JPH052036A - Detecting device ac abnormal current - Google Patents

Abstract

PURPOSE:To obtain a detecting device of an AC abnormal current which is so designed that it can detect abnormality in as short a time as possible when the abnormality occurs. CONSTITUTION:A set value for detecting an abnormal current is made not to be fixed, a set pattern made to be approximate to an AC load current waveform is stored beforehand in a memory 17, a threshold waveform is prepared by repeating the set pattern synchronously with a voltage waveform of a power system, and a detected AC load current is subjected to level discriminations 20, 22 and 24 with the threshold waveform used as a discrimination level. The current below the range of the set pattern is determined as a normal current, and when an abnormal current flows and gets out of the range of this set pattern, it is determined as abnormal. In this way, abnormality can be detected immediately.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a device for detecting an abnormally large current flowing through a load to which AC power is applied.

[0002]

2. Description of the Related Art In a typical prior art, an alternating current load current is detected, and when the load current exceeds a predetermined threshold value, a signal indicating an abnormality is generated. . For example, the detected load current is as shown by the line L1 in FIG. 4, and the threshold value for detecting an abnormality is set to the line L2 as a constant value.

[0003]

In such a prior art, for example, a load short circuit occurs at time t1 when the load current to be detected is zero, which causes the load current to increase as shown by line L3. Sometimes, from time t1 when the abnormality is detected, the large current L3 changes to the threshold value L
It takes a relatively long time W1 to be detected when it becomes 2 or more, for example, 1/4 cycle W of the alternating current applied to the load.
It is a relatively large value of about 2.

Therefore, it is required to further shorten the time W1 from the time t1 when the abnormality is detected to the time t2 when the abnormality is detected.

An object of the present invention is to provide, when an abnormality occurs,
An object of the present invention is to provide a device for detecting an abnormal AC current, which can detect the abnormality in the shortest possible time.

[0006]

SUMMARY OF THE INVENTION The present invention comprises means for detecting an AC load current, threshold waveform creating means for creating an approximated threshold waveform corresponding to a normal AC load current, and an AC Abnormality detection, which responds to the outputs of the load current detection means and the threshold waveform generation means and derives a signal indicating an abnormality when the detected load current exceeds a value corresponding to the threshold waveform. And a means for detecting an abnormal alternating current.

Further, the present invention is characterized in that the threshold waveform is a synthetic waveform synchronized with the phase of the voltage applied to the load.

According to the present invention, the load current detecting means is configured to detect an AC load current and obtain a full-wave rectified output, and the threshold waveform forming means has a half cycle of the AC load current. It is characterized by deriving a threshold waveform.

[0009]

According to the present invention, an approximated threshold waveform is created corresponding to the AC load current at the normal time, and the detected AC load current is level discriminated using this threshold waveform as a discrimination level. This makes it possible to immediately detect the occurrence of an abnormality such as a load short circuit.

According to the invention, the threshold waveform has a composite waveform synchronized with the phase of the voltage applied to the load. Generally, the load is a motor or the like, is an inductive load, and is an AC load. The current lags the phase of the voltage applied to the load. Therefore, the threshold waveform synchronized with the voltage phase is used as the discrimination level to discriminate the level of the detected AC load current.For example, it is equivalent to connecting an inductive load at the time of a short circuit, and Due to the large phase shift of, the detected waveform easily exceeds the threshold waveform, and it becomes possible to immediately detect the occurrence of abnormality.

Furthermore, the AC waveform detected by the AC load current detecting means is full-wave rectified, and the full-wave rectified waveform thus obtained and the alternating load current, that is, the half cycle of the AC voltage is a repeating threshold. By discriminating the value waveform as the discrimination level, it becomes possible to quickly generate an abnormality.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 is an overall electric circuit diagram of an embodiment of the present invention. The electric power of each phase of U, V and W from the three-phase AC power supply 1 is given to the load 6 via the lines 2, 3 and 4 and further via the circuit breaker 5. The circuit breaker 5 has a configuration for cutting off power by a high level signal from the line 26. The load 6 is, for example, a motor and is inductive. The AC load current of each line 2, 3 and 4 is
8 and 9, respectively, full-wave rectification circuit 10,
Given to 11,12. The signal waveform corresponding to the detected AC load current that the full-wave rectifier circuit 10 leads to the line 13 in a normal state is shown by reference numeral 14 in FIG.

The zero-cross detection circuit 15 derives a pulse based on the voltage waveform from the line 2 at each time of each half cycle when the voltage waveform becomes zero, as shown in FIG.
A zero-cross pulse synchronized with the AC voltage is given to the threshold waveform forming means 16. Threshold waveform forming means 16
Has a memory 17 in which the AC power supply 1 and thus the AC load current or voltage half cycle W3.
The minute threshold waveform is stored as indicated by reference numeral 18 in FIG. The threshold waveform forming means 16 is responsive to the zero-cross pulse received every half cycle to derive the threshold waveform 18 on line 19. This threshold waveform is applied to one input of comparison circuit 20, and the other is applied a signal corresponding to the detected AC load current via line 13 described above. The threshold waveform derived on the line 19 is output by the phase shift circuit 21 to 120
It is given to the comparison circuit 22 with a delay. Furthermore, the threshold waveform from this line 19 is set to 2 by the phase shift circuit 23.
It is given to the comparison circuit 24 with a delay of 40 degrees. Comparison circuit 2
2, 24 are also provided with a signal corresponding to the detected AC load current from the full wave rectifier circuits 11, 12. The signals from the comparison circuits 20, 22, and 24 are given to the OR gate 25, and the high level signal from the OR gate 25 is given to the circuit breaker 5 via the line 26, so that the circuit breaker 5 generates an abnormality. The power supply to the load 6 is cut off at times.

At the normal time when no load abnormality occurs,
The signal indicated by the line 14 in FIG. 2B is derived from the line 13 in accordance with the AC load current detected as described above. In addition, the comparison circuit 20 starts from line 19 to FIG.
The threshold waveform shown by line 18 in (2) is provided. In the normal state, the waveform 14 of the line 13 is less than the threshold waveform 18, so that the output of the comparison circuit 20 remains at the low level. Similarly, when the outputs of the comparator circuits 22 and 24 are low level, the output of the line 26 is low level, so that the circuit breaker 5 remains conductive.

For example, assume that a short circuit occurs in the load 6 at time t3 in FIG. 2 (2), the AC load current flowing in the line 2 suddenly increases, and the signal obtained in the line 13 increases as indicated by 14a. To do. At this time, the signal on line 13 has a threshold waveform 1 at time t4.
8 or more. The comparison circuit 20 derives a high-level signal after the time t4, whereby the breaker 5 is cut off. The comparison circuit 20 starts from time t3 when the abnormality occurs in this way.
The time (W1-W4) until the time t4 when the high-level signal is derived and the breaker 5 is cut off can be shortened as compared with the above-mentioned prior art.

Further, in the embodiment of the present invention, the waveform of the line 13 corresponds to the AC load current, while the threshold waveform generated by the threshold waveform forming means 16 is:
A signal having a waveform 18 synchronized with the phase of the voltage applied to the load 6 is led out to the line 19 and applied to the comparison circuit 20. The load 6 is a motor as described above, and therefore the current phase has a phase difference as indicated by reference numeral θ1 in FIG. 2 (2) as compared with the threshold waveform. The waveform 14 is less than the threshold waveform 18 as described above. When the load 6 is short-circuited, the angle θ1 in which the current phase lags behind the voltage phase becomes, for example, close to 90 degrees, whereby the abnormal waveform 14 becomes
Immediately, the threshold waveform becomes 18 or more. This also makes it possible to quickly detect an abnormality in the load 6.

FIG. 3 shows a threshold waveform obtained by the threshold waveform forming means 16 in another embodiment of the present invention. In synchronization with the zero-cross pulse of FIG.
The threshold waveform of (2) is thus derived with a triangular wave. Alternatively, the threshold waveform may have a waveform approximated to the AC load current other than the triangular wave in the normal state.

The load 6 may be a capacitive load as well as an inductive one.

[0019]

As described above, according to the present invention, an AC power is applied to a load, and an approximated threshold waveform is created corresponding to the AC load current under normal conditions. When the detected load current becomes equal to or higher than the corresponding threshold value, a signal indicating that the load is abnormal is derived, so that it becomes possible to immediately detect the load abnormality.
The time delay from the occurrence of an abnormality to the detection of the abnormality can be shortened as much as possible.

In particular, according to the present invention, the threshold waveform is a waveform having the same phase as the phase of the voltage applied to the load, which makes use of the fact that the voltage and current generally differ in phase due to an inductive load. However, it becomes possible to detect the occurrence of an abnormality in a shorter time.

Further, according to the present invention, the detected AC load current is a full-wave rectified waveform, and the threshold waveform is a threshold waveform having a half cycle, and thus the abnormality is quickly detected. Will be able to.

[Brief description of drawings]

FIG. 1 is a block diagram showing the overall configuration of an embodiment of the present invention.

FIG. 2 is a waveform diagram for explaining the operation of the embodiment shown in FIG.

FIG. 3 is a threshold waveform forming means 1 according to another embodiment of the present invention.
It is a figure which shows the threshold-value waveform produced by 6.

FIG. 4 is a waveform diagram for explaining the prior art.

[Explanation of symbols]

1 AC power supply 5 circuit breakers 6 load 10, 11, 12 full-wave rectifier circuit 15 Zero cross detection circuit 16 Threshold waveform creating means 17 memory 20,22,24 Comparison circuit 21,23 Phase shift circuit 25 OR gate

Claims (3)

[Claims] 1. A means for detecting an AC load current, a threshold waveform creating means for creating an approximated threshold waveform corresponding to an AC load current under normal conditions, an AC load current detecting means and a threshold waveform. And an abnormality detecting means for deriving a signal indicating an abnormality when the detected load current exceeds a value corresponding to the threshold waveform in response to each output of the creating means. AC abnormal current detection device. 2. The apparatus for detecting an abnormal AC current according to claim 1, wherein the threshold waveform is a composite waveform that is synchronized with the phase of the voltage applied to the load. 3. The load current detecting means is configured to detect an AC load current to obtain a full-wave rectified output, and the threshold waveform forming means has a threshold value having a half cycle of the AC load current. The apparatus for detecting an abnormal AC current according to claim 1, wherein a waveform is derived.