JPH01270722A - Circuit breaker - Google Patents

Abstract

PURPOSE:To reduce the number of analog circuit elements and to simplify a circuit by conducting a tripping operation on the basis of a maximum load current value of those of respective phases indicated by digital voltage values. CONSTITUTION:When an accident occurs, analog voltage signals Va-Vc corresponding to load current values Ia-Ic of respective phases are input to signal selecting means 34 controlled by operation command signals Sa-Sc from a signal processor 37. An analog voltage signal obtained through a differential amplifier 35 is converted by an A/D converter 36 to a digital voltage signal, and input to the processor 37. The signals are squared and added, and the accumulated data of the selected maximum phase is divided by a set counted value in the processor 37. If the divided result arrives at an overcurrent operation level, a trigger pulse is output from an output port P0, a tyristor 38 is turned ON, and conducted to a tripping unit 39. Thus, the number of analog circuit elements is reduced and is simplified.

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 upon detecting a fault current.

(Prior Art) FIG. 5 shows a circuit breaker such as that seen in, for example, Japanese Patent Application Laid-Open No. 173930/1983. That is, in this FIG. 5, la, lb.

The IC is a power supply side terminal connected to a three-phase AC power supply, and these are connected to load side terminals 4a, 4 via main circuit contacts 2a, 2b, 2c and main circuit conductors 3a, 3b, 3c, which are AC power lines, respectively.
b, 4c.

5a, 5b, 5C are main circuit conductors 3a, 3b of each phase.

Current transformers 6a and 6b each have 3C as a secondary conductor.

6C is a rectifier circuit that performs full-wave rectification of the secondary side outputs of the current transformers 5a, 5b, and 5c for each product. Also, 7a.

7b and 7c are rectifier circuits 6a, 6b*6C
This is a load circuit that converts the output current of the output current into an analog voltage signal for each product, and the voltage level of the analog voltage signal corresponds to the load current value of each phase. That is, the current transformers 5a to 5c, the rectifier circuits 6a to 6C, and the burden circuits 7a to
Current detection means 8 for detecting load current by 7C
is configured. Note that the negative output terminals of the rectifier circuits 6a, 6b, and 6c and the terminals of the burden circuits 7a, 7b, and 7c on the opposite side to the output terminals are connected to a line 9, which is a common potential line.

Then, the burden circuit 7a in the current detection means 8 as described above
, 7b, 7c are connected to the diode O
The signal is applied to a line 11 via an R circuit 10, and is also input individually to a maximum discrimination circuit 12. The maximum discrimination circuit 12 is configured to select and output the maximum signal among the input analog voltage signals of each phase, and its output is input to the signal conversion circuit 13. This signal conversion circuit 13 calculates the effective value of the input analog voltage signal, and the calculated result value is converted into a digital voltage signal by the A-D conversion circuit 14 and then sent to the microcomputer 15. It will be done. This microcomputer 15 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, and its output port po is connected to the thyristor 16. connected to the gate. The thyristor 16 has its anode connected to the line 11 via a release-type trip device 17 and its cathode connected to the line 9.

The trip device 17 is configured to open the main circuit contacts 2a, 2b, and 2c via a trip mechanism (not shown) when energized in response to the thyristor 16 being turned on. Reference numeral 18 denotes a time-limited control circuit connected between lines 11 and 9 via a constant voltage diode 19 with the polarity shown in the figure. It is configured to output a trigger pulse and apply it to the gate of the thyristor 16 after a time limit corresponding to the size has elapsed. A power supply circuit 20 is supplied with power from the line 11, and power for the A-D conversion circuit 14 and the microcomputer 15 is obtained from this power supply circuit 20.

In the circuit breaker configured as described above, when a load current flows through the main circuit conductors 3a, 3b, and 3c, the current detection means 8 and the diode OR
An analog voltage signal is provided through the circuit 10. Therefore, a potential difference is generated between the lines 11 and 9, and the power is supplied, and the power supply circuit 20 functions and the A-D
Power is now supplied to the conversion circuit 14 and microcomputer 15.

In such a state, when a small-scale fault current that does not result in a short-circuit accident flows through the main circuit conductors 3a, 3b, and 3C, the following actions occur. That is, analog voltage signals of voltage levels corresponding to the load current values of each phase are output from the load circuits 7''+7b*7c in the current detection means 8, and the waveforms of these voltage signals are well known. When the analog voltage signals for each product are output in this way, the maximum discrimination circuit 12 selects the largest voltage signal, and the signal conversion circuit 13 selects the largest voltage signal. The effective value of the selected analog voltage signal is calculated.The signal from the signal conversion circuit 13 is converted into a digital voltage signal by the A-D conversion circuit 14 and then input to the microcomputer 15. At this time, the microcomputer 15 executes a level determination of the load current value indicated by the digital voltage signal based on a preset program, and further performs a predetermined time-limited operation based on the level determination result. Output boat P
A trigger pulse is output from O. Then, the thyristor 16 whose gate receives this trigger pulse is turned on and the tripping device 17 is energized, so that a delayed tripping operation is performed in which the main circuit contacts 2a, 2b, and 2c are opened. .

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, the voltage level of the analog voltage signals from the load circuits 7a, 7b, and 7c in the current detection means 8 rises rapidly, and the voltage between the lines 11 and 9 exceeds the Zener voltage of the voltage regulator diode 19. It becomes like this. Then, the constant voltage diode 19 breaks down and the time limit control circuit 18 becomes energized, so that a trigger pulse is output from the time limit control circuit 18 after a predetermined time has elapsed. Therefore, this trigger pulse causes the rethyristor 16 to
is now turned on, and the tripping device 17 is now turned on.
An instantaneous tripping operation is performed in which the main circuit contacts 2a, 2b, and 2c are opened.

(Problems to be Solved by the Invention) In the circuit breaker with the above-mentioned conventional configuration, the analog signal processing circuit performs discrimination of the maximum voltage level signal among the analog voltage signals for each city and calculation of the effective value of the load current. This is performed by a maximum phase discrimination circuit 12 and a signal conversion circuit 13. For this reason, it becomes necessary to combine a large number of analog circuit elements, which not only complicates the circuit configuration and increases the overall manufacturing cost, but also requires troublesome work to adjust the output level of the analog circuit part. There was a problem that came up.

The present invention has been made to solve the above-mentioned problems, and its purpose is to simplify the circuit configuration and reduce manufacturing costs, as well as to eliminate the need for troublesome adjustment work. It is necessary to provide a circuit breaker to perform the operation.

[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 fish load current flowing in a multi-phase AC power line,
In a circuit breaker configured to perform a tripping operation based on a load current value indicated by each municipal analog voltage signal from the current detection means, A-D conversion is performed to digitally convert each municipal analog voltage signal. circuit, and a signal processing circuit that executes the tripping operation based on the calculation of the digital voltage signal from the A-D conversion circuit.
squaring calculation means for squaring the values indicated by the respective municipal digital voltage signals from the A-D converter circuit; and first addition means for accumulating the respective municipal calculation results of the squaring calculation means at regular intervals. , a counting means for counting the number of times of accumulation by this addition means, and a maximum phase selection for selecting the largest one among the accumulated data for each city by the first addition means when this counting means reaches a set count value. means, a dividing means for dividing the accumulated data selected by the maximum phase selection means by the set count value, a determining means for determining whether the division result of the dividing means has reached a predetermined operating level;
a second addition means for accumulating the division result of the division means at regular intervals when it is determined by the determination means that the division result has reached a predetermined level; It is constructed by a trip calculation means that generates a trip operation command when the value exceeds the value.

(Function) The current detection means outputs each municipal analog voltage signal of a voltage level corresponding to the load current value flowing through the AC line of multiple phases, and this analog voltage signal is digitally converted by the A-D conversion circuit. given to the signal processing circuit. Then, the signal processing circuit squares the value indicated by each input municipal digital voltage signal, that is, the value corresponding to each commercial fish current value, and calculates the squared value corresponding to each phase. They are accumulated at regular intervals, and when the number of accumulations reaches the set count value, the largest one is selected among the accumulated data for each phase of the squared value, and the accumulated data selected in this way is The data is divided by the set count value, and when the division result reaches a predetermined level, the division result is accumulated at regular intervals, and when the accumulated result exceeds the predetermined value, a tripping operation command is issued. occurs, thereby causing a tripping operation. Therefore, arithmetic processing for the tripping operation can be performed only using digital voltage signals.

(Example) An example of the present invention will be described below with reference to FIGS. 1 to 4.

In FIG. 2 schematically showing the overall electrical configuration, 21a
, 21b, and 21c are power supply side terminals connected to a three-phase AC power supply consisting of A, B, and C phases; 1. These are connected to load side terminals 24a, 2 via main circuit contacts 22a, 22b, 22c and main circuit conductors 23a, 23b, 23c, which are AC circuits, respectively.
4b and 24c. 25a, 25b, 25
c is the main circuit conductor 23a, 23b, 2 of each phase
Current transformers, 26a and 26b, with 3 c as secondary conductors, respectively.
, 26c is A.

Current transformers 25 a, 25 b, 2 for each phase of B and C
This is a rectifier circuit that performs full-wave rectification of the secondary side output of 5c. At this time, the negative side output terminals of the rectifier circuits 26a, 26b, and 26c are commonly connected to the line 27, and the positive side output terminals are connected to the lines 28a, 28b, and 28C, respectively. 29a, 29b, 29c are rectifier circuits 26a, 26b
, 26c is a load circuit that converts the output current of each city into an analog voltage signal for each city, and as shown in FIG. It is constructed by connecting resistors R1, R2, and R3, respectively. Therefore, line 2
8a.

28b and 28C are analog voltage signals Va and Vb corresponding to voltage drops across the respective resistors R1, R2 and R3.

Vc is output, and each analog voltage value qVa
, Vb, and Vc are the load current value 1a of each phase,
It depends on Ib and Ic. That is, the main circuit conductors 23a, 2
A current detection means 31 is configured to detect the load currents of each phase of A, B, and C flowing through 3b and 23c.

Then, the line 28 is connected to the current detection means 31 as described above.
Each municipal analog voltage signal Va, Vb, Vc outputted to diodes 32a, 32'a, 28'b, 28c, respectively
The signal is applied to a line 33 via a diode OR circuit 32 consisting of circuits b and 32c, and is also applied to a signal selection means 34. The signal selection means 34 repeatedly performs a selection operation of selectively passing analog voltage signals Va, Vb, and Vc in a predetermined order based on an external operation command signal. The configuration will be described later. Reference numeral 35 denotes a differential amplifier circuit for amplifying the output of the signal selection means 34, and its specific configuration will be described later.

36 is an A-D converter circuit that digitally converts the output of the differential amplifier circuit 35 (that is, voltage signals corresponding to the analog voltage signals Va, Vb, and Vc), and the converted output is fed to the microcomputer 37, which is a signal processing circuit. It will be done. This microcomputer 37 controls the conversion operation by the A-D conversion circuit 38, and also controls the main circuit contact 22a based on the load current value indicated by the input digital voltage signal.
~22c is for controlling the tripping operation of opening the thyristor 38, and its output port P0 is connected to the thyristor 38
connected to the gate. The microcomputer 37 is also configured to control the signal selection means 34, and receives operation command signals Sa, Sb, Sc for operating the signal selection means 34 from its output port Pl.
is output as described below. The thyristor 38 has its anode connected to the line 3 via a release-type tripping device 39.
3 and the cathode is connected to line 27. The above-mentioned tripping device 39 is a thyristor 3
8 is turned on, the main circuit contacts 22a, 22b, and 22c are opened via a tripping mechanism (not shown).

40 is a time-limited control circuit connected between the line 33 and the line 27 via a constant voltage diode 41 of the polarity shown in the figure. The trigger pulse is outputted and applied to the gate of the thyristor 38 after a time limit corresponding to the magnitude of the trigger pulse has elapsed. Incidentally, power for the signal selection means 34, A-D conversion circuit 36, microcomputer 37, etc. is obtained from the power supply circuit 30.

FIG. 3 shows a specific configuration example of the signal selection means 34 and the differential amplifier circuit 35 together with related circuits, and will be described below with reference to FIG. 3. That is, as mentioned earlier, the resistors R1 and R constituting the load circuits 29a, 29b, and 29C
2 and R3 are connected between the lines 28a, 28b, 28c and the power supply circuit 30. This power supply circuit 30 outputs an analog ground voltage to a line 42 connected to it, and this line 42 and the resistor R
1, R2, and R3 are connected in common to a line 43, and a negative voltage is output between a line 42 and the line 27.

In the signal selection means 34, 44a, 44b.

44c is an analog switch, and each of these input side terminals is connected to the lines 28a and 28a through resistors R4, R5, and R6, respectively.
28b and 28c, and each output side terminal is commonly connected to line 45.

At this time, the line 45 is connected to the analog ground potential line 42 via a resistor R7, and a noise absorbing capacitor C1 is connected in parallel to this resistor R7. Each of the above analog switches 44a, 44b, 44
c has the microcomputer 37 connected to its gate terminal.
It is designed to receive operation command signals Sa, Sb, and Sc from the terminals, and becomes conductive when the signals are input.

Further, in the signal selection means 34, the analog switch 4
The input side terminals of 4a, 44b, and 44c are respectively connected to the anodes of diodes D1*Dt r D3 for preventing excessive voltage from being applied when they are off, and these diodes DI + Dt +
Each cathode of D3 is commonly connected to the line 43.

On the other hand, in the differential amplifier circuit 35, 46 is an operational amplifier using lines 43 and 27 as power supplies, and its non-inverting input terminal (+) is connected to line 45, and its inverting input terminal (-) connects resistor R8. It is connected to line 43 via. Further, a parallel circuit including a feedback resistor R9 and a noise absorbing capacitor C2 is connected between the output terminal of the operational amplifier 46 and the 5-inverting input terminal (-). Further, the output terminal of the operational amplifier 46 is connected to the input terminal AD of the AD conversion circuit 36. In this case, when the resistance values of the resistors R4 to R9 are expressed by their signs, the respective resistance values are R4-R5-Re -R8-Ra, R7-R9
-Rb.

Now, below, the operation of the above configuration will be explained together with the details of control by the microcomputer 37. Now, with the load current flowing through the main circuit conductors 23a, 23b, and 23c, the line 28a.

Analog voltage signals Va and Vb are applied to 28b and 28c.

Since Vc is now output, the power supply circuit 30 functions and the signal selection means 34. Power is now supplied to the differential amplifier circuit 35, the A-D converter circuit 36, and the microcomputer 37.

In this power-on state, the main circuit conductor 23a.

When a small-scale fault current that does not result in a short-circuit accident flows through 23b and 23c, the following actions occur.

That is, the lines 28a, 28b, 2 from the current detection means 31
8c, the load current values of each phase of A, B, and C Ia, Ib,
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, lines 43 and 42 are connected by power supply circuit 30.
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 37 repeatedly outputs the operation command signals Sa, Sb, and Sc in this order in a time-divided manner at a predetermined period, as will be described later, to the signal selection means 34. give. Therefore, during the period when the operation command signal Sa is output, the analog switch 44a is conductive, and the analog voltage signal Va output to the line 28a is transmitted to the differential amplifier circuit 35 via the resistor R4, the analog switch 44a, and the line 45. The input signal is applied to the non-inverting input terminal (+) of the operational amplifier 46 within the circuit. 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 28b and 28c are applied to the resistor R5 and the analog switch in accordance with the conduction of the analog switches 44b and 44C, respectively. 44b, line 45 or resistor R6, analog switch 4
4c and is applied to the non-inverting input terminal (+) of the operational amplifier 46 via line 45. At this time, the line 45 is connected to the resistor R7 with respect to the analog ground potential line 42.
Since the analog voltage signal V'a is connected to the non-inverting input terminal (+) of the operational amplifier 46 in response to each conduction of the analog switches 44a, 44b, and 44c as described above.

V'b and V'c are given by the following equations. However, in the following equation, vO is the potential of line 42 (analog ground potential)
It is.

V'a - (R11a + Vz - Vo) R7/ (R4
+R7) V'b - (R21b+Vz-Vo) R7/
(R5+R7)V'c - (R31c+Vz-Vo)
(R7/CR8+R7) Therefore, the operational amplifier 46 has a voltage (V) from the line 43 to its inverting input terminal (-).
z-Vo) is applied via the resistor R8, and any of the analog voltage signals V'a, V'b, and V'c is input to the non-inverting input terminal (+). Therefore, the amplified output voltage by the operational amplifier 46 is
It is obtained by the following formula. However, in the following, the amplified output voltages of the operational amplifier 46 in each case where the analog voltage signals V'a, V'b, and V'c are input are referred to as Vxa and Vxa, respectively.
It will be expressed as V xb and V xc.

Vxa -V'a (R8+R9) /R8-(Vz-
Vo) R9/R8Vxb -V'b (R8+R9)
/R8-(Vz-Vo) R9/R8Vxc-V'c
(R8+R9)/R8-(Vz-Vo)R9/R8 Here, since it is set to R4-R5-Re -R8-Ra and R7-R9-Rb, V'a,
V'b, V'c and Vxa, Vx
b and V xc are obtained by the following equations.

V'a= (R11a+Vz-Vo) Rb/ (R
a+Rb)V'b= (R21b+Vz-Vo)R
b/ (Ra + Rb) V'c - (R31c + Vz-
Vo) Rb/ (Ra+Rb)Vxa -V'a (
Ra + Rb) /Ra - (Vz-Vo) Rh/Ra
-1aRIRb/ Ra Vxb -V'b (Ra+Rb) /Ra -(Vz
-Vo) Rb/Ra-IbR2Rb/ Ra Vxc-V'c (Ra+Rb)/Ra-(Vz-Vo
)Rb/Ra-IcR3R1>/Ra As described above, by controlling the signal selection means 34 with the microcomputer 37, the differential amplifier circuit 35
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, burden circuits 29a, 29b, 29c
If the resistors R1+R2+R3 constituting are set equal, each of the analog voltage signals Vxa, Vxb
, V xc can be compared on the same basis.

The analog voltage signals VXa, Vxb, obtained in this way,
Vxc is input to the microcomputer 37 after being converted into a digital voltage signal by the A-D conversion circuit 36. At this time, the microcomputer 37 selects the maximum load current indicated by the digital voltage signal based on a preset program, calculates its effective value, and calculates each load current indicated by the effective value. This is to determine the level of fish load current value,
The contents of these calculations will be explained later based on FIG. It should be noted that the microcomputer 37 uses the signal selection means 3 based on the operation command signals Sa, Sb, and Sc as described above.
Simultaneously with the time division control of 4, the A-D conversion circuit 36 is also time division controlled. Then, the microcomputer 37 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. A trigger pulse is output from the output port Po.

Then, the thyristor 38 whose gate receives this trigger pulse is turned on and the tripping device 39 is energized, so that the main circuit contact 22a.

A normal tripping operation occurs in which 22b and 22C are opened.

On the other hand, when a large-scale fault current such as a short circuit current flows through the main circuit conductors 23a, 23b, and 23c, the following effects occur. That is, in this case, the current detection means 31
From the lines 28a, 28b.

Analog voltage signals Va, Vb output to 28c.

Since the voltage level of Vc rises rapidly, the voltage between line 33 and line 27 also rises through diode OR circuit 32 and exceeds the Zener voltage of voltage regulator diode 41. Then, the constant voltage diode 41 breaks down and the time limit control circuit 40 becomes energized, so that the time limit control circuit 40 outputs a signal after a predetermined time period corresponding to the magnitude of the applied voltage (i.e., load current value). A trigger pulse is output. This trigger pulse therefore causes the thyristor 38 to be turned on, thereby causing the tripping device 39 to close the main circuit contact 22a.

An instantaneous tripping operation is performed in which 22b and 22c are opened.

Now, FIG. 1 shows the calculation contents of the microcomputer 37, and this will be explained below along with related operations.

In FIG. 1, first, after executing initialization step a in response to power-on of the microcomputer 37, a variable K is set to an initial value "1" (step b). Thereafter, in step C, an operation command signal Sa is outputted to the signal selection means 34, and a digital conversion start command is outputted to the A/D conversion circuit 36. Then, the signal selection means 34 passes the A-phase analog voltage signal Va, and this voltage signal Va is converted into an A-phase digital voltage signal by the A-D conversion circuit 36.

Next, in step d corresponding to the square calculation means,
Digital data A indicated by the above digital voltage signal
A square calculation of k is performed, and the calculation result value Akf is stored as data Dk.

Furthermore, in the next step e (corresponding to the first addition means), the digital data Dk (-
Akl) is accumulated in the accumulation memory data Ek. After that, steps c, d, and e as described above are repeated at a constant cycle until it is judged as ``YESJ'' in the step-by-step program described below.Therefore, the above-mentioned squaring and accumulation are performed at every constant cycle. It is done.

After this, in step f, the operation command signal sb is outputted to the signal selection means 34, and at the same time, a digital conversion start command is outputted to the A-D conversion circuit 36. Therefore, in this case, the B-phase analog voltage signal vh passes through the signal selection means 34 and is converted to B-phase by the A-D conversion circuit 36.
It is converted into a digital voltage signal for municipal use. Next, in step g, which corresponds to a square calculation means, a square calculation is performed on the digital data Bk indicated by the digital voltage signal, and the calculation result value Bkl is stored as data Fk, and further corresponds to a first addition means. In step h, data Fk (
-Bkf) is added to the accumulation memory data Gk. Also in this case, the above-described squaring and accumulation are performed at regular intervals.

Subsequently, in step i, the operation command signal Sc is output to the signal selection means 34, and the A-reconversion circuit 3
A digital conversion start command is output to 6. Therefore,
In this case, the C-phase analog voltage signal Vc passes through the signal selection means 34 and is converted by the A-D conversion circuit 36 into a C-phase digital voltage signal. Next, in step j, which corresponds to a square calculation means, a square calculation is performed on the digital data Ck indicated by the digital voltage signal, and the calculation result value Ckl is stored as data Hk, and further corresponds to the first addition means. In step k, data Hk (-Ck
l) to the accumulation memory data Ik. and,
In this case as well, the above-described squaring and accumulation are performed at regular intervals.

After this, in step (), it is determined whether the variable K has reached the set count value N, and in the case of rNOJ, the variable K
After executing step m (corresponding to a counting means) of incrementing by "1", the process returns to step C. In this case, the period of one cycle in step c- is to
In this case, the time T required until the step is determined to be rYESJ is T-N-tO, and therefore, N in steps e, h, and step is expressed as N-T/lo.

If rYESJ is determined in the above step (that is, step c-k is executed N times and each city digital data Dk (-Ak''), Fk (-Bk'), Hk (
-Ck') is sampled N times to obtain the respective accumulated data Ek, Gk, Ik, in step n corresponding to the maximum phase selection means, the accumulated data Ek, Gk.

1, and use it as the maximum value data J
Store as k. Next, in step 0 corresponding to the dividing means, the maximum value data Jk is set to a set count value N.
and the division result J k/N (-
J k −tO/T) is stored as division data Lk.

After this, in step p corresponding to the determining means,
It is determined whether the divided data Lk has reached the overcurrent operation level. If YESJ is obtained in this step p, in step q corresponding to the second addition means, the above-mentioned division data Lk is added to the accumulation memory data Mk.
Accumulate to .

Further, when rNOJ is obtained in step p, the division data Lk is subtracted from the accumulation memory data Mk in step r. Such steps q and ``are repeated at a constant cycle until rYESJ is determined in the subsequent step S, so the above-mentioned accumulation or subtraction is performed at a constant cycle.The above step S So,
This is to judge whether the accumulation memory data Mk exceeds a predetermined value P, and when rYEsJ, the output port P
. Step t is executed to output a trigger pulse from 1 to 5, and the arithmetic operation is completed. Therefore, at the end of such calculation operation, the above-mentioned tripping operation is performed by the above-mentioned trigger pulse. Further, when the answer in step S is "NO", the process returns to step b, and the following steps are repeated in the same manner as described above. Incidentally, the above steps s and t correspond to a trip calculation means.

Here, the protection characteristics of a general circuit breaker are set as shown in FIG. That is, when the load current value exceeds the overcurrent operation level, depending on the magnitude of the load current, long-time operation,
Executes short-time operations and instantaneous operations. Particularly, in the long time limit operation region corresponding to the overcurrent protection operation performed by the microcomputer 37 of this embodiment, the operation time is set to an inverse time limit characteristic in which it is inversely proportional to the square of the load current value. That is, in the long-time operation region, an operation is performed such that (load current)'X (operation time)--a constant value.

Therefore, in the following, it will be explained that the arithmetic processing by the microcomputer 37 shown in FIG. 1 realizes the calculation of the effective value of the load current and the inverse time limit characteristic.

That is, as is well known, the instantaneous value t (T).

The effective value 1e of the current with period T is given by the following equation.

Data obtained by sampling the instantaneous value i (t) at a period to are l 1 (t), i 2 (t), ... t k
(t), the effective value! e is approximated by the following equation.

Here, the number of samplings K (corresponding to the set count [N in this example) is obtained by K-T/lO(-N) since the time required for K samplings, that is, the total period is T. . Therefore, the effective value 1e is determined by the following equation.

On the other hand, when the operating time is set as Top, the inverse time characteristic is as mentioned before, Ie' *Top-Pa (However, Pa is a constant value)
Therefore, the following formula is required.

Therefore, the operating time Top is It can be obtained with

When each of the above formulas corresponds to Fig. 1, A and B are obtained.

T/L.

Accumulated data Σ ik 2(t) for each phase of C is at step e
.

h and n, and the largest one among such accumulated data for each phase is selected in step n, and based on the selected data, division data Lk of the following equation is obtained.

If the division data Lk thus obtained exceeds the overcurrent operation level, the division data Lk is accumulated at regular intervals as accumulation memory data Mk in step q. Therefore, when the accumulation period is Ta, the time until the accumulation memory data Mk reaches the predetermined value P, that is, the operation time Top is given by the following equation.

Here, if P-Ta-P (constant value), then holds true,
This becomes consistent with the above equation (1).

As a result, it can be seen that the calculation of the effective value of the load current and the inverse time characteristic are realized by the calculation processing shown in FIG.

It should be noted that the present invention is not limited to the above-described embodiments, and may be modified in various ways without departing from the spirit thereof, for example, the signal processing circuit may be realized by a digital circuit formed by combining discrete circuits. It can be implemented.

[Effects of the Invention] According to the present invention, as is clear from the above description,
An A-D conversion circuit that digitally converts each municipal analog voltage signal indicating the load current value flowing in a multi-phase AC line, and the load current value of each phase indicated by the digital voltage signal from this A-D conversion circuit. A signal processing circuit is provided for performing a tripping operation based on the coarsest one of Division means, maximum phase selection means, division means.

Since it is configured by the determination means, the addition means, and the trip calculation means, the number of necessary analog circuit elements can be reduced, and the circuit configuration can be simplified and the manufacturing cost can be suppressed. Furthermore, since the configuration is such that the signal processing for the tripping operation is digitally performed as described above, the troublesome output level adjustment work that was conventionally required is no longer necessary. Furthermore, since the time required for digitally calculating the effective value of the load current by the signal processing means can be made sufficiently faster than the overcurrent protection operation time, it is possible to expect an improvement in the accuracy of the calculated value.

[Brief explanation of the drawing]

1 to 4 show an embodiment of the present invention. FIG. 1 is a flowchart showing the control contents of the main parts, FIG. 2 is a schematic diagram of the overall circuit configuration, and FIG. 3 is the same. 2 is a circuit configuration diagram showing a part of FIG. 2 in detail, and FIG. 4 is a protection characteristic curve diagram. Further, FIG. 5 is a diagram corresponding to FIG. 2 for explaining the conventional example. In the figure, 22a, 22b, 22c are main circuit contacts, 23a
, 23 b, 23 c are main circuit conductors (AC line),
25a, 25b, 25c are current transformers, 26a, 26b, 2
6c is a rectifier circuit, 29a, 2.9b, 29C are burden circuits, 30 is a power supply circuit, 31 is a current detection means, 34 is a signal selection means, 35 is an operational amplifier circuit, 36 is an A-D conversion circuit,
37 is a microcomputer (signal processing circuit), 38 is a cyrisk, and 3 are tripping devices.

Claims (1)

[Claims] 1. Current detection means for detecting the load current flowing in the AC circuit of multiple phases and outputting an analog voltage signal for each phase at a voltage level corresponding to the load current value of each phase, as indicated by the analog voltage signal. A circuit breaker configured to perform a tripping operation based on a load current value includes an A-D conversion circuit that digitally converts analog voltage signals for each phase from the current detection means, and the A-D and a signal processing circuit that executes the tripping operation based on a digital voltage signal from a conversion circuit, the signal processing circuit comprising:
squaring calculation means for squaring the values indicated by the digital voltage signals for each phase from the A-D conversion circuit; and a first squaring calculation means for accumulating the calculation results for each phase of the squaring calculation means at regular intervals. an adding means, a counting means for counting the number of times of accumulation by the first adding means, and a counting means for counting the number of times of accumulation by the first adding means, and when the counting means reaches a set count value, among the accumulated data for each phase by the first adding means maximum phase selection means for selecting the maximum phase selection means; division means for dividing the accumulated data selected by the maximum phase selection means by the set count value; and a division result of the division means reaching a predetermined operation level. determination means for determining whether or not the division result has reached a predetermined operation level; and second addition means for accumulating the division result of the division means at regular intervals when the determination means determines that the division result has reached a predetermined operation level. and trip calculation means for generating a trip operation command when the cumulative result of the second addition means exceeds a predetermined value.