JPH0295128A - Circuit breaker - Google Patents

Abstract

PURPOSE:To improve the accuracy of a tripping operation, to simplify a circuit configuration, to reduce its cost and to eliminate a complicated regulating work by A/D-converting the difference between a voltage level corresponding to a load current value flowing to a plurality of phases of AC circuits and a reference voltage, and processing it by a microcomputer. CONSTITUTION:Signal selecting means 14 for selectively passing phase analog voltage signals Va, Vb, Vc indicating load current values flowing to a plurality of phases of AC circuits in a predetermined order is provided. Differential amplifying means 15 for outputting the difference between an analog voltage signal passing the means 14 and a predetermined reference voltage as an amplified analog voltage signal corresponding to the load current value of each phase is provided. Further, a A/D converter 16 for digitally converting the output from the means 15, and a signal processor 17 for executing a tripping operation on the basis of the load current value of each phase indicated by the digital voltage signal from the converter 16 are provided. Thus, the number of necessary analog circuit elements can be reduced to simplify a circuit configuration, to decrease its cost and to eliminate the regulation of the output level.

Description

DETAILED DESCRIPTION OF THE INVENTION [Objective of the Invention (Industrial Application Field) The present invention relates to a circuit breaker that performs a tripping operation of opening a main circuit contact when a fault current is detected.

(Prior Art) As an example of this type of circuit breaker, Japanese Patent Application Laid-Open No. 62-1.
A device described in Japanese Patent No. 73930 is known, and has a configuration as outlined below. That is, main circuit contacts are interposed between the three-phase AC power supply and the main circuit conductors of each phase ratio, and these main circuit contacts are opened in response to the automatic tripping device being driven. It has become so. The main circuit conductors of each phase mentioned above are each equipped with a current transformer for each phase that detects the load current flowing through them, and the secondary output of the current transformer is individually full-wave rectified. In the phase ratio load circuit, it is converted into three types of analog voltage signals indicating the load current value of each phase. A maximum phase discrimination circuit is provided on the output side of the burden circuit, and this discrimination circuit selects the largest signal among the analog voltage signals of each phase and supplies it to the signal conversion circuit. This signal conversion circuit calculates the effective value or average value of a manually inputted analog voltage signal, and the calculated result value is converted into a digital voltage signal by an A-D conversion circuit and then sent to a microcomputer. It will be done. This microcomputer determines the level of the load current value indicated by the input digital voltage signal, performs a predetermined timed operation based on the level determination result, and then drives the automatic tripping device. Performs a tripping operation to open the main circuit contacts.

(Problems to be Solved by the Invention) In the circuit breaker having the above-mentioned conventional configuration, it is difficult to discriminate the signal with the maximum voltage level among the analog voltage signals of each phase ratio, and the effective value or average value of the analog voltage signal discriminated in this way. In order to perform the calculation, a human face discrimination circuit and a signal conversion circuit are used, which require a large number of analog circuit elements, which complicates the circuit configuration and increases costs.

This not only increases the overall manufacturing cost, but also requires troublesome work to adjust the output levels of these maximum coarse discrimination circuits and signal conversion circuits.

The present invention has been made to solve the above-mentioned problems.The purpose of the present invention is to simplify the circuit configuration to reduce the cost, eliminate the need for troublesome adjustment work, and further improve the performance of the tripping operation. It is an object of the present invention to provide a circuit breaker that can reduce signal errors during signal processing and perform stable protection operations.

[Structure of the Invention] (Means for Solving the Problems) In order to achieve the above object, the present invention includes current detection means for detecting each phase load current flowing in a plurality of phase AC power lines,
In a circuit or disconnector configured to perform a tripping operation based on a load current value indicated by each phase ratio analog voltage signal from the current detection means, each phase ratio analog voltage signal from the current detection means is A signal selection means repeats a selection operation of selectively passing the signal in a predetermined order, and receives the analog voltage signal passed through the signal selection means and a predetermined reference voltage at an inverting input terminal and a non-inverting input terminal, and selects both input voltages. A differential amplification means that outputs the difference as an amplified analog voltage signal corresponding to the load current value of each phase, an A-D conversion circuit that digitally converts the output from this differential amplification means, and an A-D conversion circuit that converts the output from this differential amplification means into a digital signal. A signal processing circuit for performing the tripping operation based on the load current value of each phase indicated by a digital voltage signal is provided, and the signal selection means is configured to perform the differential amplification means in addition to the selection operation. configured to output an amplified auxiliary analog voltage signal from the differential amplification means by applying an auxiliary analog voltage signal having the same voltage level as the reference voltage applied to the other input terminal to one input terminal of the differential amplifier; The tripping operation by the signal processing circuit is performed based on the difference between digital voltage signals corresponding to the amplified analog voltage signal and the amplified auxiliary analog voltage signal, respectively.

At this time, if the signal processing circuit is configured by a microcomputer and calculates at least the effective value or average value of the load current based on the input digital voltage signal, the tripping operation is performed based on the calculation result. It can also be configured to run.

Further, the signal processing circuit may be configured to control the selection operation of the signal selection means and perform a tripping operation based on a digital voltage signal in synchronization with the control.

(Function) The current detection means outputs each phase ratio analog voltage signal having a voltage level corresponding to the load current value flowing through the AC circuit of multiple phases. Then, the signal selection means selectively passes each phase ratio analog voltage signal in a predetermined order, and
The differential amplification means outputs the difference between the analog voltage signal from the signal selection means and a predetermined reference voltage as an amplified analog voltage signal corresponding to the load current value of each phase.

Further, at this time, the signal selection means applies an auxiliary analog voltage signal having the same level as the reference voltage to one input terminal of the differential amplification means, so that the auxiliary analog voltage signal and the reference voltage are supplied from the differential amplification means to one input terminal of the differential amplification means. An amplification auxiliary analog voltage signal is output according to the voltage difference. The amplified auxiliary analog voltage signal output in this way should originally be at zero level, but in reality, it is due to fluctuations in the reference voltage caused by changes in ambient temperature, variations in circuit constants of elements, etc. A corresponding voltage level will now appear. In this case, since the amplified analog voltage signal corresponding to the load current value is the difference between the reference voltage and each phase ratio analog voltage signal,
As a result, the voltage level of the amplified auxiliary analog voltage signal indicates the error included in the load current value indicated by the amplified analog voltage signal.

Thus, the amplified analog voltage signal and the amplified auxiliary analog voltage signal outputted from the differential amplification means as described above are digitally converted by the AD conversion circuit. As a result, the A-D converter circuit repeatedly outputs a digital voltage signal corresponding to the load current value flowing through the AC circuit of multiple phases for each phase, and also outputs a digital voltage signal corresponding to the value of the load current flowing in the AC circuit of multiple phases, and also A digital voltage signal corresponding to the amplification auxiliary analog voltage signal indicating the error included in the indicated load current value is output. In the signal processing circuit, the load current value of each phase is indicated by a digital voltage signal corresponding to the amplified analog voltage signal, and the load current value is indicated by a digital voltage signal corresponding to the amplified auxiliary analog voltage signal. The tripping operation is performed based on the difference between the error amount and the error amount. Therefore, signal processing for the tripping operation can be performed using digital signals, and signal errors during the signal processing can be suppressed, so that a stable tripping operation can be performed.

At this time, the signal processing circuit is configured by a microcomputer, and the arithmetic processing for the tripping operation by the signal processing circuit is performed based on the calculation result of the effective value or average value of the load current based on the digital voltage signal. In this case, the accuracy of the tripping operation is improved. Furthermore, if such a signal processing circuit controls the selection operation of the signal selection means and performs the above-described tripping operation in synchronization with this control,
There is no need to provide a separate means for synchronizing the selection operation control by the signal selection means and the signal processing by the signal processing circuit.

(Example) Hereinafter, an example of the present invention will be described with reference to the drawings.

In FIG. 1 schematically showing the overall electrical configuration, la,
lb and lc are power supply side terminals connected to a three-phase AC power supply consisting of A, B, and C phases, and these are the main circuit contacts 2a and 2a, respectively.
2b, 2c and main circuit conductors 3a, 3by3 which are AC circuits
It is connected to load side terminals 4a, 4b, and 4c via c. 5a, 5b.

5c is a current transformer in which the main circuit conductors 3a, 3b, and 3c of each phase are secondary conductors, and 6a, 6b, and 6c are A.

This is a rectifier circuit that performs full-wave rectification of the secondary side outputs of current transformers 5a, 5b, and 5c for each phase of B and C. At this time, the rectifier circuit 6a
, 6b, 6c are commonly connected to line 7, and their positive output terminals are connected to lines 8a, 8b, 8, respectively.
connected to c.

Reference numerals 9a, 9b, and 9c are load circuits that convert the output currents of the rectifier circuits 6a, 6b, and 6c into analog voltage signals of each phase ratio, and these are connected to the lines 8a, 8 as shown in FIG.
Resistors R1 are connected between b, 8c and a power supply circuit 10, which will be described later.
, R2, and R3. Therefore, lines 8a, 8b, 8c have respective resistors R1, R2,
Analog voltage signals Va, Vb according to voltage drop at R3
.

Vc is output, and each analog voltage signal Va
, Vb, and Vc are the load current value 1a of each phase,
It depends on Ib and Ic. That is, the current transformers 5a to 5c, the rectifier circuits 6a to 6c, and the burden circuit 9a described above.
~9c constitute a current detection means 11 for detecting the load currents of each phase of A, B, and C flowing through the upper circuit conductors 3a, 3b, and 3c.

Then, the line 8a is connected to the current detection means 11 as described above.
, 8b, 8c, respectively, are outputted to the diodes 1.2a, 12b, 1.
line 1 through a diode OR circuit 12 consisting of
3 and also to the signal selection means 14.

The signal selection means 14 selects an analog voltage signal Va.

It has a function of repeatedly performing a selection operation of selectively passing Vb and Vc in a predetermined order based on an operation command signal from the outside, and its specific configuration will be described later. Make it.

Reference numeral 15 designates a differential amplification circuit as a differential amplification means for amplifying the output of the signal selection means 14, and its specific configuration will be described later.

Reference numeral 16 denotes an A-D converter circuit for digitally converting the output of the differential amplifier circuit 15 (that is, analog voltage signals Va, Vb, Vc), and the converted output is applied to the microcomputer 17, which is a signal processing circuit.

This microcomputer 17 is for controlling the tripping operation of opening the main circuit contacts 2a to 2c based on the load current value indicated by the manually inputted digital voltage signal. This will be explained later. The microcomputer 17 is also configured to control the signal selection means 14, and outputs operation command signals Sa, Sb, Sc, and Sd for operating the signal selection means 14 from its output photo P1. . The output photo Po of the microcomputer 17 is connected to the gate of a thyristor 18, whose anode is connected to the line 13 via a release-type tripping device 19, and whose cathode is connected to the line 13. 7 is connected. The trip device 19, when energized in response to the thyristor 18 being turned on, connects the main circuit contacts 2a, 2b via a trip mechanism (not shown).

2c is open. 20 is a time limit control circuit connected between line 13 and line 7 via constant voltage diode 21 with the polarity shown;
When it becomes energized according to the breakdown of 1,
It is configured to output a trigger pulse and apply it to the gate of the cyrisk 18 after a time limit corresponding to the magnitude of the applied voltage has elapsed. Note that the signal selection means 14. Power for the A-D conversion circuit 16 and the microcomputer 17 is obtained from the power supply circuit 10.

FIG. 2 shows a specific example of the configuration of the signal selection means 14 and the differential amplifier circuit 15 together with related circuits, and FIG. 2 will be described below. That is, as mentioned before, the resistors R1, R2, and R constituting the burden circuits 9a, 9b, and 9c
3 is line 8a.

It is connected between 8b, 8c and the power supply circuit 10. This power supply circuit 10 outputs an analog ground voltage to a line 22 connected to it, and outputs a positive voltage between this line 22 and a line 23 to which the resistors R1, R2, and R3 are commonly connected. and line 22
It is configured as a dual power supply type that outputs a negative voltage between the line 7 and the line 7].

In the signal selection means 14, 24a, 24b.

24c and 24d are analog switches whose input terminals are connected to the lines 8a, 8b, 8c and 23 via resistors R4, R5, Re and RIO, respectively, and whose output terminals are common to the line 25. It is connected to the. At this time, the line 25 is connected to the analog ground potential line 22 via a resistor R7, and a noise absorbing capacitor C1 is connected in parallel to this resistor R7. Each of the above analog switches 24a, 24b
24c and 24d have operation command signals Sa, 5bSc, and 5bSc from the microcomputer 17 at their gate terminals.
It receives Sd, and becomes conductive when that signal is input. Further, in the signal selection means 14, diodes DI, D2, D3 are installed at each input terminal of the analog switches 24a, 24b, 24c to prevent excessive voltage from being applied when these switches are off.
are connected to each other, and these diodes D1+D2 . Each cathode of D3 is commonly connected to the line 23.

On the other hand, in the differential amplifier circuit 15, 26 is an operational amplifier using lines 23 and 7 as power supplies, and its non-inverting input terminal (
+) is connected to line 25, and the inverting input terminal (-) is connected to line 23 via resistor R8. In addition, the output terminal of the operational amplifier 26 and the inverting input terminal (
-) is connected with a parallel circuit of a feedback resistor R9 and a noise absorbing capacitor C2. In this case, when the resistance values of resistors R4 to RIO are expressed by their signs, each resistance value is R4-R5-R6-R8-RIO=
It is set as RaSR7=R9-Rb.

Now, below, the operation of the above configuration will be explained together with the control contents by the microcomputer 17. Now, with load current flowing through main circuit conductors 3a, 3b, and 3c, lines 8a and 8b.

Since the analog voltage signals Va, Vb, and Vc are outputted to the terminals 8c, the power supply circuit ]0 functions and the signal selection means 14. Differential amplifier circuit 15. Power is now supplied to the A-D conversion circuit 16 and the microcomputer 17.

In this power-on state, the main circuit conductor 3a.

When a small-scale fault current that does not result in a short circuit fault flows through 3b and 3c, the following actions occur. That is, from the current detection means 11 to the lines 8a, 8b, 8c, A, B, C
Load current values Ia and Ib of each phase.

Analog voltage signals Va with voltage levels corresponding to Ic, respectively.
, Vb, and Vc are output, and the waveforms of these voltage signals Va, Vb, and Vc are absolute value waveforms, as is well known. Here, the lines 23 and 22 are connected by the power supply circuit 10.
If the voltage output between them is Vz, then Va, Vb, V
c is expressed by the following formula.

Va-RI Ia+Vz Vb-R2lb+Vz Vc-Ra Ic+Vz On the other hand, the microcomputer 17 receives the operation command signal Sa.
.

It performs the selection operation of Vb and Vc and the output operation of the auxiliary analog voltage signal Vd, which will be described later. In this case, the operation command signal S
During the period when a is output, the analog switch 24a is conductive, and the analog voltage signal Va output to the line 8a is
It is applied to the non-inverting input terminal (+) of the operational amplifier 26 in the differential amplifier circuit 15 via the resistor R4, the analog switch 24a and the line 25. In addition, during each period when the operation command signals sb and Sc are output, analog voltage signals vb and Vc output to the lines 8b and 8C are applied to the resistor R5 in accordance with the conduction of the analog switches 24b and 24c, respectively.
, analog switch 24b, line 25 or resistor R6,
It is applied to the non-inverting input terminal (+) of the operational amplifier 26 via the analog switch 24c and the line 25. At this time, the line 25 is the analog ground potential line 2.
2 through the resistor R7, the analog switches 24a, 24b, 24c
The non-inverting input terminal (+
) analog voltage signals V'a, Vb, V'c given to
is given by the following equation when the potential of line 22 is taken as a reference. However, in the following equation, Vo is the potential of the line 22 (analog ground potential).

V a = (RIIa + Vz - Vo) R7/ (R
4+I27) V'b = (R21b+ Vz - Vo
) R7/ (R5+ R7)V'c-(R31c+
Vz −Vo) R7/ (R6+ R7) Therefore,
The operational amplifier 26 has (Vz-V
A voltage with a value indicated by o) is applied as a reference voltage after passing through a resistor R8, and the above-mentioned analog voltage signals V'a, V'b, V'c are applied to the non-inverting input terminal (+).
The amplified output voltage of the operational amplifier 26 is obtained by the following equation. However, in the following, each amplified analog voltage signal output from the operational amplifier 26 in each case where the analog voltage signals V'a, V'b, and V'c are input is expressed as V xa, It will be expressed as V xb and V xc.

Vxa= V'a (R8+R9) /R8-(Vz-
Vo) R9/R8Vxb= Vob (R8+R9
) /R8-(Vz-Vo) R9/R8Vxc-=
V'c (R8+R9) /R8-(Vz-Vo
) R9/R8 Here, as mentioned above, R4=R5=
R6=R8=Ra, and R7=R9'=Rb
Voa, V'b, V'
c and V Xa.

V xb and V xe are obtained by the following equations, respectively.

V a= (1?'lla+ Vz -Vo) Rb/
(1?a+Rb)V'b-(1?21b+Vz
-Vo) I? b/ (1?a+Rb)V'c=
(R31c+ Vz -Vo) Rb/ (Ra+
Rb) Vxa= V'a (Ra+Rb) /l? a
-(Vz -'Vo) R6/Ra= 1aRIRb/
Ra Vxb= V'b (Ra+Rb) /Ra - (Vz
-Vo) Rb/Ra= IbR2t? b/ Ra Vxc-V'c (Ra+Rb) /Ra-(Vz-
Vo) Rb/Ra-IcR3Rb/Ra On the other hand, amplified analog voltage signals Vxa, Vxb, Vxc from the differential amplifier circuit 15 as described above
The A-D conversion circuit 16 receiving these voltage signals Vxa
, V xb, and V xc are manually calculated using the potential of the common potential line 7 as a reference, not the analog ground potential Vo of the line 22. Therefore, the A-D conversion circuit 16
The actual amplified analog voltage signal V'xa input to the
V'xb and V'xc are given by the following equations.

Vxa = 1aRIRb/Ra+V.

V'xb -1bR2Rb/Ra10V.

V we -1cR3Rb/Ra+V.

Here, the value when the analog ground potential Vo fluctuates due to the influence of ambient temperature or variations in the circuit constants of elements is
'o, Voff the offset voltage of the operational amplifier 26
', then the amplified analog voltage signal V'xa,
V'xb and V'xc are expressed as follows.

Vxa-1aRIRb/l? a+ V'o
10V ofrV 'xb = lbl? 21? b/I
? a+ V 'o+ V orfV 'xc -1c
R3Rb/Ra+V'o+VofrOn the other hand, when the operation command signal Sd is output from the microcomputer 17, the signal selection means 14 operates as follows.

That is, when the operation command signal Sd is output, the analog switch 24d is conductive, and the voltage V between the lines 23 and 22 is
z is applied as an auxiliary analog voltage signal Vd to the non-inverting input terminal (+) of the operational amplifier 26 via the resistor R10, the analog switch 24d and the line 25.

At this time, since the line 25 is connected to the analog ground potential line 22 via the resistor R7, the auxiliary analog voltage signal Vd is given by the following equation when the analog ground potential Vo is used as a reference. .

V d = (Vz-'Vo) R? / (RIO+I
? 7) Therefore, the inverting input terminal (-) of the operational amplifier 26
, the voltage (Vz-Vo) is manually applied as a reference voltage via the resistor R8, so the amplified auxiliary analog voltage signal Vxd output from the differential amplifier circuit 15 including the operational amplifier 26 is given by the following equation. .

V xd -Vd (R8+R9) /R8-(Vz
-Vo), R9/R8 Here, as mentioned above, R
8=RIO=Ra.

Since R7=R and 9=Rb are set, and the auxiliary analog voltage signal Vd is given as a cutting allowance, the amplified auxiliary analog voltage signal Vxd is expressed by the following equation.

V xd= (Vz −Vo) I? b/I? a-
(Vz -Vo) I? b/I? a=0 In other words, the signal selection means 14 selects the non-inverting input terminal (+) of the operational amplifier 26 when the operation command signal Sd is applied.
, the reference voltage (-(Vz -Vo) R9/
An auxiliary analog voltage signal Vd having the same voltage level as (R8+R9) ) is provided.

Further, since the A-D conversion circuit 16 inputs the amplification auxiliary analog voltage signal Vxd with reference to the potential of the common potential line 7, the amplification auxiliary analog voltage signal V' actually input to the A, -D conversion circuit 16. xd is V'xd -V
o. At this time, the value when the analog ground potential Vo fluctuates as described above is v'0
．． When the offset voltage of the operational amplifier 26 is Voff, the amplified auxiliary analog voltage signal V-xd is expressed by the following equation.

V'xd = V'o+Vofr In short,
The microcomputer 17 controls the signal selection means 14 to select the signal from the differential amplifier circuit 15 to the A-D conversion circuit 1.
Against 6, A.

An amplified analog voltage signal V'Xa· with a voltage level proportional to the load current values Ia, Ib, and Ic of each phase of B and C.

V'xb, V'xe, and the amplification auxiliary analog voltage signal V'xd are sequentially given in a time-division manner.

At this time, IaRIRb/I? a= V r , I
bl? 2Rb/I? a-Vs.

1cR3Rb/I? When a - V t, V'x
a-Vr+Vxd, V'xb=Vs+V'x
d, V'xc - V t +Vxd. In this case, each resistor R1, which constitutes the load circuits 9a, 9b, 9C,
, R2, and R3 are set equal, each of the above analog voltage signals v'xa.

V'xb and V'xc can be compared on the same basis. Then, each analog voltage signal V'xa, V'xb, V'xc and V'x obtained as described above
d is input to the microcomputer 17 after being converted into a digital voltage signal by the A-D conversion circuit 16.

Based on a preset program, the microcomputer 17 receives the digital voltage signals corresponding to the amplified analog voltage signals V'Xa, V'Xb, and V'xc input as described above, and the amplified auxiliary The difference between the analog voltage signal V'xd and the corresponding digital voltage signal, that is, V
Calculation of the effective value or )14 average value of the load current indicated by r, Vs, and Vt, selection of the maximum of each phase load current value obtained by such calculation, and level determination of each phase load current value Execute. In this case, the microcomputer 17 controls the A-D conversion circuit 16 in a time-division manner simultaneously with the time-division control of the signal selection means 14 using the operation command signals Sa, Sb, Sc, and Sd as described above. It has become. And microcomputer 17
detects the presence or absence of a fault current based on the above level discrimination result, and if it detects that a fault current has flowed, it performs a time-limited operation according to the magnitude of the fault current and then triggers from the output photo Po. Outputs pulses. Then, the thyristor 18 whose gate receives this trigger pulse is turned on and the tripping device 19 is energized, so that a normal tripping operation is performed in which the main circuit contacts 2a, 2b, and 2c are opened. .

By the way, the amplification auxiliary analog voltage signal V'Xd is
Originally, it should be at zero level, but in reality, changes in ambient temperature, variations in circuit constants of elements, and operational amplifiers 26
The voltage level corresponds to the variation in the analog ground potential Vo caused by the offset voltage Vor[', etc. (and the variation in the reference voltage applied to the inverting input terminal (-) of the operational amplifier 26 via the resistor R8). and each amplified analog voltage signal V'xa, V'xb
, V'xc 1. : Included as an error corresponding to the above fluctuation. At this time, the microcomputer 17 outputs each amplified analog voltage signal V'xa, V'
From each digital voltage signal corresponding to xb and V'xc, an amplification auxiliary analog voltage signal V corresponding to the error is obtained
Since the level of the load current is determined based on signal processing of the result of subtracting the digital voltage signal corresponding to 'xd (that is, the digital voltage signal corresponding to the voltage signals Vr, Vs, and Vt), Signal errors during signal processing can be suppressed, and stable tripping operations can be performed.

On the other hand, when a large-scale fault current such as a short circuit current flows through the main circuit conductors 3a, 3b, and 3c, the following actions occur.

That is, in this case, from the current detection means 11 to the line 8a
, 8b, 8c are analog voltage signals V a ,
V b', V C chisel pressure L/Her increases rapidly, so the voltage between line 13 and line 7 is also diode OR
circuit] 2 and exceeds the Zener voltage of the constant voltage diode 21. Then, the constant voltage diode 21 breaks down and the time limit control circuit 20 becomes energized, so that the time limit control circuit 20 outputs the voltage after a predetermined time period depending on the magnitude of the applied voltage (i.e., load current value). A trigger pulse is output. Therefore, this trigger pulse turns on the thyristor 18, and the tripping device 19 causes the main circuit contact 2a to
An instantaneous tripping operation is performed in which 2b and 2c are opened.

In the above embodiment, the auxiliary analog voltage signal Vd from the signal selection means 4 is the analog voltage signal Va, Vb, V
Although the configuration is such that the voltage signals Va, Vb, and Vc are output the same number of times as c, it may be configured that they are output only once each time the voltage signals Va, Vb, and Vc are output multiple times, and in this case, the auxiliary analog voltage The configuration may be such that the signal Vd is stored in the microcomputer 17 through the A-D conversion circuit 16.

[Effects of the Invention] As is clear from the above description, according to the invention of claim 1, each phase ratio analog voltage signal indicating the load current value flowing in a multi-phase AC line is selectively passed in a predetermined order. a signal selection means for receiving the analog voltage signal passed through the signal selection means and a predetermined reference voltage at the inverting input terminal and the non-inverting input terminal, and converting the difference between the two input voltages into an amplifying analog signal corresponding to the load current value of each phase. Differential amplification means for outputting as a voltage signal, A- for digitally converting the output from this differential amplification means
Since the configuration includes a D conversion circuit and a signal processing circuit that executes a tripping operation based on the load current value of each phase indicated by the digital voltage signal from this A-D conversion circuit, the number of required analog circuit elements can be reduced. This makes it possible to simplify the circuit configuration and reduce costs accordingly.

Further, since the configuration is such that signal processing for the tripping operation is performed digitally, the troublesome output level adjustment work that was conventionally required is no longer necessary. Furthermore, in the invention of claim 1, the signal selection means, in addition to the selection operation,
An auxiliary analog voltage signal having the same voltage level as the reference voltage applied to the other input terminal is applied to one input terminal of the differential amplifying means, thereby outputting an amplified auxiliary analog voltage signal from the differential amplifying means. In addition, the tripping operation by the signal processing circuit is performed based on the difference between the digital voltage signals corresponding to the amplified analog voltage signal and the amplified auxiliary analog voltage signal, so that the tripping operation is Therefore, signal errors during signal processing can be reduced, and stable protection operation can be performed.

Further, according to the second aspect of the invention, the signal processing circuit is configured by a microcomputer, and the tripping operation is performed based on the effective value or average value of the load current obtained by digital signal processing. This improves the accuracy of the tripping operation.

According to the third aspect of the invention, since the signal processing circuit also controls the selection operation of the signal selection means and performs the digital arithmetic processing in synchronization with such control, the selection operation of the signal selection means is controlled. There is no need to provide a separate means for synchronizing the control and the digital calculation by the signal processing circuit.

[Brief explanation of the drawing]

FIG. 1 is a schematic circuit diagram showing a first embodiment of the present invention, and FIG. 2 is a circuit diagram showing a main part of the same embodiment. In the figure, 2a, 2b, 2c are main circuit contacts, and 3a. 3b, 3c are main circuit conductors (AC line), 5a, 5b, 5
c is a current transformer, 6a, 6b, 6c are rectifier circuits, 9a, 9b
, 9c is a burden circuit, 10 is a power supply circuit, 11 is a current detection means, 14 is a signal selection means, 15 is a differential amplification circuit (differential amplification means), 16 is an A-D exchange circuit, and 17 is a microcomputer ( (signal processing circuit), 18 indicates a cyrisk, and one indicates a tripping device. Applicant: Toshiba Corporation

Claims (1)

[Scope of Claims] 1. Current detection means for detecting load current flowing in a plurality of phases of AC power lines and outputting analog voltage signals for each phase at a voltage level corresponding to the load current value of each phase, In a circuit breaker configured to perform a tripping operation based on a load current value indicated by an analog voltage signal, analog voltage signals for each phase from the current detection means are selectively passed in a predetermined order. It has a signal selection means for repeating the selection operation of activating the signal, and an inverting input terminal and a non-inverting input terminal to which the analog voltage signal passed through the signal selection means and a predetermined reference voltage are applied, respectively. A differential amplification means that outputs an amplified analog voltage signal corresponding to the phase load current value, an A-D conversion circuit that digitally converts the output from this differential amplification means, and a digital voltage from this A-D conversion circuit. a signal processing circuit that is provided to receive the signal and executes the tripping operation based on the load current value of each phase indicated by the digital voltage signal,
In addition to the selection operation, the signal selection means applies an auxiliary analog voltage signal to one input terminal of the differential amplification means at the same voltage level as the reference voltage applied to the other input terminal. The differential amplification means is configured to output an amplified auxiliary analog voltage signal, and the signal processing circuit performs the tripping operation on each digital voltage signal corresponding to the amplified analog voltage signal and the amplified auxiliary analog voltage signal, respectively. A circuit breaker or breaker characterized in that it is configured to operate based on a difference. 2. The signal processing circuit is composed of a microcomputer, and is configured to calculate at least the effective value or average value of the load current based on the input digital voltage signal, and to perform a tripping operation based on the calculation result. 2. The circuit breaker according to claim 1, characterized in that: 3. The signal processing circuit is configured to control the selection operation of the signal selection means and perform a tripping operation based on a digital voltage signal in synchronization with the control. circuit break or break.