JP2523924B2 - Overcurrent detection device - Google Patents

Description

The present invention relates to an overcurrent detection device incorporated in, for example, a circuit breaker or the like.

[Conventional technology]

As shown in FIG. 16, a conventional overcurrent detecting device of this type detects a current I flowing in a circuit 52 drawn from a commercial AC power source 51 and delays a predetermined time when the current I exceeds a reference value. With the characteristics, energize the trip coil 59 of the circuit breaker,
This opens the main contact 60 of the circuit breaker. For this reason, the conventional overcurrent detection device applies the voltage on the load side of the main contact 60 of the circuit breaker to the constant voltage circuit 58 so that the comparison circuit 56 and the output circuit 57 can be operated from the constant voltage circuit 58.
By adding a constant operating power supply voltage V _CC to the current, the current I flowing in the electric path 52 is detected by the current detector 54 through the current transformer 53, and the output of the current detector 54 is integrated by the time delay circuit 55. In addition to the comparison circuit 56 with a predetermined time delay characteristic, the comparison circuit 56
In order to compare with the reference value.

The current detector 54 shown in FIG. 17 (b) having a voltage value proportional to the amplitude of the current i as shown in FIG. 17 (a) output from the secondary side of the current transformer 53. DC voltage like
Convert to v ₁ and output. Further, the time delay circuit 55 integrates the DC voltage v ₁ output from the current detector 54 and outputs a voltage v ₂ as shown in FIG. Furthermore, the comparison circuit
As shown in FIG. 19A, reference numeral 56 compares the output voltage v ₂ of the time delay circuit 55 with the reference voltage v _3, and when the voltage v ₂ becomes higher than the reference voltage v _3, FIG. As shown in b), the output voltage v ₄
To a high level (to generate an overcurrent detection signal). When the high level output voltage v ₄ is input to the output circuit 57 from the comparison circuit 56, the output circuit 57 causes the trip coil 59 of the circuit breaker to operate.
The main contact 60 is opened by applying a tripping current to.

[Problems to be Solved by the Invention]

The above-mentioned conventional overcurrent detection device, when a motor or a power supply smoothing capacitor is connected to the electric path 52, for example, an excessive inrush current flows at the time of starting the motor or starting charging of the power supply smoothing capacitor. The output voltage v ₂ of the delay circuit 55 may exceed the reference voltage v ₃ , and in this case, there is a problem that an overcurrent detection signal is output (malfunction).

In addition, there is a problem that the interruption time based on the time-delay operation characteristic by the time delay circuit 55 and the comparison circuit 56 in the overcurrent state slightly exceeding the rated current is greatly affected by the slight variation in the reference voltage v ₃ . This is the output voltage of the time delay circuit 55 in an overcurrent condition that slightly exceeds the rated current.
This is because v ₂ rises at a relatively gentle slope and intersects the reference voltage v _{3 at} a small angle.For example, as shown in FIG. 20, the reference voltage v ₃ is v ₃₀ , v ₃₁ , _20. If there is a slight deviation from v ₃₂ , the voltage v ₂ will be the reference voltage v after the overcurrent begins to flow.
The cutoff time until the overcurrent detection signal is output exceeding ₃₀ , v ₃₁ , and v ₃₂ greatly changes to t ₀ , t ₁ , and t ₂ .

Further, the time delay operation characteristics of the time delay circuit 55 and the comparison circuit 56 are constant and cannot be arbitrarily changed.

An object of the present invention is to reduce malfunction due to inrush current, to reduce variation in interruption time in an overcurrent state slightly exceeding the rated current, and to further change the time-delayed operation characteristic. It is to provide a detection device.

[Means for solving the problem]

The overcurrent detection device according to claim (1) is a current detector that detects a current flowing in an electric path and outputs a DC voltage proportional to its amplitude, and noise absorption that is built in the current detector and removes a noise component of the current. Capacitor, a time delay circuit that integrates the DC voltage output from the current detector, a reference voltage generation circuit that generates the reference voltage, the output voltage of the time delay circuit, and the reference voltage output from the reference voltage generation circuit. And a comparison circuit that generates an overcurrent detection signal when the output voltage of the time delay circuit exceeds the reference voltage, and a step-down resistor that steps down the circuit voltage and supplies the power supply voltage to the reference voltage generation circuit and the comparison circuit. The noise absorbing capacitor is heated by the heat generated by the step-down resistor to reduce the capacity.

The overcurrent detection device according to claim (2) is according to claim (1).
In the overcurrent detection device described, the reference voltage of the reference voltage generation circuit immediately after the voltage is applied to the electric circuit is set to a value higher than the steady value, and then the reference voltage is lowered with time to stabilize at the steady value. Is characterized by.

[Action]

According to the configuration of claim (1), the current detector including the noise absorbing capacitor for removing the noise component of the detected current has a large amount of suppression of the output voltage immediately after the voltage is applied to the electric path, and the time elapses thereafter. At the same time, a DC voltage with a characteristic that the amount of suppression is reduced is output to the time delay circuit, so immediately after the voltage is applied to the circuit, an inrush current flows in the circuit and the AC voltage input to the current detector is abnormal. The output voltage of the time delay circuit can be kept small even at this time, and the output voltage of the time delay circuit rarely exceeds the reference voltage due to the inrush current. The output (malfunction) of the detection signal can be reduced.

Also, because the current detector has the above characteristics, the output voltage of the time delay circuit crosses the reference voltage at a large angle, and the reference voltage in the overcurrent state slightly exceeding the rated current is exceeded. It is possible to reduce variations in interruption time due to variations in voltage.

Further, the current detector has the above-mentioned characteristics, so that the time-delayed operation characteristics can be arbitrarily changed.

According to the configuration of claim (2), the current detector having the built-in noise absorbing capacitor for removing the noise component of the detected current has a large suppression amount of the output voltage immediately after the voltage is applied to the electric circuit, and the time elapses thereafter. A DC voltage with a characteristic that the amount of suppression becomes smaller is output to the time delay circuit, and the reference voltage output from the reference voltage generation circuit is set to a value higher than the steady value immediately after the voltage is applied to the circuit, and As the rush current flows in the circuit immediately after the voltage is applied to the circuit and the AC voltage input to the current detector rises abnormally, The output voltage of the time delay circuit is suppressed to a small level, and since the reference voltage is also high at this time, it is more likely that the output voltage of the time delay circuit will exceed the reference voltage due to the inrush current. It is possible to further reduce the output of the overcurrent detection signal (malfunction) by eliminating the inrush current.

In addition, the output voltage of the time delay circuit crosses the reference voltage at a larger angle by providing the current detector with the above characteristics and changing the reference voltage as described above. Therefore, it is possible to further reduce the variation of the interruption time due to the variation of the reference voltage in the overcurrent state slightly exceeding the rated current.

Also, by providing the current detector with the above characteristics or by changing the reference voltage,
The timed operation characteristics can be changed arbitrarily.

〔Example〕

Embodiment 1 A first embodiment of the overcurrent detection device of the present invention will be described with reference to FIGS. 1 to 6. That is, this overcurrent detection device is built in, for example, a circuit breaker, detects the current I flowing in the electric path 2 drawn from the commercial AC power source 1,
When the current I exceeds the reference value, the trip coil 9 of the circuit breaker is energized with a predetermined time delay characteristic, whereby the main contact 10 of the circuit breaker is opened.

Therefore, in the overcurrent detection device of this embodiment, the step-down voltage obtained from the step-down resistor 12 connected to the load side of the main contact 10 of the circuit breaker is added to the constant voltage circuit 8 to keep a constant operating power supply voltage. V _CC is obtained, and this voltage V _CC is applied to the comparison circuit 6, the output circuit 7 and the reference voltage generation circuit 11, while the current I flowing in the electric path 2 is detected by the current detector 4 via the current transformer 3, By integrating the output of the current detector 4 by the time delay circuit 5, a predetermined time delay characteristic is added to the comparison circuit 6, and the reference voltage v ₃ output from the reference voltage generation circuit 11 and the CR time constant are also added. The output voltage v ₀ of the circuit 5 is compared by the comparison circuit 6.

The reference voltage generation circuit 11 is composed of a series circuit of a resistor R ₂ and a resistor R _3, and has an operating power supply voltage V _CC from the constant voltage circuit 8.
Is divided and the reference voltage v ₃ is output from the connection point of resistors R ₂ and R ₃ .

The time delay circuit 5 comprises a series circuit of a resistor R ₁ and a capacitor C, and a resistor R ₄ is connected in parallel with the capacitor C.
The DC voltage v ₁ ′ output from the current detector 4 is applied across both ends thereof, and the output voltage v ₀ is output from the connection point of the resistor R ₁ and the capacitor C.

The current detector 4 detects the current I flowing in the electric path 2 through the current transformer 3, and enters the secondary side of the current transformer 3 by the low-pass filter circuit 4a including the resistor Ra and the noise absorbing capacitor Ca. The voltage Va at both ends of the noise absorbing capacitor Ca is converted into a DC voltage v ₁ ′ by the amplifying rectifier circuit 4b and the noise component such as lightning surge is removed and output.

In the current detector 4, the noise absorbing capacitor Ca of the low-pass filter circuit 4a rises in temperature due to the heat generation of the step-down resistor 12 and its capacitance is reduced. For example, as the noise absorbing capacitor Ca, a ceramic capacitor that has a large change in electrostatic capacitance with respect to temperature changes, is linear, and has reproducibility is used. From these facts, the low-pass filter circuit 4a has a time constant that is large immediately after the voltage is applied to the electric path 2 and then decreases with the passage of time and stabilizes at a steady value.
Immediately after the voltage is applied to the capacitor, the amount of suppression of the voltage Va across the noise absorbing capacitor Ca is large, and thereafter, the amount of suppression becomes small with the passage of time.

Therefore, looking at the operation of the current detector 4 as a whole, when the main contact 10 of the circuit breaker is closed and a voltage is applied to the step-down resistor 12, a current flows through the step-down resistor 12 and accordingly The step-down resistor 12 generates heat, and the heat is transmitted to the noise absorbing capacitor Ca of the current detector 4, so that the temperature of the noise absorbing capacitor Ca rises.

In this case, the temperature of the noise absorbing capacitor Ca is the same as the room temperature immediately after the main contact 10 of the circuit breaker is closed, and then rises with the passage of time, and equilibrates when it rises to a certain point. As the temperature of the noise absorbing capacitor Ca changes, as shown in FIG. 2 (a), the capacitance of the noise absorbing capacitor Ca gradually decreases from the initial value and equilibrates at some point. Then, as shown in FIG. 2 (b), the time constant of the resistor Ra and the noise absorbing capacitor Ca also gradually decreases from the initial value and equilibrates at some point.

As a result, as described above, the noise absorbing capacitor Ca
As shown in FIG. 3 (a), the voltage Va across both ends of the voltage rises with a small gradient from a value smaller than the steady value, rises with a large gradient from a certain time, and stabilizes at the steady value.

Corresponding to this, the voltage output from the amplification rectifier circuit 4b
As shown in FIG. 3B, v ₁ ′ initially rises with a small gradient from a value smaller than the steady value, rises with a large gradient from a certain time, and stabilizes at the steady value.

That is, the voltage v ₀ output from the time delay circuit 5, which is obtained by integrating the voltage v ₁ ′ output from the amplifying rectifier circuit 4b, initially rises with a small gradient from zero as shown in FIG. 3 (c). ,
From a certain time, it rises with a large gradient and stabilizes at a steady value.

Further, the comparison circuit 6 compares the output voltage v ₀ of the time delay circuit 5 with the reference voltage v _3, and sets the output voltage v ₄ to a high level when the output voltage v ₀ becomes higher than the reference voltage v ₃ ( Generates an overcurrent detection signal). High-level output voltage v ₄ from the comparison circuit 6
Is input to the output circuit 7, the output circuit 7 causes a tripping current to flow through the tripping coil 9 of the circuit breaker to cause the main contact 10
To open.

This overcurrent detection device is a current detector 4 with a built-in noise absorbing capacitor Ca that removes the noise component of the detected current.
However, since the DC voltage v ₁ ′ having a characteristic that the amount of suppression of the output voltage is large immediately after the voltage is applied to the electric path 2 and the amount of suppression decreases thereafter with time, is output to the time delay circuit 5. Immediately after the voltage is applied to the electric line 2, even if an AC voltage input to the current detector rises abnormally due to an inrush current flowing in the electric line 2 at the time of starting the motor or charging the power source capacitor, for example, will be rising slope of the output voltage v ₀ of Tokinobe circuit 5 is suppressed, the less the output voltage v ₀ of the time extension circuit 5 exceeds the reference voltage v ₃ by rush current, overcurrent due to inrush current The output (malfunction) of the detection signal can be reduced.

In addition, since the current detector 4 has the above-mentioned characteristics, the output voltage v ₀ of the time delay circuit 5 crosses the reference voltage v _{3 at a} large angle, which slightly exceeds the rated current. Moreover, it is possible to reduce the variation in the interruption time due to the variation in the reference voltage in the overcurrent state.

This point will be described with reference to FIG. In the case of the conventional example, the output voltage v _{2 of the time} delay circuit 55 is the reference voltage after the overcurrent starts to flow when the reference voltage v ₃ varies from v ₃₀ , v ₃₁ , and v _32.
The cutoff time until the overcurrent detection signal is output exceeding v ₃₀ , v ₃₁ , and v ₃₂ is t ₀ , t ₁ , and t ₂ (see FIG. 20). On the other hand, in the case of the first embodiment, when the reference voltage v ₃ varies with v ₃₀ , v ₃₁ , and v ₃₂ with the same width as the conventional example,
The cutoff time from when the overcurrent starts flowing until the output voltage v ₀ of the time delay circuit 5 exceeds the reference voltages v ₃₀ , v ₃₁ , and v ₃₂ and the overcurrent detection signal is output is t ₀ ′, t ₁ ′, T ₂ ′.

Therefore, comparing the first embodiment with the conventional example,
The variation T'of the interruption times t ₀ ′, t ₁ ′, t ₂ ′ in the first embodiment is smaller than the variation T of the interruption times t ₀ , t ₁ , t ₂ in the conventional example. it is obvious.

Further, the current detector 4 has the above-described characteristics, so that the time-delayed operation characteristics can be arbitrarily changed. This point will be described with reference to FIGS. 5 and 6.

FIG. 5 shows that when the secondary current of the current transformer 3 is i ₁ , i ₂ and i ₃ ,
Output voltage v ₂ (i ₁ ), v ₂ (i ₂ ), v of the time delay circuit 55 of the conventional example
₂ (i ₃ ) and changes in the output voltages v ₀ (i ₁ ), v ₀ (i ₂ ), v ₀ (i ₃ ) of the time delay circuit 5 in the first embodiment. In FIG. 5, the output voltages v ₂ (i ₁ ), v ₂ (i ₂ ), v ₂ (i ₃ ) of the time delay circuit 55 of the conventional example are the reference voltage v ₃ and the times t ₁₁ , t ₁₂ , intersect at t _13, the output voltage v ₀ of the time extension circuit 5 in the first embodiment _{(i 1), v 0 (} i 2), v 0 (i 3) are each time t _21, t _22, t It intersects at ₂₃ .

The relationship of FIG. 5 is shown as a time-delayed operating characteristic on a graph in which time is plotted on the ordinate and current i is plotted on the abscissa. As shown in FIG. 6, in the case of the conventional example, a solid line A ₁ is used. The solid line A ₂ in the case of the first embodiment, and the output voltage of the current detector 4 in the case of the first embodiment.
By changing the gradient of v ₁ ′, the output voltage of the time delay circuit 5
The gradient of v ₀ can be changed, and the time-delay operation characteristic can be arbitrarily changed as described above.

Further, in the first embodiment, since the current detector 4 incorporates the noise absorbing capacitor Ca which is a temperature sensitive element, the current detector 4 for detecting the current I flowing through the electric line 2 (the current transformer 3 and the current transformer 3 Even if the constituent elements of the current detector 4 have temperature dependence, the temperature characteristic of the noise absorbing capacitor Ca can reduce the change in the output DC voltage v ₁ ′ of the current detector 4 due to the temperature change, and the time-delayed operating characteristic. The temperature dependence of can be reduced.

Second Embodiment A second embodiment of the overcurrent detecting device of the present invention will be described with reference to FIGS. 7 to 13.

This overcurrent detection device uses a reference voltage generation circuit 13 instead of the reference voltage generation circuit 11 of the first embodiment, and the other configurations are the same as those of the first embodiment.

This reference voltage generating circuit 13 makes the reference voltage v ₃ ′ higher than the steady value immediately after the voltage is applied to the electric circuit 2, and then lowers the reference voltage v ₃ ′ with time and stabilizes at the steady value. Therefore, as a concrete circuit configuration example of the reference voltage generating circuit 13, ones as shown in FIGS. 8 and 9 can be considered.

First, in the example of FIG. 8, the voltage Vcc output from the constant voltage circuit 8 is applied across the resistor R ₅ and the thermistor having a negative characteristic.
A series circuit of R _TH and resistor R ₆ is shown, and the reference voltage v ₃ ′ is output from the connection point of the resistor R ₅ and the thermistor R _TH . The reference voltage generating circuit 13 shown in FIG.
Place _TH close to the step-down resistor 12
The temperature of the thermistor R _TH rises due to the heat generated by and the resistance value is lowered.

Therefore, according to the operation of the reference voltage generation circuit 13, when the main contact 10 of the circuit breaker is closed and a voltage is applied to the step-down resistor 12, a current flows through the step-down resistor 12 and accordingly resistor 12 generates heat, the heat is transmitted to the thermistor R _TH of the reference voltage generating circuit 13, the temperature θ of the thermistor R _TH is 10
It will rise as shown in FIG. in this case,
The temperature θ of the thermistor R _TH rises at room temperature immediately after the main contact 10 is closed, then rises with the passage of time, and equilibrates when it rises to a certain point. With the temperature change of the thermistor R _TH, will the resistance value of the thermistor R _TH is decreased gradually from the initial value, so that the equilibrium at a certain place. As a result, as described above, the reference voltage v ₃ ′ output from the reference voltage generating circuit 13 gradually decreases from the initial value higher than the steady value as shown in FIG. 10 (b), and stabilizes at the steady value. Will be done.

Next, the example of FIG. 9 is a circuit that was considered by focusing on the fact that the forward voltage drop of the diode has a negative characteristic with respect to temperature. The voltage Vcc output from the constant voltage circuit 8 is across both ends. The series circuit of the applied resistance R ₇ and the diodes D ₁ and D ₂ is shown, and the reference voltage v ₃ ′ is output from the connection point of the resistance R ₇ and the diode D ₁ . In the reference voltage generating circuit 13 shown in FIG. 9, the diodes D ₁ and D ₂ are arranged in close proximity to the step-down resistor 12, and the diode is heated by the step-down resistor 12.
The temperature of D ₁ and D ₂ rises and its forward voltage drop is reduced. The operation of the reference voltage generating circuit 13 in this case is similar to that in the case of FIG.

In addition to the configuration of the first embodiment, this overcurrent detection device sets the reference voltage v ₃ ′ output from the reference voltage generation circuit 13 to a value higher than the steady value immediately after the voltage is applied to the electric line 2, and then the Since the voltage is lowered with time to stabilize at a steady value, the rising gradient of the output voltage v ₀ of the time delay circuit 5 can be suppressed to a small level even if a rush current flows in the electric line 2 immediately after the voltage is applied to the electric line 2. Furthermore, since the reference voltage v ₃ ′ is also high at this time, it is less likely that the output voltage v ₀ of the time delay circuit 5 exceeds the reference voltage v ₃ ′ due to the inrush current, and the overcurrent detection signal due to the inrush current is reduced. Output (malfunction) can be further reduced.

In addition, the output voltage v ₀ of the time delay circuit 5 is set to the reference voltage because the current detector 4 has the above characteristics and the reference voltage v ₃ ′ is changed as described above.
Since it intersects with v ₃ ′ at a larger angle, it is possible to further reduce the variation in the interruption time due to the variation in the reference voltage v ₃ ′ in the overcurrent state slightly exceeding the rated current.

This point will be described with reference to FIG. In the case of the first embodiment, the output voltage v ₀ of the time delay circuit 5 is the reference voltage v ₃₀ , v ₃₁ after the overcurrent starts to flow when the reference voltage v ₃ fluctuates with v ₃₀ , v ₃₁ , v _32. , v _32, and the interruption time until the overcurrent detection signal is output is t ₀ ′, t ₁ ′, t ₂ ′ (see FIG. 4). On the other hand, in the case of the second embodiment, when the reference voltage v ₃ ′ varies with v _3a , v _3b , v _{3c in the} same width as in the first embodiment, the time delay circuit starts after the overcurrent starts to flow. 5 the output voltage v ₀ is the reference voltage v _3a, v _3b, breaking time until v _3c beyond each overcurrent detection signal is output, a _{t a, t b, t c} .

Therefore, in comparison with the second embodiment and the first embodiment, interruption time t _a in the second embodiment, t _b, variation T "of t _c, interruption time in the first embodiment t ₀ ′, T ₁ ′,
It is clear that the variation of t ₂ ′ is smaller than that of T ′.

Further, not only the slope of the output voltage v ₀ of the time delay circuit 5 is changed, but also the reference voltage v ₃ ′ is changed, so that the time delay operation characteristic can be arbitrarily changed.

This point will be described with reference to FIGS. 12 and 13. FIG. 12 shows that when the secondary current of the current transformer 3 is i ₁ , i ₂ , i ₃ , the output voltage v ₂ (i ₁ ), v ₂ (i ₂ ), v of the time delay circuit 55 of the conventional example. ₂ (i ₃ ) intersects with the reference voltage v ₃ at times t ₁₁ , t ₁₂ , and t ₁₃ , respectively, and the output voltage v ₀ (i ₁ ), v ₀ (i ₂ of the time delay circuit 5 in the second embodiment. ),
v ₀ (i ₃ ) is the reference voltage v ₃ ′ and time t ₃₁ , t ₃₂ , t ₃₃ , respectively.
Cross at.

The relationship of FIG. 12 is shown as a time-delayed operating characteristic on a graph in which time is plotted on the ordinate and current i is plotted on the abscissa. As shown in FIG. 13, in the case of the conventional example, the solid line A ₁ , Second
In the case of the second embodiment, the solid line A ₃ is shown, and in the case of the second embodiment, the time-delay operating characteristic can be arbitrarily changed by changing the slope of the reference voltage v ₃ ′. Becomes

Further, in this second embodiment, since the current detector 4 has the noise absorbing capacitor Ca which is a temperature sensitive element built therein, the current detector 4 for detecting the current I flowing through the electric path 2 (the current transformer 3 and the current transformer 3 Even if the current detector 4 has a temperature dependence, the temperature dependence of the time-delayed operation characteristic can be reduced as in the first embodiment (effect of temperature compensation on the current detection element). 1).

Further, in the second embodiment, the reference voltage generating circuit 13
Since the thermistor R _TH and the diodes D ₁ and D ₂ which are temperature sensitive elements are used, the temperature of the current detection element (the constituent elements of the current transformer 3 and the current detector 4) for detecting the current I flowing in the electric path 2 is reduced. The current detector 4 is dependent on the temperature rise due to the surrounding temperature.
Even if the level of the DC voltage v ₁ ′ output from the device decreases, the reference voltage v ₃ ′ decreases as the ambient temperature rises due to the temperature characteristics of the thermistor R _TH and the diodes D ₁ and D _2. To compensate the temperature dependence of the DC voltage v ₁ ′,
It is possible to reduce the temperature dependence of the time-delayed operating characteristic (effect 2 of temperature compensation on the current detection element).

Third Embodiment A third embodiment of the overcurrent detection device of the present invention will be described with reference to FIGS. 14 and 15.

This overcurrent detection device uses a reference voltage generation circuit 14 instead of the reference voltage generation circuit 11 of the first embodiment, and the other configurations are the same as those of the first embodiment.

This reference voltage generating circuit 14 uses a CR timer, unlike the one that changes the reference voltage v ₃ ′ by utilizing the heat generation of the step-down resistor 12 connected to the electric path 2 as in the second embodiment. To change the reference voltage v ₃ ′.

More specifically, the reference voltage generating circuit 14 includes a constant voltage circuit 8 connected to the load side of the main contact 10 of the circuit breaker.
Voltage divider circuit 14a that divides the operating power supply voltage Vcc output from
, A time constant circuit 14b that charges with the operating power supply voltage Vcc, a divider 14c that divides the output voltage v _X of the voltage divider circuit 14a by the output voltage v _Y of the time constant circuit 14b, and an output voltage v of the divider 14c. _{And a} voltage dividing circuit 14d for dividing _Z.

What this case, the voltage dividing circuit 14a comprises a series circuit of a resistor R ₈ resistors R _9, the time constant circuit 14b is connected to the capacitor C ₁ in series circuit of a resistor R ₁₀ resistor R ₁₁ in parallel with the resistor R ₁₁ Therefore, the voltage dividing circuit 14d is composed of a series circuit of a resistor R ₁₂ and a resistor R ₁₃ .

In the reference voltage generating circuit 14, when the main contact 10 of the circuit breaker is closed and a voltage is applied to the electric circuit 2, the output voltage v _X of the voltage dividing circuit 14a is rapidly fixed as shown in FIG. It rises to a value and holds that state. On the other hand, the output voltage v _Y of the time constant circuit 14b becomes a constant value where it gradually increases from zero. Therefore, the reference voltage v ₃ ′ output from the voltage dividing circuit 14d that divides the output voltage v _{ZJ of the} divider 14c rapidly becomes steady immediately after the main contact 10 of the circuit breaker is closed and the voltage is applied to the electric circuit 2. It rises above the value, then falls over time, and then stabilizes at a steady value.

The third embodiment has the same effect as that of the second embodiment except the effect 2 of the temperature compensation for the current detecting element in the second embodiment.

In the above embodiment, the overcurrent detection device is described as being built in the circuit breaker, but it is naturally conceivable that the overcurrent detection device is provided as a single unit.

〔The invention's effect〕

The overcurrent detection device according to claim (1) is a current detector having a built-in noise absorbing capacitor that removes noise components of the detected current. Since the direct current voltage, which has the characteristic that the suppression amount decreases with the passage of time, is output to the time delay circuit, the rush current flows in the electric line immediately after the voltage is applied to the electric line, and the alternating voltage input to the current detector is Even if the voltage rises abnormally, the output voltage of the time delay circuit is kept small at this time, so that the output voltage of the time delay circuit does not exceed the reference voltage due to the inrush current. The output (malfunction) of the detection signal can be reduced.

Also, because the current detector has the above characteristics, the output voltage of the time delay circuit crosses the reference voltage at a large angle, and the reference voltage in the overcurrent state slightly exceeding the rated current is exceeded. It is possible to reduce variations in interruption time due to variations in voltage.

Further, the current detector has the above-mentioned characteristics, so that the time-delayed operation characteristics can be arbitrarily changed.

The overcurrent detection device according to claim (2) is a current detector having a built-in noise absorbing capacitor that removes noise components of the detected current. A DC voltage having a characteristic that the amount of suppression decreases with time is output to the time delay circuit, and the reference voltage output by the reference voltage generation circuit is set to a value higher than the steady value immediately after the voltage is applied to the electric path, and then Since the voltage is lowered with time to stabilize at a steady value, even if an inrush current flows in the circuit immediately after the voltage is applied to the circuit and the AC voltage input to the current detector rises abnormally, this In this case, the rising slope of the output voltage of the time delay circuit is suppressed to a small level, and since the reference voltage is also high at this time, the output voltage of the time delay circuit may exceed the reference voltage due to the inrush current. More it is possible to reduce the output (malfunction) of the overcurrent detection signal by less and less rush current Ri.

Also, by providing the current detector with the above characteristics and changing the reference voltage as described above, the output voltage of the time delay circuit crosses the reference voltage at a larger angle. Further, it is possible to further reduce the variation of the interruption time due to the variation of the reference voltage in the overcurrent state slightly exceeding the rated current.

Also, by providing the current detector with the above characteristics, or by changing the reference voltage,
The timed operation characteristics can be changed arbitrarily.

[Brief description of drawings]

FIG. 1 is a block diagram of a first embodiment of an overcurrent detection device of the present invention, FIG. 2 is a diagram showing changes in the capacitance of a capacitor and changes in time constant with temperature changes, and FIG. 3 is each part of a current detector. 4 is a time chart showing the time variation of the output voltage of the delay circuit and the output voltage of the time delay circuit, FIG. 4 is a time chart showing the difference in the variation of the interruption time between the first embodiment and the conventional example, FIG. 5 and FIG. Are characteristic diagrams showing the difference in time-delay operation characteristics between the first embodiment and the conventional example, respectively, and FIG. 7 is a block diagram of the second embodiment of the overcurrent detection device of the present invention, FIGS. 8 and 9. Is a circuit diagram showing a concrete configuration of the reference voltage generating circuit, FIG. 10 is a time chart showing temporal changes in the thermistor temperature and the reference voltage, and FIG. 11 is a cutoff in the second embodiment and the first embodiment. This indicates the difference in time variation. FIG. 12 and FIG. 13 are characteristic charts showing the difference in time-delay operation characteristics between the second embodiment and the conventional example, respectively, and FIG. 14 is the third embodiment of the overcurrent detection device of the present invention. Block diagram, FIG. 15 is a time chart of each part of the reference voltage generating circuit, FIG. 16 is a block diagram of a conventional overcurrent detection device, and FIGS. 17, 18, and 19 are time charts of each part, FIG. 20 is a time chart showing a difference in variation in interruption time in the conventional example. 2 ... Electric circuit, 4 ... Current detector, 5 ... Time delay circuit, 6 ...
… Comparison circuit, 11,13,14 …… Reference voltage generation circuit, 12 …… Step-down resistor, Ca …… Noise absorption capacitor

Claims (2)

(57) [Claims] 1. A current detector for detecting a current flowing in an electric circuit and outputting a DC voltage proportional to its amplitude, a noise absorbing capacitor built in the current detector for removing a noise component of the current, and the current detection. Delay circuit for integrating the DC voltage output from the voltage regulator, a reference voltage generating circuit for generating a reference voltage, and comparing the output voltage of the time delay circuit and the reference voltage output from the reference voltage generating circuit. A comparison circuit for generating an overcurrent detection signal when the output voltage of the time delay circuit exceeds the reference voltage, and a step-down resistor for stepping down a circuit voltage and supplying a power supply voltage to the reference voltage generation circuit and the comparison circuit. And a device for reducing the capacitance by heating the noise absorbing capacitor by heat generation of the step-down resistor. 2. The reference voltage of the reference voltage generation circuit immediately after the voltage is applied to the electric circuit is set to a value higher than a steady value, and then the reference voltage is lowered with time to stabilize at the steady value. 1) The overcurrent detection device described.