JPH0619396B2 - Zero-phase current transformer - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a zero-phase current transformer that detects a zero-phase current that flows when a ground fault occurs.

[Prior Art] FIG. 5 shows the configuration of a zero-phase current transformer according to the prior art shown on page 79 of "Modification Generator for Instrument" (published by Denki Shoin) by Miho Ikeda. In the figure, three-phase distribution lines (1a), (1
b) and (1c) are provided so as to penetrate an annular iron core (2), and a secondary winding (3) is wound around the iron core (2). Secondary winding
A secondary load (4) such as a ground fault detection relay is connected to (3).

Next, the principle of detecting the zero-phase current will be described. The currents flowing through the three-phase distribution lines (1a), (1b), and (1c) are only the positive phase component and the negative phase component in the steady state, and the magnetic flux induced in the iron core (2) is the positive phase component of each phase. Since the magnetic field is combined in proportion to the current of the opposite phase, the magnetic flux of the iron core in the steady state is zero. Therefore, no current is induced in the secondary winding (3) wound around the iron core (2). When a ground fault occurs in one of the distribution lines, the combined magnetic field due to the current flowing in the three-phase distribution line does not become zero, and a zero-phase current flows, which causes a magnetic flux in the iron core (2) and Winding
A secondary current proportional to the zero-phase current flows in (3).

Further, according to the technique described in Japanese Unexamined Patent Publication No. 62-1101620, "Conventional Technology and Problems" and shown in FIG. 4, an optical magnetic field sensor is provided for each phase of a three-phase transmission line. The light source incorporated in the optical-electrical converter sends light to the optical magnetic field sensor. Then, the light passing through the optical magnetic field sensor is converted into an electric signal by an optical-electrical converter to obtain an electric signal corresponding to the current of each phase. Since this electric signal is a direct current signal including an alternating current signal, an alternating current signal of each phase excluding the direct current signal is obtained and these are added by an adder circuit to obtain a zero phase current output.

[Problems to be Solved by the Invention] When a ground fault occurs in recent years, there is a demand for means for early and accurate discovery of an accident area in order to limit a power failure section and shorten a recovery time as much as possible. For this purpose, it is necessary to install many zero-phase current transformers not only in the substation premises but also in the middle of the distribution line.

However, the conventional zero-phase current transformer cannot be installed on an outdoor distribution pole because of the structure in which three distribution lines are penetrated into one iron core. Moreover, since the distribution line is surrounded by the iron core, which is a conductor, there is a risk that an accident will spread when a lightning strike occurs.

Further, in the technique disclosed in Japanese Patent Laid-Open No. 62-110162, it is as if the zero-phase current does not flow after three-phase power distribution due to the change in characteristics of the optical magnetic field sensor and the opto-electric converter due to the temperature change. There is a case where an output as if a zero-phase current is flowing is output from the adder circuit.

[Means for Solving the Problems] The zero-phase current transformer of the present invention is provided for each phase of the photodetecting means for outputting the optical output of each phase corresponding to the current value of each phase of the three-phase distribution line. A photoelectric conversion unit that converts the optical output of each phase transmitted by an optical fiber that transmits an optical output into an electric signal, and separates the output of each phase of the photoelectric conversion unit into an AC component and a DC component,
A signal processing circuit for obtaining an output obtained by dividing the AC component by the level of the DC component for each phase is provided, and the output for each phase obtained by the signal processing circuit is added by an addition circuit, and the output signal of the addition circuit is obtained. Memory means for storing one cycle, output means for the one cycle stored in the memory means, output means for the next one cycle of the stored one cycle, operation means for performing subtraction operation, and a result of the subtraction operation Means for comparing with a predetermined reference value, updating the stored output signal with the output signal of the next cycle when the value is less than the reference value, and fixing the stored output signal when the value is not less than the reference value Is provided with a correction arithmetic circuit.

[Operation] Since the photodetecting means for detecting the current of the distribution line is provided for each phase and the output thereof is transmitted by the optical fiber, the respective phases and the photodetecting means and the measuring circuit are electrically separated. It

[Embodiment] FIG. 1 is a block diagram showing a first embodiment of a zero-phase current transformer according to the present invention. In the figure, three-phase distribution line (1a),
(1b) and (1c) are arranged so as to penetrate through the central portions of the three environmental iron cores (2a), (2b) and (2c). Annular core (2a),
(2b) and (2c) are voids (3a) and (3b) in a part of the annular part, respectively.
And (3c) are provided, and the optical magnetic field sensor (5
a), (5b) and (5c) are arranged. The optical magnetic field sensor uses, for example, a Faraday effect element whose polarization plane of light rotates in proportion to the strength of the magnetic field. Light from the light emitting elements (6a), (6b) and (6c) provided in the measuring circuit (12) passes through optical fibers (8a), (8b) and (8c), respectively, and a magnetic field sensor (5a),
It is incident on (5b) and (5c). In addition, the optical magnetic field sensor (5a), (5
The light that has passed through b) and (5c) is the optical fiber (13a), (13b) and
Light receiving element (7a) provided in the measurement circuit (12) via (13c),
It leads to (7b) and (7c). Light receiving element (7a), (7b) and (7c)
The detection output of each of the signal processing circuits (9a), (9b) and (9
Entered in c). The outputs of the signal processing circuits (9a), (9b) and (9c) are added in the addition circuit (10), and the correction calculation circuit (11) is added.
Entered in. The output of the correction arithmetic circuit (11) is configured to be applied to a relay (not shown).

Next, the operation of this embodiment will be described.

By the current flowing through the three-phase distribution lines (1a), (1b) and (1c),
A magnetic field proportional to the current is induced in the annular cores (2a), (2b) and (2c). On the other hand, the light emitted from the light emitting elements (6a), (6b) and (6c) passes through the respective optical fibers (8a), (8b) and (8c), and the optical magnetic field sensors (5a), (5b) and (5c) Be led to. The optical magnetic field sensors (5a), (5b) and (5c) are the respective annular cores (2a), (2
The plane of polarization rotates in proportion to the magnetic field in the air gap of b) and (2c),
The amount of light transmitted through the optical fibers (8a), (8b) and (8c) changes. After passing through the optical magnetic field sensors (5a), (5b) and (5c), the respective light receiving elements (in the measurement circuit (12) provided through the respective optical fibers (13a), (13b) and (13c) ( 7
It is incident on a), (7b) and (7c) and converted into an electric signal. The outputs of the light receiving elements (7a), (7b) and (7c) are signals in which alternating current is superimposed on direct current.

Each electric signal is supplied to the respective signal processing circuit (9a), (9b) and (9
It is input to c), first separated into AC component and DC component, then the AC component is divided by the DC component, and the three-phase distribution line (1
An output signal proportional to the current flowing through a), (1b) and (1c) is output. The outputs of the signal processing circuits (9a), (9b) and (9c) are added by the adding circuit (10). The output of the adder circuit (10) becomes zero when the current flowing through the three-phase distribution lines (1a), (1b) and (1c) is normal, but when a ground fault occurs on any of the distribution lines. Even if the outputs of the signal processing circuits (9a), (9b) and (9c) are added by the adding circuit (10), the outputs do not become zero, and a good output for zero-phase current is generated. The output of the adder circuit (10) is proportional to the zero-phase current, so that the occurrence of a ground fault can be detected.

The output of the addition circuit (10) is input to the correction calculation circuit (11).
Generally, emitting elements (6a), (6b), (6c), light receiving elements (7a), (7b), (7
c), optical magnetic field sensor (5a), (5b), (5c) and signal processing circuit (9
The characteristics change depending on the ambient temperature of a), (9b), and (9c), and the same output as when the zero-phase current flows even though the zero-phase current does not flow in the three-phase distribution line is added to the adder circuit (10). There is a case that it is output from the erroneous ground fault detection. The correction arithmetic circuit (11) is to prevent such a malfunction of the ground fault detection, and the optical magnetic field sensors (5a), (5b), (5c) and the signal processing circuits (9a), (9b), (9c) The output signal generated in the adder circuit (10) due to the temperature characteristics such as is due to the change in ambient temperature, so the change is gradual, while the output signal due to a ground fault accident occurs at the same time as the accident occurs, so the change is rapid. It was constructed by focusing on. The correction arithmetic circuit (11) is constructed by using, for example, a microprocessor, and a flowchart of the processing is shown in FIG. First, in step (1), the output signal of the adder circuit (10) is input and stored for one cycle. Next, in step (2), the signal input and stored in the previous cycle is subtracted from the above input signal, and the result is output from the output terminal (20) of FIG. 1 to the outside in step (3). At the same time, in step (4), it is compared with a predetermined constant reference value. When the subtraction result is less than the reference value, step (5)
In, the storage signal input and stored in the previous cycle is updated with the signal input this time. When it is not less than the reference value, in step (6), the stored signal is fixed as it is without being changed. It is suitable that the reference value is about 50 to 90% of the operation level of the relay operated by the ground fault detection signal. Correction calculation circuit (1
By performing the above process in 1), for the output signal of the adder circuit (10) that gradually occurs due to changes in ambient temperature,
Since the signal to be subtracted is updated every AC cycle, the output of the correction arithmetic circuit (11) is kept at zero. On the other hand, for the output signal of the adder circuit (10) that occurs when a ground fault occurs,
Since the signal to be subtracted is the signal immediately before the occurrence of the ground fault accident, the output of the correction calculation circuit (11) becomes a signal due to the zero-phase current component generated by the ground fault accident. After the ground fault is recovered, the zero-phase current component due to the ground fault disappears, and the process returns to the processing mode of step (5) in the flowchart.

In the first embodiment, as a detector, an optical magnetic field sensor utilizing the Faraday effect is provided in the air gap provided in the annular iron core. However, in the second embodiment shown in FIG. Each of the windings (18a), (18b), and (18c) wound around the penetrating annular cores (2a), (2b), (2c) has a resistance (14
a), (14b), (14c) are connected in parallel and windings (18a), (18b), (18
The secondary current generated in c) is converted into a voltage, and the optical voltage sensors (15a), (15b), (15c) utilizing the Pockels effect are connected in parallel, respectively, so that light is emitted in the same manner as in the first embodiment. The zero-phase current can be detected by the outputs of the fibers (19a), (19b) and (19c).

Further, as a third embodiment, as shown in FIG. 4 as a light detecting means, materials (16a), (16a) having a Faraday effect are used.
b) and (16c) are placed around the three-phase distribution lines (1a), (1b) and (1c), respectively, and the light incident from the optical fibers (8a), (8b) and (8c) repeats reflection. Even if the optical fiber is constructed so that it returns to the original position and enters the optical fiber again when it rotates, the same effect as that of the above-mentioned embodiment is obtained. Examples of the use of these light detecting means are shown, for example, in Japanese Patent Publication No. 55-34905 and Japanese Patent Publication No. 58-153174.

[Effects of the Invention] According to the present invention, the detecting means for detecting the current of the distribution line is individually provided for each of the three-phase distribution lines, so that it can be installed on an outdoor power pole. Further, since the detecting means and the measuring circuit are connected by an optical fiber, it is safe against accidents such as lightning strikes. Further, since the correction calculation circuit corrects the change in the characteristics due to the temperature between the respective detection means, which is caused by providing the detection means individually, there is no erroneous detection.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a first embodiment of the present invention, FIG. 2 is a flow chart of a correction operation circuit of the present invention, and FIG. 3 is a configuration of a photodetector section of a second embodiment of the present invention. FIG. 4 is a circuit diagram showing the structure of the photodetector of the third embodiment of the present invention, and FIG. 5 is a diagram showing the structure of a conventional zero-phase current transformer. 1a, 1b, 1c: Distribution line 5a, 5b, 5c: Optical magnetic field sensor 8a, 8b, 8c, 13a, 13b, 13c: Optical fiber 12: Measuring circuit

Claims (4)

[Claims] 1. A light detecting means for outputting a light output of each phase corresponding to a current value of each phase of a three-phase distribution line, an optical fiber for transmitting the light output of each phase of the light detecting means, and an optical fiber for transmitting the light output. Photoelectric conversion means for converting the optical output of each phase into an electrical signal, the output of each phase of the photoelectric conversion means is separated into an AC component and a DC component, and the output obtained by dividing the AC component by the level of the DC component Signal processing circuit for obtaining, adder circuit for adding outputs for each phase obtained by the signal processing circuit, means for storing the output signal of the adding circuit for one cycle, output for the one cycle stored in the storing means A calculation means for performing a subtraction operation between the signal and the stored output signal of the next cycle of one cycle, and the result of the subtraction operation is compared with a predetermined reference value. The output signal is changed by the output signal of the next cycle. Update, zero-phase current transformer with a correction computation circuit having means for fixing the output signal said stored when not less than the reference value. 2. The zero-phase current transformer according to claim 1, wherein the light detecting means is provided with an optical magnetic field sensor in a gap provided in an annular portion of an annular iron core surrounding the distribution line. 3. The zero-phase current transformer according to claim 1, wherein the light detecting means is an optical voltage sensor based on the Pockels effect for detecting a voltage generated in a secondary winding provided on an annular core surrounding a distribution line. . 4. The zero-phase current transformer according to claim 1, wherein the light detection means is a light detection element that surrounds the distribution line and uses the Faderer effect.