring 16 separates the movable plunger 15 from the core 14, a breaker device 17 functions to interrupt the supply of power to a load device. The core 14, the movable plunger 15, and the breaker device 17 may be referred to as an interruption mechanism.

The full-wave rectified voltage Vrec is supplied to a power supply circuit 18. The power supply circuit 18 generates a DC power voltage Vc based on the full-wave rectified voltage Vrec. Then, the full-wave rectified voltage Vrec supplies the DC power voltage Vc to an undervoltage detection unit 19 and a delay unit 20.

The undervoltage detection unit 19 functions when supplied with the DC power voltage Vc. As shown in Fig. 3, when the full-wave rectified voltage Vrec becomes lower than a first threshold voltage Vtl, the undervoltage detection unit 19 generates an undervoltage detection signal Vd having a high level, and provides the undervoltage detection signal Vd to the delay unit 20.

The delay unit 20 integrates the undervoltage detection signal Vd and generates a delay signal SI having a voltage level that corresponds to the integrated undervoltage detection signal Vd. When the voltage level of the delay signal SI becomes higher than a predetermined second threshold Vt2, the delay unit 20 provides the switch circuit 13 with an excitation current interruption signal S2. The excitation current interruption signal S2 switches from a high level to a low level when the voltage level of the delay signal SI is higher than the second threshold voltage Vt2.

The switch circuit 13 functions to interrupt the excitation current Ic when the excitation current interruption signal S2 switches from a high level to a low level. When the excitation current Ic is interrupted, the interruption mechanism interrupts the supply of power VL to a load device.

Fig. 4 shows one example of the switch circuit 13. The excitation current interruption signal S2 is provided via a diode D to the base of an npn transistor Tr3. The collector of the transistor Tr3 is connected to a node between the capacitor CI and the coil 12. The emitter of the transistor Tr3 is connected to ground Vg. Accordingly, when the excitation current interruption signal S2 has a high level, the transistor Tr3 is activated, and the excitation current Ic is supplied to the coil 12. When the excitation current interruption signal S2 has a low level, the transistor Tr3 is deactivated, and the excitation current Ic is interrupted.

The undervoltage detection unit 19 and the delay unit 20 will now be described with reference to Fig. 2.

The undervoltage detection unit 19 is configured to detect undervoltage condition based on a first threshold voltage Vtl and a voltage corresponding to a voltage of a power supply, such as the commercial power supply AC. In the illustrated embodiment, the undervoltage detection unit 19 includes resistors Rl and R2 and a comparator 21. The resistors Rl and R2 are connected in series between a connection point having the full-wave rectified voltage Vrec and ground Vg. The resistors Rl and R2 divide the full-wave rectified voltage Vrec and generate a comparison voltage Vx. The comparator 21 is configured to compare the comparison voltage Vx and a first threshold voltage Vtl. When the comparison voltage Vx becomes lower than the first threshold voltage Vtl, the comparator 21 outputs the undervoltage detection signal Vd having a high voltage.

The delay unit 20 includes an npn transistor Trl, an npn transistor Tr2, a capacitor C2, and a comparator 24. The undervoltage detection signal Vd output from the comparator 21 of the undervoltage detection unit 19 is provided to the base of the npn transistor Trl. Further, the undervoltage detection signal Vd is inverted by an inverter circuit 22 and provided to the base of the npn transistor Tr2.

The collector of the transistor Trl is provided with a constant current from a connection point having the DC power voltage Vc via a constant current source circuit 23. The emitter of the transistor Trl is connected to ground Vg via the capacitor C2.

The emitter of the transistor Trl is connected to the collector of the transistor Tr2 and to a negative input terminal of the comparator 24. The emitter of the transistor Tr2 is connected to ground Vg.

In the delay unit 20, when the undervoltage detection signal Vd has a low level, the transistor Trl is deactivated and the transistor Tr2 is activated. Then, the capacitor C2 is discharged, and the delay signal SI is maintained at a low level.

When the undervoltage detection signal Vd shifts to a high level, the transistor Trl is activated and the transistor Tr2 is deactivated. As a result, the collector current of the transistor Trl charges the capacitor C2, and the voltage level of the delay signal SI starts to rise. The voltage level of the time signal SI may gradually rise up to an upper limit voltage that is lower than the DC power voltage Vc by an amount corresponding to the voltage decrease between the collector and the emitter of the transistor Trl.

Due to such a configuration, the transistor Trl functions as a charge circuit that charges the capacitor C2. The transistor Tr2 functions as a discharge circuit that discharges the capacitor C2. The delay signal SI that has a voltage level corresponding to the charge amount of the capacitor C2 is applied to the negative input terminal of the comparator 24.

The comparator 24 compares the voltage level of the delay signal SI with the second threshold voltage Vt2. When the voltage level of the delay signal SI becomes higher than the second threshold voltage Vt2, the comparator 24 provides the switch circuit 13 with an excitation current interruption signal S2 having a low level.

In response to the low level excitation current interruption signal S2, the switch circuit 13 disconnects the coil 12 and ground Vg. This interrupts the excitation current Ic.

The operation of the undervoltage trigger device will now be described with reference to Fig. 3.

When the commercial power supply AC has a normal voltage level, the crest value of the full-wave rectified voltage Vrec exceeds the first threshold Vtl in fixed cycles. Accordingly, the undervoltage detection signal Vd output from the undervoltage detection unit 19 is a pulse-shaped signal. Under this situation, the transistors Trl and Tr2 of the delay unit 20 are alternately activated and deactivated in a repetitive manner. Thus, the voltage level of the delay signal SI does not exceed the second threshold voltage Vt2. This maintains the excitation current interruption signal S2 at a high level, and the switch circuit 13 functions to continuously supply the coil 12 with the excitation current Ic. Accordingly, the movable plunger 15 remains attracted to the core 14, and the breaker device 17 does not function.

When the voltage at the commercial power supply AC decreases and the crest value of the full-wave rectified voltage Vrec is continuously lower than the first threshold voltage Vtl, the undervoltage detection signal Vd of the undervoltage detection unit 19 is maintained at a high level. Under this situation, in the delay unit 20, the transistor Trl remains activated, and the transistor Tr2 remains deactivated. Accordingly, the capacitor C2 is charged, and the voltage level of the delay signal SI rises. When the delay signal SI exceeds the second threshold voltage Vt2, the delay unit 2 0 outputs the excitation current interruption signal S2 at a low level, and the switch circuit 13 functions to interrupt the excitation current Ic to the coil 12. Consequently, the movable plunger 15 is separated from the core 14, and the breaker device 17 functions to interrupt the supply of power VL to the load device.

The first embodiment has the advantages described below.

(1) When the voltage level of the commercial power supply AC is continuously less than or equal to a predetermined level for over a predetermined time or longer, the movable plunger 15 is separated from the core 14, and the breaker device 17 starts to function. Accordingly, the undervoltage trip device of the first embodiment obviates problems that would occur if the load device were to function when the commercial power supply AC is in an undervoltage state.

(2) In the undervoltage trip device, the voltage sensitivity for detecting whether or not the voltage level of the commercial power supply AC is insufficient is changed in accordance with the first threshold voltage Vtl, which is set by the comparator 21 of the undervoltage detection unit 19. Accordingly, a stable voltage sensitivity may easily be set or adjusted.

(3) The transistor Trl and the capacitor C2 of the delay unit 20 configure a time constant circuit. The delay time from when the voltage level of the commercial power supply AC decreases to an undervoltage to when the excitation current interruption signal S2 is output to interrupt the excitation current Ic may be set in accordance with a constant of the time constant circuit and the second threshold voltage Vt2. Accordingly, the delay time may be set without using a capacitor having a large capacitance. This allows for the undervoltage trip device to be reduced in size and cost.

A second embodiment will now be described with reference to Figs. 5 to 8. The second embodiment is applied to an overvoltage-undervoltage that interrupts the supply pf power voltage to a load device when the commercial power supply AC supplies undervoltage like in the first embodiment and when the commercial power supply AC supplies overvoltage, which is higher than a predetermined voltage.

Referring to Fig. 5, in the overvoltage-undervoltage trip device, a single phase-two line commercial power supply AC is connected via a switch 31 to a power supply circuit 32 and a voltage signal generation unit 33. The power supply circuit 32 generates a DC power voltage Vc based on the voltage of the commercial power supply AC and supplies the DC power voltage Vc to a delay time setting overvoltage detection unit 34 and a delay time setting undervoltage detection unit 35.

Referring to Fig. 6, the voltage signal generation unit 33 performs full-wave rectification on the commercial power supply AC to generate a full-wave rectified voltage. Then, the voltage signal generation unit 33 supplies the full-wave rectified voltage Vrec to the delay time setting overvoltage detection unit 34 and the delay time setting undervoltage detection unit 35.

The commercial power supply AC is connected to a coil 36. The coil 36 is connected to ground Vg via the switch circuit 37. When the switch circuit 37 is closed, the coil 36 is supplied with the excitation current Ic.

In the same manner as the first embodiment, the coil 3 6 is wound around the core. The overvoltage-undervoltage trip device of the second embodiment may include an interruption mechanism similar to that of the first embodiment.

The delay time setting undervoltage detection unit 3 5 is configured in the same manner as the combination of the undervoltage detection unit 19 and the delay unit 20 of the first embodiment shown in Fig. 2. The delay time setting undervoltage detection unit 35 provides the switch circuit 3 7 with an excitation current interruption signal S2. In the example illustrated in Fig. 6, when a constant voltage full-wave rectified voltage Vrec becomes lower than a first threshold voltage Vtl, the voltage level of a delay signal SI rises. When the voltage level of the delay signal SI exceeds the second threshold voltage Vt2, the excitation current interruption signal S2 shifts to a low level. As a result, the switch circuit 3 7 opens and the excitation current Ic is interrupted.

As shown in Fig. 7, the delay time setting overvoltage detection unit 34 includes an overvoltage detection unit 3 8 and a delay unit 39. The delay unit 39 is configured in the same manner as the delay unit of the first embodiment except in that the charging characteristics of the transistor Trl and the capacitor C2.

The overvoltage detection unit 38 is configured in the same manner as the undervoltage detection unit 19 of Fig. 2 except in that a third threshold voltage Vt3 is supplied to the negative input terminal of the comparator 21 and that the comparison voltage Vx is supplied to the positive input terminal of the comparator 21. The comparator 21 of the overvoltage detection unit 3 8 compares the comparison voltage Vx and the third threshold voltage Vt3 and provides the delay unit 39 with an overvoltage detection signal Vd2.

In the overvoltage detection unit 38, when the crest value of the full-wave rectified voltage Vrec becomes higher than the third threshold voltage Vt3, the overvoltage detection unit 38 outputs an overvoltage detection signal Vd2 having an H level, and the voltage level of the delay signal S3 of the delay unit 39 rises. When the H level overvoltage detection signal Vd2 is continuously output and the delay signal S3 of the delay unit 3 9 exceeds the threshold voltage Vt4, the excitation current interruption signal S4 shifts to a low level. This interrupts the supply of the excitation current Ic to the coil 36.

In the same manner as the first embodiment, interruption of the interruption current Ic results in the interruption mechanism functioning to interrupt the supply of power to the load device.

Further, interruption of the excitation current Ic decreases or cancels the magnetic attraction force of the coil 36. Thus, the switch 31 opens and the supply of commercial power AC to the power supply circuit 32 and the voltage signal generation unit 33 is interrupted.

Each of the detection units 34 and 35 includes an interface circuit that outputs the excitation current interruption signals S2 and S4 to the switch circuit 37. Each interface circuit is configured to provide the switch circuit 37 with input signals giving priority to those having a low level.

Referring to Fig. 8, the delay time setting undervoltage detection unit 35 sets a first threshold voltage Vtl to be higher than the voltage Vfl input to the comparator 21 when the excitation current Ic decreases and the coil 36 and the core can no longer attract the movable plunger. Simultaneously, the first threshold voltage Vtl is set to be higher than the voltage Vf2 at which the delay time setting overvoltage detection unit 34 and the delay time setting undervoltage detection unit 3 5 can no longer function due to a decrease in the voltage supplied from the power supply circuit 32 when the commercial power voltage decreases. The voltage Vfl may be referred to as an attractable lower limit voltage, and the voltage Vf2 may be referred to as a functional lower limit voltage of the detection units 34 and 35.

The second embodiment has the advantages described below.

(1) The movable plunger is separated from the core so that the interruption mechanism functions not only when the voltage level of the commercial power supply AC is continuously less than or equal to the predetermined level over a predetermined time or longer but also when the voltage level of the commercial power supply AC rises to a predetermined level or greater over a predetermined time or longer. Accordingly, the overvoltage-undervoltage trip device of the second embodiment obviates problems that would occur if the load device were to function when the commercial power supply AC is in an undervoltage state or an overvoltage state.

(2) The voltage sensitivity for detecting whether or not the voltage level of the commercial power supply AC is insufficient is changed in accordance with the threshold voltage Vtl, which is set by the comparator 21 of the undervoltage detection unit 19. Further, the voltage sensitivity for detecting whether or not the voltage level of the commercial power supply AC is excessive is changed in accordance with the threshold voltage Vt3, which is set by the comparator 21 of the overvoltage detection unit 38. Accordingly, a stable voltage sensitivity may easily be set or adjusted.

(3) The delay time from when the voltage level of the commercial power supply AC decreases to an undervoltage to when the excitation current interruption signal S2 is output to interrupt the excitation current Ic may be set by the time constant circuit (transistor Trl and capacitor C2) of the delay unit 20. In the same manner, the delay time from when the voltage level of the commercial power supply AC increases to an overvoltage to when the excitation current interruption signal S4 is output to interrupt the excitation current Ic may be set by the time constant circuit (transistor Trl and capacitor C2) of the delay unit 39.

Accordingly, the delay time may be set without using a capacitor having a large capacitance. This allows for the undervoltage trip device to be reduced in size and cost.

It should be apparent to those skilled in the art that the present invention may be embodied in many other specific forms without departing from the spirit or scope of the invention. Particularly, it should be understood that the present invention may be embodied in the following forms.

The undervoltage detection unit 19 of the first embodiment and the delay time setting undervoltage detection unit 3 5 of the second embodiment may be configured to integrate the commercial power supply voltage and calculate an effective value that is compared with the threshold voltage Vtl.

The undervoltage detection unit 19 of the first embodiment and the delay time setting undervoltage detection unit 35 of the second embodiment may be configured to calculate an average voltage of the commercial power supply and then compare the average voltage with the threshold voltage Vtl.

The overvoltage detection unit 3 8 of the second embodiment may be configured to integrate the commercial power supply voltage and calculate an effective value that is compared with the threshold voltage Vt3.

The overvoltage detection unit 38 of the second embodiment may be configured to calculate the average voltage of the commercial power supply and compare the average voltage with the threshold voltage Vt3.

Referring to Fig. 9, in the switch circuits of the first and second embodiments, an npn transistor Tr4 may be used in lieu of the npn transistor, and the excitation current interruption signal S2 or S4 may be input via an inverter circuit 40 to the base of the transistor Tr4. In such a configuration, when the excitation current interruption signals S2 and S4 shift to a high level and the excitation current Ic flows to the coil 12, the base voltage of the transistor Tr4 is substantially the level of ground Vg.

Accordingly, even when noise decreases the full-wave rectified voltage Vrec, the transistor Tr4 remains activated, and the coil 12 may be stably supplied with the excitation current Ic.

All examples and conditional language recited herein are intended for pedagogical purposes t-o aid the reader in understanding the principles of the invention and the concepts contributed by the inventor to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions, nor does the organization of such examples in the specification relate to a showing of the superiority and inferiority of the invention. Although embodiments of the present invention have been described in detail, it should be understood that various changes, substitutions, and alterations could be made hereto without departing from the spirit and scope of the invention.

CLAIMS

1. An undervoltage trip device for a circuit breaker, the undervoltage trip device comprising:

an undervoltage detection unit configured to compare a voltage corresponding to a voltage of a power supply with a first threshold voltage and output an undervoltage detection signal;

a delay unit configured to output an excitation current interruption signal when the undervoltage detection signal is continuously output over a predetermined time or longer; a switch circuit configured to interrupt an excitation current of a coil in accordance with the excitation current interruption signal; and

an interruption mechanism configured to interrupt the supply of power from the power supply to a load device when the excitation current to the coil is interrupted, wherein
the undervoltage detection unit includes a first comparator configured to compare a comparison voltage, which changes when the voltage of the commercial power supply changes, with the first threshold voltage, which is settable to the first comparator, and the delay unit includes a capacitor,

a charge circuit connected to the capacitor to charge the capacitor when the undervoltage detection signal is received,

a discharge circuit that discharges the capacitor when the undervoltage detection signal is not output from the undervoltage detection unit, and

a second comparator including a second threshold voltage that may be set, wherein the second comparator compares the voltage level of the capacitor with a predetermined second threshold voltage to output the excitation current interruption signal.

2. The undervoltage trip device according to claim 1, wherein the undervoltage detection unit is configured to integrate the voltage of the commercial power supply to calculate an effective value, and compare the effective value with the first threshold voltage to output an undervoltage detection signal.

3. The undervoltage trip device according to claim 1, wherein the undervoltage detection unit is configured to integrate the voltage of the commercial power supply to calculate an average voltage value, and compare the average voltage value with the first threshold voltage to output an undervoltage detection signal.

4. The undervoltage trip device according to any one of claims 1 to 3, wherein the switch circuit includes a transistor which is deactivated to interrupt the excitation current in response to the excitation current interruption signal.

5. The undervoltage trip device according to any one of claims 1 to 4, wherein the first threshold voltage of the first comparator and the second threshold voltage of the second comparator are separately settable.

6. An overvoltage-undervoltage trip device for a circuit breaker, the overvoltage-undervoltage trip device comprising:

a delay time setting undervoltage detection unit

configured to compare a voltage corresponding to a voltage of a power supply with a first threshold voltage to generate an undervoltage detection signal and, when the undervoltage detection signal is continuously output over a predetermined time or longer, output an excitation current interruption signal;

a delay time setting overvoltage detection unit configured to compare the voltage corresponding to the voltage of the commercial power supply with a predetermined third threshold voltage to generate an overvoltage detection signal and, when the overvoltage detection signal is continuously output over a predetermined time or longer, output the excitation current interruption signal;

a switch circuit configured to interrupt an excitation current that is supplied to a coil in accordance with the excitation current interruption signal; and

an interruption mechanism configured to interrupt the supply of power to a load device when the excitation current to the coil is interrupted, wherein the delay time setting undervoltage detection unit includes
an undervoltage detection unit that includes a first comparator configured to compare a comparison voltage, which changes when the voltage of the commercial power supply changes, with the first threshold voltage, which is settable to the first comparator, to generate the undervoltage detection signal, and

a delay unit that receives the undervoltage detection signal from the undervoltage detection unit, wherein the delay unit includes

a charge circuit that charges a capacitor when the undervoltage detection signal is received,

a discharge circuit that discharges the capacitor when the undervoltage detection signal is not received, and

a second comparator configured to compare the voltage level of the capacitor with a predetermined second threshold voltage, which is settable to the second comparator, to output the excitation current interruption signal.

7. The overvoltage-undervoltage trip device according to claim 6, wherein the first threshold voltage is set to be higher than the comparison voltage when the excitation current decreases and the interruption mechanism thereby stops functioning, and the third threshold voltage is set to be lower than the comparison voltage when the delay time setting overvoltage detection unit and the delay time setting undervoltage detection unit become non-functional.

8. The overvoltage-undervoltage trip device according to claim 6, wherein the first threshold voltage is equal to or slightly higher than an attractable lower limit voltage and higher than a functional lower limit voltage of the delay time setting overvoltage detection unit and the delay time setting undervoltage detection unit, wherein the attractable lower limit voltage corresponds to a minimum magnetic attraction force generated by the coil to continue supplying power to a load device.

9. The overvoltage-undervoltage trip device according to any one of claims 6 to 8, wherein the first threshold voltage of the first comparator and the second threshold voltage of the second comparator are separately settable.