JPH07170651A - Electronic circuit breaker for wiring protection - Google Patents

Abstract

PURPOSE:To provide an electronic wiring protection circuit breaker which can positively protect wiring by trip operation securely even if an arithmetic processing part is repeatedly set by an intermittent overcurrent. CONSTITUTION:In an electronic wiring protection circuit breaker for breaking wiring with a time delay or instantly by detecting the load current of the wiring, an AC/DC conversion circuit 1 for converting a load current to a DC voltage signal, an arithmetic processing part 3 for converting the DC voltage signal to coarse and dense pulses according to a voltage level, a voltage/current conversion circuit 4 for converting the pulses output from the arithmetic processing part 3 to current, and a capacitor 5 for time delay which is charged by the output current of the voltage/current conversion circuit 4 are provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electronic wiring protection circuit breaker which uses a microcomputer to timely or instantaneously interrupt a load circuit.

[0002]

2. Description of the Related Art Conventionally, as shown in FIG. 5, an electronic wiring protection circuit breaker detects a load current flowing in each wiring by a current transformer CT and converts it into a DC voltage signal by an AC / DC conversion circuit. The voltage signals Er, Es, Et are input to the arithmetic processing unit, and the cutoff characteristic arithmetic program of the arithmetic processing unit causes
Selects the maximum voltage phase from the input voltage signals, determines the overcurrent level based on the voltage of the maximum voltage phase, sets the time, and outputs the trigger signal E ₀ to the trip circuit after a lapse of a predetermined time. Then, the trip coil of the trip mechanism is excited to disconnect the load circuit.

However, since the arithmetic processing unit uses the secondary current of the current transformer CT as a power source because it is insulated from the power source line in order to improve reliability, the load current is intermittently applied in a short time. , The reset function of the arithmetic processing unit is repeatedly activated and it is not possible to set the time according to the overcurrent,
Since the trip operation cannot be obtained, there is a problem in that the overcurrent flowing intermittently causes the wiring to generate heat and cause a melting damage to the coating, so that the wiring cannot be reliably protected. Also, if noise enters the arithmetic processing unit, it will be initialized and restore normal operation, but if a signal is output to the trip circuit before the arithmetic processing unit is initialized, the circuit breaker will malfunction. There was a problem.

[0004]

SUMMARY OF THE INVENTION The object of the present invention is to solve the above-mentioned problems and to ensure the wiring protection by reliably performing the trip operation even if the arithmetic processing unit is repeatedly reset due to intermittent overcurrent. (EN) Provided is an electronic wiring protection circuit breaker which can be applied to

[0005]

SUMMARY OF THE INVENTION The present invention is an electronic wiring protection circuit breaker for detecting a load current of a wiring to interrupt the wiring in a timed or instantaneous manner. The AC / DC conversion converts the load current into a DC voltage signal. A circuit, an arithmetic processing unit for converting the DC voltage signal into a coarse / fine pulse according to a voltage level, a voltage / current conversion circuit for converting the pulse output by the arithmetic processing unit into a current, and the voltage / current conversion And a time-limit capacitor charged by the output current of the circuit.

[0006]

The electronic wiring protection circuit breaker of the present invention converts the load current flowing in each phase of the wiring into a DC voltage signal by the AC / DC conversion circuit, and in the arithmetic processing unit to which the voltage signal is input, The maximum voltage signal among them is selected, and the coarse and fine pulses corresponding to the DC voltage signal level are output. This pulse output is converted into a current by the voltage / current conversion circuit, and intermittent or continuous current according to the density of the pulse is supplied to the capacitor for the timed operation for charging. When the capacitor reaches the trip voltage, the trigger output is input to the trip circuit, the trip coil of the trip mechanism is excited, and the load circuit is shut off.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the illustrated embodiments. Reference numeral 1 denotes an AC / DC conversion circuit that detects a load current of each phase of the wiring 2 and converts it into a DC voltage signal Er, Es, Et, and the AC / DC conversion circuit detects a current of each phase of the wiring 2. The current transformer 2a is connected.

Reference numeral 3 denotes an arithmetic processing unit composed of a microcomputer connected to the AC / DC conversion circuit 1, and the power source of the arithmetic processing unit 3 depends on the secondary current of the current transformer 2a. Then, the arithmetic processing unit 3 uses the voltage / frequency conversion output program to input the DC voltage signals Er, Es,
The maximum voltage phase is selected from Et and coarse and fine pulse output is performed according to the DC voltage signal level.

Instantaneous or short time delay characteristics C shown in FIG.
In the case of, the continuous pulse shown in C of FIG. 3 is output,
In the case of the long time delay characteristic B shown in FIG. 2, the intermittent pulse shown in B of FIG. 3 is output. Further, in the case of the characteristic A at the rated current, as shown in A of FIG. 3, pulses having a larger interval than the above pulses are intermittently output. Therefore, the charging voltage E ₁ for each of the characteristics A, B, and C becomes as shown in the graph of A, B, and C shown in FIG.

Reference numeral 4 denotes a voltage connected to the arithmetic processing unit 3 /
In the current conversion circuit, the voltage / current conversion circuit 3 converts the pulse output E ₀ of the arithmetic processing unit 3 into a current according to the pulse.

Reference numeral 5 denotes a capacitor for timed operation which is connected to the voltage / current conversion circuit 4, and the capacitor 5 charges the current i output from the voltage / current conversion circuit 4. R ₁ connected in parallel with the capacitor 5
Is a capacitor 5 in order to simulate the heat dissipation of the wiring 2.
Is to be discharged.

Reference numeral 6 denotes an operational amplifier as an operational amplifier connected to the capacitor 5 for the timed operation. The operational amplifier 6 is a trip circuit which will be described later when the charging voltage E ₁ of the capacitor 5 reaches a set voltage E _2. The trigger output ET is output to 7.

Reference numeral 7 denotes a trip circuit connected to the operational amplifier 6. The trip circuit 7 excites a trip coil 9 of a trip mechanism 8 when a trip trigger output is input from the operational amplifier 6. To cut off the load circuit.
Reference numeral 10 is a power supply unit of the AC / DC conversion circuit 1.

Reference numeral 11 in the drawing denotes an external measuring terminal used when the detected current of the current transformer 2a for detecting the load current of each phase of the wiring 2 is externally measured at the time of maintenance and inspection. Since a measuring instrument (not shown) is connected via the externally installed resistors Rr, Rs, and Rt, the resistance value can be adjusted or changed according to the size of the load current measurement area. Therefore, the load current and each output can be accurately scaled, and the scaling can be accurately performed even when the gain of the transducer is not sufficient. Further, the external measuring terminal 11 is Vr,
When Vs and Vt outputs are not required, they are short-circuited by the jumper wire J.

In such a configuration, each load current is detected by the current transformer 2a provided for each phase of the wiring 2, and each load current is detected by the AC / DC conversion circuit as the DC voltage signals Er, Es ,. Converted to Et. The voltage signals Er, E
s and Et are input to the arithmetic processing unit 3, and the voltage / frequency conversion output program of the arithmetic processing unit 3 selects the maximum voltage signal of each phase.

Then, the arithmetic processing unit 3 outputs a coarse / fine pulse according to the DC voltage signal level. As for the pulse output at this time, as shown in FIG. 3, a continuous pulse is output in the case of the instantaneous or short time delay characteristic C, and a pulse is output intermittently in the case of the long time delay characteristic B. Further, in the case of the characteristic A at the rated current, a pulse having a larger interval than the pulse outputted in the case of the long-time characteristic B is intermittently output.

The coarse / fine pulse output output from the arithmetic processing unit 3 according to the load current is converted into the current i by the voltage / current conversion circuit 4, and the charging voltage of the capacitor 5 is generated by the intermittent or continuous current i. When E ₁ reaches the set voltage E ₂ for trip operation, the operational amplifier 6 outputs the trigger output ET to the trip circuit 7, so the trip circuit 7
Is turned on and the trip coil 9 of the trip mechanism 8 is excited to cut off the load circuit. Therefore, intermittent overcurrent is repeated by charging and discharging the capacitor, and trips with delay.
When the overcurrent changes from the load current that does not reach the overcurrent, it is tripped sooner than when the overcurrent occurs at the time of turning on, and the protection of the wiring is ensured.

[0018]

As is apparent from the above description, the present invention converts the coarse / fine pulse output according to the load current by the arithmetic processing unit, and intermittently or continuously outputs the coarse / fine pulse output by the voltage / current conversion circuit. Since the load current flows intermittently and the power supply voltage of the arithmetic processing unit is repeatedly turned on and off due to the conversion into a different current, the arithmetic processing is intermittently reset. Since the capacitor is additionally charged by the intermittent pulse output from the unit, the wiring can be protected without heating the wiring, and even if the arithmetic processing unit malfunctions due to noise etc., Since the time required for the arithmetic processing unit to be initialized is shorter than the time required for the charging voltage of the time limit capacitor to reach the set voltage for trip operation, noise and rush It is possible to prevent malfunction due to flow or the like. Therefore, the present invention is extremely beneficial to the industry as an electronic wiring protection circuit breaker that solves the conventional problems.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention.

FIG. 2 is a graph showing breaking characteristics.

FIG. 3 is a graph showing pulse output at each interruption characteristic.

FIG. 4 is a graph showing a charging state of a capacitor at each load current level.

FIG. 5 is a circuit diagram of a conventional electronic wiring protection circuit breaker.

FIG. 6 is a graph showing a trigger output when an overcurrent is continuously applied to a conventional arithmetic processing unit.

FIG. 7 is a graph showing a trigger output when an overcurrent is intermittently applied to a conventional arithmetic processing unit.

[Explanation of symbols]

 1 AC / DC conversion circuit 3 Calculation processing unit 4 Voltage / current conversion circuit 5 Capacitor

Claims (1)

[Claims] 1. An electronic wiring protection circuit breaker for detecting a load current of a wiring to interrupt the wiring in a timed or instantaneous manner,
AC / DC conversion circuit for converting load current into DC voltage signal
(1), an arithmetic processing unit (3) for converting the DC voltage signal into a coarse / fine pulse according to a voltage level, and a voltage / current conversion for converting the pulse output from the arithmetic processing unit (3) into a current An electronic wiring protection circuit breaker comprising a circuit (4) and a time-limit capacitor (5) charged by the output current of the voltage / current conversion circuit (4).