JPH04261334A - Power transmission line monitoring system - Google Patents

Abstract

PURPOSE:To realize a coherent light utilized transmission line monitoring system which has no decrease in receiving sensitivity caused by a distortion of an optical signal waveform due to a refractive index change of an optical fiber accompanying the elongation of an optical ground wire(OPGW) when the OPGW is lightened in the system using the OPGW. CONSTITUTION:A coherent light transmission monitoring system in which an oscillation frequency of a transmission light source is so controlled that signal spectrum positions of terminals of iron towers are not superposed by an optical loop network having a central monitor center having a coherent light transmitter having a plurality of transmission light sources controlled at a frequency interval as a frequency reference and a coherent light receiver having a function of selectively receiving an information signal from a light transmission terminal disposed at each iron tower and the iron tower connected to the center in a loop state by an optical fiber so that the loop is composed for all lights without optoelectric conversion to raise its reliability.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to power transmission line monitoring systems. In recent years, coherent optical communication systems that utilize the wave nature of light have attracted attention as a next-generation optical communication system, and research is being actively conducted at various communication research institutes. Compared to the intensity modulation direct detection method (IM-DD method) that has been put into practical use in the past, the coherent optical communication system improves reception sensitivity by improving sensitivity by using heterodyne or homodyne detection and improving sensitivity by frequency or phase modulation/demodulation method. Sensitivity is improved by 10-20dB, so
Long distance transmission is possible. Furthermore, its narrow spectrum enables optical frequency multiplexing transmission, dramatically increasing transmission capacity. Due to these advantages, as a communication method,
It has basically an advantage over the IM-DD method, which is a simple power transmission method.

A typical example of an optical fiber communication system for power use is a system using an optical fiber composite overhead ground wire (OPGW). The OPGW, which houses optical fibers inside, is installed alongside power transmission lines, and the transmission line tower collects information on transmission line abnormalities, accidents, weather, etc. necessary for transmission line maintenance, and sequentially transmits it to a central monitoring center. However, OP
When lightning strikes the GW, the OPGW is stretched and the refractive index of the optical fiber changes. For this reason, the IM-DD method, which uses a light source with a wide spectrum, causes distortion of the pulse waveform and significantly deteriorates reception sensitivity, making it desirable to apply coherent optical communication using a light source with a narrow linewidth. There is.

0003

2. Description of the Related Art FIG. 7 shows a conventional power transmission monitoring system. In the conventional method, optical transmission terminals 1 and 2 are installed on each tower.
, 3 and 4, optical-to-electrical conversion is performed one by one. That is, as shown in FIG. 7, an optical receiver (OR) 161,
261, 271, 361, 371, 461 convert the optical signal into an electrical signal, and the TDM signal processing units 160, 260, 2
The electrical signals processed by the optical transmitters (OS) 162, 262, 272, 362, 3
At 72 and 462, the signal is converted into an optical signal again and sent to the optical fiber. By time-division multiplexing (TDM) the information from each tower, the central monitoring center 1 performs maintenance and control of the power transmission system, commands for power supply, and collects monitoring information for power generation and substation equipment.

On the other hand, optical CATV is a typical example of the application of coherent optical communication to a network. This system has a plurality of transmitting light sources at a broadcasting center, each light source is assigned a different program, and is bundled onto a single fiber optic cable and sent to each subscriber's home. Heterodyne detection allows each subscriber's home to selectively receive their favorite programs. In this case, the oscillation frequency of each transmission light source in the broadcasting center must be fixed, and the use of a reference light source using an atomic beam or control of frequency intervals using a Fabry-Perot resonator has been considered.

[0005]

[Problems to be Solved by the Invention] As mentioned above, in the conventional system, each optical transmission terminal is
Because electrical conversion is performed, if a failure occurs at any one of the tower terminals, the transmission route will be cut off and information will no longer be transmitted. Therefore, it is necessary to take some measures such as redundant configuration. Also, as mentioned earlier, OPGW
There is also the problem that reception sensitivity deteriorates when lightning strikes.

[0006] Furthermore, when considering applying the optical CATV method to a power transmission line monitoring system, since each optical transmitter is located at a different location (each tower is not located at the same location), the oscillation frequency of the optical transmitter may vary. The problem was how to control it, and it was difficult to apply it as is. The present invention introduces an effective method for remotely controlling the frequency of the transmitted light from the optical transmission terminal of each tower by transmitting reference frequency light assigned to each tower terminal from a central monitoring center. Solved the difficult problem of controlling the oscillation frequency of the transmitter,
The objective is to solve the problem of deterioration of reception sensitivity when an OPGW is struck by lightning by realizing a monitoring system using coherent optical communication.

[0007]

[Means for Solving the Problems] FIG. 1 is a diagram showing the basic configuration of the present invention. The optical transmitter 12 of the central monitoring center 1 has the same number of light sources as the number of power transmission line towers to be monitored, and the oscillation frequency of each is determined by the oscillation frequency interval using a reference oscillation light source using atomic absorption lines or a Fabry-Perot resonator. are controlled to be equal. The lights sent out from each light source are bundled by means such as an optical star coupler, and sent out to one of the optical fiber cables 51 in the OPGW 5. Each light source is used as a reference frequency by the optical transmission terminal installed on each steel tower, so no modulation is applied. The optical signal transmitted through the optical fiber cable 51 is transmitted via the optical fiber cables 61 and 71 in each tower section, and then sent to the last tower (tower N) of the plurality of towers to be monitored via another optical fiber cable, which is the return route. 42 and returns to the central monitoring center via the optical transmission terminals 4, 3, 2, 1 of each tower and the optical fiber cables 72, 62, 52 of each tower section. The central monitoring center has an optical heterodyne optical receiver 11 and an optical fiber cable 5.
The optical signal from 2 is subjected to heterodyne detection. By changing the oscillation frequency of the local oscillation light source in the optical heterodyne optical receiver 11, maintenance information from each tower can be selectively received.

In the optical transmission terminal 2 installed on the steel tower 1, a pair of input/output ports of an optical coupler 211 are connected to optical fiber cables 62, 52, and the input port of the remaining pair of input/output ports is connected to the optical transmitter 22. Furthermore, by adopting a configuration in which the output port is connected to the optical receiver 21, an all-optical loop can be constructed. Other steel towers have similar configurations and similar effects can be obtained. By doing this, it is possible to avoid loop interruption due to a failure of an optical transmission terminal other than the own tower, and it is possible to improve the reliability of the system.

[0009]

[Operation] Here, for the sake of convenience, the case where the steel tower 1 is selected will be explained as an example. Frequency reference signal (Ref) from the central monitoring center
1, Ref2, Ref3) are the optical couplers 2 of the optical transmission terminal 2.
11, mixed with the transmission output light of the optical transmitter 22, and converted into an electrical signal by the optical receiver 21. Here, the optical coupler 211 functions as a diplexer, and the output light of the optical transmitter 22 plays the role of normal local oscillation light, and the optical receiver 2
1 heterodyne detection is possible. An example of spectrum arrangement in the optical frequency domain at this time is shown in FIG. That is,
Reference frequency Ref assigned to the optical transmission terminal of steel tower 1
1 performs heterodyne detection using the transmission frequency Ft1 assigned to the steel tower 1 as the local oscillation frequency and the difference between the two frequencies IFt as the intermediate frequency, and feeds back the output of the discriminator in the intermediate frequency band to the oscillation light source in the transmitter. The frequency of the oscillation light source is maintained at a constant value Ft1. At the central monitoring center, the frequency of the local oscillation light source built into the optical heterodyne receiver 11 is switched to LO1, and heterodyne detection is performed using the difference frequency IFc from Ft1 as the intermediate frequency.

[0010] The same goes for selecting information on other towers.
The transmission frequency (Ft) from the steel tower depends on the difference in the reference frequency.
2, Ft3) and the frequency (L
O2, LO3) are moved in parallel, and the intermediate frequency (IFt) of the receiver of the optical transmission terminal of each steel tower and the intermediate frequency (IFc) of the optical heterodyne receiver 11 in the central monitoring center are shifted in parallel.
) is constant.

[0011]

Embodiment FIG. 3 is a block diagram of a power transmission line monitoring system for one-way communication, which is the basis of an embodiment of the present invention. The operation of the entire system is as described above. The details of the configuration of the central monitoring center and the optical transmission terminal equipped with the steel tower will be described below.

The central monitoring center is composed of a heterodyne optical receiver 11 and an optical transmitter 12. The heterodyne optical receiver 11 includes an optical coupler 111, a mixer 112, an AFC
113, Local oscillator laser diode (LOLD) 1
14, a channel selector (CHSEL) 115, and a demodulator (DEMOD) 116. The channel selector 115 switches the oscillation frequency of the local oscillator laser diode 114 according to the desired reception channel, and the channel selector 115 switches the oscillation frequency of the local oscillator laser diode 114, for example, to keep the oscillation frequency of the local oscillator laser diode 114 at a predetermined value. It functions to control the bias current of 114, etc. Demodulator 116
functions to regenerate information sent from the tower. The optical transmitter 12 has the same number of laser diodes 12 as the number of steel towers.
1, 122, and 123, and the oscillation frequencies of each are controlled using a reference oscillation light source using atomic absorption lines or a Fabry-Perot resonator so that the oscillation frequency intervals are equal. The lights sent out from each transmission light source are bundled by the optical star coupler 124 and sent out to one of the optical fiber cables 51 in the OPGW 5. Each transmission light source is used as a reference frequency by the optical transmission terminal installed on each steel tower, so no modulation is applied to it.

FIG. 4 shows, as an embodiment of the present invention, an example in which a two-way communication function is added to the power transmission line monitoring system described above. Reference frequency light sources 121, 122, 12
A PSK modulator 131 is applied to each reference frequency signal generated in step 3.
, 132 and 133, PSK modulation can be applied to each channel identification signal. Further, the signals from each tower are optical signals subjected to ASK modulation using an ASK modulator 225 or the like, so that the respective modulated signal components can be easily separated.

FIG. 5 shows another embodiment. Instead of the local oscillation light source used so far, the reference frequency light source 121, 1
22 and 123 are branched by optical branches 141, 142, and 143 and switched by an optical switch 117 to enable selective reception.

FIG. 6 shows another embodiment. When bidirectional communication is not performed, the bias current of one light source 151 is increased to create a multi-mode oscillation state, and this is used as a substitute for the reference frequency light source, which is effective in simplifying the center configuration. .

[0016]

As described above, in the present invention, since the coherent optical communication method is applied to the power transmission line monitoring system, it is possible to avoid deterioration in reception sensitivity due to waveform distortion caused by lightning strikes on the OPGW. Also, since it is possible to configure an all-optical loop,
It is possible to avoid loop interruption due to terminal failure and is effective in improving reliability.

[Brief explanation of the drawing]

FIG. 1 is a basic configuration diagram for explaining the principle configuration of the present invention.

FIG. 2 is an example of a spectrum arrangement of signals in the system shown in FIG. 1;

FIG. 3 is an embodiment of the present invention relating to one-way communication.

FIG. 4 is an embodiment of the present invention related to bidirectional communication.

FIG. 5 is an embodiment in which the center configuration of the present invention is simplified, in which a part of the reference frequency light source is used as a local oscillation light source.

FIG. 6 is another embodiment in which the center configuration of the present invention is simplified, in which one light source is used in a multimode oscillation state to serve as a reference frequency light source.

FIG. 7 is an example of a conventional power transmission monitoring system in which optical to electrical conversion is performed one by one at each tower.

[Explanation of symbols]

1 Central monitoring center 2, 3, 4 Optical transmission terminals installed on steel towers 5, 6, 7
OPWG 11, 21 Optical receiver (for coherent optical communication) 12
, 22 Optical transmitter (for coherent optical communication) 51, 5
2, 61, 62, 71, 72 Optical fiber cable 111, 211 Optical coupler 112, 212 Mixer 113, 213 AFC 114, 121, 122, 123, 151, 214
Laser diode light source 115 Channel selector 116, 136, 226 Demodulator 117 Optical switch 120 Frequency interval control circuit 124 Star coupler 131, 132, 133, 215, 225 Modulator 1
41, 142, 143 Optical branch 160, 260, 270, 360, 370, 460
Signal processing section 161, 261, 271, 361, 371, 461
Optical receiver 162, 262, 272, 362, 372, 462
optical transmitter

Claims (4)

[Claims] Claim 1: In a power transmission line monitoring system in which information is exchanged between multiple power transmission towers and a central monitoring center via optical fiber cables, the central monitoring center (1) has frequency interval control as a frequency reference. an optical transmitter (12) that can generate multiple transmission lights; and an optical heterodyne receiver (12) that has the function of selectively receiving information signals from each tower.
1), each tower has a pair of input/output ports of an optical coupler (211) connected to an optical loop network, and the remaining input port connected to an optical transmitter (22) for transmitting information; The output port is connected to an optical receiver (21) for frequency reference detection, and optical transmission terminals (2, 3, 4) are installed to handle the exchange of information with other towers and the central monitoring center (1). Optical transmitter (12) at the center (1), optical transmission terminals (2, 3, 4) on each tower, and optical fiber cables (51, 6)
1, 71, 72, 62, 52) are connected in a loop to form an optical loop network, and the optical transmitter (1) of the central monitoring center (1)
2), the oscillation frequency of the optical transmitter (12) is controlled so that the signal spectrum positions of the optical transmission terminals on each tower do not overlap, according to the frequency reference information from the tower that is the target of information exchange. A power transmission line monitoring system characterized by configuring an optical loop network without optical-to-electrical conversion of optical signals that include information about other steel towers. [Claim 2] In claim 1, an optical transmitter in the central monitoring center phase-modulates the output light of the laser diode light source serving as each frequency reference with information for channel identification, etc., and sends it to the optical transmission terminal of each steel tower. , a power transmission line monitoring system characterized in that information from optical transmission terminals on each tower is amplitude modulated and transmitted. 3. According to claim 1, a reference frequency light for transmitting the laser diode light source output light of the central monitoring center toward the optical transmission terminal of each steel tower through an optical branch, and an optical heterodyne receiver of the central monitoring center. A power transmission line monitoring system characterized in that the optical heterodyne receiver selects the optical information of the steel tower by switching the local oscillation light from each reference frequency light source using an optical switch. 4. The power transmission line monitoring system according to claim 1, characterized in that one light source produced by increasing the bias current of the power supply and causing multi-mode oscillation is used as the reference frequency light source.