JP2506477B2 - 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.
Is constantly applied to the operating power supply voltage Vcc, the current I flowing in the electric path 52 is detected by the current detector 54 via the current transformer 53, and the output of the current detector 54 is integrated by the time delay circuit 55 to obtain a predetermined value. In addition to the comparison circuit 56 with the time delay characteristic of
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 , v _If it is slightly different from ₃₂ , the voltage v ₂ is the reference voltage v ₃₀ ,
v _31, v breaking time until ₃₂ exceeds the overcurrent detection signal is output t _0, t _1, it will vary greatly 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 a circuit and outputs a DC voltage proportional to its amplitude, and a CR time that integrates the DC voltage output from this current detector. The output voltage of the CR time constant circuit exceeds the reference voltage by comparing the output voltage of the constant time circuit, the reference voltage generation circuit that generates the reference voltage, and the output voltage of the CR time constant circuit with the reference voltage output from the reference voltage generation circuit. It is characterized in that it has a comparison circuit that generates an overcurrent detection signal at the time of heating, and heats the circuit to heat the capacitor of the CR time constant circuit 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 CR time constant circuit is
Immediately after the voltage is applied to the electric circuit, the amount of suppression of the output voltage is large, and thereafter the amount of suppression is small over time, so that the DC voltage output from the current detector is integrated. Even if an inrush current flows in the circuit immediately after the voltage is applied and the DC voltage output from the current detector rises abnormally, the rising slope of the output voltage of the CR time constant circuit will be suppressed to a small level at this time, The output voltage of the CR time constant circuit rarely exceeds the reference voltage due to the current, and the output (malfunction) of the overcurrent detection signal due to the inrush current can be reduced.

In addition, because the CR time constant circuit has the above characteristics, the output voltage of the CR time constant circuit crosses the reference voltage at a large angle, which causes an overcurrent condition that slightly exceeds the rated current. It is possible to reduce the variation in the cutoff time due to the variation in the reference voltage.

In addition, the CR time constant circuit is provided with the above characteristics, so that the time delay operation characteristics can be arbitrarily changed.

According to the configuration of claim (2), the CR time constant circuit is
Immediately after the voltage is applied to the electric circuit, the amount of suppression of the output voltage is large, and thereafter the amount of suppression is small, so that the DC voltage output from the current detector is integrated. The reference voltage output by is set to a value higher than the steady value immediately after the voltage is applied to the circuit, and then it is lowered with time to stabilize at the steady value. Even if the DC voltage output from the current detector rises abnormally due to the flow of current, the rising gradient of the output voltage of the CR time constant circuit is suppressed at this time, and the reference voltage is also high at this time. Therefore, the output voltage of the CR time constant circuit is less likely to exceed the reference voltage due to the inrush current, and the output (malfunction) of the overcurrent detection signal due to the inrush current can be further reduced.

In addition, the output voltage of the CR time constant circuit crosses the reference voltage at a larger angle because the CR time constant circuit has the above characteristics and the reference voltage is changed as described above. Therefore, it is possible to further reduce the variation in the interruption time due to the variation in the reference voltage in the overcurrent state in which the rated current is slightly exceeded.

Further, the time-delay operation characteristic can be arbitrarily changed by providing the CR time constant circuit with the above characteristics or by changing the reference voltage.

〔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 constant operation power supply voltage Vcc is supplied from the constant voltage circuit 8 connected to the load side of the main contact 10 of the circuit breaker to the comparison circuit 6, the output circuit 7 and the reference voltage generator. In addition to the circuit 11, the current I flowing in the electric line 2
Is detected by the current detector 4 via the current transformer 3, and the output of the current detector 4 is integrated by the CR time constant circuit 5,
In addition to the comparison circuit 6 having a predetermined time delay characteristic, the reference voltage v ₃ output from the reference voltage generation circuit 11 and the CR time constant circuit 5
The comparison circuit 6 compares the output voltage v ₀ with the output voltage v ₀ .

The current detector 4 detects the current I flowing in the electric path 2 and outputs a voltage proportional to the amplitude of the current I flowing in the electric path 2. Specifically, like the conventional example, the current detector 4 The current i output from the secondary side is converted into a voltage v ₁ ′ proportional to its amplitude.
(In this case, the voltage is full-wave rectified by the resistor R and the diodes D ₁ , D ₂ , D ₃ , D ₄ ) and output.

Reference voltage generating circuit 11 includes a resistor R ₂ and the resistor becomes a series circuit of the R _3, a reference voltage v ₃ from the connection point of the operating power supply voltage Vcc from the constant voltage circuit 8 divides the resistance R ₂ and the resistor R ₃ Is output.

The CR time constant circuit 5 is composed of a resistor R ₁ and a capacitor C connected in series. The resistor R ₄ is connected in parallel with the capacitor C. The DC voltage v ₁ ′ output from the current detector 4 is It is applied across both ends and outputs the output voltage v ₀ from the connection point of the resistor R ₁ and the capacitor C. This CR time constant circuit 5
Particularly, the temperature of the capacitor C rises due to the heat generation of the electric path 2 and the capacitance thereof decreases. As heat generation of the electric circuit 2, heat generation of a contact part of a circuit breaker or bimetal can be used. As the capacitor C, a ceramic capacitor that has a large change in electrostatic capacitance with respect to temperature changes and is also direct and reproducible can be used.

From these facts, the CR time constant circuit 5 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 output voltage, the control amount of the output voltage is large, and thereafter, the suppression amount decreases with the passage of time.

Here, as to the operation of the CR time constant circuit 5 as a whole, when the main contact 10 of the circuit breaker is closed and a voltage is applied to the electric line 2 to cause a current to flow, the electric line 2 heats up, and the heat is generated.
It is transmitted to the capacitor C of the CR time constant circuit 5, and the temperature of the capacitor C rises.

In this case, the temperature of the capacitor C 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 capacitor C changes, as shown in FIG. 2 (a), the capacitance of the capacitor C gradually decreases from the initial value and equilibrates at some point. Then, as shown in FIG. 2 (b), the time constant of the resistor R ₁ and the capacitor C also gradually decreases from the initial value and equilibrates at a certain point.

As a result, as described above, the voltage v ₀ output from the CR time constant circuit 5 rises with a small gradient from zero in the initial stage as shown in FIG. 3, rises with a large gradient from a certain time, and reaches a steady value. It will be stable.

Further, the comparison circuit 6 outputs the output voltage v ₀ of the CR time constant circuit 5.
Is compared with the reference voltage v _3, and when the output voltage v ₀ becomes higher than the reference voltage v ₃ , the output voltage v _{4 is set} to a high level (an overcurrent detection signal is generated). When a high level output voltage v ₄ is input from the comparison circuit 6 to the output circuit 7, the output circuit 7 causes a trip current to flow in the trip coil 9 of the circuit breaker to open the main contact 10.

In this overcurrent detection device, the CR time constant circuit 5 has 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 then the amount of suppression is reduced with the lapse of time. Since the output DC voltage v ₁ ′ is integrated,
Immediately after the voltage is applied to the electric circuit 2, even if the output of the current detector 4 rises abnormally due to an inrush current flowing to the electric circuit 2 at the time of starting the motor or charging the capacitor for the power supply, for example, at the time of CR constant by will be rising slope of the rise of the output voltage v ₀ of the CR time constant circuit 5 is suppressed when the constant circuit 5, the output voltage v ₀ of the CR time constant circuit 5 exceeds the reference voltage v ₃ by inrush current It is possible to reduce the output (malfunction) of the overcurrent detection signal due to the inrush current.

Further, by making the CR time constant circuit 5 have the above characteristics, the output voltage v ₀ of the CR time constant circuit 5 becomes equal to the reference voltage v ₃
Therefore, it is possible to reduce the variation of the interruption time due to the variation of the reference voltage in the overcurrent state that slightly exceeds the rated current.

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 to flow until the output voltage v ₀ of the CR time constant 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, by giving the CR time constant circuit 5 the characteristics as described above, the time delay 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 CR time constant circuit 5 in the first embodiment are shown. . In FIG. 5, the time delay circuit 55 of the conventional example is shown.
The output voltages v ₂ (i ₁ ), v ₂ (i ₂ ), v ₂ (i ₃ ) of the respective outputs intersect with the reference voltage v ₃ at times t ₁₁ , t ₁₂ , and t ₁₃ , respectively, and CR in the first embodiment is Output voltage of time constant circuit 5 v ₀ (i ₁ ), v ₀ (i ₂ ), v
₀ (i ₃ ) intersects at times t ₂₁ , t ₂₂ and t ₂₃ , respectively.

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 CR time constant circuit 5 in the case of the first embodiment.
By changing the gradient of v ₀ , it becomes possible to arbitrarily change the time-delay operation characteristic as described above.

Further, in the first embodiment, since the capacitor C, which is a temperature sensitive element, is used in the CR time constant circuit 5, a current detecting element (the converter 3 and the current detector 4) for detecting the current I flowing in the electric path 2 is used. DC voltage output from the current detector 4 due to temperature rise in the
Even if the level of v ₁ ′ changes, the capacitor C
The temperature dependency of the output DC voltage v ₁ ′ of the current detector 4 is compensated by the temperature characteristic of ₁ ), and the temperature dependency of the time-delayed operating characteristic 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 a step-down resistor connected to the load side of the main contact 10 of the circuit breaker.
The step-down voltage obtained from 12 is applied to the constant voltage circuit 8 to obtain a constant operating power supply voltage Vcc, and other configurations are the same as those in 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 paying attention to the fact that the forward voltage drop of the diode has a load characteristic with respect to temperature, and the voltage Vcc output from the constant voltage circuit 8 is across both ends. A series circuit of the applied resistor R ₇ and the diodes D ₅ and D ₆ is shown, and the reference voltage v ₃ ′ is output from the connection point of the resistor R ₇ and the diode D ₅ . In the reference voltage generating circuit 13 of FIG. 9, the diodes D ₅ and D ₆ are arranged particularly close to the step-down resistor 12, and the diode is generated by the step-down resistor 12 generating heat.
The temperature of D ₅ and D ₆ 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, a rush current flows in the electric line 2 immediately after the voltage is applied to the electric line 2 and the DC voltage v ₁ ′ output from the current detector 4
Even if the voltage rises abnormally, the rising gradient of the output voltage v ₀ of the CR time constant circuit 5 is suppressed to a small level.
Since v ₃ ′ is also in a high state, the output voltage v ₀ of the CR time constant circuit 5 is less likely to exceed the reference voltage v ₃ ′ due to the inrush current, and the output (malfunction) of the overcurrent detection signal due to the inrush current is further reduced. It can be reduced.

Further, the CR time constant circuit 5 has the characteristics as described above and the reference voltage v ₃ ′ is changed as described above, so that the output voltage v ₀ of the CR time constant circuit 5 becomes equal to the reference voltage v ₃ By intersecting at a greater angle to ′,
Reference voltage in an overcurrent state that slightly exceeds the rated current
It is possible to reduce the variation of the interruption time due to the variation of v ₃ ′.

This point will be described with reference to FIG. In the first embodiment, the reference voltage v ₃ is v _30, v _31, v ₃₂ and when the varies output voltage v ₀ is the reference voltage V ₃₀ of the CR time constant circuit 5 from the start overcurrent flows, v _31, The cutoff time until the overcurrent detection signal is output in excess of v ₃₂ is t ₀ ′, t ₁ ′, t ₂ ′ (see FIG. 4). On the other hand, in the case of the second embodiment, the reference voltage v ₃ ′ is v _3a , v _3b , v with the same width as that of the first embodiment.
_3c , the cutoff time from when the overcurrent starts to flow until the output voltage v ₀ of the CR time constant circuit 5 exceeds the reference voltage v _3a , v _3b , v _3c and the overcurrent detection signal is output is
It becomes 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 CR time constant 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 of the CR time constant circuit 5 in the second embodiment is obtained.
₂ ), v ₀ (i ₃ ) is the reference voltage v ₃ ′ and time t ₃₁ , t ₃₂ ,
crossing t ₃₃

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 capacitor C, which is a temperature sensitive element, is used in the CR time constant circuit 5, a current detection element (current transformer 3 and current detector) for detecting the current I flowing in the electric path 2 is used. 4) has a temperature dependency, and the DC voltage output from the current detector 4 when the ambient temperature rises.
Even if the level of v ₁ ′ changes, the capacitor C
The temperature dependency of the output DC voltage v ₁ ′ of the current detector 4 is compensated by the temperature characteristic of the above, and the temperature dependency of the time-delayed operating characteristic can be reduced as in the first embodiment. There is (effect 1 of temperature compensation on the current detection element).

Further, in the second embodiment, the reference voltage generating circuit 13
Since the thermistor R _TH which is a temperature sensitive element and the diodes D ₅ and D ₆ are used, the temperature of the current detecting 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. Even if there is a dependency and the level of the DC voltage v ₁ ′ output from the current detector 4 decreases due to an increase in the ambient temperature, the temperature characteristics of the thermistor R _TH and the diodes D ₅ and D ₆ are used as a reference. The voltage v ₃ ′ decreases as the ambient temperature rises, compensating for the temperature dependence of the DC voltage v ₁ ′, and it is possible to reduce the temperature dependence of the time-delay operating characteristic (for the current detection element). Effect of temperature compensation 2).

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
And 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 _Z of the divider 14c rapidly increases immediately after the main contact 10 of the circuit breaker is closed and the voltage of the electric circuit 2 is applied. It rises above the normal 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) has a characteristic that the CR time constant circuit has a characteristic that the amount of suppression of the output voltage is large immediately after the voltage is applied to the electric path and then the amount of suppression becomes smaller with the passage of time. Since the DC voltage output from the detector is integrated, even if a rush current flows into the cable immediately after the voltage is applied to the cable and the DC voltage output from the current detector rises abnormally, The rising gradient of the output voltage of the CR time constant circuit can be suppressed to a small level, and
The output voltage of the CR time constant circuit rarely exceeds the reference voltage, and the output (malfunction) of the overcurrent detection signal due to the inrush current can be reduced.

Also, by giving the CR time constant circuit the characteristics described above, the output voltage of the CR time characteristic circuit crosses the reference voltage at a large angle, which causes an overcurrent slightly exceeding the rated current. It is possible to reduce the variation of the interruption time due to the variation of the reference voltage in each state.

In addition, the CR time constant circuit is provided with the above characteristics, so that the time delay operation characteristics can be arbitrarily changed.

The overcurrent detection device according to claim (2) is characterized in that the CR time constant circuit has a characteristic that the amount of suppression of the output voltage is large immediately after the voltage is applied to the electric path and thereafter the amount of suppression is reduced with the lapse of time. The DC voltage output from the detector is integrated.In addition, 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 circuit, and then it is lowered with the lapse of time to reach the steady value. Since the inrush current flows in the circuit immediately after the voltage is applied to the circuit and the DC voltage output from the current detector rises abnormally immediately after the voltage is applied to the circuit, the output voltage of the CR time constant circuit will still increase. Since the rising slope of the CR is kept small and the reference voltage is also high at this time, the output voltage of the CR time constant circuit will not exceed the reference voltage due to the inrush current, and overcurrent detection due to the inrush current will decrease. It is possible to further reduce the output of the signal (malfunction).

In addition, the CR time constant circuit has the above characteristics and the reference voltage is changed as described above, so that the output voltage of the CR time constant circuit crosses the reference voltage at a larger angle. Therefore, it is possible to further reduce the variation in the interruption time due to the variation in the reference voltage in the overcurrent state in which the rated current is slightly exceeded.

Also, by giving the CR time constant circuit the characteristics described above, 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 detecting device of the present invention, FIG. 2 is a diagram showing changes in the capacitance of a capacitor and changes in time constant with respect to temperature changes, and FIG. 3 is a CR time constant circuit. Time chart showing changes in output voltage with time, No. 4
FIG. 5 is a time chart showing the difference in the variation of the interruption time between the first embodiment and the conventional example, and FIGS. 5 and 6 are characteristics showing the difference in the time-delay operation characteristics between the first embodiment and the conventional example, respectively. FIG. 7 is a block diagram of a second embodiment of an overcurrent detecting device of the present invention, and FIGS. 8 and 9 are circuit diagrams showing a concrete configuration of a reference voltage generating circuit, respectively.
FIG. 10 is a time chart showing the time change of the thermistor temperature and the reference voltage, FIG. 11 is a time chart showing the difference in the variation of the interruption time between the second embodiment and the first embodiment, FIG. 12 and FIG. FIG. 13 is a characteristic diagram showing the difference in time-delay operation characteristics between the second embodiment and the conventional example, respectively.
FIG. 14 is a block diagram of a third embodiment of the overcurrent detection device of the present invention, FIG. 15 is a time chart of each part of the reference voltage generation circuit, and FIG. 16 is a block diagram of an overcurrent detection device of a conventional example,
Figures 17, 18, and 19 are time charts for 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 ... CR time constant circuit,
6 ... Comparison circuit, 11,13,14 ... Reference voltage generation circuit

Claims (2)

(57) [Claims] 1. A current detector for detecting a current flowing in a circuit and outputting a DC voltage proportional to its amplitude, a CR time constant circuit for integrating a DC voltage output from this current detector, and a reference voltage. When the output voltage of the CR time constant circuit exceeds the reference voltage by comparing the output voltage of the CR time constant circuit and the reference voltage output from the reference voltage generation circuit, an overcurrent is generated. An overcurrent detection device, comprising: a comparison circuit that generates a detection signal, and heating the capacitor of the CR time constant circuit by heat generation of the electric path to reduce the capacitance. 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.