JP2001268778A - Electronic overcurrent detection device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electronic overcurrent detection device for use in a circuit breaker for wiring or the like with excitation timing characteristics to accommodate external ambient temperature equivalent to those of an overcurrent detection element using a bimetal. SOLUTION: The electronic overcurrent detection device is provided with a processing unit 5 that detects a current in a distribution line, processes the detected current, turns it into a charge signal corresponding to the magnitude of the current, and sends out the signal; a capacitor 7 that stores electric charges from the processing unit 5; a discharge resistor 18 parallel-connected with the capacitor 7 and consisting of a resistor having positive temperature characteristics; and a comparator 10 that compares the potential of the capacitor 7 with a reference voltage and, when the capacitor potential > the reference voltage, produces signal output. The discharge resistor 18 is placed in a recessed portion 20 of the casing of the device where the resistor is in contact wit the outside air so that the detection device can accommodate external ambient temperature better.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electronic overcurrent detection device applied to a circuit breaker for wiring or the like.

[0002]

2. Description of the Related Art FIG.
FIG. 1 is a block diagram of an overcurrent detection device including a conventional electronic circuit disclosed in Japanese Patent Application Laid-Open Publication No. HEI 10-152139. In the figure, reference numeral 1 denotes a distribution line for supplying a current to a load, 2 denotes a switching contact for turning on / off the current of the distribution line 1, 3 denotes a current transformer serving as a current detecting means of the distribution line 1,
4 is an AC / DC conversion circuit for converting the secondary current of the current transformer 2 into a DC voltage suitable for arithmetic processing, 5 is an arithmetic processing unit including a microcomputer, and 6 is a power supply for operating the arithmetic processing unit 5 and the like. Power supply unit. Reference numeral 7 denotes a capacitor, 8 denotes a discharge resistor connected in parallel to the capacitor 7, and 10 denotes a comparator. The potential e of the capacitor 7 is compared with a preset reference voltage E to obtain "potential e> reference voltage E". Output a trigger signal. 9 is a Zener diode for setting a reference voltage of the comparator 10, 11 is a trip circuit, 1
2 is a tripping coil. Reference numeral 13 denotes a tripping mechanism, which trips a trigger member connected to the tripping mechanism 13 and trips the coil 12.
Is kicked off, the switching contact 2 is opened, and the current of the distribution line 1 is cut off.

Next, the operation will be described. The current of the distribution line 1 is detected by the current transformer 3, and the secondary current of the current transformer 3 is converted into a DC voltage signal by the AC / DC conversion circuit 4.
The arithmetic processing unit 5 selects the maximum current phase from the DC voltage signals, converts the DC current signal into a current signal having a charge corresponding to the maximum current, outputs the signal to the capacitor 7, and charges the capacitor 7. On the other hand, the charge of the capacitor 7 is discharged with a time constant determined by the values of the capacitor 7 and the discharge resistor 8 by the discharge resistor 8 connected in parallel to the capacitor 7. The potential e of the capacitor 7 increases if the charge from the arithmetic processing unit 5 is larger than the charge discharged through the discharge resistor 8. Conversely, if the charge is smaller than the discharge charge, the potential e of the capacitor 7 is descend. When the current in the distribution line 1 increases, the charge on the capacitor 7 increases, and the potential e of the capacitor 7 becomes higher than the reference voltage E. The comparator 10 outputs a trigger signal to open and close the on-off contact 2, and the distribution line 1 to protect the distribution line 1 and the load connected to the distribution line 1 from overcurrent.

A circuit breaker protects a distribution line and a connected load from an overcurrent, and a bimetal has been conventionally used as a current detecting element for the purpose of thermal protection due to a temperature rise due to a history of conduction. However, in order to provide the thermal protection function in the electronic circuit breaker, the residual potential of the capacitor 7 which simulates heat radiation by the time constant circuit including the capacitor 7 and the discharge resistor 8 has been used.

[0005]

A circuit breaker is installed for the purpose of preventing overcurrent burning of distribution lines and loads. The allowable current to the distribution line and the load changes according to the surrounding environmental temperature as shown in the temperature correction graph of the circuit breaker in FIG. That is, when the ambient temperature is low, heat dissipation is promoted, so that an allowable current of 100% or more of the rated current is possible. However, when the environmental temperature is high, the allowable current is less than 100% of the rated current. In a circuit breaker that uses a bimetal as a current detection element, the permissible current is obtained by using the deformation taking into account the environmental temperature of the bimetal to obtain the cut-off time characteristic. It is a current.

However, in the above-described electronic overcurrent detection device, the circuit breaker for wiring is operated in a time period in which the heat of the distribution line and the load is simulated by the time constant circuit including the capacitor 7 and the discharge resistor 8. Since the cutoff operation does not take place at the allowable current carrying the current in consideration of the environmental temperature but at the same time at normal temperature or high temperature, there is a problem in overheating protection of distribution lines and loads especially at high environmental temperature.

An object of the present invention is to solve such a problem, and an electronic type suitable for overheating protection of a distribution line and a load when an environmental temperature is high due to a change in a cutoff operation time depending on an environmental temperature of a wiring breaker. An object of the present invention is to provide an overcurrent detection device.

[0008]

SUMMARY OF THE INVENTION An electronic overcurrent detection device according to the present invention detects a current flowing through a distribution line, and calculates the detected current to generate a charge signal corresponding to the magnitude of the current. An arithmetic processing unit for transmitting and receiving the electric charge from the arithmetic processing unit, a discharge resistor including a resistor having a positive temperature characteristic connected in parallel to the capacitor, and a potential and a reference voltage of the capacitor. In comparison, a signal is output when “potential of capacitor> reference voltage”.

[0009] The discharge resistor is disposed at a portion in contact with the outside air outside the device housing.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1 FIG. 1 is a block diagram of an electronic overcurrent detection device according to Embodiment 1 of the present invention. In the figure, reference numerals 1 to 7 and 9 to 13 are the same as those in the description of the conventional apparatus. Reference numeral 18 denotes a discharge resistor having a positive temperature characteristic and connected in parallel with the capacitor 7. A thermistor or the like can be applied as a resistor having a positive temperature characteristic.

A charge corresponding to the current of the distribution line 1 is charged from the arithmetic processing unit 5 to the capacitor 7. Since the discharge resistor 18 has a positive temperature characteristic, as the environmental temperature increases, the resistance value increases, and the discharge of electric charge from the capacitor 7 decreases. For this reason, the potential rise of the capacitor 7 becomes faster than at normal temperature, and the cutoff time due to the overcurrent is shortened. Conversely, when the environmental temperature decreases, the resistance value of the discharge resistor 18 decreases, and the discharge of electric charge from the capacitor 7 increases. Therefore, the potential rise of the capacitor 7 becomes slower than at normal temperature, and at low temperature, interruption due to overcurrent occurs. The time limit becomes longer. As a result, an electronic overcurrent detection device having an energization heat history characteristic and an environmental temperature time characteristic as in the case of the bimetallic current detection element is obtained.

Embodiment 2 FIG. It is desirable that the time characteristic for determining the allowable current depending on the temperature of the wiring breaker corresponds to the outside air temperature.
Since the wiring breaker 8 is disposed in the housing of the circuit breaker, the temperature characteristic of the circuit breaker itself may not be suitable for the external environmental temperature due to the temperature rise of the circuit breaker itself. The second embodiment has a configuration that improves this point.

FIG. 2 is a block diagram of an electronic overcurrent detection device according to a second embodiment of the present invention. In the figure, 1
7, 9 to 13, and 18 are the same as those described in the first embodiment. Reference numeral 20 denotes a housing recess provided outside the housing of the circuit breaker for wiring, and a discharge resistor 1 having a positive temperature characteristic.
Numeral 8 is arranged in the housing recess 20 so as to come into contact with the outside air. As a result, the discharge resistor 18 always has a resistance value based on the external environmental temperature without being affected by a rise in the temperature of the circuit breaker itself, so that it is possible to obtain a timed characteristic corresponding to the outside air temperature.

Since the discharge resistor 18 does not come into contact with another device or a human contact cannot accurately reflect the outside temperature in the timed characteristic, it is desirable to dispose it in the housing recess 20 and protect it with a grid-like cover. .

[0015]

As described above, the discharge resistor 18 connected in parallel to the capacitor 7 for setting the time limit characteristic of the electronic overcurrent detection device is made of a resistor having a positive temperature characteristic. Even in the case of the device, the same thermal history characteristic and environmental temperature time characteristic as those of the bimetal element are provided, and the overheating protection of the distribution line and the load becomes possible.

[Brief description of the drawings]

FIG. 1 is a block diagram of an electronic overcurrent detection device according to a first embodiment of the present invention.

FIG. 2 is a block diagram of an electronic overcurrent detection device according to a second embodiment of the present invention.

FIG. 3 is a block diagram of a conventional electronic overcurrent detection device.

FIG. 4 is a graph showing a temperature correction of the distribution circuit breaker.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Distribution line, 2 Switching contact, 3 Current transformer 4 AC / DC conversion circuit, 5 Arithmetic processing part, 7
Capacitor 8 Discharge resistor, 9 Zener diode, 10 Comparator 11 Trip circuit, 12 Trip coil 18 Discharge resistor with positive temperature characteristic, 20 Housing recess

Claims (2)

[Claims] 1. A current detecting means for detecting a current flowing through a distribution line, an arithmetic processing unit for arithmetically processing the detected current and sending it as a charge signal corresponding to the magnitude of the current, and And a discharge resistor connected in parallel with the capacitor, and a comparator for comparing the potential of the capacitor with a reference voltage. In the comparison between the comparators, "capacitor potential> reference voltage" is obtained. An electronic overcurrent detection device that outputs a signal when the electric discharge occurs, wherein the discharge resistor is a resistor having a positive temperature characteristic. 2. The electronic overcurrent detection device according to claim 1, wherein the discharge resistor having a positive temperature characteristic is arranged at a portion in contact with outside air outside the device housing.