JP2501902B2 - Anti-time circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to an overcurrent trip device mounted on a circuit breaker or the like for the purpose of protecting an electric wire, and controls an electric wire temperature which rises due to an overcurrent flowing in an electric circuit. The present invention relates to an anti-time limit circuit that detects and outputs an output when a set reference temperature is exceeded.

[Conventional technology]

In the conventional anti-time limit circuit, when the electric circuit is overloaded as shown in FIG. 2, the square current circuit 1 charges the capacitor 4 with a charging current I ² proportional to the square of the energizing current I, and the terminal of the capacitor 4 is charged. The voltage Vc rises (6 is a discharging resistor).
Further, the comparison circuit 7 outputs a trip signal when the terminal voltage Vc of the capacitor 4 becomes higher than the reference voltage Vref.

That is, the overcurrent detection circuit detects the overcurrent state of the circuit by the anti-time limit circuit, and then detects the capacitor 4 in the anti-time limit circuit.
After a lapse of time until the terminal voltage Vc becomes higher than the reference voltage Vref, the trip of the comparison circuit 7 outputs.

[Problems to be Solved by the Invention]

In Fig. 3, after a load current smaller than the overload current flows and the wire rises to a specific temperature T ₁ within the allowable temperature,
When an overload current flows in the circuit, the wire starts to rise in temperature with T ₁ as the initial temperature. However, in the conventional device,
Assuming the initial temperature of the electric wire as the electric wire temperature T ₀ when there is no energization, the capacitor starts charging after an overload condition occurs.
In some cases, a temperature error of (T ₁ −T ₀ ) occurred when the temperature of the wire increased. Further, in FIG. 4, after an overload current flows and the wire temperature rises to a temperature T ₂ within the allowable temperature,
When the energizing current decreases to a current value I ₃ that is smaller than the rated current, the wire temperature drops from the temperature T ₂ with specific heat dissipation characteristics, and finally converges to the steady temperature T ₃ when the current I ₃ flows in the wire. .

However, in the conventional device, the capacitor discharges in accordance with the heat dissipation characteristic that finally converges to the wire temperature T ₀ when no current is applied, so that the temperature drop becomes larger than the heat dissipation characteristic of the wire temperature. Therefore, if an overload current is supplied again while the temperature of the wire is decreasing, an error may occur due to a difference in discharge characteristics, and reliable wire protection may not be performed.

[Means for solving the problem]

In order to solve the above problems, the present invention relates to a square current generating means having two output terminals for outputting a current signal proportional to the square of a current flowing in an electric circuit, and one end of the square current generating means is connected to one output terminal of the square current generating means. And a non-grounded terminal is connected to the other output terminal of the square current generating means, the other end of which is grounded, and the first diode so that a current signal flows from the output terminal, A capacitor whose ground terminal is grounded, a second diode connected to both output terminals so that a current flows from the other output terminal to one output terminal, a non-ground terminal of the capacitor, and the current-voltage conversion circuit. A resistor connected between one end of the means and a comparing means for comparing the terminal voltage of the capacitor with a preset voltage.

[Work]

According to the present invention, the capacitor is pre-charged to the voltage Va proportional to the square of the energizing current even when the energizing current of the circuit is smaller than the rated current. Further charged by a current proportional to the surplus, the charging voltage of the capacitor is the voltage value Va
To rise in line with the rising characteristics of the wire temperature. Further, when the current flowing through the circuit is decreased, the load of the capacitor is discharged through a discharge resistor until it converges to a voltage Vb proportional to the square of the current flowing, and the terminal voltage of the capacitor follows the decrease characteristic of the wire temperature. To descend.

〔Example〕

 Hereinafter, the present invention will be described in detail with reference to the drawings.

In FIG. 1, in a square current circuit 10 having two systems of output terminals 01 and 02 proportional to the square of the energizing current of the electric circuit,
The anode terminal of the backflow prevention diode 30 is connected to the other output terminal 02, the cathode terminal of the backflow prevention diode 30 is connected to the positive electrode of the delay capacitor 40, and the negative electrode of the delay capacitor 40 is grounded.

One end of the current-voltage conversion resistor 20 is connected to one output end 01 of the square current circuit 10 and the other end is grounded. Next, the anode end of the diode 50 is connected to the anode end of the backflow prevention diode 30, and the cathode end of the diode 50 is connected to the output end 01 of the square current circuit 10.

The positive electrode of the capacitor 40 and the current-voltage conversion resistor
Connect a discharge resistor 60 to the non-grounded end of 20
The positive electrode of 40 is connected to the compared input terminal of the comparison circuit 70. Further, the reference voltage Vref is input to the comparison input terminal of the comparison circuit 70.

According to the above configuration, the terminal voltage of the current-voltage conversion resistor 20 connected to the one output terminal 01 of the square current circuit 10 is proportional to the square of the current flowing in the electric path, and the wire temperature is finally determined. The value is proportional to the converged temperature value.

In Fig. 5, when the current flowing in the electric circuit increases from I ₁ to I ₂ and the wire temperature rises from T ₁ to T ₂ , the terminal voltage Vc of the delay capacitor 40 is the voltage V representing the wire temperature T _{1. 1}
Since the voltage rises with an increment proportional to the square of the energizing current and becomes constant at the voltage V ₂ representing the wire temperature T ₂ , the same change as the wire temperature rising characteristic occurs.

Further, in FIG. 6, the energization current path from the I ₂ '
When the wire temperature decreases to I ₁ ′ and the wire temperature drops from T ₂ ′ to T ₁ ′, the terminal voltage Vc of the delay capacitor 40 is the wire temperature.
From the voltage V ₂ ′ representing T ₂ ′, the voltage drops with the characteristics determined by the electrical characteristics of the discharge resistor 60 and the delay capacitor 40,
Since it is constant at the voltage V ₂ ′ representing the wire temperature T ₂ ′, it changes in the same manner as the decrease characteristic of the wire temperature.

Therefore, the terminal voltage Vc of the capacitor 40 has the same characteristic as the wire temperature, and more reliable wire protection can be performed by comparing with the voltage representing the allowable temperature of the wire.

〔The invention's effect〕

As described above, according to the present invention, it is possible to provide an anti-time limit circuit that accurately detects a change in wire temperature.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an embodiment of an anti-time limit circuit embodying the present invention, FIG. 2 is a configuration diagram of a conventional anti-time limit circuit, and FIGS. 3 and 4 are wire temperature in the conventional anti-time limit circuit. FIGS. 5 and 6 are diagrams showing changes in the terminal voltage of the delay capacitor, and FIGS. 5 and 6 are diagrams showing changes in the wire temperature and the terminal voltage of the delay capacitor in the embodiment of the anti-time delay circuit embodying the present invention. 10: Square current generator circuit, 20: Current-voltage conversion resistor, 30: Backflow prevention diode, 40: Delay capacitor, 50: Diode, 60: Discharge resistor, 70: Comparison circuit.

Claims (1)

(57) [Claims] 1. A square current generating means having two systems of output terminals for outputting a current signal proportional to the square of a current flowing through an electric circuit, and one end of the square current generating means is connected to one output terminal of the square current generating means and the other end thereof is connected. Is connected to a current-voltage converting means to be grounded, and the other output terminal of the square current generating means is connected to a non-ground terminal via a first diode so that a current signal flows from the output terminal, and the ground terminal is grounded. A capacitor, a second diode connected to both output terminals so that a current flows from the other output terminal to one output terminal, a non-grounded terminal of the capacitor, and one end of the current-voltage converting means. An anti-time limit circuit comprising: a resistor connected between the capacitor and a comparator for comparing a terminal voltage of the capacitor with a preset voltage.