JP4404717B2 - Photocurrent sensor - Google Patents

Description

  The present invention relates to a photocurrent sensor.

  The photocurrent sensor using the Faraday effect has an advantage that it is not affected by electromagnetic noise, and is used for current measurement in the power field. Such a photocurrent sensor is disclosed in, for example, the IEEJ Electric Wire and Cable Research Society document EC-98-8 published in 1998 and JP-A-7-248338.

  FIG. 2 shows an outline of the configuration of the photocurrent sensor described in the study group document (EC-98-8). The photocurrent sensor includes a signal processing unit 10 including a light source 11, a depolarizing element (depolarizer) 13, and a photoelectric converter 14, a sensor unit 30, an input optical fiber 21 that connects the signal processing unit 10 and the sensor unit 30, and The optical transmission line 20 is composed of an output optical fiber 22. Here, a high-intensity light-emitting diode (high-intensity LED) is used for the light source 11, and a single mode fiber is used for the input optical fiber 21 and the output optical fiber 22.

  In the photocurrent sensor having this configuration, the polarization intensity of the light source 11 is eliminated by the depolarization element 13 and then sent to the sensor unit 30 via the input optical fiber 21, whereby the light intensity supplied to the sensor unit 30 is increased. Can be constant. Therefore, the output fluctuation of the photocurrent sensor caused by the disturbance received by the input optical fiber 21 can be reduced.

  On the other hand, a power transmission line (OPGW) having a structure in which a single mode optical fiber is built in an aerial ground wire is widely used. Therefore, by using a single mode fiber for the optical transmission line 20 that connects the signal processing unit 10 and the sensor unit 30, the photocurrent sensor can be used without newly laying the optical transmission line.

  Next, FIG. 3 shows an outline of the configuration of the photocurrent sensor described in the publication (Japanese Patent Laid-Open No. 7-248338). The photocurrent sensor includes a signal processing unit 10 including a light source 11, a spectroscopic element 12, and a photoelectric converter 14, a sensor unit 30 including a polarizing element 31, an optical bias element 32, a Faraday element 33, and a reflection mirror 34, and a signal processing unit. The optical transmission line 20 is composed of an input optical fiber 21 and an output optical fiber 22 that connect the 10 sensors and the unit 30. Here, a polarization-dependent circulator comprising a polarizing element and a 45-degree Faraday rotator is used as the spectroscopic element 12, a polarization plane holding fiber is used as the input optical fiber 21, and a multimode fiber is used as the output optical fiber 22.

  In the photocurrent sensor having this configuration, the Faraday element 33 is formed of an optical fiber, and the reflection mirror 34 is provided at one end thereof, so that the sensor unit 30 can be attached without separating the conductor 40 through which the current to be measured flows. Further, by using two optical signals whose phases outputted from the sensor unit 30 are inverted, the influence of birefringence caused by the disturbance received by the Faraday element 33 can be canceled, so that the current measurement accuracy can be improved.

  However, in the configuration of FIG. 2, when the maximum distance of the optical transmission line 20 is calculated from the light emission amount of the high-intensity LED used for the light source 11 and the minimum light reception amount of the photoelectric converter 14, it is about 5 km.

  On the other hand, in the electric power field, when an accident occurs on a mixed line of overhead and underground transmission lines, a device that can determine whether the accident section is caused by an overhead transmission line or an underground transmission line (ground Middle line accident section judgment device) has been put into practical use. For this determination, it is necessary to compare the magnitude and phase of the zero-phase current flowing through the connection with the overhead power transmission line existing at both ends of the underground power transmission line. Therefore, the photocurrent sensor used in this apparatus must be able to transmit current information over a long distance. Since some underground transmission lines exceed 20 km, a photocurrent sensor that can further increase the conventional transmission distance is desired.

  In addition, since the photocurrent sensor having the configuration of FIG. 2 uses only one light emitted from the sensor unit 30, the influence of the disturbance received by the sensor unit 30 cannot be removed. As a result, the current measurement accuracy of the photocurrent sensor decreases.

  On the other hand, in the underground accident section determination apparatus described above, a photocurrent sensor with higher current measurement accuracy is desired in order to increase the determination accuracy.

  In addition, in the configuration of FIG. 3, although current measurement can be performed with high accuracy, since the polarization maintaining fiber is used for the input optical fiber 21, it is difficult to use the single mode fiber housed in the OPGW described above. It is. Therefore, in order to transmit the output of this photocurrent sensor for a long distance, it is necessary to newly lay an optical transmission line. However, since the polarization-maintaining fiber is more expensive than the single mode fiber, it is not practical to install the polarization-maintaining fiber.

  If the input optical fiber 21 in FIG. 3 is formed of a single mode fiber, the single mode fiber does not have a function of stably transmitting the polarization direction, and therefore a straight line that has passed through the polarization-dependent circulator as the spectroscopic element 12. The direction of the polarized light is arbitrarily changed during propagation of the single mode fiber due to birefringence caused by the disturbance of the single mode fiber. As a result, the polarization direction of the light reaching the sensor unit 30 changes with time. When the polarization direction of the light incident on the sensor unit 30 changes with time, the amount of light that passes through the polarizing element 31 and is supplied to the Faraday element 33 varies accordingly. As a result, the amount of light incident on the photoelectric converter 14 changes when the measured current is not energized. This variation in the amount of light causes a decrease in the current measurement accuracy of the photocurrent sensor.

  Therefore, the present invention proposes a configuration of a photocurrent sensor that uses a single mode fiber for an optical transmission line, has high measurement accuracy, and can perform long-distance transmission.

  Another object of the present invention is to propose an underground line accident zone determination device using the photocurrent sensor.

  According to a first aspect of the present invention, there is provided means for circulating a Faraday element formed of an optical fiber around a conductor through which a current to be measured flows, and converting the polarization direction of light rotated by the Faraday effect into light intensity. In the photocurrent sensor for calculating the magnitude of the current flowing through the measured conductor from the change of the light source, the sensor section for converting the magnitude of the current flowing through the measured conductor into two light intensity signals whose phases are inverted, and Formed with a photoelectric converter that converts two optical signals obtained from the sensor unit into electrical signals and calculates the current value by calculating the electrical signal, and a single mode fiber that connects the light source and the sensor unit The input optical fiber, the output optical fiber formed by a single mode fiber connecting the sensor unit and the photoelectric converter, and the light source and the input optical fiber. A light cancellation element, disposed between the light source and the depolarization element, and supplies the light emitted from the light source to the polarization cancellation element without changing the polarization state and intensity, and the input optical fiber and the And a spectroscopic element that supplies light input from the sensor unit via the depolarization element to the photoelectric converter without changing the polarization state and intensity.

  According to a second aspect of the present invention, the light source is a light source utilizing a phenomenon in which spontaneous emission light generated by exciting the rare earth element-added fiber with an excitation light source such as a semiconductor laser is amplified as it is guided in the fiber. It is characterized by being.

  According to a third aspect of the present invention, in the fault section determination apparatus for a power transmission line in which an overhead line and an underground line are mixed, the photocurrent sensor according to the first and second aspects is provided.

  In the photocurrent sensor having the above-described configuration, it is possible to provide a photocurrent sensor that can use a single mode fiber for the optical transmission line, has high measurement accuracy, and can perform long-distance transmission.

  Moreover, it is possible to provide an underground accident section determination device using the photocurrent sensor.

  As described above, in the photocurrent sensor having the above-described configuration, it is possible to provide a photocurrent sensor that can use a single mode fiber for an optical transmission line, has high measurement accuracy, and can perform long-distance transmission. Moreover, it is possible to provide an underground accident section determination device using the photocurrent sensor.

  Two examples will be described below.

  Embodiments of the present invention will be described below with reference to the drawings. In the following description, in the drawings referred to in the above prior art, the same or corresponding parts are denoted by the same reference numerals, and the description thereof is omitted.

  FIG. 1 shows an example of the configuration of a photocurrent sensor according to the first and second embodiments of the present invention. In FIG. 1, the spectroscopic element 12 is disposed between the light source 11 and the depolarizing element 13. The sensor unit 30 outputs two optical signals to improve current measurement accuracy. One output light is output via the output optical fiber 22, and the other output light is the input optical fiber 21. The light is incident on the photoelectric converter 14 via the element 13 and the spectroscopic element 12.

  Here, the light source 11 is a light source (ASE) using a phenomenon in which spontaneous emission light generated by exciting a rare earth element-doped fiber with a pumping light source such as a semiconductor laser is amplified as it is guided in the fiber. To do. In addition, single-mode optical fibers are used for the input optical fiber 21 and the output optical fiber 22. ASE has features such as a large output light quantity (several tens of mW), low temporal coherence, and high spatial coherence, and is suitable as a light source for a photocurrent sensor. In addition, since the degree of polarization of the output light is small, it becomes easy to depolarize by the depolarizing element. Therefore, it is excellent as a light source in a photocurrent sensor in which the input optical fiber 21 is a single mode fiber.

  In addition, a polarization-independent circulator is used for the spectroscopic element 12. By using a polarization-independent circulator as the spectroscopic element 12, the light emitted from the light source 11 is supplied to the depolarization element 13 without changing the polarization state and intensity, and the input optical fiber 21, depolarization element The light input from the polarizing element 31 via 13 can be supplied to the photoelectric converter 14 without changing the polarization state and intensity.

  The reason why long distance transmission is possible with the configuration of the photocurrent sensor shown in FIG. 1 will be described below based on test data. In order to confirm that the long-distance transmission is possible, a sufficient amount of return light can be secured with the optical transmission line 20 in a long distance, and the output of the photocurrent sensor does not fluctuate due to the disturbance that the optical transmission line 20 receives. Two items were verified.

  First, as a test to show that the configuration of the photocurrent sensor shown in FIG. 1 enables long-distance transmission, the spectroscopic element 12 uses three types of light, a polarization-independent circulator, a polarization-dependent circulator, and a coupler. The insertion loss was measured. The results are shown in the table below. The light loss (P) indicates a value obtained by subtracting the amount of light received by the photoelectric converter 14 (P1 on the spectroscopic element 12 side and P2 on the output optical fiber 22 side) from the light emission amount (P0) of the light source 11. In this test, the lengths of the input optical fiber 21 and the output optical fiber 22 are each 10 km. From this table, it can be seen that by using a polarization-independent circulator for the spectroscopic element 12, it can be reduced by about 6 dB from that using other spectroscopic elements.

  On the other hand, the light emission amount (P0) when ASE is used for the light source 11 is +10 dBm or more. Further, in order to guarantee current measurement accuracy, a light amount of at least −20 dBm is required. Here, assuming that the optical loss of the photocurrent sensor including the optical loss of the optical transmission line 20 of 10 km one way is 20 dB and the optical loss of the optical transmission line 20 is 0.5 dB / km, the distance of the optical transmission line 20 used in the test. It can be seen that the distance can be further extended by 10 km. That is, the photocurrent sensor having the configuration shown in FIG. 1 can perform long-distance transmission of 20 km or more.

  Next, a test result for verifying that the output of the photocurrent sensor does not fluctuate due to the disturbance received by the optical transmission line 20 with the configuration of the photocurrent sensor shown in FIG. 1 will be described. In the test, the input optical fiber 21 using a single mode fiber was swung in the configuration of the photocurrent sensor shown in FIG. 1, and the output of the photocurrent sensor at that time was measured. Further, in order to compare the characteristics of the spectroscopic element 12, three types of polarization independent circulator, polarization dependent circulator, and coupler were used. The test results are shown in the table below. From this test result, the influence on the oscillation of the input optical fiber 21 when using a polarization-independent circulator and when using a coupler is so small that there is no practical problem, but a polarization-dependent circulator is used. It can be seen that it is affected to such a degree that it cannot be put into practical use.

  FIG. 4 shows an example of an underground line fault section determination device according to the third embodiment of the present invention. In a transmission line in which an overhead line and an underground line are mixed, a sensor part 30a is attached near one connection part between the overhead transmission line 41 and the underground transmission line 42, and a sensor part 30b is attached near the other connection part.

  The light emitted from the light source 31a enters the sensor unit 30a via the spectroscopic element 12a, the depolarization element 13a, and the input optical fiber 21a. By utilizing the Faraday effect, the sensor unit converts the rotation angle of the polarization direction of the light depending on the magnitude of the magnetic field generated by the current flowing through the underground transmission line 42 into two light intensities. Exit. One optical signal enters the photoelectric converter 14a through the output optical fiber 22a. The other optical signal enters the photoelectric converter 14a via the input optical fiber 21a, the depolarizing element 13a, and the spectroscopic element 12a. In the photoelectric converter 14a, two optical signals are converted into electric signals, and then a predetermined calculation is performed to calculate the current flowing through the underground power transmission line 42 at the position where the sensor unit 30a is attached.

  Similarly, the photoelectric converter 14b calculates the current flowing through the underground power transmission line 42 at the position where the sensor unit 30b is attached.

  Current information obtained by the photoelectric converters 14a and 14b is sent to the section detection device 15, and whether a ground fault has occurred in the overhead power transmission line 41 or in the underground power transmission line 42 from the current value and the phase difference. Determine.

It is a figure which shows an example of a structure of the photocurrent sensor concerning the 1st Embodiment of this invention. It is the figure which showed an example of the structure of the conventional photocurrent sensor. It is the figure which showed another example of the structure of the conventional photocurrent sensor. It is a figure which shows an example of the underground line fault area determination apparatus structure using a photocurrent sensor concerning the 2nd Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Signal processing part 11 Light source 12 Spectroscopic element 13 Depolarization element 14 Photoelectric converter 15 Section detection apparatus 20 Optical transmission path 21 Input optical fiber 22 Output optical fiber 30 Sensor part 31 Polarization element 32 Optical bias element 33 Faraday element 34 Reflection mirror 40 Conductor 41 Overhead transmission line 42 Underground transmission line

Claims (2)

A Faraday element formed of an optical fiber is circulated in the conductor through which the current to be measured flows, and a means for converting the polarization direction of the rotating light to the light intensity by the Faraday effect is provided, and flows from the change in the light intensity to the conductor to be measured. In the photocurrent sensor that calculates the magnitude of the current,
A light source;
The light from the light source is sent to the depolarization element, and the Faraday element is sent from the depolarization element.
A spectroscopic element that sends one of the two output lights (hereinafter referred to as A light) to the photoelectric converter without changing the polarization state and intensity;
The light of the light source is formed of a single mode fiber by depolarizing the light passing through the spectroscopic element.
Sending to the input optical fiber and depolarizing the A light from the input optical fiber,
A depolarizing element to be sent to the spectroscopic element;
Receiving light from the light source from the depolarizing element, sending light to the polarizing element of the Faraday element,
The input optical fiber for sending the A light coming from the polarizing element of the Faraday element to the depolarizing element;
Linearly polarized light is generated in order to send the light transmitted from the input optical fiber to the Faraday element. At the same time, light having a polarization angle rotated by the Faraday effect from the Faraday element has the polarization component orthogonal to the A light. A polarizing element that decomposes into light (hereinafter referred to as B light);
A photocurrent sensor comprising: an output optical fiber formed of a single mode fiber for sending the B light to the photoelectric converter .
The light source is a light source utilizing a phenomenon in which spontaneous emission light generated by exciting a rare earth element-doped fiber with a pumping light source such as a semiconductor laser is amplified as it is guided in the fiber. Item 2. The photocurrent sensor according to Item 1.

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