JPS60113617A - Overcurrent detector - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to an overcurrent detection device that detects a fault current in an electrical circuit and enables optimal protection.

[Prior art]

Generally, in a static overcurrent detection device equipped with a microcomputer, the detection characteristics (protection characteristics) against fault current in the electrical circuit are determined by the ROM I in the microcomputer.
It is configured to be obtained by executing a predetermined program written in c. The above-mentioned detection characteristic is such that, for example, an inverse time limit characteristic as shown in FIG. 1 can be obtained in order to normally insure the electric circuit and the load. Generally, the detection characteristics as shown in FIG. 1 are set in consideration of the heat resistance of the distribution line, the fusing characteristics of the upper fuse, and the like.

A conventional device of this type includes current sensor means for detecting fault current, means for sampling the detection signal at a predetermined sampling rate, means for determining the Q level of the fault detection signal, and a device corresponding to the level as shown in FIG. It was configured to include means for performing a time-limiting operation based on inverse time-limiting characteristics. Even in the conventional equipment described above, in order to respond to cases where the fault current changes or the fault current returns to a normal state within a set time period, the heat dissipation characteristics of the electrical circuit and load are taken into consideration. It is possible to store the heat dissipation characteristics in the program.In general, it is known that the heat dissipation characteristics of distribution lines and loads have a characteristic in which the temperature decays exponentially. Therefore, by calculating in a microcomputer based on this damping characteristic, or by having already known calculation results as a data table in the ltOM in advance, it is possible to realize a device that can respond to the summer movement of one accident. However, when performing processing that takes the above-mentioned heat dissipation characteristics into consideration in a program, the following problems arise. That is, when calculating on a program, a complicated and enormous program is required in order to obtain heat dissipation characteristics with high efficiency. Therefore, the processing time becomes extremely long, making it difficult to achieve optimal protection.
If the data table is stored in M, the program itself can be shortened, but in order to obtain accurate heat dissipation characteristics, the amount of data per piece becomes enormous, and a large-capacity IIM is required. Particularly when using a one-chip microcomputer or the like, the RAM capacity is extremely limited and cannot store enough data, making it difficult to obtain optimal characteristics.

There is also an even more serious problem. In other words, if there is a temporary power outage or a disturbance such as a 1-surge noise occurs,
The microcomputer will be reset. When the microcomputer is restarted after such an unexpected reset operation, all processing is restarted from the beginning in conventional devices, and the data stored up to that point is also erased.

This is a major problem regarding the basic function of the overcurrent detection device. Furthermore, when the secondary output of the current sensor means is used as a power source for a microcomputer, this problem has a particularly serious effect. That is, if no current or normal current flows, the operating power supply for the microcomputer is lost, so the above-mentioned restart process is executed each time for intermittent currents. Therefore, it has the disadvantage that thermal preservation (that is, the operation of outputting a detection signal in response to heat generation due to one excessive torrent) cannot be performed at all.

[Summary of the invention]

The present invention has been made to solve the problems in conventional devices as described above. That is, when a fault current occurs, as a means of time-limited generation processing by a microcomputer, a capacitor is periodically charged with a predetermined pulse corresponding to the thermal energy generated by the fault current. When the fault current returns to a normal state, an exponential attenuation characteristic based on the heat dissipation characteristics is generated using the discharge characteristics of the capacitor, and 1. When the fault current flows again, It is an object of the present invention to provide an ideal overflow detection device that has a memory effect of accumulated heat against intermittent accident flow by reading the residual voltage of the capacitor as an initial value into a microcomputer.

[Embodiments of the invention]

The present invention will be clarified by describing embodiments of the present invention in detail below using the drawings.

FIG. 2 is a block diagram showing an overcurrent detection device as an embodiment of the present invention. In Figure 2, the AC” electric circuit (I
A current transformer (E) for QIc current detection is provided. A rectifier circuit (■) for obtaining the absolute value of the secondary output is connected to the secondary side of the current transformer (■). A burden circuit is connected to the output side of the rectifier circuit. The burden circuit section converts the output (direct current) of the current transformer (e) into a voltage signal, and also serves as a level adjustment circuit for obtaining output No. 1 within a predetermined level range. The output side of the burden circuit is a waveform conversion circuit (9LI
K is connected. The waveform conversion circuit is for obtaining the effective value of the output signal induced in the burden circuit. IM,
The output terminal of the converter circuit is connected to the first input terminal (101) of the converter circuit for converting the analog output signal into a digital signal. Δ4) Conversion circuit 01
The output of XI is input to a microcomputer (110). An output device having a false output terminal is connected to this output port (117a). Also, one end is grounded and the other end is connected to the second input terminal (1) of the conversion circuit (4).
02) is provided. A resistor ALL (for discharging) is arranged in parallel to this capacitor. A diode 4 is connected between the output port (o7b) of the microcomputer (110) and the other end of the capacitor in the forward direction toward the capacitor (for backflow prevention). A charging resistor is connected to the anode side of the diode Vq.

The configuration of the microcomputer (110) will be summarized in the block diagram of FIG. In FIG. 8, the microcomputer (110) is 1. The CPU (111) is connected to a data bus (112) and an address bus (i18) via a ROM (114) + RAM (115) and a board (116). ■ Output boat (117a) of boat (116), (117
As mentioned above, b) is connected to the output device (2) and the anode of the diode (4).

A part of the data bus (112) and address (118) are connected to the above-mentioned (4) conversion circuit 0fll. Generally, the OM (114) includes a program for executing predetermined signal processing, and the CPU (111) executes the program in synchronization with a predetermined clock signal. Also ItA
M (115) functions as a register necessary for signal processing.

The signal processing process in the above-mentioned microcomputer (110) K is shown in the main flowchart of FIG.
and time limit generating means (1002) for executing a predetermined time limit operation based on the level determined value. This flowchart also includes steps to generate accurate heat dissipation characteristics when the overcurrent condition is no longer present (in order to operate the overcurrent detection device according to the discharge characteristics and the heat storage characteristics as described above). Means (1008) are included.

Next, the operation of the inventive apparatus configured as described above will be explained below.

When a fault DC flows in the AC line 00, the current transformer (E) detects the fault current at its own current transformation ratio and induces an output DC on the secondary side. This output current is passed through the rectifier circuit (G). ) converts it into direct current. The output current of the rectifier circuit converted into direct current is supplied to the burden circuit 101.

The output signal of the burden circuit is converted by the waveform conversion circuit 01 into a signal corresponding to its effective value.
The effective value output of Q is input to the insect conversion circuit a (to). /
The D conversion circuit 4 is controlled by a microcomputer (110) and converts the human input signal into a digital signal in a time-sharing manner. These digital (iIli%) are supplied to the data node (112) of the microcomputer (110). The microcomputer (110) executes level determination of these digital input signals according to a predetermined program. Further, based on the result of this level determination, a predetermined time-limited operation is performed and an output signal is emitted from the output port (117a).The time-limited operation in this case is performed, for example, along the characteristic curve shown in FIG. 4. Microcomputer (
The output device is driven by the output signal emitted from the output port (117a) of the output port (110). From the output terminal 0311 of the output device, an output signal for displaying a fault current or protecting a circuit can be obtained.

Further, in the processing of the above-mentioned time-limited operation, a fourth-order processing is also executed. Namely, 1. A capacitor is periodically charged with a square wave output corresponding to the thermal energy generated by the fault current during a certain period of the above processing.

This will be explained in more detail based on FIGS. 4 and 6.

FIG. 4 is a characteristic diagram showing the state of change in the current flowing through the electric circuit and the operating characteristics of the overcurrent detection device of the present invention. i da 5th
The figure is a waveform diagram showing how the capacitor is charged and discharged. As shown in FIGS. 4 and 6, during the period To during which one fault current 1 is flowing, the pulse width 1. A pulse having the following values is periodically generated (every predetermined unit time) in the work boat (116) to charge the capacitor.Here, the pulse width t1 is equal to the period To during which the fault current of 1° flows; Operating time T] Ratio To//
TI (or the ratio of heat energy consumption) is determined so as to generate a voltage α■ that is the same as the saturation level of the capacitor j after the period To. That is, the ratio '1'o7T
1 is thick, the pulse width t1 is small, and if To//TI is small, the pulse width 1. Make it bigger.

Next, as shown in Fig. 1, when the faulty electrician 1 returns to the normal electrician 2 after the period To has elapsed, the charge in the capacitor is exponentially discharged via the discharging resistor ID. Next, when the fault current flows again, the microcomputer (110) determines the level of the input signal from the /D conversion circuit 0[1 and executes the program to perform the predetermined time-limited operation again. At this time, At time TS in FIG. 5, the microcomputer (110) reads the residual voltage vTs of the capacitor via the 1/IJR conversion circuit O, and uses this read voltage level as the initial voltage level for generating a new time period. Treat as a value.

FIG. 6(b) shows a charging/discharging waveform of a capacitor using a constant voltage according to this embodiment, and FIG. 6(C) shows a charging/discharging waveform using a constant current according to another embodiment.

The above-mentioned (7) signal processing process in the microcomputer (110) will be explained in detail along the main flowchart of FIG.

When the microcomputer (110) is activated and becomes operational, the program starts, initializes the system (i.e., configures the i10 board (116), sets flags, resets, etc.), and performs the main processing of overcurrent detection. Control operation of the 6th order A/1) conversion circuit that enters the flow (
1″/D conversion process).

Through this control operation, the signal of the effective value of the current in the electric circuit and the voltage signal of the capacitor outputted from the waveform conversion circuit (2) are selected in a time-sharing manner and converted into digital signals.
Microcomputer (110) Inside A M (1
15) Write 0 to RAM (
115), an operation is performed to determine whether the value is an overcurrent value or not. As a result, if there is no overcurrent, the heat storage routine shown in FIG. 6 is exited and the process returns to the above-mentioned spatula conversion process. Next, if there is an overcurrent, first set the heat storage flag ■ and execute a timed operation according to the level of the input signal (CPUt
A predetermined number of heat storage bits is added every predetermined unit time using the register in (111) or RAM (115).The above predetermined number of heat storage bits realizes a time-limited operation along the characteristic curve shown in Fig. 1. The operation for determining whether the number of bits added as described above reaches a value corresponding to a predetermined time period is executed.

When the above-mentioned added bit number reaches a value corresponding to a predetermined time limit, an output signal is generated via the output port (117a) to drive the output device.

If the number of bits added by 1 here does not reach the value corresponding to the predetermined time limit, the capacitor is charged with an amount of charge corresponding to the overcurrent value, and the process returns to "/D change processing" again. .

Next, a case will be described in which the overcurrent returns to a current within a normal range. As mentioned above, when the heat storage flag H is set and the 3F operation is in progress for a certain period of time,
``/1) When the maximum value of the converted data falls below a predetermined level, the overcurrent determination routine is skipped and the heat storage flag ■, which indicates the state at the stage immediately before the current stage, is set. As a result, if the heat storage flag H is not set, return to each conversion process.Next, if the heat storage flag is set, the heat storage bit is added. Achieve the heat dissipation characteristic by subtracting the heat dissipation bit based on the heat dissipation characteristic set to 7 from the count register, and determine whether the subtraction result is zero. If it is not zero, leave as is 4] Returns to the climate change process, and if it is zero, resets the heat storage flag H and returns to the A/D summer change process.The program is configured as described above and the process is executed, but the microcomputer (110 ) The voltage of the capacitor is constantly read during the "H"/D conversion process. By doing this, when an overcurrent begins to flow, the counting register is started using the residual voltage value of the capacitor as an initial value. Even when a fault current flows intermittently, or when the microcomputer (110) Even if the circuit is reset and restarted for some reason, the capacitor retains the residual voltage equivalent to the thermal energy that had accumulated in the circuit until then. Therefore, the device of the present invention can realize an operation that conforms to the heat storage and heat dissipation characteristics of the electric circuit.

In addition, in the above processing, the voltage signal due to the residual charge of the capacitor is processed in the Y/D conversion process every time, but the data is read only at the beginning when the microcomputer (110) starts.
0) can be used only as the initial value of the heat storage data as information on the heat storage large number thermal characteristics during the period when the heat storage is stopped for some reason. (Aside from the voltage signal of the capacitor) Execute in the initialization process when starting the microcomputer (110), and do not read it in the processing flow while the microcomputer (110) continues to operate. It is also possible. Furthermore, in the above embodiment, the operating power supply for the microcomputer (110) etc. is supplied from the current transformer member, but a second
A current transformer may be provided, and the operating power source may be supplied from this second current transformer.

〔Effect of the invention〕

According to this invention, by appropriately selecting the discharge time constant of the above-mentioned capacitor ← 0 (in the above example, appropriately selecting the value of the discharge resistance width υ), the heat dissipation characteristics of the actual distribution line and load can be adjusted. It is possible to obtain damping characteristics (operating characteristics) that are very similar to
An ideal overcurrent detection device with a high degree of S can be realized from the viewpoint of protecting the electric wires and loads according to the heat damage caused by the I discharge current. In addition, power supply voltage drops and surges
Even if the detection operation is restarted after being temporarily stopped due to disturbances such as noise, the heat storage data up to that point is retained, so appropriate protection can be provided. Furthermore, since capacitor charging processing is performed during each overcurrent heat storage process, similar processing is performed only when the capacitor is depleted due to overcurrent (it is necessary to perform the processing before the control power supply decreases).
(Compared with an IC), sufficient charging power can be obtained for the condenser (condenser), and the space required for the control power supply including the microcomputer (110) can be reduced, making the power supply circuit extremely simple.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the general characteristics of an overcurrent detection device, Figure 2
Figure 8 is a block diagram showing an embodiment of the overcurrent detection device of the present invention. Figure 8 is a block diagram of the microcomputer and its peripheral elements in the overcurrent detection device of Figure 2. Figure 4 is a block diagram of the current flowing through the electrical circuit. A characteristic diagram showing the state of ashing and the operating characteristics of the overcurrent detection device of the present invention, FIG. 5 is a waveform diagram showing the state of charging and discharging of the capacitor in the overcurrent detection device of FIG. 2, and FIG. This is a flowchart I of the basic operation of the microcomputer in the overcurrent detection device. In the figure, αO is an AC line, (E) is a current transformer, 紧 is a rectifier circuit, (CA is a load circuit, 純 is a capacitor, !0° beak is a resistor, 4 is a diode, - is an output device, and aO+ is a waveform The conversion device, 4 is a "/D conversion circuit, and (110) is a microcomputer. The same symbol in each figure indicates the same part. Agent: Masuo Oiwa, Patent Attorney Figure 1 → Accident @ Flow I (Al Fig. 2 Fig. 4 1) HAl Fig. 5 Fig. 6 ■■]-1 Procedural amendment (spontaneous) Showa Care Year Month/21'' To the Commissioner of the Japan Patent Office l Display of the case Patent Application Showa No. 58-222668 No. 2, Title of the invention Overcurrent detection device 3, Detailed explanation of the invention column 6 of the specification by the person making the amendment, Contents of the amendment (1) In the specification, page 12, line 6, " (2) In the same page, page 12, line 6, it says "increase the width t." is corrected to ``The width t is controlled to be small.J''.

Claims (5)

[Claims] (1) Current sensor means for detecting fault current flowing in an electrical circuit; level determination means for determining the level of the secondary output of the current sensor means 1 Performs a predetermined time-limited operation corresponding to the level determined by the level determination means. Time limit generation means 1
output means that responds to the time-limited operation of the time-limit generating means; and charging/discharging circuit means that periodically charges electric charges corresponding to thermal energy generated by fault current during the time-limited operation of the time-limit generating means and discharges them at a predetermined time constant. , wherein at least the level determining means and the time limit generating means are constituted by a microcomputer, and when a fault current occurs again, the residual voltage of the charging/discharging circuit means is used to calculate the generation time of the time limit generating means. An overcurrent detection device characterized in that the overcurrent detection device is configured to be read into the microcomputer as an initial value for. (2) The charging/discharging circuit means includes a capacitor, a charging means for generating a pulse having a pulse width controlled by the microcomputer, and a discharging means in the form of a C time constant circuit including one resistor. An overcurrent detection device according to claim (1). (3) The charging/discharging circuit means is configured to include a capacitor and a charging means that is driven by a pulse having a pulse width controlled by the YAC computer to generate a constant current. The overcurrent detection device according to any one of range (1) or (2). (4) The current sensor means is configured to include a current transformer; The overcurrent detection device according to any one of claims (1), (2), or (3), which is configured so that power is supplied to the overcurrent detection device. (5) The overcurrent detection device according to claim (4), wherein the operating power source is supplied from the secondary side of the second current transformer.