JPH0284007A - Circuit breaker - Google Patents

Abstract

PURPOSE:To simplify the circuitry and to eliminate output level regulating work by providing a signal selecting means, an A/D converter and a signal processor for controlling trip operation based on the magnitude of each phase load current represented by sampling signals fed from the A/D converter. CONSTITUTION:Analog phase voltage signals Va, Vb, Vc are fed from a current detecting means 11 through lines 8a, 8b, 8c to a signal selecting means 14. The signal selecting means 14 executes selective operation for passing the analog voltage signals Va, Vb, Vc alternatively in predetermined order, repeatedly based on an external operation command signal. Output from the signal selecting means 14 is fed to an A/D converter 16 which provides a converted output to a signal processor, i.e., a microcomputor 17. The microcomputor 17 controls trip operation where main circuit contacts 2a-2c are opened based on a load current level represented by a digital input voltage signal.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object 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,
A device described in Japanese Patent No. 3930 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 for each phase, and these main circuit contacts are opened when the automatic tripping device is 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 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 the input analog voltage signal, and the calculation result value is converted into a digital voltage signal by the A-D conversion circuit and then sent to the 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 for each phase, and the effective value or average value of the analog voltage signal discriminated in this way. For the calculation, a most human face discrimination circuit and a signal conversion circuit are used, which have a configuration including a large number of analog circuit elements, which complicates the circuit configuration and increases costs. This not only causes a rise in overall manufacturing costs, but also
There is a problem in that a troublesome work is required to adjust the output levels of the human face discrimination circuit and the signal conversion circuit to yA.

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 provide a system that can be used regardless of the power frequency. It is an object of the present invention to provide a circuit breaker that exhibits effects such as being able to 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 tank load current flowing in a multi-phase AC circuit,
In a circuit or disconnector that performs a tripping operation based on a load current value indicated by each phase-in analog voltage signal from the current detection means, each phase-in phase analog voltage signal from the current detection means is connected to a predetermined value. A signal selection means that returns a selection operation of selectively passing the signal in green, an A-D conversion circuit that digitally converts the analog voltage signal that has passed through the signal selection means, and a digital voltage signal from the A-D conversion circuit. A signal processing circuit that samples the digital voltage signal in a time-division manner and executes the tripping operation based on the load current value of each phase indicated by the sampling signal is provided, and the digital voltage signal is processed by the signal processing circuit. This configuration is such that sampling is performed at irregular intervals.

At this time, the signal processing circuit determines the sampling interval of the digital voltage signal by a timer operation based on specific time data selected from several types of time data stored in advance, and at the same time determines the sampling interval of the digital voltage signal at each sampling time. A configuration may also be adopted in which new specific time data is selected from among them.

In addition, the signal processing circuit is configured to determine the sampling interval of digital voltage No. 13 in the same manner as described above based on time data of multiple captures stored in advance, and each time the number of samplings reaches a predetermined value, a new A configuration may also be adopted in which specific time data is selected.

Further, 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, and executes a tripping operation based on the calculation result. It can also be configured.

(Function) The current detection means outputs analog voltage signals for each tank circumference at 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 of the tank circumferential analog voltage signals in a predetermined order, and
The A-D conversion circuit digitally converts the analog voltage signal that has passed through the signal selection means. As a result, A
The -D conversion circuit repeatedly outputs a digital voltage signal corresponding to the load current value flowing through the AC line of multiple phases for each phase. The signal processing circuit samples the output digital voltage signal in a time-division manner, and performs a tripping operation based on the load current value of each phase indicated by the sampling signal. Therefore, the arithmetic processing for the tripping operation can be performed by digital No. 2. At this time, in order to improve the calculation accuracy of the load current value of each phase as described above, it is possible to increase the number of digital voltage signals to be sampled by accelerating the sampling period, but if the sampling period is constant In this case, especially when a variable frequency power supply is used, the power supply frequency and the above-mentioned sampling period may be inadvertently synchronized, and in this case, the universality of the sample becomes poor, and the calculation accuracy of the load current value is greatly reduced. There is a risk of a decline in

In contrast, in the present invention, sampling of the digital voltage signal is performed at irregular intervals, so even if a variable frequency power supply is used, the power supply frequency and the sampling cycle may be inadvertently synchronized. Things will go away.

Further, the signal processing circuit is configured to determine the sampling interval based on specific time data selected from a plurality of types of stored time data, and select new specific time data from among the stored data for each sampling. In this case, the sampling interval of the digital voltage signal changes every time, and the power supply frequency and the sampling period will not be inadvertently synchronized.

Further, the signal processing circuit determines the sampling interval based on specific time data selected from among multiple types of stored time data, and each time the number of samplings reaches a predetermined value, new specific time data is generated from among the stored data. In this case, the sampling interval of the digital voltage signal changes every time the sampling is performed a predetermined number of times, so that the power supply frequency and the sampling period may be inadvertently synchronized in this case as well. You won't have to do anything like that.

In addition, the signal processing circuit is configured by a microcomputer, and the signal processing circuit performs arithmetic processing for the tripping operation 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.

(Example) Hereinafter, the first example of the present invention will be described with reference to FIGS. 1 to 3.
This will be explained with reference to the figures.

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, 3b, 3 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 rectifies 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.

9a, 9b, 9C are rectifier circuits 5a, 6b, 6c
As shown in FIG. 2, these circuits are responsible for converting the output current of the circuit into an analog voltage signal for each cycle of the tank, and as shown in FIG. It is constructed by connecting R2 and R3. Therefore, lines 8a, 8b, 8c each have a resistor R1.
, R2, R3
a, Vb.

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. In other words, the current transformers 5a to 5c, the rectifier circuits 68 to 6c, and the burden circuit 98 described above.
~9C constitute a current detection means 11 for detecting the load current of each phase of A, B, and C flowing through the main circuit conductors 3a, 3b, and 3c.

Then, the line 8a is connected to the current detection means 11 as described above.
, 8b, 3c, respectively, are outputted to diodes 12a, 12b, 12.
line 13 through a diode OR circuit 12 consisting of
The signal is applied to the signal selection means 14 as well as to the signal selection means 14.

The fJ number selection means 14 selects the analog voltage signal Va.

The selection operation of selectively passing Vb and Vc in a predetermined order is repeatedly executed based on an operation command signal from the outside, and its specific configuration will be described later. Reference numeral 15 denotes a differential amplifier circuit for amplifying the output of the signal selection means 14, and the specific configuration thereof will be described later.

Reference numeral 16 denotes an A-D converter circuit that digitally converts the output (that is, analog voltage signals Va, Vb, Vc) of the differential amplifier circuit 15, and the converted output is given 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 input 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, and Sc for operating the signal selection means 14 from its output port P1. . And the output port P of the microcomputer 17. is connected to the gate of thyristor 18, and this thyristor 1
8 has its anode connected to line 13 via a release type trip device 19 and its cathode connected to line 7. The tripping device 19 is an in-type device that opens the main circuit contacts 2a, 2b, and 2c via a tripping mechanism (not shown) when energized in response to turning on the cyrisk 18. 20 is a time-limited control circuit connected between the line 13 and the line 7 via a constant voltage diode 21 with the polarity shown in the figure. is configured to output a trigger pulse and apply it to the gate of the thyristor 18 after a time limit corresponding to the magnitude of the pressure 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 RI R2 and R3 are commonly connected. along with line 2
It is configured as a dual power supply type that outputs a negative voltage between the line 2 and the line 7.

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

24C is an analog switch, and each of these input terminals is connected to the lines 8a and 8 through resistors R4, R5, and RG, respectively.
b and 8c, and each output side terminal is commonly connected to line 25. 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 analog switches 24a, 24b, 24c receives operation command signals Sa, Sb from the microcomputer 17 at its gate terminals.
, Sc, and becomes conductive in the signal input state. Further, in the signal selection means 14, diodes Dl, D2, . Each anode of D3 is connected respectively, and these diodes D
,,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 (
10) 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 addition, in this case, when the resistance values of the resistors R4 to R9 are expressed by their signs, each resistance value is R4-R5絢RG-R8=RaS
It is set to become R7-R9-Rb.

Now, below, the operation of the above configuration will be explained with reference also to FIG. 3, which shows the contents of control by the microcomputer 17. It should be noted that FIG. 3 shows only those parts of the control contents of the microcomputer 17 that are directly related to the gist of the present invention. Now, the main circuit conductors 3a and 3b.

3C, line 8a.

Since the analog voltage signals Va, Vb, and Vc are output to the terminals 8b and 8c, the power supply circuit 10 functions and the signal selection means 14. Differential amplifier circuit 15. Power is now supplied to the A-0 conversion circuit 16 and the microcomputer 17.

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

When a small-scale fault current flows through 3b and 3c due to the short circuit i1, the following actions occur. That is, lines 8g, 8b, 8c from the current detection means 11
l: On the other hand, the load current values 1a and Ib of each phase of A, B, and C.

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 direct 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-R31c+Vz On the other hand, the microcomputer 17 receives the operation command signal Sa
.

A selection operation of Vc is performed. In this case, the operation command signal Sa
is output, the analog switch 24a is conductive, and the analog voltage signal Va output to the line 8a is passed through the resistor R4, the analog switch 24a, and the line 25 to the non-inverting operational amplifier 26 in the differential amplifier circuit 15. Given to input terminal (+). In addition, operation command signals sb and S
During each period when the analog voltage signals vb and Vc are output to the lines 8b and 8C, the analog voltage signals vb and Vc are applied to the resistors R5 and 8C, respectively, in accordance with the conduction of the analog switches 24b and 24c.
It is applied to the non-inverting input terminal (+) of the operational amplifier 26 via the analog switch 24b, line 25 or resistor RQ, analog switch 24C, and line 25. At this time,
The line 25 is the analog ground potential line 22.
Since the analog switches 24 a, 24 b, 24 c are connected to each other via the resistor R7 as described above,
The non-inverting input terminal (+
) are applied to the analog voltage signals v'a, respectively.

V'b and V'e are given by the following equations when the potential of the line 22 is used as a reference. However, in the following formula, V.

is the potential of line 22 (analog ground potential).

V'a = (R11a+Vz-Vo) R7/ (R
4+R7)V'b-(R21b+Vz-Vo)R7
/ (R5+R7)V'c = (R31c+Vz-
Vo) R7/ (R6+R7) Therefore, the operational amplifier 26 receives a voltage of a value shown by (Vz-Vo) with respect to its inverting input terminal (-) using the potential from the line 23 to the line 22 as a reference via the resistor R8. The analog voltage signal v'a is given to the non-inverting input terminal (+).

Since either V'b or V'c is input, the amplified output voltage by the operational amplifier 26 is obtained by the following equation. However, in the following, analog voltage signals Va, V'b
, the operational amplifier 26 in each case where V'c is input.
The amplified output voltages of are expressed as Vxa, Vxb, and Vxc, respectively, with the analog ground potential as a reference.

Vxa= V'a (R8+R9) /Rg - (V
z-Vo) R9/R8Vxb-V'b (R8+R9
) /R8-(Vz-Vo) R9/R8VXC-V'
c (R8+l?9) /R8-(Vz-Vo) R9
/R11 Here, since R4-R5-Re = R8-Ra and R7-R9-Rb,
V'a, V'b, V'c and VXa,
V Xb and V Xe are obtained by the following formulas, respectively.

V'a - (R11a+vz-Vo) Rb/ (1?
a+Rb)V'b-(R21b+Vz-Vo)
Rb/ (Ra+ Rb)V'c-(R31cm11
z−Vo) Rb/ (Ra+Rb)Vxa −V
'a (Ra+Rb) /Ra - (Vz-Vo) R
h/Ra-Iat? IRb/ Ra Vxb -V'b (Ra+Rb) /Ra -(vz
-Vo) R9/R11IbR2Rb/I? a Vxc= V'c (Ra+Rb) /Ra - (Vz
-vo) Rb/Ra-IcR3Rb/Ra By controlling the signal selection means 14 with the microcomputer 17 as described above, the differential amplifier circuit 15
From the output terminal of the A, B, C phase load current value 1a, I
b, an analog voltage signal V with a voltage level proportional to Ic
It is possible to extract xa, V xb, and V xc. In this case, each resistor R1, R2 constitutes the load circuits 9a, 9b, 9c.

By setting R3 equal, the analog voltage signals Vxa, Vxb, and Vxc can be compared using the same standard. The analog voltage signals Vxa, Vxb, Vy:c obtained in this way are converted into digital voltage signals by the AD conversion circuit 16.

Therefore, the microcomputer 17 uses the signal selection means 1 based on the operation command signals Sa, Sb, and Sc as described above.
4, the conversion operation of the A-D conversion circuit 16 is also time-division controlled at the same time, so that each phase load current value 1a.

A digital voltage signal proportional to Ib and Ic is sampled through the A/D conversion circuit 16. Specifically, such sampling is performed as shown in FIG. 3, and will be explained below.

That is, in FIG. 3, the microcomputer 17
the? l! Execute initialization step a according to i-poster,
After this, for example, a variable K set in an internal counter is set to the initial value "1" (step b). After this, in step C, the time data stored at address rKJ of the internal memory is set as the timer time of the internal timer. In this case, [N
Different time data is stored up to the JTR location. Specifically, if the center value of the period suitable for sampling three phases of the digital voltage signal as described above is, for example, 2 ms, the above time data is 2 m
A random time around s is chosen. In addition, the above rNJ
are main circuit contacts 2a and 2b.

This corresponds to the number of samplings that can ensure sufficient calculation accuracy when calculating the effective value or the average value of the load current value required for the tripping operation of 2c, and in this embodiment, r
It is set to 128J. In other words, from address 1 to address 128 of the internal memory of the microcomputer 17, there are 2
Random time data of 128 squares in the vicinity of ms is stored. Note that the internal timer starts a timer operation corresponding to the set time in accordance with the setting of time data.

After executing step C above, the operation command signals Sa and D
- Step d of outputting a digital conversion command to the A conversion circuit 16, operation command signal sb and D-Ai conversion circuit 16;
Step e of outputting a digital conversion command to the DA converter circuit 16, and step f of outputting a digital conversion command to the operation command signal Sc and the DA converter circuit 16 are sequentially executed. When steps d, e, and f are executed, the analog voltage signals Va, Vb, and VC of each phase are converted into digital voltage signals in this order as described above, and the load current is thereby changed. Each phase digital voltage signal proportional to f11a, Ib, and Ic is sampled by the microcomputer 17. Next, it is determined in step g) whether or not the internal timer has timed up. If the determination is "NO", another control program (not shown) is executed. When rYESJ is determined in the above step g, it is determined in the next step h whether or not the variable K has reached N (-128). If rNOJ is determined here, step i is executed to increment variable K by "1", and then the process returns to step C. Therefore, from this point forward, a loop is formed to repeatedly execute steps C to i, and sampling of the digital voltage signal is repeatedly performed. At this time, the sampling interval m1 changes randomly according to the plurality of types of time data stored in the internal timer, so that as a result, sampling of the digital voltage signal is performed at irregular intervals.

However, when such sampling is performed N times, that is, when the variable K reaches N, the microcomputer 17 calculates the digital voltage of each phase based on the above sampling results, although it is not shown in FIG. Calculation of the effective value or average value of the load current indicated by the signal, and selection of the maximum load current value of each phase obtained by such calculation,
Also, the level of each phase load current value is determined. Note that when the variable K reaches N as described above, rYESJ is determined in step h and the process returns to step b, so that N sampling operations similar to those described above are newly started. Then, the microcomputer 17 detects the presence or absence of a fault current based on the level determination 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. Output boat P. Outputs a trigger pulse from. Then, the thyristor 18 whose gate receives the pulse of the fourth bird is turned on, and the tripping device 19 is energized, so that the main circuit contact 2
A normal tripping operation is performed in which ports a, 2b, and 2c are opened.

By the way, if the sampling period of the digital voltage signal by the microcomputer 17 is made constant, the following problem may occur.

That is, the power frequency is 50H2 like commercial frSliA.
Alternatively, if the frequency is constant at 60 Hz, even if the sampling cycle is set to a constant value of, for example, 2ehs, there is no risk that the power supply frequency and the sampling cycle will synchronize, and there will be no problem with the tripping operation by the microcomputer 17. . However, when a variable frequency power supply is used, there is a possibility that the power supply frequency and the sampling period become synchronized.

When such a synchronization occurs, only a specific value of the digital voltage signal is sampled, and the universality of the sample becomes less common.

Therefore, in this case, the calculation accuracy of the load current value by the microcomputer 17 is reduced, causing problems in operational reliability such as unstable tripping characteristics. In order to deal with this problem, it may be possible to shorten the sampling period of the digital voltage signal, but such a measure would increase the operating frequency of the microcomputer 17 or increase the speed of the A-D converter circuit 16. It is necessary to use something with a shape. However, if the operating frequency of the microcomputer 17 is increased, its current consumption will increase, and in order to cope with this, it is necessary to increase the size of the power supply, etc. I will come. Furthermore, since high-speed A-Di switching circuits are expensive, this causes an increase in costs.

In contrast, in the present embodiment described above, sampling of the digital voltage signal by the microcomputer 17 is performed at irregular intervals, so even if a variable frequency power supply is used, the power supply frequency and the sampling cycle are synchronized. Therefore, the above-mentioned problems can be reliably solved.

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 Va, Vb output to
, Vc rises rapidly, the voltage between line 13 and line 7 also rises through diode OR circuit 12 and exceeds the Zener voltage of voltage regulator 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 a signal after a predetermined time period corresponding to the magnitude of the applied voltage (i.e., load current fiiI). A trigger pulse is output. Therefore, the trigger pulse turns on the thyristor 18, and the instantaneous tripping operation is performed in which the tripping device 19 opens the main circuit contacts 2a, 2b, and 2c.

The control contents of the microcomputer 17 are not limited to those shown in FIG. 3, but may be as shown in FIG. 4, which shows the second embodiment of the present invention. A second embodiment will be described. That is, in FIG. 4, after executing the initialization step j, the microcomputer 17 sets the variable K set in the internal counter to the initial value "1" and sets the variable ■ in the other internal counters. (In step (). After this, in step m, the time data stored in address rKJ of the internal memory is set as the timer time of the internal timer. In this case, from address "1" of the internal memory to rMJ
Time data is stored between each address. Specifically, the above time data is, for example, 2
M types of random times near the IIS are selected, and in this case, the rMJ is set to "16".

That is, 16 types of random time data of around 2 ms are stored in addresses 1 to 16 of the internal memory of the microcomputer 17.

After executing step m, steps n, o, and p, which are similar to steps d, e, and f shown in FIG.
Each phase digital voltage signal corresponding to Vb and Vc is sampled. Next, it is determined in step q) whether or not the internal timer has timed up, and if rNOJ is determined, another control program (not shown) is executed. If rYESJ is determined in the above step q, the variable I is incremented by "1" in the next step r, and then it is determined whether the variable l has reached N+1 (however, N-128) (step S) If rNOJ is determined here, the process returns to step m, and therefore step m''-s is executed N times.When it is determined that ``YESJ'' in step S, that is, the sampling operation If so, it is determined in step [ whether the variable K has reached M(-16).

If rNOJ is determined here, step U is executed in which variable K is incremented by "1", and then the process returns to the above-mentioned step.

In short, in the configuration shown in FIG. 4, sampling of the digital voltage signal is repeatedly performed based on one of the random time data stored between address "1" and address rMJ in the internal memory, and When the sampling reaches N times, the operation of sampling N times based on new time data is repeated, and in this case as well, sampling of the digital voltage signal is performed at irregular intervals. Become.

[Effects of the Invention] As is clear from the above explanation, according to the invention of claim 1.2.3, each cycle analog voltage signal indicating the negative bending current value flowing in a multi-phase AC line is arranged in a predetermined order. A signal selection means for selectively passing the signal and an A-D conversion circuit for digitally converting the signal passed through the signal selection means are respectively provided, and the digital voltage signal from the A-D conversion circuit is time-divided. The configuration includes a signal processing circuit that performs sampling and performs a tripping operation based on the load current value of each phase indicated by the sampling signal, which reduces the number of required analog circuit elements and simplifies the circuit configuration. In addition, it is possible to reduce costs associated with this. In addition, since the configuration digitally performs signal processing for the tripping operation, the troublesome output level that was previously required can be reduced to 1m.
Preparation work becomes unnecessary. Furthermore, since the digital voltage signal is sampled by the signal processing circuit at irregular intervals, ? A stable protection operation can always be performed regardless of the li source frequency.

According to the invention set forth in claim 4, 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. Particularly in this case, it is possible to make the sampling period irregular by only changing the software, which is advantageous in terms of cost.

[Brief explanation of the drawing]

1 to 3 show a first embodiment of the present invention, in which FIG. 1 is a schematic circuit configuration diagram, FIG. 2 is a circuit diagram of the main part, and FIG. 3 is a signal processing circuit diagram. It is a flowchart which shows the control content. Further, FIG. 4 is a diagram corresponding to FIG. 3 showing a second embodiment of the present invention. In the figure, 2a, 2b, 2c are main circuit contacts, and 3a. 3b 3c is the main circuit conductor (AC line), 5a, 5b,
5c is a current transformer, 6a, 6b, 6c are rectifier circuits, 9a, 9
b, 9c are burden circuits, 10 is a power supply circuit, 11 is a current detection means, 14 is a signal selection means, 15 is a differential amplifier circuit, 16
17 is a microcomputer (signal processing circuit), 18 is a cyrisk, and 19 is a tripping device. Applicant Toshiba Corporation Figure 2 Figure 3

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. a signal selection means that repeats a selection operation of selecting a signal, an A-D conversion circuit that digitally converts the analog voltage signal that has passed through the signal selection means, and a digital voltage signal from the A-D conversion circuit that is sampled in a time-division manner. and a signal processing circuit configured to perform the tripping operation based on the load current value of each phase indicated by the sampling signal, the signal processing circuit sampling the digital voltage signal at irregular intervals. A circuit disconnector characterized by being configured as follows. 2. The signal processing circuit stores multiple types of time data, and determines the sampling interval of the digital voltage signal by timer operation based on specific time data selected from the time data, and also determines the sampling interval of the digital voltage signal for each sampling. The circuit breaker according to claim 1, characterized in that it is configured to select new specific time data. 3. The signal processing circuit stores multiple types of time data, determines the sampling interval of the digital voltage signal by timer operation based on specific time data selected from the time data, and determines the number of sampling times. 2. The circuit breaker according to claim 1, wherein the circuit is configured to select new specific time data every time a predetermined value is reached. 4. The signal processing circuit is constituted by 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 execute a tripping operation based on the calculation result. 2. The circuit breaker according to claim 1, characterized in that: