JPH0579147B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Object of the Invention (Field of Industrial Application) The present invention relates to a zero-phase voltage detector.

(Prior art) In the conventional zero-sequence voltage detection method, the voltage sensor attached to the distribution line is a potential transformer (hereinafter referred to as PT) or a capacitor-divided voltage transformer (hereinafter referred to as PD). ) have been used, and in recent years, products other than PT that apply optoelectronic technology have also been proposed. The optoelectronic technology is called an optical power transformer (hereinafter referred to as optical PT), and many of them are being researched. This light PT is produced by placing an element with the Pockels effect in an electric field, and when linearly polarized light is incident on it in the same direction as the electric field, the curvature of the two orthogonal components changes differently with the strength of the electric field and propagates. This method takes advantage of the fact that the speeds are different, and as a result, a phase difference occurs between two orthogonal components of light, and the emitted light becomes elliptically polarized light.

(Problems to be Solved by the Invention) The conventional PT or PD as described above is a contact method in which it is attached directly to the charged part of the cable etc. for the distribution line, so it is necessary to consider insulation. Not only that, PT and PD use coils, iron cores, capacitors, etc., which increases the overall size and weight, which poses the problem of requiring time and effort to install.

Furthermore, the latter type of optical PT is of a non-contact type, and although it has excellent insulation properties, it requires a laser oscillator or the like to obtain linearly polarized light, making the entire device expensive.

Although the above-mentioned zero-phase voltage detector has become lightweight and relatively inexpensive, it is necessary to provide a detection section for each phase, making installation complicated and requiring a large number of parts. There still remained problems in terms of manufacturing costs. Therefore, it has been desired to realize a zero-sequence voltage detector that is easy to install and has a lower manufacturing cost. The present invention has been made in view of this point, and its object is to provide a zero-sequence voltage detector that is easy to install and has low manufacturing costs.

Structure of the Invention (Means for Solving Problems) In order to achieve the above-mentioned objects, this invention has the following three points:
In a zero-sequence voltage detector that detects zero-sequence voltage by synthesizing detection signals from phases, three window holes are made through the top surface of an electrically grounded shielding container made of a conductive material. Inside the container, plate-shaped detection electrodes supported for each phase by rod-shaped support members made of insulating material are disposed, and each window hole is connected to the inner surface of the container on the upper surface of each detection electrode. A detection section is arranged so as to be closed with a space in between, and a signal processing circuit consisting of an amplifier circuit and a bandpass filter is interposed in the passage of the detection signal from each detection electrode.

(Function) By adopting the above-mentioned means, the present invention not only has a simple structure of the detection part by utilizing the displacement current flowing from the charged part through the space, but also integrates three phases into one. It is easy to manufacture, and it is easy to mount the detection section opposite to the charging section.

(Example) Hereinafter, a first example embodying this invention will be described.
This will be explained in detail with reference to FIGS.

The shield container C of the voltage sensor S, which is arranged at a distance from the three-phase power distribution lines Lu, Lv, and Lw, is composed of a case 1 having a channel-shaped cross section and a lid 2 placed over the case 1. As shown in FIG. 3, mounting pieces 3 are formed by bending inward at right angles at both ends of the side walls and both ends of the bottom wall of the case 1, which face each other. Also, as shown in Figure 2,
The lid 2 of the shield container C has a reverse channel shape so as to cover the openings at both ends and the upper part of the case 1,
It is fastened and fixed to the mounting piece of the case 1 by screws 4 inserted through both end walls thereof. The lid 2 has a rectangular window hole 5 as a displacement radio wave inlet.
u, 5v, 5w are each distribution line Lu shown in Fig. 1,
There are three transparent holes lined up in the length direction to correspond to Lu and Lw. In the shield container C, three insulating support members 6 are fixedly installed in the case 1 at positions corresponding to the window holes 5u, 5v, 5w, and the upper ends of the support members 6 are connected to the respective distribution lines Lu, Lv. , Lw, flat detection electrodes 7u, 7v, and 7w are respectively tightened and fixed by screws 11. Note that this shield container C is made of a conductive material such as aluminum, and is connected to the detection electrodes 7u, 7v, 7w.
It serves as a shield electrode.

The detection electrodes 7u, 7v, 7w are made of a conductive member such as metal, conductive resin, conductive rubber, etc.
In this embodiment, aluminum is used because it is easy to process. Then, the support member 6 and the detection electrodes 7u, 7v, 7w are assembled to the case 1 as described above, and the case 1, the lid 2, the support member 6, and the detection electrodes 7
A detection unit is composed of u, 7v, and 7w. Further, each detection electrode 7u, 7v, 7w is connected to each phase branch lead wire Ru, Rv, Rw as each phase signal circuit.
are connected individually, and these phase branch lead wires Ru, Rv, and Rw are combined together using connectors, etc.
It is connected to a composite signal circuit consisting of a lead wire R. A signal processing circuit 9, which will be described later, is interposed in this composite signal circuit.

The signal processing circuit 9 will be explained according to FIG. 4. The signal processing circuit 9 is housed in a detector box K together with a power supply circuit 20 described later, and is roughly divided into an amplifier circuit A and a bandpass filter circuit B. It is structured as follows.

When the amplifier circuit A inputs the displacement current synthesized from the detected powers 7u, 7v, and 7w, it amplifies the displacement current and outputs a waveform similar to the displacement current. It is composed of That is, the input terminal P of the signal processing circuit 9
1 is connected to the grounding wire B1 via the resistor R1, and the shield container C is connected to the branch lead wires Ru, Rv,
Connect Rw and lead wire R to terminal P using a method such as using a single-core shielded wire with a shielded braided wire.
2 to the ground wire E1. A parallel circuit of a pair of diodes D1 and D2 oriented in opposite directions is connected between both terminals of the resistor R1, and detection electrodes 7u, 7v and 7w serve as a protection circuit for preventing excessive input.

The resistor R2 is connected to the inverting input terminal of the operational amplifier OB1, and the non-inverting input terminal of the operational amplifier OP1 is connected to the ground line E1 via the resistor R3. A capacitor C1 and a resistor R are connected between the inverting input terminal and the output terminal of the operational amplifier OP1.
A parallel circuit with 4 is connected. Note that the capacitors C2 and C3 are used to stabilize the power supply of the operational amplifier OP1.

The resistors R1 to R4, the diodes D1 and D2,
An amplifier circuit A is constituted by the capacitor C1 and the operational amplifier OP1, and the output terminal of the amplifier circuit A is connected to the bandpass filter B at the next stage.

The bandpass filter B is set to selectively amplify and extract a frequency of 60Hz or 50Hz based on the signal when a signal similar to the displacement current sent from the amplifier circuit A is applied. , Specifically, it is structured as follows.

That is, a capacitor C4 is connected between the output terminal of the amplifier circuit A and the inverting input terminal of the operational amplifier OP2.
and a resistor R5 are connected in series, and the non-inverting input terminal of the operational amplifier OP2 is connected to the ground line E1 via a resistor R6. the operational amplifier
A parallel circuit consisting of a series circuit of capacitors C5 and C6 and a series circuit of resistors R7 and R8 is connected between the inverting input terminal and the output terminal of OP2. Further, a capacitor C7 is connected between a point a between the resistors R7 and R8 and the ground line E1. A resistor R9 is connected between the output terminal of the operational amplifier OP2 and the output terminal P3 of the signal processing circuit 9.

A bandpass filter B is constituted by the resistors R5 to R8, capacitors C4 to C7, and operational amplifier OP2.

Next, to explain the power supply circuit 20 according to FIG. 5, a power transformer 21 is connected to the 100VAC power terminal.
A full-wave rectifier 22 is further connected to the secondary side of the power transformer 21. A grounding wire E2 is connected to point b on the secondary side of the power transformer 21, and a smoothing capacitor C8 and a capacitor C9 are connected between the positive terminal of the full-wave rectifier 22 and the grounding wire B2.

Further, a three-terminal regulator 23 is connected between the positive terminal of the full-wave rectifier 22 and the grounding wire E2, and the output terminal of the three-terminal regulator 23 is connected to the +Vc.c. A capacitor C10 and a capacitor C11 are connected between the output terminal of 23 and the ground line E2.

Furthermore, a smoothing capacitor C12 and a capacitor C13 are connected between the negative terminal of the full-wave rectifier 22 and the ground wire E2. Further, a three-terminal regulator 24 is connected between the negative terminal of the full-wave rectifier 22 and the grounding wire E2, and the output terminal of this three-terminal regulator 24 is connected to the -Vc.c. A capacitor C14 and a capacitor C15 are connected between the output terminal of 24 and the ground line E2.

Now, the operation of the zero-sequence voltage detector configured as above will be explained.

In Figure 1, when a steady load current is flowing through each distribution line Lu, Lv, Lw, the distribution line Lu, Lv, Lw
The displacement current flowing through the capacitances Cu, Cv, and Cw formed between the ground and the ground, which is a reference potential point, flows through the window hole 5u of the voltage sensor S, which serves as a displacement current inflow part.
5v, 5w and is collected by the detection electrodes 7u, 7v, 7w.

This displacement current is then synthesized and output to the amplifier circuit A of the signal processing circuit 8. The amplifier circuit A converts the displacement current into a voltage and amplifies it, and outputs a waveform similar to the displacement current to the bandpass filter B. do.
In this case, the input impedance seen from terminals P1 and P2 is considered to be a parallel value of resistors R1 and R2. As is well known, in typical applications of operational amplifiers, the resistance R2 has a value on the order of KΩ. Also,
Closed loop gain R4/R2 is set to obtain sufficient output.
It is taken around 1000.

Therefore, the above-mentioned input impedance is effectively kept at a sufficiently low value by the resistor R2, yet a large signal is obtained at the output of the operational amplifier OP1 due to the high closed-loop gain. As is well known, the phase difference between the input and output of the operational amplifier OP1 changes depending on the magnitude relationship between the impedances of the resistor R4 and the capacitor C1, and if the former is relatively small, the phase difference is ignored and the output proportional to the displacement current is can get. In the opposite case, an integral value, ie a value proportional to the potential of the distribution line, is obtained. In any case, this output has a waveform similar to the displacement current.

Next, when a signal similar to the displacement current is applied, the bandpass filter B selectively amplifies and extracts a signal having a center frequency of 60Hz or 50Hz based on the signal, and generates a zero-phase voltage Vo signal. is output to the output terminal P (see Fig. 6). This sixth
In the figure, α, β, γ are each distribution line Lu, Lv,
This is the waveform of the voltage applied to Lw.

In this way, in normal cases, the ground voltage of each phase is balanced, so the three detection electrodes 7u, 7v, 7
The zero-sequence voltage Vo obtained by combining the voltages of w is 0
becomes.

Next, if a ground fault occurs in any one phase of the distribution line Lu, Lv, Lw, the balance of the ground voltage of each phase will be disrupted, so the three-phase detection electrodes 7u, 7
After the voltages synthesized by voltages v and 7w are input to the signal processing circuit 9, a signal corresponding to the input voltage is output, and a zero-phase voltage is detected. As a result, it is detected that a ground fault has occurred in the power distribution line.

In addition, the shield container C of the voltage sensor S has a case 1 and a lid 2 that serve as shield electrodes. There is no negative influence from other distribution lines.

Next, a second embodiment of the present invention will be described in detail with reference to FIGS. 7 and 8.

In this embodiment, as shown in FIG. 7, each phase branch lead wire Ru, which serves as each phase signal circuit, is connected to three-phase detection electrodes 7u, 7v, and 7w, respectively.
Rv and Rw are individually provided with signal processing circuits 9 similar to those in the above embodiment, and are not combined with each other.
It is connected to an adder circuit 25 provided in the detector box K together with the power supply circuit 20, and the adder circuit 25 combines three phase voltages. The difference from the first embodiment is that the signal processing circuit 9 is individually installed in each phase branch lead wire Ru, Rv, Rw as each phase signal circuit before three-phase synthesis.

The addition circuit 25 connects each detection electrode 7u, 7v, 7
The signal outputted from w and selected at a predetermined frequency is synthesized and a zero-phase voltage Vo is outputted to its output terminal Po. The specific configuration of the adder circuit 25 will be described below with reference to FIG.

That is, variable input resistors R10 and R1 are connected to the G point of the inverting input terminal of the operational amplifier OP3, respectively.
1, the detection electrodes 7u, 7v, 7 via R12
The output terminals Pv, Pu, and Pw of w are connected, and its non-inverting input terminal is grounded via a resistor R13. Also, the output terminal of operational amplifier OP3 is connected to resistor R
It is connected to the point G via 14. Furthermore, the output terminal of the operational amplifier OP3 is connected to the operational amplifier OP3.
It is connected to the output terminal Po via a voltage follower using 4 and a resistor 15. This voltage follower converts the impedance by increasing the input impedance and decreasing the output impedance.

The resistors R10 to R15 and the operational amplifier OP3,
An adder circuit 25 is configured by OP4.
Furthermore, the adder circuit 25 is housed in the detector box K together with the power supply circuit 20 to constitute a zero-phase voltage detector 26, but the configuration of the power supply circuit 20 is the same as that of the first embodiment. , the explanation thereof will be omitted.

Next, a third embodiment of the present invention will be described with reference to FIG.

In this embodiment, another example of the detection section is shown, in which the shield container C is formed into a channel-shaped cross section and the bottom part is omitted, and three-phase detection electrodes 7u, 7v, and 7w are connected via a pair of insulating support members 27, respectively. It hangs down from the inside of the upper surface of the shield container C. Insulating pleats 28 are formed on the insulating support member 27 to reduce leakage of current flowing from the detection electrodes 7u, 7v, 7w to the shield electrode. Further, similarly to the second embodiment, each detection electrode 7u,
Each phase branch lead wire Ru, Rv, Rw as each phase signal circuit connected to 7v, 7w respectively,
Each signal processing circuit 9 is interposed similarly to the second embodiment, and the voltages are not combined with each other but are connected to the adding circuit 25 in the detector box K, and the voltages are combined in the adding circuit 25. After that, the zero-phase voltage Vo is output to the output terminal P.

Effects of the Invention As detailed above, the present invention provides a zero-phase voltage detector that detects a zero-sequence voltage by combining detection signals from three phases. Three window holes are made through the top surface, and plate-shaped detection electrodes are arranged in the container for each phase supported by rod-shaped support members made of insulating material. A detection section is arranged to close each window hole on the upper surface with a space between it and the inner surface of the container, and a layer width circuit and a bandpass filter are provided in the passage path of the detection signal from each detection electrode. By interposing the signal processing circuit consisting of the following, manufacturing costs can be reduced and installation is easy.

[Brief explanation of the drawing]

FIG. 1 is an overall view of a zero-phase voltage detector according to a first embodiment embodying the present invention, FIG. 2 is a sectional view of the voltage sensor, and FIG. 3 is an exploded perspective view of the voltage sensor excluding the molding material. Figure 4 is an electric circuit diagram of the amplifier circuit and filter, Figure 5 is an electric circuit diagram of the detection circuit of the zero-phase voltage detector, and Figure 6 is the zero-phase voltage detected by this zero-phase voltage detector and each Voltage oscilloscope of phase distribution line, Fig. 7 is an overall diagram showing the second embodiment, Fig. 8 is an electric circuit diagram also showing the second embodiment, and Fig. 9 is a sectional view showing the third embodiment. It is. Shield container...C, window hole...5u, 5v, 5
w, Support member...6, Detection electrode...7u, 7v,
7w, signal processing circuit...9, amplifier circuit...A, bandpass filter...B, lead wire...R, branch lead wire...Ru, Rv, Rw.

Claims (1)

[Claims] 1 In a zero-sequence voltage detector that detects zero-sequence voltage by combining detection signals from three phases, three
Inside the container, plate-shaped detection electrodes supported for each phase by rod-shaped support members made of insulating material are arranged, and on the top surface of each detection electrode. A signal processing device comprising a detection unit arranged to close each of the window holes with an air space between them and the inner surface of the container, and an amplifier circuit and a bandpass filter in the passage path of the detection signal from each detection electrode. A zero-phase voltage detector characterized by having a circuit interposed therein.