JPH0641963B2 - Optical zero-phase current transformer - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an optical zero-phase current transformer that uses light to detect a ground fault in a power distribution source.

[Conventional technology]

Figure 3 shows, for example, the "Transformer for measuring instruments" issued in August 1957.
(Published by Denki Shoin, written by Miho Ikeda) FIG. 1 is a block diagram of a conventional zero-phase current transformer shown in P and 79, where (1) is a three-phase distribution line, (1A), (1B), (1C) is a distribution line for each phase. (2) is a hollow cylindrical iron core arranged so as to surround the three-phase distribution line (1) inside. (3) is a secondary winding wound around the iron core (2). (4) is a zero-phase current detector connected to the secondary winding (3).

The conventional zero-phase current transformer is configured as above, and the three-phase distribution line is
Regarding the currents flowing through the respective-phase distribution lines (1A), (1B), and (1C) in (1), it may be considered that only the positive phase current and the negative phase current flow in a steady state. On the other hand, the magnetic flux induced in the iron core (2) surrounding the distribution line (1) is induced by a combination of the magnetic fields generated in proportion to the magnitudes of the positive-phase component current and the negative-phase component current. Because
The above-mentioned magnetic flux at a constant time is zero and does not exist. Therefore, no current flows in the secondary winding (3) wound around the iron core (2), and the secondary current detected by the zero-phase current detection unit (4) is zero.

Next, when a ground fault occurs in the three-phase distribution line (1), each phase distribution line
Even if the currents flowing in (1A), (1B), and (1C) are added vector-wise, a zero-phase current that does not become zero flows, so a magnetic flux is induced in the iron core (2) and the secondary winding A secondary current having a magnitude proportional to the above zero-phase current flows through the line (3). Zero-phase current detector
(4) detects the occurrence of a ground fault by detecting the magnitude of this secondary current. That is, the conventional zero-phase current transformer is provided with an iron core (2) that collectively surrounds the three-phase distribution line (1) to detect the zero-phase current flowing when a ground fault occurs and It detects ground faults in the electric wire (1), and is often installed in the substation premises and serves to prevent the spread of the accident by disconnecting the distribution line (1) where the ground fault has occurred from the grid. In recent years, due to undergrounding of distribution line (1), there is a rapid transition from overhead distribution line (1) to underground cable laying, and zero-phase current transformers are used in the event of a ground fault of the above cable. The needle-shaped electric current seen in is also detected as in the case of the overhead distribution line (1). This needle wave current is generated when the incomplete ground fault occurs in the cable, and when each phase distribution line (1A), (1B), (1C) approaches the peak voltage, zero-phase current The detector functions to detect this current and prevent a large-scale accident from occurring.

In recent years, even in the event of a ground fault, it has been required to be able to find the accident point promptly and accurately in order to limit the power outage section and shorten the recovery time as much as possible. It has become necessary to install many current transformers not only in the substation premises but also in the middle of the distribution line (1).

[Problems to be solved by the invention]

In the conventional zero-phase current transformer as described above, since the three-phase distribution line (1) is surrounded by one iron core (2), the iron core (2) can be installed on an outdoor distribution pole. There is a problem that it is large and it is difficult to place it, and that the distribution line (1) is surrounded by the iron core (2) that is a conductor, which may cause an accident to spread when a lightning strike occurs. There was a point.

The present invention has been made to solve the above problems, and is suitable for being installed on an outdoor power distribution pole, does not use an iron core, has no fear of expanding an accident, and has a high-frequency signal component of zero-phase current. An object of the present invention is to obtain an optical zero-phase current transformer capable of detecting a commercial frequency signal component and ensuring stable detection accuracy.

[Means for solving problems]

The optical zero-phase current transformer according to the present invention is provided in the vicinity of each phase distribution line of a three-phase distribution line in order to solve the above problems and to achieve the above object, and a current flowing through each phase distribution line. An optical element that modulates the characteristics of an optical signal by the optical element, and an optical element that transmits the optical signal to each of the optical elements, receives the optical signal whose characteristics are modulated by the optical elements, and converts the optical signal into an electrical signal. The transmission conversion circuit and the output electrical signals for three phases output from the optical transmission conversion circuit are separated into a high frequency signal component and a commercial frequency signal component,
The signal synthesizing circuit detects the zero-phase current by adding each component.

[Action]

In the present invention, the optical transmission conversion circuit transmits an optical signal to each optical element, the optical element modulates the characteristics of the optical signal according to the current flowing in each phase distribution line, and the individual optical elements modulated by each optical element are modulated. The optical transmission conversion circuit receives the optical signal, converts it into an electric signal, and the signal combining circuit electrically adds the converted electric signals for the three phases to detect a zero-phase current.

〔Example〕

FIG. 1 is a block diagram of an optical zero-phase current transformer showing an outline of an embodiment of the present invention, in which (1), (1A), (1B) and (1C) are the same as the conventional one.

(5A), (5B), (5C) are each optical element arranged in the vicinity of each phase distribution line (1A), (1B), (1C), and constitute the optical element (5) as a whole. . (6) is an optical transmission conversion circuit that transmits an optical signal to the optical element (5), receives the optical signal whose characteristics are modulated by the optical element (5), and converts the optical signal into an electric signal. Reference numeral (7) is an optical fiber for transmitting an optical signal between the optical transmission conversion circuit (6) and the optical element (5). (8) is a signal synthesizing circuit for adding the three-phase electric signals output from the optical transmission conversion circuit (6).
Reference numeral (9) is an electric wire for transmitting the three-phase electric signals output from the optical transmission conversion circuit (6) to the signal combining circuit (8).

In the optical zero-phase current transformer configured as described above, the optical transmission conversion circuit (6) transmits an optical signal to the optical element (5) via each optical fiber (7). Each optical element (5A),
(5B) and (5C) modulate the characteristics of the optical signal according to the currents flowing through the phase distribution lines (1A), (1B) and (1C). The optical transmission conversion circuit (6) receives, via each optical fiber (7), an individual optical signal in which the above characteristics are modulated by each optical element (5A), (5B), (5C). Is converted into an electric signal and output. The electric signals (3) for the output three-phase electric signals are output.
A signal synthesizing circuit (8) receives the signal through the signal and electrically adds it to detect a zero-phase current (zero-phase current) flowing through the three-phase distribution line (1). Therefore, this optical zero-phase current transformer should ensure stable detection accuracy without being affected by variations in the characteristics (modulation degree) of each optical element (5A), (5B), (5C), light source, etc. You can Also, when installing this optical zero-phase current transformer on the outdoor distribution pole,
Only the electrically insulating optical element (5) is electrically insulated
It only needs to be installed near the three-phase distribution line (1) via (7), and other parts can be installed in the middle of the distribution pole or on the ground.
Therefore, even if a lightning strike occurs, there is no fear of expanding the accident. Moreover, since a large heavy object is not installed on the distribution pole, the installation becomes easy.

FIG. 2 is a block diagram showing the details of this embodiment. (1)
(7) are the same as in FIG. The optical transmission conversion circuit (6) consists of three parts (6A), (6A) corresponding to each phase distribution line (1A), (1B), (1C).
B) and (6C), and accordingly the electric wire (9) and (9A) (9
It is divided into B) and (9C). (8) is a signal combining circuit, which is a low-pass filter (8A), (8B), (8) that extracts only the commercial frequency signal component from the output electric signal from the optical transmission conversion circuit (6).
C), high-frequency filters (8D), (8E), and (8F) that extract only high-frequency needle wave signal components, a commercial frequency signal synthesis circuit (8G) that adds only commercial frequency signal components, and high-frequency signals It is composed of a high frequency signal synthesis circuit (8H) that adds only the components and a final signal synthesis circuit (8I) that adds both the commercial frequency signal component and the high frequency signal component.

In the signal synthesizing circuit (8) of the present embodiment, the low-pass filters (8A) to (8C) and the high-pass filters (8D) to (8F) are output from the optical transmission conversion circuits (6A) to (6C). The electric signal is separated into a commercial frequency signal component and a high frequency signal component in advance, and each is added by the commercial frequency signal synthesis circuit (8G) and the high frequency signal synthesis circuit (8H), and then the added frequency signal components are finalized. Three-phase distribution line, which is finally added by the signal synthesis circuit (8I)
Detect the zero-phase current flowing in (1). Therefore, the measurement accuracy of both frequency signal components can be improved, and the zero-phase current can be detected with high accuracy.

[Advantages of the Invention] As described above, the present invention transmits an optical signal to the optical element provided in the vicinity of the three-phase distribution line, and transmits an optical signal to the optical element to generate an individual optical signal whose characteristics are modulated by each optical element. An optical transmission conversion circuit that receives and converts these electrical signals, and these electrical signals,
Each of the optical elements (5A), (5) is composed of a signal combining circuit that separates a high-frequency signal component and a commercial-frequency signal component and adds each component to detect a zero-phase current.
Even if there are variations in the characteristics (modulation degree) of (B) and (5C), the light source, etc., stable detection accuracy can be secured. Further, since the iron core is not required, it is suitable for being installed on an outdoor power pole, and there is an effect that there is no fear of expanding an accident when a lightning strike occurs. Further, the high frequency signal component of the zero-phase current and the commercial frequency signal component can be detected with high accuracy.
Therefore, the needle wave current generated when the underground cable is incompletely grounded can be detected with high accuracy.

[Brief description of drawings]

FIG. 1 is a block diagram showing an outline of an embodiment of an optical zero-phase current transformer according to the present invention, and FIG. 2 is a block diagram showing details of the same embodiment,
FIG. 3 is a block diagram showing a conventional zero-phase current transformer. In the figure, (1) is a three-phase distribution line, (5) is an optical element, (6) is an optical transmission conversion circuit, and (8) is a signal combining circuit. In the drawings, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Claims] 1. An optical element which is provided in the vicinity of each phase distribution line of a three-phase distribution line and modulates the characteristics of the optical signal by a current flowing through each phase distribution line, and the optical signal is transmitted to each of the optical elements. At the same time, an optical transmission conversion circuit that receives an optical signal whose characteristics are modulated by each of the optical elements and converts the optical signal into an electric signal, and output electric signals for three phases output by the optical transmission conversion circuit An optical zero-phase current transformer, comprising: a signal synthesis circuit that separates a signal component and a commercial frequency signal component and adds each component to detect a zero-phase current.