JPH078104B2 - Zero-phase measuring device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Use The present invention relates to a zero-phase measuring device for measuring a zero-phase voltage or a zero-phase current generated when a ground fault occurs in a transmission line and a distribution line.

(B) Prior Art Conventionally, a configuration shown in FIG. 3 is known as a zero-phase measuring device. In FIG. 3, magnetic field sensors 2R, 2S, 2T are provided on the three-phase power transmission lines 1R1S, 1T, respectively, and each magnetic field sensor detects a change in the magnetic field caused by the current flowing through each power transmission line, and responds respectively. The output is detected and output to the amplifiers 3R, 3S, and 3T. When the detection output from the magnetic field sensor is light, a photoelectric converter is used instead of the amplifier. Each amplifier 3R, 3S, 3T
The outputs from are correspondingly input to the amplifiers 4R, 4S, 4T. Variable resistors 5R and 5T for gain adjustment are connected to the amplifiers 4R and 4T, and the gain of the amplifier is adjusted. Each amplifier 4R, 4S,
The output corresponding to the current flowing in each R, S, and T phase of 4T is the adder 6
Is input to and added. The addition output from the adder 6 is indicated by the meter 7 as an indication of zero-phase current. When measuring the zero-phase voltage, the measurement was performed with the same configuration as described above.

(C) Problems to be solved by the present invention FIG. 4 (A) shows a normal transmission current or transmission voltage of the transmission lines 1R, 1S, 1T, and three phases of R phase, S phase, and T phase. Since the zero-phase voltage or the zero-phase current is ideally zero in the normal state where B is balanced, the output of the adder 6 becomes zero. However, when there are slight differences in gain and phase between the three-phase magnetic field sensors 2R, 2S, 2T or the amplifiers 3R, 3S, 3T and 4R, 4S, 4T, the addition output of the adder 6 is three-phase. Among the outputs of the amplifiers 4R, 4S, and 4T, the output waveform approximates the output of the phase with the largest gain. This means that even when adjustment is made so that the gains of the three-phase amplifier and the voltage or current detector are perfectly matched in the assembly stage of the device, the zero-phase output appears due to various factors.
Change. This is referred to as the residual component, and the factors are as follows. (I) Variations in sensitivity due to the mounting state when the magnetic field sensor is attached to the transmission and distribution lines and variations due to changes in temperature over time, (ii) Variations in the temperature characteristics of the amplifier,
(Iii) Generation and fluctuation of zero-phase voltage in the system due to unbalanced impedance of the transmission / distribution system to ground, (iv) Gain and phase differences among the three phases due to reasons (i) and (ii) above , A zero-phase current output appears due to a change in load current. These factors have no regularity, and it is impossible to predict when and how they will occur. That is, as shown in FIG. 4 (B), the zero-phase output may occur from the adder even in a normal time with a considerable frequency.

In the above-mentioned state, even if a ground fault occurs and a zero-phase voltage or a zero-phase current to be detected occurs, the zero-phase detection output is always added by an adder as shown in FIG. 4 (C). There was a problem that the information of the accident occurrence G could not be accurately measured because it was buried in the output of.

An object of the present invention is to provide a zero-phase measuring device capable of accurately measuring a zero-phase current or a zero-phase voltage without being affected by gain imbalance of each detector and amplifier in a three-phase alternating current. Is.

(D) Means for Solving the Problems The present invention relates to detection means for detecting respective voltages or currents of a three-phase alternating current, amplifiers for amplifying respective detection outputs, adders for adding outputs from the amplifiers, and addition Monitoring means for monitoring the output, processing means for outputting a control signal after a sufficient time for detecting the zero-phase voltage or zero-phase current is delayed when the monitored output exceeds the reference ground, the control signal And a gain adjusting means for adjusting the gain of the amplifier so that the added output falls within a certain range.

(E) Action The addition output of the adder is constantly monitored by the monitoring means, and if the monitoring output exceeds the reference value, after a sufficient time for detecting the zero-phase voltage or zero-phase current is delayed, By automatically adjusting the gain of the amplifier so that the added output falls within a certain range, the normal output of the adder after the delay time elapses falls within a certain range. As a result, the output of the adder due to the imbalance of the gain due to the detection and amplification of the three-phase alternating current in the normal state is improved, and the output of the adder of the zero-phase voltage or the zero-phase current generated at the time of the ground fault can be accurately measured.

(F) Embodiment FIG. 1 shows an embodiment of the present invention, in which the three-phase alternating currents flowing through the three-phase transmission lines 1R, 1S, 1T are detected by the corresponding magnetic field sensors 2R, 2S, 2T. The detected signals are input to the amplifiers 11R, 11S, 11T via the amplifiers 3R, 3S, 3T, respectively.
The amplifiers 11R, 11S, and 11T are composed of operational amplifiers, and among them, the amplifiers 11R and 11T include a digital / digital amplifier for gain adjustment.
Analog (D / A) converters 12R, 12T are connected between their inputs and outputs. The output of each amplifier 11R, 11S, 11T is the adder 1
It is input to 3 and added. The adder 13 is composed of an operational amplifier. The output of the adder 13 is taken out as a measurement output of zero-phase current or zero-phase voltage, further amplified by the operational amplifier 14, and then output to the RMS / DC / converter 15. This RMS value / DC / converter 15
Instead of this, a converter for converting the average value or the peak value of the addition output into a DC voltage may be provided. This RMS value / DC / converter
Reference numeral 15 converts the input AC signal into a DC voltage proportional to its effective value and applies it to the sample-and-hold circuit 16.
The sample-and-hold circuit 16 stores the DC voltage value applied every fixed time and outputs the value to the analog / digital (A / D) converter 17. The analog / digital converter 17 is supplied with a constant voltage (+ 5V) from the standard power supply 18, converts the input DC voltage into a digital value proportional to the value, and outputs the digital value to the CPU (central processing unit) 19. The standard power source 18 also applies a standard voltage to the digital / analog converters 12R and 12T for gain adjustment.

The CPU 19 is constituted by an 8-bit one-chip microcomputer, compares the digital value input corresponding to the effective value of the output of the adder 13 with a preset reference value, and when the reference value is exceeded, Is a digital-to-analog converter 12R, 12T that sends a control signal after a certain delay.
To adjust the gain of each amplifier 11R, 11T. CPU
The delay function provided in 19 is amplifier 11R, 1 for approximately 0.1 seconds from the occurrence of a ground fault to the operation of the circuit breaker.
This is for surely detecting the zero-phase output from the adder 13 without performing 1T gain adjustment, and is preferably set to about 10 times the cycle of the three-phase AC.

In the zero-phase current detection device configured as described above, the output from the adder 13 is the amplifier 11R, 11S, 11 due to temperature change or the like.
When it changes gradually based on the gain imbalance of T etc. and becomes larger than the reference value, the amplifier 14, RMS value / DC converter 1
5, sample and hold circuit 16, analog / digital converter 17, input to CPU19, it is judged whether the output of the amplifier 14 is sufficiently small, when the amplifier output is larger than the set value D / A converter 12R, The resistance value inside the 12T is changed to change the gains of the amplifiers 11R and 11T. As a result, the output of the amplifier 14 is adjusted to be sufficiently small. That is,
The D / A converter is a combination of a large number of resistors and switches, and it works as an automatic setting variable resistor that can have various resistance values depending on the signal from the CPU. As a result, as shown in FIG. 2 (A), the output of the adder 13 always fluctuates within a range close to a constant zero in normal times.
By the way, when a ground fault occurs on one of the transmission lines 1R, 1S, 1T, the zero-phase detection output from the adder 13 is clearly shown at the same time as the accident occurrence G as shown in FIG. 2 (B). The detected output is supplied to the operation of a circuit breaker before gain control by the digital / analog converters 12R and 12T.

The delay function provided in the CPU 19 may be configured to control the digital / analog converter from the CPU 19 via a delay circuit.

(F) Effect In the present invention, the output from the adder is constantly monitored and the output is controlled to a value close to zero in a normal state. Therefore, the zero-phase voltage or zero-phase current generated at the time of a ground fault accident is high. It can be taken out with sensitivity. Therefore, it is possible to detect the zero-phase voltage or the zero-phase current with high sensitivity without being affected by the unbalanced output in the detection due to the temperature or the like.

[Brief description of drawings]

FIG. 1 is a circuit configuration diagram showing an embodiment of the present invention, FIGS. 2A and 2B are output waveform diagrams of the adder of FIG. 1, and FIG. 3 is a circuit configuration of a conventional zero-phase measuring device. Figure, Figure 4 (A) (B)
(C) is a waveform diagram for explaining the operation of the zero-phase measuring device of FIG. 3. 1R, 1S, 1T ... Transmission line 2R, 2S, 2T ... Magnetic field sensor 11R, 11S, 11T ... Amplifier 12R, 12T ... Digital / analog converter 13 ... Adder 15 ... RMS value / DC converter 16 ... Sample and hold Circuit 17 ... Analog / digital converter 19 ... CPU

Claims (3)

[Claims] 1. A detection means for detecting each voltage or current of a three-phase alternating current, an amplifier for amplifying each detection output from the detection means, an adder for adding outputs from each amplifier, and the addition. Monitoring means for monitoring the addition output from the vessel, when the monitoring output from the monitoring means exceeds a reference value,
Processing means for outputting a control signal after a sufficient time for detecting the zero-phase voltage or zero-phase current of the three-phase AC voltage or current is delayed; and adjusting the gain of the amplifier based on the control signal. Then, a zero-phase measuring device comprising: a gain adjusting means for keeping the added output of the adder within a fixed range. 2. The zero-phase measuring device according to claim 1, wherein the gain adjusting means adjusts only the gains of the amplifiers for two phases. 3. The converting means converts the effective value, average value or peak value of the addition output of the adder into a DC voltage, and the analog / digital conversion converting the output from the converting means into a digital signal. A zero-phase measuring instrument according to claim 1, further comprising a digital / analog converter, wherein the gain adjusting means includes a digital / analog converter that adjusts a gain according to an output of the control signal.