JPS636467A - Zero-sequence current detection device using magneto-optical element - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a zero-sequence current detection device, and particularly to a zero-sequence current detection device suitable for detecting a zero-sequence current component of an optical current transformer using a magneto-optical element. This invention relates to a phase current detection device.

[Conventional technology]

A zero-phase current transformer (hereinafter referred to as ZCT) is used in combination with a ground protection relay to detect zero-phase current components based on differences in current values between each phase due to ground faults, etc. This is used to prevent the accident from spreading by activating the earth protection relay and interrupting the circuit. and,
Conventional methods for detecting zero-sequence current include providing a tertiary winding for zero-sequence current detection in an ordinary wire-wound current transformer (CT);
There is a method of using a dedicated ZCT.

FIG. 8 is used to detect zero-sequence current,
This figure shows a conventional method of connecting a current transformer (CT).

Figure 8 (A) shows a very simple zero-sequence current detection method when a neutral point can be grounded.A current transformer CT is installed at the grounding part of the neutral point N, and when a ground fault current I flows, Second, the ground protection relay GR is operated by the current i induced in the current transformer CT. Fig. 8(B) shows a method of operating the earth protection relay by the residual current i using the residual circuit of the current transformer CT installed in each phase R, S, and T. Fig. 8(C)
This is a three-phase, discarded type ZCT, and is a method used for relatively low voltage lines. In addition, Fig. 8 (D) is a method that is widely used as a method for detecting zero-sequence current in large power transmission and distribution. are connected in delta, and a ground protection relay OR is connected to the tertiary winding.

As described in Japanese Utility Model Publication No. 57-21303 and Japanese Unexamined Patent Publication No. 57-84114, these conventional ZCTs are wound on the same core as the current transformer, so the negative current rating is As the current transformer becomes larger, there is a problem that the zero-sequence current detection winding also becomes larger.

Therefore, in order to solve the problem of increasing the size and weight of current transformers, an optical current transformer using a photocurrent sensor using the magneto-optic effect was developed, as described in Japanese Patent Application Laid-Open No. 60-207068. being developed.

This optical current transformer attaches a Faraday element having a magneto-optic effect to a conductor, rotates the plane of polarization of polarized light guided to the Faraday element by the magnetic field generated by the current flowing through the conductor, and detects this rotation angle. This method determines the magnitude of the phase current, allowing current transformers to be made smaller and lighter.

[Problem that the invention seeks to solve]

However, photocurrent sensors that apply the magneto-optical effect have a small capacity of the output photocurrent signal, and cannot directly operate a ground protection relay, so zero-sequence current is detected using an optical current transformer. There wasn't.

An object of the present invention is to provide a zero-sequence current detection device using a magneto-optical element that allows a sensor having a magneto-optic effect to also be used as an optical current transformer for phase current detection.

[Means for solving problems]

The present invention provides a photocurrent sensor having a magneto-optical element placed near each phase in which current flows, a light source that supplies light to the photocurrent sensor, and a sum of the outputs of the respective photocurrent sensors. This is a zero-sequence current detection device characterized by comprising a calculation unit for calculating the amount of current.

[Effect]

In the present invention configured as described above, the amount of current flowing through each phase is detected by a photocurrent sensor that utilizes the magneto-optic effect, and the sum of each detected value is calculated by a computing unit so that the zero-sequence current can be detected. , it is possible to achieve the above purpose.

[Embodiment] A preferred embodiment of the zero-sequence current detection device according to the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is an explanatory diagram showing an embodiment of a zero-sequence current detection device according to the present invention.

In FIG. 1, a detection unit 14 of a photocurrent sensor 12 is attached to each conductor 10 of three phases R, S, and T. The detection unit 14 includes a circuit-integrating type detector 16 made of a Faraday element having a magneto-optic effect as a magneto-optical element, and a polarizer 1 that makes linearly polarized light incident on the detector 16.
8 and an analyzer 2o that detects the light emitted from the detector 16. The polarizer 18 is rotated parallel to the optical axis so that the optical axis differs from the analyzer 20 by π/4 in the electric field vector of the light wave.

- On the other hand, the photoelectric conversion section 22 of the photocurrent sensor 12 is provided with a light source 24 made of a light emitting diode, a laser diode, or the like. This light source is connected to the polarizer 1 by an optical fiber 26.
It is connected to 8. Further, the photoelectric conversion section 22 has a photodetector 28 made of a photodiode and an operational amplification section 29, and the photodetector 28 is connected to the analyzer 20 via an optical fiber 30. Then, in the photoelectric conversion section 22,
The analyzer 20 is provided with an optical CT output terminal a and a zero-phase output terminal A, and the zero-phase output terminal of each photoelectric conversion unit 22 is connected to the input side of the arithmetic unit 31. As shown in the figure, two are provided so that two components of orthogonal polarization can be detected. Each analyzer 20.20 is connected to a photoreceiver 28.28 via a respective optical fiber 30.30. The photodetector 28.28 is connected to the input side of the arithmetic circuit section 32 of the operational amplification section 29. A first amplifier circuit section 34 is connected to the output side of the arithmetic circuit section 32.
The outputs thereof are input to the second amplifier circuit section 36 and the third amplifier circuit section 38, respectively. Further, the output side of the second amplifier circuit section 36 is connected to the optical CT output terminal a, and the output side of the third amplifier circuit section 38 is connected to the zero-phase output terminal A. In addition,
The second amplifier circuit section 36 is used for phase current detection and therefore requires a wide dynamic range, but the third amplifier circuit section 38 does not require a wide dynamic range.

The operation of the embodiment configured as described above is as follows.

The light emitted by the light source 24 is guided to the polarizer 18 by an optical fiber 26, and is incident on the detector 16 as linearly polarized light with a polarization angle of 45 degrees. When the linearly polarized light passes through the detector 16, the plane of polarization is rotated by the magnetic field induced by the current flowing through the conductor 10. This rotation angle is
It is proportional to the strength of the magnetic field, that is, the amount of current flowing through each phase, and is emitted to the analyzer 20.20 as two orthogonal components. The polarized light incident on the analyzer 20 is input to the photodetector 28 via the optical fiber 30, converted into electrical signals Vt and Vz, and then input to the arithmetic circuit section 32.

The arithmetic circuit section 32 is V1 + Vx 1-V2 is calculated to remove the influence of fluctuations in the light g24.

The output of the arithmetic circuit section 32 is amplified by the first amplification circuit section 34 and then amplified by the second amplification circuit section 36 and the third amplification circuit section 38.
These amplifier circuit sections 36 and 38
The light C is amplified as a voltage proportional to the phase current of each phase.
It is output to the T output terminal a and the zero phase output terminal. The voltage output to the optical CT output terminal a is used for measuring phase current. Further, the voltage output to the zero-phase output terminal is input to the arithmetic unit 31. The calculator 31 calculates each phase current IR, Is obtained from the input voltage.

From IT, calculate the following equation to find the zero-sequence current Io.

Io=(IR+IS+IT)/3 The zero-sequence current Io obtained in this way is usually Io
=O, and if a ground fault occurs in any one of the R, S, and T phases, Io≠0 and a ground protection relay (not shown) is activated. This cuts off the circuit and prevents the accident from spreading.

As described above, in this embodiment, the zero-sequence current can be detected by simply branching the output of the photocurrent sensor 12 used in a conventional optical current transformer, and the phase current and zero-sequence current can be measured simultaneously. Can be done.

In the above embodiment, a case has been described in which two orthogonal polarized components are detected, but it is also possible to detect phase current and zero-sequence current using either of the two components.

Further, the detector 16 is not limited to a circular integral type.

FIG. 3 is an explanatory diagram showing another embodiment of the zero-sequence current detection device according to the present invention. In this embodiment, the photoelectric conversion unit 22 includes two operational amplifier units 29, one for phase current detection and one for zero-phase current detection.
a and 29b are provided. Because the zero-sequence current is smaller than the phase current.

In order to measure the zero-sequence current and the phase current with one operational amplifier section 29, an amplifier with a wide dynamic range is required. However, by dividing the current into phase current and zero-phase current as in this embodiment, the dynamic range can be narrowed. In particular, the operational amplifier section 29b for zero-phase current detection does not need to have a wide dynamic range, and costs can be reduced.

FIG. 4 is an explanatory diagram showing still another embodiment. In this embodiment, the emitted light from the detector 16 of each phase is input to the optical demultiplexer 40, 40 via the analyzer 2o, and after being demultiplexed, the light is input to the photodetector 28 of the photoelectric converter 22a, 22b. This is what I did. The output of the photoelectric converter 22a is used for phase current measurement, and the output of the photoelectric converter 22b is input to the calculator 31 in order to detect the zero-sequence current. Also in this embodiment, a wide dynamic range amplifier is not required for zero-phase current detection.

What is shown in FIG. 5 is an implementation in which one component of the light emitted from the detector 16, for example, the P-polarized component, is used for phase current detection, and the other component, for example, the S-polarized component, is used for zero-phase current detection. According to this embodiment, the light emitted from the detector 16 is detected by the two analyzers 20°20 as two orthogonal polarized components, so the optical signal or the electrical signal after photoelectric conversion is detected. There is no need to branch, and the configuration can be simplified.

In the embodiment shown in FIG. 6, one component of the emitted light from the detector 16 of each phase, for example, the P-polarized light component, is sent to the photoelectric conversion unit 22a for phase current detection, as in the embodiment shown in FIG. input. − side, the other component of each phase.

For example, the S-polarized light component is input to the light combiner 42. and,
The output light ΔIO of the light combiner 42 is incident on the photodetector 28 provided in the photoelectric conversion section 22b for zero-phase current detection. The photoelectric conversion unit 22b has the following formula: Io=(ΔIo−ΔIo)/ΔI.

is calculated to find the zero-sequence current Io. However, ΔIO is
This is the average value of the polarization components of each phase detected by the analyzer 16.

According to this embodiment, since the sum is calculated using only optical signals,
Excellent electrical noise resistance.

FIG. 7 is an explanatory diagram showing still another embodiment of the zero-sequence current detection device according to the present invention. This example is.

A polarizer 18 is placed at the input end of the detector 16 provided in an arbitrary phase, for example, the T phase, and an analyzer 20 is placed at the output end of the detector 16 in one of the other two phases, for example, the R phase. At the same time, the plane of polarization is maintained between the output end of the T-phase detector 16 and the input end of the S-phase detector 16, and between the output end of the S-phase detector 16 and the input end of the R-phase detector 16. Fiber 44.
46. With this configuration, the linearly polarized light emitted from the polarizer 18 undergoes rotation of the plane of polarization corresponding to the phase current within the detector 16 of each phase, and the polarized light emitted from the R-phase detector 16 becomes zero. The plane of polarization is rotated corresponding to the phase current component, and the zero-sequence current IO can be obtained by the photoelectric conversion unit 22. According to this embodiment, the sum of the phase currents can be calculated using only the optical signal. In this embodiment, the emitted light from the detector of each phase is demultiplexed and used for phase current detection. Of course, you can use it.

〔Effect of the invention〕

As explained above, according to the present invention, since the zero-sequence current can be detected using the emitted light of the magneto-optical element for detecting phase current, the photocurrent sensor can also be used as an optical current transformer for detecting phase current. Can be shared.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram showing one embodiment of the zero-phase current detection device according to the present invention, Fig. 2 is a detailed explanatory diagram of the photoelectric conversion section of the embodiment shown in Fig. 1, and Fig. 3 is a phase current detection diagram. 4th explanatory diagram of an embodiment provided with an operational amplification section for detecting zero-phase current and an operational amplification section for zero-phase current detection.
The figure is an explanatory diagram of an example in which the light is split into phase current detection and zero-phase current detection using an optical demultiplexer. Figure 5 shows that one component of linearly polarized light is used for phase current detection, and the other component is used for phase current detection. An explanatory diagram of an embodiment used for zero-sequence current detection, Fig. 6 is an explanatory diagram of an embodiment using a photosynthesizer, and Fig. 7 is an explanatory diagram of an embodiment in which the detectors of each phase are connected with polarization preserving fibers. 8(A) to 8(D) are explanatory diagrams of a zero-sequence current detection method using a conventional wire-wound current transformer. 10... Conductor, 12... Photocurrent sensor, 16...
Detector (magneto-optical element), 18...Polarizer, 20...
-Analyzer, 22, 22a, 22b-Photoelectric conversion unit, 24...Light source, 28...Photoreceiver, 29, 29a
, 29b... operational amplifier section, 31... computing unit.

Claims (1)

[Claims] 1. A photocurrent sensor having magneto-optical elements arranged near the conductors of each phase through which current flows, a light source that supplies light to this photocurrent sensor, and an output of each of the photocurrent sensors. A zero-sequence current detection device characterized by comprising a calculation unit that calculates a sum. 2. In the zero-sequence current detection device according to claim 1, each photocurrent sensor has a photoelectric conversion section that outputs an electrical signal according to the amount of light, and the arithmetic unit is configured to A zero-sequence current detection device characterized by determining the sum of output electrical signals. 3. The zero-sequence current detection device according to claim 2, wherein the photoelectric conversion section outputs a phase current detection signal and a zero-sequence current detection signal. 4. The zero-sequence current detection device according to claim 1, wherein the photocurrent sensor outputs a detection light for detecting a phase current and a detection light for detecting a zero-sequence current. . 5. In the zero-sequence current detection device according to claim 4, the detection light for zero-sequence current detection is one of two orthogonal polarized components emitted from the photocurrent sensor, and A zero-sequence current detection device characterized in that the detection light is the other polarized component. 6. In the zero-sequence current detection device according to claim 3, the photoelectric conversion section includes a phase current detection conversion section that photoelectrically converts the phase current detection detection light, and a phase current detection conversion section that photoelectrically converts the phase current detection detection light. A zero-sequence current detection device comprising: a zero-sequence current detection conversion section. 7. In the zero-sequence current detection device according to claim 1, the photocurrent sensor arranged in each phase is provided with a polarizer on the input end side of any one phase, and a polarizer is provided on the input end side of each phase. A zero-phase current detection device characterized in that the output end side is connected in series via a polarization maintaining optical fiber, and the output light of the photocurrent sensor at the terminal end is guided to a photoelectric conversion section.