JP2567439B2 - 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. 10, a conventional overcurrent detection device of this type detects a current I flowing in a circuit 52 drawn from a commercial AC power supply 51, and when a current I exceeds a threshold value, a predetermined time delay characteristic is detected. With this, the trip coil 59 of the circuit breaker is energized to open 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 I, 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. In addition to the comparison circuit 56 with a predetermined time delay characteristic, the comparison circuit 56
The threshold value is compared with.

The current detector 54 shown in FIG. 11 (b) having a voltage value proportional to the amplitude of the current i output from the secondary side of the current transformer 53 as shown in FIG. 11 (a). 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. 13 (a), reference numeral 56 compares the output voltage v ₂ of the time delay circuit 55 with the threshold voltage v _3, and when the voltage v ₂ becomes higher than the threshold 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 potential v ₂ of the delay circuit 55 may exceed the threshold 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 threshold 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 threshold voltage v _{3 at} a small angle.For example, as shown in FIG. 14, the threshold voltage v ₃ is v ₃₀ , v ₃₁ , v _If it is slightly different from ₃₂ , the voltage v ₂ is the threshold 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]

In the overcurrent detection device of the present invention, the current detector detects the current flowing in the electric path, and the current detector outputs a current voltage having a voltage value proportional to the amplitude of the current flowing in the electric path. The direct current voltage is integrated by the time delay circuit.

On the other hand, immediately after the voltage is applied to the electric circuit, the threshold voltage generation circuit generates a threshold voltage higher than the steady value, and then the threshold voltage generation circuit generates a threshold voltage that decreases with time and stabilizes at the steady value. There is.

Then, in the comparison circuit, the output voltage of the time delay circuit is compared with the threshold voltage generated from the threshold voltage generation circuit, and when the output voltage of the time delay circuit exceeds the threshold voltage, the overcurrent detection signal is generated from the comparison circuit. I am trying.

[Action]

According to the configuration of the present invention, the threshold voltage output from the threshold 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 it is lowered with time to stabilize at the steady value. Even if an inrush current flows through the circuit immediately after the voltage is applied to the circuit and the output voltage of the time delay circuit rises abnormally, the threshold voltage is also high at this time, so the rush current causes The output voltage rarely exceeds the threshold voltage, and the output (malfunction) of the overcurrent detection signal due to the inrush current can be reduced.

Also, by changing the threshold voltage as described above, the output voltage of the time delay circuit crosses the threshold voltage at a large angle, and the threshold voltage in the overcurrent state slightly exceeding the rated current. It is possible to reduce the variation of the interruption time due to the variation of.

Further, the time-varying operation characteristic can be arbitrarily changed by changing the threshold voltage.

〔Example〕

A first embodiment of the present invention will be described with reference to FIGS. 1 to 7. That is, this overcurrent detection device is incorporated in, for example, a circuit breaker, detects the current I flowing in the electric path 2 drawn from the commercial AC power supply 1, and has a predetermined time delay characteristic when the current I exceeds a threshold value. Energizes the trip coil 9 of the circuit breaker, which causes the main contact of the circuit breaker to
It is to open 10. For this reason, the overcurrent detection device of this embodiment applies the step-down voltage obtained from the step-down resistor 12 connected to the load side of the main contact 60 of the circuit breaker to the constant voltage circuit 8, thereby A constant operating power supply voltage V _cc is applied from 8 to the comparison circuit 6, the output circuit 7 and the threshold voltage generating circuit main body 11a, and the current I flowing through the electric line 2 is changed.
Is detected by the current detector 4 via the current detector 4 and the output of the current detector 4 is integrated by the time delay circuit 5 to give a predetermined time delay characteristic to the comparison circuit 6 and the threshold voltage generating circuit main body 11
The comparison circuit 6 compares the threshold voltage v ₀ output from the threshold voltage generation circuit 11 including the a and the step-down resistor 12 with the output voltage v _{2 of the time} delay circuit.

The current detector 4 detects the current I flowing in the electric path 2 and outputs a DC voltage proportional to the amplitude of the current I flowing in the electric path 2. Specifically, the current transformer 3 is similar to the conventional example. The current i output from the secondary side of is converted into a DC voltage v ₁ having a voltage value proportional to its amplitude and output. Further, the time delay circuit 5 integrates the DC voltage v ₁ output from the current detector 4 and outputs a voltage v ₂ as in the conventional example.

Further, the threshold voltage generation circuit 11 sets the threshold voltage v ₀ to a value higher than the steady value immediately after the voltage is applied to the electric path 2, and then lowers the threshold voltage v ₀ with the lapse of time to stabilize it at the steady value. , As described above, the threshold voltage generating circuit body
11a and step-down resistance 12
As a concrete circuit configuration example of 1a, those shown in FIGS. 2 and 3 are conceivable.

First, in the example of FIG. 2, the voltage V _cc output from the constant voltage circuit 8 is applied across the resistor R ₁ and the thermistor having a negative characteristic.
A series circuit of R _TH and resistor R ₂ is shown, and a threshold voltage v ₀ is output from the connection point of the resistor R ₁ and the thermistor R _TH . The threshold voltage generating circuit main body 11a shown in FIG.
_TH is arranged in the vicinity of the step-down resistor 12 so that the temperature of the thermistor R _TH rises due to the heat generation of the step-down resistor 12 to lower its resistance value.

Therefore, when the operation of the threshold voltage generation circuit 11 as a whole is observed, 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 the step-down voltage is accordingly reduced. use resistor 12 generates heat, the heat is transmitted to the thermistor R _TH threshold voltage generating circuit body 11a, the thermistor R _TH
As a result, the temperature θ increases as shown in FIG. 4 (a). 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 threshold voltage v ₀ output from the threshold voltage generating circuit main body 11a gradually decreases from an initial value higher than the steady value as shown in FIG. 4 (b), and stabilizes at the steady value. Will be done.

Next, the example of FIG. 3 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, and the voltage V _cc output from the constant voltage circuit 8 is between both ends. A series circuit of a resistor R ₃ and diodes D ₁ and D ₂ applied to is shown, and a threshold voltage v ₀ is output from a connection point of the resistor R ₃ and the diode D ₁ . In the threshold voltage generating circuit main body 11a shown in FIG. 3, the diodes D ₁ and D ₂ are arranged especially close to the step-down resistor 12, and the diode 12 is generated by the step-down resistor 12 generating heat.
The temperature of D ₁ and D ₂ rises and its forward voltage drop is reduced. The operation of the threshold voltage generating circuit 11 as a whole in this case is the same as in the case of FIG.

Further, the comparison circuit 6 compares the output voltage v ₂ of the time delay circuit 5 with the threshold voltage v _0, and sets the output voltage v ₄ to a high level when the voltage v 2 becomes higher than the threshold voltage v ₀ (overcurrent Generate a detection signal). 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 threshold voltage v ₀ output by the threshold voltage generation circuit 11 is set to a value higher than the steady value immediately after the voltage is applied to the electric path 2 and then lowered over time to stabilize at the steady value. Therefore, immediately after the voltage is applied to the electric line, an inrush current flows into the electric line 2 at the time of starting the motor or charging the power source capacitor, and the output voltage v ₂ of the time delay circuit 5
May rise abnormally, but at this time the threshold voltage
Since v _{0 is} also high, the time delay circuit 5
The output voltage v ₂ of is less likely to exceed the threshold voltage v ₀ ,
It is possible to reduce the output (malfunction) of the overcurrent detection signal due to the inrush current.

In addition, since the threshold voltage v ₀ is changed as described above, the output voltage v ₂ of the time delay circuit 5 crosses the threshold voltage v _{0 at a} large angle, which slightly exceeds the rated current. Further, it is possible to reduce the variation of the interruption time due to the variation of the threshold voltage v ₀ 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 5 is the threshold voltage after the overcurrent starts to flow when the threshold 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. 14). On the other hand, in the case of the embodiment, when the threshold voltage v ₀ varies with v ₀₀ , v ₀₁ , v _{02 within the} same width as the conventional example, the output voltage v _{2 of the time} delay circuit 5 starts after the overcurrent starts to flow. Is the threshold voltage v
The interruption time until the overcurrent detection signal is output beyond ₀₀ , v ₀₁ , v ₀₂ is t ₀ , t ₁ ′, t ₂ ′. Therefore, comparing the conventional example with the example, the variation T'of the interruption times t ₀ , t ₁ ′, t ₂ ′ in the example is compared with the variation T of the interruption times t ₀ , t ₁ , t _{2 in} the conventional example. It is clear that the number is decreasing.

In addition, the configuration for changing the threshold voltage v ₀ can arbitrarily change the time-delay operation characteristic. This point will be described with reference to FIGS. 6 and 7. FIG. 6 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 of the time delay circuit 5.
₂ (i ₂ ), v ₂ (i ₃ ) changes and the threshold voltage v ₃ in the conventional example
3 shows changes in the threshold voltage v _{0 in} the example.
In FIG. 6, the output voltage v ₂ (i ₁ ), v ₂ (i ₂ ), v
₂ (i ₃ ) intersects with the threshold voltage v ₃ at times t ₁₁ , t ₁₂ , and t ₁₃ , and intersects with the threshold voltage v ₀ at times t ₂₁ , t ₂₂ , and t ₂₃ , respectively.

The relationship between the Figure 6, indicating the time limit operation characteristics on a graph taking the electric current i to the horizontal axis with taking time on the vertical axis, as shown in FIG. 7, in the case of prior art in solid lines A ₁ In the case of the embodiment, it becomes as shown by the solid line A ₂ ,
In the case of the embodiment, by changing the gradient of the threshold value v ₀ , it becomes possible to arbitrarily change the time-delay operation characteristic as described above.

Further, in this embodiment, since the threshold voltage generating circuit main body 11a uses the thermistor R _TH which is a heat sensitive element and the diodes D ₁ and D ₂ , a current detecting element (current transformer) for detecting the current I flowing in the electric path 2 is used. 3 and the components of the current detector 4) have temperature dependence, and even if the level of the DC voltage v ₁ output from the current detector 4 decreases due to the rise in ambient temperature, the thermistor R _TH and the diode Due to the temperature characteristics of D ₁ and D ₂ , the threshold voltage v ₀ decreases as the ambient temperature rises, compensating for the temperature dependence of the DC voltage v ₁ and reducing the temperature dependence of the time-delayed operation characteristics. be able to.

A second embodiment of the present invention will be described with reference to FIGS. 8 and 9. This overcurrent detection device uses a threshold voltage generation circuit 13 in place of the threshold voltage generation device 11 and a current detector 4'in place of the current detector 4, and other configurations are the same as those of the first embodiment. Similar to the example.

The threshold voltage generating circuit 13 uses the heat generated by the step-down resistor 12 connected to the electric circuit 2 as in the above-described embodiment to generate the threshold voltage.
Unlike the one that changes v ₀ , it uses a CR timer to change the threshold voltage v ₀ .

More specifically, the threshold voltage generating circuit 13 includes a constant voltage circuit 8 connected to the load side of the main contact 10 of the circuit breaker.
Voltage divider circuit 13a that divides the operating power supply voltage V _cc output from
And a time constant circuit 13b that charges with the operating power supply voltage V _cc , a divider 13c that divides the output voltage v _X of the voltage divider circuit 13a by the output voltage v _Y of the time constant circuit 13b, and an output potential v of the divider 13c. _{And a} voltage dividing circuit 13d for dividing _Z.

In this case, the voltage dividing circuit 13a comprises a series circuit of resistors R _11, R _12, time constant circuit 13b comprises a series circuit of a resistor R ₁₃ and the resistor R ₁₄ and capacitor C ₁ in parallel circuit, the voltage dividing circuit 13d is It consists of resistors R ₁₅ and R ₁₆ .

In this threshold voltage generating circuit 13, 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 13a is rapidly fixed as shown in FIG. It rises to a value and holds that state. On the other hand, the output potential v _Y of the time constant circuit 13b becomes a constant value where it gradually increases from zero. Therefore, the threshold voltage v ₀ output from the voltage dividing circuit 13d that divides the output voltage v _Z of the divider 13c 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 current detector 4 ', a resistor R ₁₈ and diode D ₃ to D ₆ Prefecture, will generate a full wave rectified voltage as an output to a DC voltage.

The time delay circuit 5 is composed of a resistor R ₁₇ and a capacitor C ₂ .

This embodiment has the same effect as that of the first embodiment except the effect of temperature compensation for the current detecting element in the first 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〕

According to the overcurrent detection device of the present invention, the threshold voltage output by the threshold 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 lowered with time to stabilize at the steady value. Therefore, even if the inrush current flows in the circuit immediately after the voltage is applied to the circuit and the output voltage of the time delay circuit rises abnormally, the threshold voltage is also high at this time, so the time due to the inrush current increases. The output voltage of the delay circuit is less likely to exceed the threshold voltage, and the input (malfunction) of the overcurrent detection signal due to the inrush current can be reduced.

Also, by changing the threshold voltage as described above, the output voltage of the time delay circuit crosses the threshold voltage at a large angle, and the threshold voltage in the overcurrent state slightly exceeding the rated current. It is possible to reduce the variation of the interruption time due to the variation of.

Further, the time-varying characteristic can be arbitrarily changed by changing the threshold voltage.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a first embodiment of the present invention, FIGS. 2 and 3 are circuit diagrams showing a concrete configuration of a threshold voltage generating circuit, and FIG. 4 is a thermistor temperature and a threshold voltage. FIG. 5 is a time chart showing a change with time, FIG. 5 is a time chart showing a difference in variation in breaking time between the embodiment and the conventional example, and FIG. 6 is each voltage showing difference in time-delay operation characteristic between the embodiment and the conventional example. Time chart,
FIG. 7 is a characteristic diagram showing the difference in time-delay operation characteristics between the embodiment and the conventional example, FIG. 8 is a block diagram showing the configuration of the second embodiment of the present invention, and FIG. 9 is a diagram showing the threshold voltage generating circuit. Time chart of each part, Fig. 10 is a block diagram showing the configuration of a conventional example, and Fig. 11, Fig. 12 and Fig. 13 are respectively
FIG. 10 is a time chart of each part of FIG. 10, and FIG. 14 is a time chart showing the variation of the interruption time in the conventional example. 2 ... Electric circuit, 4 ... Current detector, 5 ... Time delay circuit, 6 ...
… Comparison circuit, 11 …… Threshold voltage generation circuit

Claims (1)

(57) [Claims] 1. A current detector for detecting a current flowing in an electric line and outputting a DC voltage proportional to its amplitude, a time delay circuit for integrating a DC voltage output from the current detector, and a voltage to the electric line. Immediately after the application, the threshold voltage is set to a value higher than the steady value, and then the threshold voltage is lowered with the passage of time to stabilize at the steady value, and the output voltage of the time delay circuit and the threshold voltage generation circuit. An overcurrent detection device comprising: a comparison circuit that compares an output threshold voltage with an output voltage of the time delay circuit to generate an overcurrent detection signal when the output voltage exceeds the threshold voltage.