JP2567440B2 - 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. 9, 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 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 a voltage on the load side of the main contact 60 of the circuit breaker to the low voltage circuit 58 so that the comparison circuit 56 and the output circuit 57 perform a constant operation from the low voltage circuit 58. A current I flowing in the electric path 52 by applying the power supply voltage V _cc
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 to add a predetermined time delay characteristic to the comparison circuit 56, Circuit 56
The threshold value is compared with.

The current detector 54 described above uses a DC voltage as shown in FIG. 10 (b) which is proportional to the amplitude of the current i as shown in FIG. 10 (a) output from the secondary side of the current transformer 53. 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. Further, as shown in FIG. 12A, the comparison circuit 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. As shown in FIG. 12 (b), the output voltage v _{4 is set} to a high level (overcurrent detection signal is generated). 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 a trip current to flow in the trip coil 59 of the circuit breaker to open the main contact 60.

[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 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 with a relatively gentle slope and intersects the threshold voltage v _{3 at} a small angle.For example, as shown in FIG. 13, the threshold voltage v ₃ is v ₃₀ , v ₃₁ , and v 3. _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 direct current voltage (full-wave rectified voltage) proportional to the amplitude of the current flowing in the electric path is output from the current detector. The DC voltage output from is integrated by the self-extending circuit.

On the other hand, by providing a temperature sensitive element in the threshold voltage generation circuit and raising the temperature of the temperature sensitive element due to heat generation in the electric circuit due to the current flowing in the electric circuit, when the temperature of the temperature sensitive element immediately after energizing the electric circuit is low, A threshold voltage with a value higher than the steady value is generated, and after starting the energization of the circuit, the threshold voltage generation circuit generates a threshold voltage that decreases with the temperature rise of the temperature sensitive element due to heat generation in the circuit and stabilizes at the steady value. .

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.

[Work]

According to the configuration of the present invention, the temperature sensing element is provided in the threshold voltage generating circuit, and the temperature sensing element is heated by the heat generated in the circuit due to the current flowing through the temperature sensing element. When the temperature of the temperature element is low, the threshold voltage generated by the threshold voltage generation circuit is set to a value higher than the steady value, and after the energization of the electric circuit, the threshold voltage generation circuit is generated according to the temperature rise of the temperature sensitive element due to heat generation of the electric circuit. Since the threshold voltage is lowered to stabilize at a steady value, even if the rush voltage may flow in the circuit immediately after the voltage is applied to the circuit and the output voltage of the time delay circuit may rise abnormally, Since the threshold voltage is also high, the output voltage of the time delay circuit rarely exceeds the threshold voltage due to the inrush current, 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〕

An embodiment of the present invention will be described with reference to FIGS. 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. The trip coil 9 of the circuit breaker is energized to open the main contact 10 of the circuit breaker.

Therefore, in the overcurrent detection device of this embodiment, by applying a voltage to the constant voltage circuit 8 connected to the load side of the main contact 10 of the circuit breaker, the constant voltage circuit 8 outputs the comparison circuit 6 and the output circuit 7. And a constant operating power supply voltage for the threshold voltage generating circuit 11.
By adding V _cc , the current I flowing in the electric path 2 is detected by the current detector 4 through the current transformer 3, and the output of the current detector 4 is integrated by the time delay circuit 5 to obtain a predetermined time delay characteristic. In addition to the comparison circuit 6, the comparison circuit 6 compares the threshold voltage v ₀ output from the threshold voltage generation circuit 11 and the output voltage v ₂ of the time delay circuit 5.
I try to compare with.

The current detector 4 detects the current I flowing in the electric path 2 and outputs a direct current voltage (a full wave by the resistor R and the diodes D ₃ , D ₄ , D ₅ , D ₆₎ proportional to the amplitude of the current I flowing in the electric path 2. The current i output from the secondary side of the current transformer 3 is converted into a DC voltage v ₁ ′ proportional to its amplitude and output, 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, as a concrete circuit configuration of the threshold voltage generating circuit 11, those shown in FIGS. 2 and 3 can be considered.

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 . In the threshold voltage generating circuit 11 of FIG. 2, in particular, the thermistor R _TH is arranged close to the electric line 2 so that the temperature of the thermistor R _TH rises due to heat generation of the electric line 2 and its resistance value decreases.

Therefore, when the operation of the threshold voltage generating circuit 11 as a whole is observed, the main contact 10 of the circuit breaker is closed and the current I
When the flows, this accompanied path 2 generates heat, the heat is transmitted to the thermistor R _TH threshold voltage generating circuit 11, that the temperature θ of the thermistor R _TH is increased as shown in FIG. 4 (a) Become.

In this case, the temperature θ of the thermistor R _TH is room temperature immediately after the main contact 10 is closed, and then rises with the passage of time,
It equilibrates when it rises to a certain point. This thermistor R
With the temperature change of the _TH, the resistance value of the thermistor R _TH is gradually lowered 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 generation circuit 11 gradually decreases from an initial value higher than the steady value and stabilizes at the steady value, as shown in FIG. 4 (b). It will be.

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. shows a series circuit of a resistor R ₃ and a diode D _1, D ₂ are applied to the threshold voltage v ₀ from the connection point of the resistor R3 and the diode D ₁ is output. Threshold voltage generating circuit 11 of the third diagram, in particular a diode D _1, disposed close to the path 2 of D _2, the forward voltage drop diode D _1, D ₂ by heat generation of the path 2 is increased temperature Is trying to lower. 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 output voltage v ₂ becomes higher than the threshold voltage v ₀ ( 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.

In this overcurrent detection device, a temperature sensitive element is provided in the threshold voltage generation circuit 11, and the temperature sensitive element is heated by the heat generated in the electrical path 2 by the current I flowing through the temperature sensitive element in the electrical path 2. Threshold voltage generation circuit when the temperature of the temperature sensitive element is low immediately after energization
The threshold voltage v ₀ generated by 11 is set to a value higher than a steady value, and after the energization of the electric circuit 2 is started, the threshold voltage v ₀ generated by the threshold voltage generation circuit 11 according to the temperature rise of the temperature sensing element due to the heat generation of the electric circuit 2.
Since it is lowered to stabilize at a steady value,
Immediately after the voltage is applied to the electric line 2, even if the output voltage v ₂ of the time delay circuit 5 rises abnormally, for example, a rush current may flow in the electric line 2 at the time of starting the motor or charging the power source capacitor. At this time, since the threshold voltage v ₀ is also high, the output voltage v ₂ of the time delay circuit 5 rarely exceeds the threshold voltage v _{0 due} to the inrush current, and the output of the overcurrent detection signal due to the inrush current (malfunction) ) Can be reduced.

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 55 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 after exceeding v ₃₀ , v ₃₁ , and v ₃₂ is t ₀ , t ₁ , and t ₂ (see FIG. 13). 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 cutoff time until the overcurrent detection signal is output beyond ₀₀ , v ₀₁ , v ₀₂ is t ₀ , t ₀ ′, 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 the output voltage v ₂ (i ₁ ), v ₂ (i ₂ ), v ₂ (i of the time delay circuit 5 when the secondary current of the current transformer 3 is i ₁ , i ₂ , and i _{3. 3} ) and the threshold voltage v ₃ in the conventional example and the threshold voltage v _{0 in} the example. In FIG. 6, the output voltages v ₂ (i ₁ ), v ₂ (i ₂ ), v ₂ (i ₃ ) cross the threshold voltage v ₃ at times t ₁₁ , t ₁₂ , t ₁₃ respectively, and It intersects the 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 slope of the threshold voltage v ₀ ,
As described above, it is possible to arbitrarily change the time delay operation characteristic.

Further, in this embodiment, since the thermistor R _TH which is a heat sensitive element and the diodes D ₁ and D ₂ are used in the threshold voltage generating circuit 11, a current detecting element (current transformer 3) for detecting the current I flowing in the electric path 2 is used. And the components of the current detector 4) have temperature dependence and the level of the DC voltage v ₁ ′ output from the current detector 4 changes due to an increase in ambient temperature, the thermistor R _TH or 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 ′, reducing the temperature dependence of the time-delayed operation characteristics. can do.

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 temperature sensitive element is provided in the threshold voltage generating circuit, and the temperature sensitive element is heated by the heat generated in the electric path due to the current flowing through the temperature sensitive element in the electric path.
The threshold voltage generated by the threshold voltage generation circuit is set to a value higher than the steady value when the temperature of the temperature sensing element is low immediately after energizing the circuit, and after the energization of the circuit, the temperature of the temperature sensing element rises due to heat generation of the circuit. Since the threshold voltage generated by the threshold voltage generation circuit is lowered and stabilized at a steady value, an inrush current may flow in the circuit immediately after the voltage is applied to the circuit and the output voltage of the time delay circuit may rise abnormally. However, since the threshold voltage is also high at this time, the output voltage of the time delay circuit rarely exceeds the threshold voltage due to the inrush current, and the output (malfunction) of the overcurrent detection signal due to the inrush current is reduced. can do.

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.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of an embodiment of the present invention, FIGS. 2 and 3 are circuit diagrams showing a specific configuration of a threshold voltage generating circuit, and FIG. 4 is a time change of the thermistor temperature and threshold voltage. 5 is a time chart showing the difference in the variation of the breaking time between the embodiment and the conventional example, and FIG. 6 is a time chart of each voltage showing the difference in the time-delay operation characteristics between the embodiment and the conventional example. 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 time chart showing the difference in threshold voltage change between the embodiment and the conventional example, and FIG. A block diagram showing the configuration of an example, FIG. 10, FIG. 11 and FIG.
FIG. 12 is a time chart of each part of FIG. 9, and FIG. 13 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 current flowing in the electric line. Has a temperature sensitive element that heats up due to heat generation of the electric circuit, and when the temperature sensitive element has a low temperature, the threshold voltage is set to a value higher than a steady value, and the threshold voltage is increased according to a temperature rise of the temperature sensitive element due to heat generation of the electric circuit. By comparing the output voltage of the time delay circuit and the threshold voltage output from the threshold voltage generation circuit with the threshold voltage generating circuit that lowers and stabilizes at the steady value. An overcurrent detection device comprising: a comparison circuit that generates an overcurrent detection signal when the voltage exceeds the voltage.