JPH01136522A - Zero phase current sensor signal discriminating circuit - Google Patents

Abstract

PURPOSE:To make circuits to eliminate DC components for each phase unnecessary and to eliminate the effect of variations in characteristic of these elements by discriminating ground-fault accidents by time variation in an instantaneous sum of three phase current. CONSTITUTION:The current of each phase is detected by sensors 1-3, and is added by means of an adder 13 through amplifiers 4-6 and filters 7-9, the zero phase current is thereby detected. This signal is delayed through a delayer 14, and is compared with a signal not delaying by means of a comparator 15, when the difference is in excess of a threshold value set by a setting 16, the decision of ground-fault accidents is made. The decision is made by difference, so that it is not affected by DC components.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a zero-phase current sensor signal discrimination circuit that converts the sum of current values of each phase of three-phase alternating current into an interrupt level for a CPU.

(Prior art) Fig. 5 shows a circuit block diagram of a conventional example, in which the output signal of a sensor that detects the current of each phase of a three-phase alternating current is
As shown in the figure, it contains a DC component. In order to remove these DC components, the DC component signals of each phase are detected by a low-pass filter, and the DC components are removed by a subtracter from the signals containing the aforementioned DC components. FIG. 6 shows the three-phase signal waveform output from the subtracter and the waveform of the instantaneous sum of these three lease signs. If a ground accident occurs in any phase of the three-phase AC, the instantaneous sum signal will no longer be zero, as shown in FIG. In this conventional example, a ground fall accident is determined when this instantaneous sum exceeds a certain set value.

(Problems to be Solved by the Invention) As described above, in the conventional zero-phase current sensor signal discrimination circuit, the instantaneous sum of the signals indicating the current values of each phase of alternating current with a 120° phase shift is used to detect ground failure. In order to determine this, three low-pass filters and three subtracters are required for each phase to remove the DC component contained in the signal from the sensor that detects the current in each phase. Unless the characteristics of these low-pass filters and subtracters are made exactly the same for all three phases,
The instantaneous sum of the three phases under normal conditions does not show zero, making it difficult to determine whether a ground fall accident is due to a disturbance in the instantaneous sum. However, since it is impossible to completely eliminate variations in the characteristics of these elements,
There is a problem in that variations in the characteristics of each phase due to the low-pass filter and subtractor must be absorbed by the set value of the comparator for determining a ground fall accident based on the instantaneous sum of the three phases.

(Means for Solving the Problems) In order to solve the above problems, the first invention of the present invention includes three sensors that detect the currents of each phase of three-phase alternating current whose phases are shifted by 120 degrees. , three amplifiers that amplify the signals from the sensor, three filters that limit the band of these amplified signals, an adder that adds the band-limited three-phase signals, and an adder that adds the band-limited three-phase signals. It consists of a delay device that delays the added signal, and a comparator that compares the delayed signal and the added signal using a certain threshold value. The feature is that it is configured to perform discrimination based on the temporal change in the sum.

The second aspect of the present invention also provides three sensors that detect the currents of each phase of three-phase alternating current whose phases are shifted by 12 degrees, three amplifiers that amplify the signals from the sensors, and three amplifiers that amplify the signals from the sensors. Three filters to limit the band of the amplified signal, three A/D converters to digitize the band-limited three-phase signal, and arithmetic processing of the A/D converted digital signal. The present invention is characterized in that it is configured to identify a ground failure occurring in any phase of a three-phase alternating current based on a temporal change in the instantaneous sum of three-phase current signals.

(Function) The function of the first invention is that the output signals from the three sensors that detect the current values of each phase of the three-phase alternating current whose phases are shifted by 120° are added together while including the DC component signal. Find the instantaneous sum using a container. Then, by comparing the difference between the signal obtained by delaying this instantaneous sum and the instantaneous sum using a delay device set to a time sufficiently longer than the change in the DC component, the DC component contained in both is removed. be done.

Further, the operation of the second invention is that the output signals from the three sensors that detect the current values of each phase of the three-phase alternating current whose phases are shifted by 120 degrees are sent to the A/D converter while containing the DC component signal. The data is digitized by a converter, taken into the CPU, and the instantaneous sum of the three phases is calculated. Then, at intervals that are sufficiently smaller than the change in the DC component, the CPU takes in the digitized signal and calculates the difference from the previously sampled signal data.
C component is removed.

=4- (Example) An example of the present invention will be described below with reference to the drawings.

FIG. 1 shows a circuit block diagram in an embodiment of the first aspect of the present invention, in which three sensors 1, 2, . 3 and
Three amplifiers 4, 5 . amplify the signals from the sensor.
6 and 3 for limiting the band of these amplified signals.
an adder 13 that adds the band-limited three-phase signals, a delay device 14 that delays the addition result, and an output signal of the delay device 14 and the addition result. , and a comparator 16 that compares using a threshold value specified by a setter 15, constitute a zero-phase current sensor signal discrimination circuit.

Next, the operation of the above embodiment will be explained. sensor 1,
The signal output from 2.3 is band-limited through an amplifier 4.5.6 and a filter 7.8.9, and as shown in Fig. 2, a signal indicating a current value containing a DC component is generated. becomes. These signals are added while including the DC component, and the resulting signal is delayed by a delay device 14 by a time τ that is sufficiently small compared to the change in the DC component. Then, the difference between the output signal from the adder 13 and the output signal from the delay device 14 is compared with a threshold value α designated by the setter 16. Adder 13
Both the output signal from D and the output signal from the delay device 14 are D.
Since it contains a C component, the DC component is removed by finding the difference between them. Therefore, since the change in the instantaneous sum of the current values of each of the three phases over time τ exceeds the threshold value α as shown in FIG. 3, the output of the comparator 15 is turned ON, and a ground fall accident is determined.

FIG. 4 shows a circuit block diagram in an embodiment of the second aspect of the present invention, in which three sensors 1, 2, . 3 and
Three amplifiers 4, 5 . amplify the signals from the sensor.
6 and 3 for limiting the band of these amplified signals.
A/D converter 1'7.18.19 that digitizes the band-limited three-phase signal, and a CPU that processes these digitized signals.
20 constitutes a zero-phase current sensor signal discrimination circuit.

Next, the operation of the above embodiment will be explained. sensor 1,
The signal output from 2.3 passes through amplifier 4.5.6 and filter 7.8.9 and is band-limited, resulting in a signal indicating a current value containing a DC component, as shown in Figure 2. . These signals are digitized by A/D converters 10, 11, and 12 and taken into the CPU 17. The CPU 17 calculates the instantaneous sum of these data and stores it in the register 18. After a time τ, which is sufficiently small compared to the change in the DC component, the CPU 17 takes in the next data from the A/D converters 10, 11, and 12, calculates the instantaneous sum of these data, and compares this result with the data in the register 18. . A/D converter 10.11.1
The consecutive data imported from 2 have the same size D.
Since the C component is included, the DC component is removed by calculating the difference between them. Therefore, when a ground accident occurs in any phase of the three-phase AC, the change in the instantaneous sum of the current values of each of the three phases over time τ exceeds the threshold α as shown in Fig. 3. C=7- PU17 determines a ground fall accident.

As described above, according to the present invention, the instantaneous sum of the signals from the sensor that detects the three-phase alternating current with the phase shifted by 120 degrees is obtained while including the DC component, and the temporal change of the signal is calculated as follows.
In order to determine a ground fall accident that occurred in any phase of a three-phase AC,
There is no need for a filter or a subtracter for removing DC components for each phase, and therefore it is possible to perform ground fall accident determination with DC components removed without being affected by variations in the characteristics of these elements.

Furthermore, the present invention can also be used as a zero-phase voltage sensor signal discriminating circuit for discriminating earth-fall accidents by similarly processing signals from sensors that detect three-phase AC voltages whose phases are shifted by 120 degrees. .

(Effects of the Invention) The first aspect of the present invention includes three sensors that detect the current of each phase of a three-phase alternating current whose phase is shifted by 120 degrees, and three amplifiers that amplify the signals from the sensors. , three filters to limit the band of these amplified signals, an adder to add the band-limited three-phase signals, and a delay to delay the added signal. The device is composed of a comparator that compares the added signal with the added signal using a certain threshold, and is configured to identify a ground accident that has occurred in any phase of the three-phase alternating current based on a temporal change in the instantaneous sum of the three-phase current signals. Therefore, there is no need for an element to remove the DC component included in the signal from the zero-phase current sensor for each phase, and therefore it is possible to eliminate the effects of variations in the characteristics of these elements for each phase. can.

Further, the second invention of the present invention includes three sensors that detect the current of each phase of three-phase alternating current whose phase is shifted by 1206, three amplifiers that amplify the signals from the sensors, and these amplifiers. three filters to limit the band of the converted signal, three A/D converters to digitize the band-limited three-phase signal, and arithmetic processing to the A/D converted digital signal. To obtain the same effect as the first invention, by comprising a CPU and configured to determine a ground accident occurring in any phase of three-phase alternating current based on a temporal change in the instantaneous sum of three-phase current signals. Can be done.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the first aspect of the present invention, FIG. 2 is a diagram showing a normal three-phase AC current waveform with a phase shift of 120 degrees and its instantaneous sum waveform, and FIG. The figure shows a ground accident waveform of a current waveform containing a DC component and its instantaneous sum waveform, Fig. 4 is a block diagram showing an embodiment of the second invention of the present invention, and Fig. 5 shows a conventional example. Circuit block diagram. Figure 6 is a normal AC current waveform that does not include a DC component and its instantaneous sum waveform. Figure 7 is a current waveform that does not include a DC component in an earth accident waveform and its instantaneous sum. FIG. 3 is a diagram showing waveforms. 1.2.3...Current detection sensor, 4,5゜6...
Amplifier, 7, 8.9... Filter, 10, 11.
12... A/D converter, 13... Adder, 14...
... Delay unit, 15... Comparator, 16... Setting device, 17... CPU, 18... Register, 19.
20°21...Low pass filter, 22.23.
24...Subtractor. 2nd drawing 1 3rd drawing 6th drawing 7th ■

Claims (2)

[Claims] (1) Three sensors that detect the current of each phase of three-phase AC whose phase is shifted by 120 degrees, three amplifiers that amplify the signals from the sensors, and limit the band of these amplified signals. an adder that adds band-limited three-phase signals, a delay device that delays the added signals, and a comparison between the delayed signal and the added signal using a certain threshold. 1. A zero-phase current sensor signal discriminating circuit comprising a comparator configured to discriminate a ground accident occurring in any phase of a three-phase alternating current based on a temporal change in an instantaneous sum of three-phase current signals. (2) Three sensors that detect the current of each phase of three-phase alternating current whose phase is shifted by 120 degrees, three amplifiers that amplify the signals from the sensors, and limit the band of these amplified signals. It consists of three filters to convert the band, three A/D converters to digitize the band-limited three-phase signal, and a CPU to process the A/D-converted digital signal. A zero-phase current sensor signal discrimination circuit characterized in that it is configured to discriminate a ground accident occurring in any phase based on a temporal change in the instantaneous sum of three-phase current signals.