JP2002034144A - Photoelectric current transformer and protection relay system using it - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce the digital output signals of a photo-CT(photoelectric current transformer) without using an accurate A-to-D converter and enhance the reliability of a protection relay system. SOLUTION: The angle of polarization by the Faraday effect brought about in a sensor fiber wrapped around a conductor is detected as variation in intensity by photodetectors 120 and 130, and the signal difference obtained from the output of amplifiers (123 and 133) or (124 and 134) with a high or low amplication factor according to the high or low value thereof is digitized in a conversion portions (A/D2) or (A/D3). Thus, the individual conversion portions (A/D2) and (A/D3) do not require an especially large number of bits. In addition, sampling is performed at a frequency 360 or higher than the frequency of the photo-CT system current and any delay arising from transmission is corrected at a digital relay processing portion, so that protection relay processing can be performed at a current with less phase delay. The value of the current of the photo-CT and presence/absence of a sensor trouble are transmitted as transmission data to a digital relay, so that malfunction of the digital relay due to malfunction of the photo-CT is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power transmission equipment such as a transmission substation, in which a sensor fiber is circulated around a conductor through which a current to be measured flows, and the current flowing through the conductor is measured using the Faraday effect of propagating light. The present invention relates to a photocurrent transformer and a protection relay system using the same.

[0002]

2. Description of the Related Art As a current transformer (hereinafter abbreviated as CT) used in an electric station such as a transmission substation, a winding type CT is conventionally used, which is used for a system constituting a bus or the like of an electric power system. Since a current proportional to the current flowing through the conductor is induced in the coil surrounding the conductor, this is detected. The output is input to the protection relay processing unit, and is used for controlling the opening / closing operation of a circuit breaker provided for protecting the transmission line. The output of the wire-wound CT is an analog current value, and since the protection relay is mostly composed of a digital circuit in recent years, the output current value of the wire-wound CT is converted into a voltage, digitized, and input to the protection relay. .

On the other hand, a photocurrent transformer (hereinafter abbreviated as optical CT)
Is a sensor in which a sensor fiber is circulated around a conductor and current is detected from the rotation angle of the plane of polarization of propagating light due to the Faraday effect, and has features such as miniaturization of the sensor and no magnetic saturation as compared with the wound CT. Such an optical CT is disclosed in
No. 221379, JP-A-9-196973, JP-A-7-270505 and the like.

[0004]

In order to perform digital processing by the protection relay, the optical CT output must also be a digital value, and the quantization accuracy of this digital value is determined for the CT for power equipment. Accuracy must be met. In the accuracy class 1PS class indicating the accuracy of power CT, 1% at the rated current, 1.5% at the rated current of 20%,
At a rated current of 5%, it is necessary to achieve a detection accuracy of 3%, and at a current higher than the rated current, an error of up to a maximum current of 10% is allowed. Therefore, for example, when the rated current is 1 A and the maximum current is 100 A, 1.5 mA (0.05 × 0.03
It is necessary to digitize with a precision of × 1A) or less, and 16 bits or more are required to represent the maximum current of 100A with the precision of the digitization. That is, the A / D converter is required to have 16 bits or more. However, such a high-precision A / D converter has a problem that it is difficult to cope with real-time processing due to its operation speed, and it is expensive even if realized.

In an electric power station such as a transmission substation, CT outputs at a plurality of measurement points are taken into one protection relay and processed, and three CTs are usually provided at each measurement point for each phase. I have. When digitally outputting these plurality of CTs as optical CTs, if the sampling time of the system current in each CT differs greatly, each of the system current values input to the protection relay becomes a value at a different phase. In this case, accurate protection relay processing cannot be performed. Conventional winding type CT
, The output is an analog signal and each winding type C
The signal of T is directly input to the protection relay, and is sampled and digitized at 96 times the frequency of the transmission current of 50 Hz or 60 Hz, so that the synchronization of the output signal of each CT is ensured. However, in optical CT, the signal component (AC) representing the system current in the output from the sensor fiber is a small amount and is proportional to the light intensity of the light source. Therefore, this signal component is amplified and depends on the light intensity of the light source. Processing for obtaining an output that is not required is required. This processing is executed by a processing unit provided immediately adjacent to the optical CT, and signal digitization is also performed at the same time. For this reason, in order to synchronize sampling at each measurement point, it is conceivable to send a synchronization signal from the protection relay to each measurement point, but this complicates the apparatus. Also, the digital signal output for each optical CT at each measurement point is multiplexed and transmitted to the protection relay. However, if the signal processing circuit breaks down, the protection relay operation becomes impossible or abnormal, and high reliability cannot be realized. There are also problems.

SUMMARY OF THE INVENTION An object of the present invention is to provide an optical CT capable of outputting a digital signal with an accuracy required for the operation of a protection relay without using a high-precision A / D converter.
It is an object of the present invention to provide a protection relay system which can realize high reliability without a fear of sampling deviation between them.

[0007]

According to the present invention, linearly polarized light is propagated through a sensor fiber installed around a conductor, and a current value flowing through the conductor is detected by detecting a Faraday rotation angle of the propagated light. In a photocurrent transformer configured to obtain a current signal to be expressed and digitize and output the signal by A / D conversion means, the A / D conversion means may be used as a first amplifier for amplifying the current signal. Means, second amplifying means having an amplification factor greater than the amplifying means, and first and second A / D converters for digitizing output signals of the first and second amplifying means, respectively. A selecting means for selecting and outputting one output of the first or second A / D converter according to the magnitude of the current signal is disclosed.

Further, according to the present invention, in the above-mentioned photocurrent transformer, a range of a current value in the conductor to be measured is divided into a low current region and a high current region by two, and the selecting means includes When the value is in the high current range, the output of the first A / D converter is selected, and when the current value is in the low current range, the output of the second A / D converter is selected. A photocurrent transformer characterized by the above configuration is disclosed.

Further, the present invention provides a photocurrent transformer provided for each measurement point and a digital relay operation using current signals from these photocurrent transformers to perform a current protection operation according to the result. Digital relay processing means for performing;
A protection relay system is disclosed, comprising transmission means for transmitting a current signal from each of the photocurrent transformers to the digital relay processing means.

[0010] Further, the present invention provides a photocurrent transformer according to the first aspect.
And a second A / D converter which samples the input current signal at least at 360 times the system frequency and digitizes the current signal.

Further, the present invention discloses a protection relay system, wherein the digital relay processing means includes a correction means for correcting a transmission delay of a current signal transmitted via the transmission means.

Further, in the present invention, the photocurrent transformer is provided with a means for detecting an abnormal operation of the transformer, and a means for transmitting a signal indicating the presence or absence of the abnormal operation together with the current signal. The present invention discloses a protection relay system having a function of discarding a current signal corresponding to a signal indicating the presence of the abnormality and not using the current signal.

[0013]

Embodiments of the present invention will be described below. FIG. 2 is a block diagram showing an example of the configuration of a protection relay system according to the present invention. Conductors 1, 2, and 3 are conductors of a power system at three measurement points, and the system current of each of these conductors is equal to that of optical CT. Optical signal 1 by the sensor heads 10, 20, 30
These are detected as 0R, 20R, and 30R, respectively, and converted into digital electric signals 11A, 21A, and 31A indicating system current by the current detection processing units 11, 21, and 31, respectively, and output. These digital signals 11A, 21
A and 31A are subjected to optical wavelength multiplexing in the optical wavelength multiplexing transmission processing unit 4 and sent to the protection relay processing unit via the transmission fiber 5. In the protection relay processing unit, the signal transmitted through the fiber 5 is divided by the fiber coupler 6, and the optical wavelength separation transmission processing units 7, 8, and 9 separate the signals into optical signals representing system currents corresponding to the respective conductors. Input to the digital relay processing units 70, 80 and 90. The digital relay processing units 70, 80, and 90 perform arithmetic processing for determining whether the electric quantity at the target measurement point is normal or abnormal, and control relays, circuit breakers, and the like based on the processing results. Although the number of measurement points and the number of digital relay processing units are three, each may be any number as required. FIG. 1 shows one conductor and one light CT at each measurement point. However, in a three-phase system, three light CTs are provided at one measurement point when current detection of each phase is performed.

The sensor head 10 comprises a sensor fiber 101 circling the conductor 1, a polarizer 102 and an analyzer 103 provided at input and output ends thereof. The input light 11R from the light source 110 provided in the current detection processing unit 11 is input to the polarizer 102, where it is converted into linearly polarized light and propagates through the sensor fiber 101. The light propagating through the sensor fiber 101 is subjected to the Faraday effect by the magnetic field generated by the current flowing through the conductor 1, and the plane of polarization rotates. If the Faraday rotation angle is θ,

(Equation 1) Here, n is the number of turns around the conductor of the sensor fiber, I is the system current (instantaneous value), and V is the Verdet constant. The light propagated through the sensor fiber and subjected to Faraday rotation is analyzed by the analyzer 103.
Are split into two linearly polarized light beams 10RP and 10RS which are orthogonal to each other, and each of the photodetectors 12 is separated via a light receiving fiber.
At 0 and 130, the intensity is detected as an electrical signal. When the Faraday rotation angle θ is 0, if the polarization planes of the analyzer and the polarizer 102 are set so that the intensities of the two linearly polarized lights detected by the analyzer 103 are equal, when the Faraday rotation is performed, The light intensities IP and IS of the two polarized lights detected by the analyzer are as follows.

(Equation 2) Here, A is a constant proportional to the light source intensity. Here, the Faraday rotation angle θ is an extremely small value, and 2θ is 9
The light intensity IP, IS, which is always smaller than 0 ° and is (Equation 2), may be considered as a monotone function of the rotation angle θ.

FIG. 1 is a block diagram showing the configuration of the current detection processing unit 11. The linearly polarized light intensities IP and IS detected by the photodetectors 120 and 130 are directly input to an A / D converter 140. In addition, the DC components PDC and SDC and the AC components PAC and SAC (50 or 60 Hz) correspond to the low-pass filters 121 and 131 and the band-pass filters 122 and 13.
2 respectively. Among them, the AC component PAC is amplified by amplifiers 123 and 124, and is divided by a divider 125,
By being divided by the DC component PDC at 126,
The signals are converted into intensity signals PAC1 and PAC2 that do not depend on the light source intensity. Similarly, the AC component SAC is also used for the amplifiers 133 and 13.
4 and the DC components S in the dividers 135 and 136.
By dividing by DC, the signals are converted into intensity signals SAC1 and SAC2 that do not depend on the light source intensity. Here, the amplification factors of the amplifiers 123 and 133 are constant values μ1,
134 so that the amplification factor of 134 becomes a constant value μ2.
It is assumed that 50 is controlling. This control is possible with the prior art, and the control system is not shown in FIG. Thus, the PAC1-SAC is subtracted by the subtractors 127 and 128.
1 and PAC2-SAC2 respectively, their outputs P1, P2 are

(Equation 3) Becomes Here, C is a constant determined by the loss of each filter.

The current I flowing through the conductor of the power system to be measured has a large dynamic range as described above. If the entire range is digitized as it is, for example, 1
It requires an A / D converter of 6 bits or more. In the present invention, in order to solve this problem, two sets of amplifiers having different amplification factors are used, and the signals P1 and P2 having different amplitudes shown in (Equation 3) are used.
P2 is generated and input to the A / D converter 140.
Here, the amplification factor μ1 of the amplifiers 123 and 133 is determined by the signal P
1 is the maximum current to be detected by the optical CT and the A / D converter 140
Is set to be the maximum input voltage of the conversion unit A / D2,
The amplification factor μ2 of each of the amplifiers 124 and 134 is determined by setting the signal P2 to A / D at a rated current (generally, an appropriately determined value).
The setting is made so as to be the maximum input voltage of the converter A / D3 of the converter 140. With such a configuration, the conversion unit A / D
2 may digitize the range from the rating to the maximum current with the required accuracy, and the conversion unit A / D3 may digitize the range from the minimum to the rated current with the required accuracy. Since the microcomputer 150 can easily determine which value should be taken from the output digital signals of the conversion units A / D2 and A / D3, the microcomputer 150 fetches the value and sends it via the digital optical transmission circuit 160 to the digital relay processing unit. Send to

The configuration and operation of the optical CT sensor head and the current detection processing unit shown in FIG. 1 are the same for the optical CT sensor heads 20 and 30 and the current detection processing units 21 and 31. According to these configurations, for example, as described in the related art, when the minimum current is 1.5 mA, the rated current is 1 A, and the maximum current is 100 A, the minimum to rated current is detected from the signal P2, and the rated to maximum current is detected from the signal P1. If it is to be detected, the conversion unit A / D2 digitizes up to 100A in units of 10% (= 0.1A) or less of 1A.
Since the conversion unit A / D3 digitizes up to 1A in units of 1.5 mA or less, there is still room for 10 bits. Thus, digitization with a smaller number of bits is possible as compared with 16 bits or more in the case of one A / D converter.

Next, a description will be given of a method of solving the difference in sampling time between the respective optical CTs according to the present invention. For this purpose, first, the configuration of the digital relay processing unit 70 (the same applies to other parts) will be described with reference to FIG. The optical signals 71A, 72A, and 7 separated by the optical wavelength separation / transmission processing unit 7 based on the optical wavelength.
2B is the digital electric signal 11A, 21A, 31 of FIG.
A, and these optical signals are transmitted to the data receiving section 7.
1, 72 and 73, respectively. The configuration of each of these data receiving sections is the same, and FIG. 3 shows only the details of the data receiving section 71. The input optical signal is converted into an electric signal 71B by a digital optical receiving circuit 711, The sampling pulse is delayed by the transmission delay correction circuit 713 and the latch circuit 7
Latched to 12. This latched signal is applied to bus 76
Is taken into the CPU 75 via the CPU and used for digital relay processing calculations.

Here, the frequency of the clock generator 170 shown in FIG. 1 is set to be 360 times or more the current frequency of the system. Further, the digital relay processing section is set so as to sample and take in the current value at a frequency 96 times the current frequency of the system, so that the sampling synchronization circuit 74 of FIG. Assume that a sampling signal having a double frequency is output. Further, the transmission delay correction circuit 713 outputs the light CT corresponding to the optical signal 71A.
This is for correcting a transmission delay from (the optical CT sensor head 10 and the processing unit 11 in FIG. 1) to the data receiving unit 71. That is, the transmission delay differs for each of the optical signals 71A to 73A input to the digital relay processing unit 70, and the difference is a fixed amount. The transmission delay amount in the receiving units 71 to 73 is set. Then, the phase difference of the current signal finally taken into the CPU from the latch circuit can be made equal to or less than the allowable value of the phase delay required for the power CT of 1 degree. With such a configuration, the synchronization signal is transmitted from one oscillator to each light C
There is no need to supply T, and the configuration can be simplified.

Since the CT used in a substation or the like detects three-phase alternating currents, as described above, one CT is used.
In many cases, three CTs are installed at one measurement point. In this case, it is easy to configure the current detection processing unit in one housing for each optical CT at one measurement point, and in this case, the clock generator for each optical CT is used. You only need one,
Synchronization of sampling between them can be completely achieved.

Next, a method of monitoring the operation of the optical CT will be described. The A / D converter 140 in FIG. 1 converts the light amount L of the light source and the output signals IP and IS of the photodetectors 120 and 130, in addition to the signals P1 and P2, into conversion units A / D0, A / D1, and A / D.
The data is digitized in D4 and input to the microcomputer 150. In the microcomputer 150, if the light source light amount L decreases, it cannot be detected by the photodetector. Therefore, the threshold value L0 of the light source amount calculated from the detection lower limit of the photodetectors 120 and 130 is set in advance, and the input light source light amount If L is equal to or less than the threshold value L0, it is determined that the light source is abnormal. Similarly, thresholds are set for the outputs IP and IS of the photodetector, and when the outputs of the photodetectors IP and IS fall below the threshold when the light source light amount L is normal, the optical CT sensor head is used. Is determined to be abnormal. Further, the ratio between the signals P1 and P2 is constant (μ1 / μ2) during normal operation as can be seen from (Equation 3), but when the ratio changes more than (μ1 / μ2) to some extent, the current detection circuit becomes abnormal. Can be determined. As described above, the optical CT
Is determined, and information indicating the presence or absence of a sensor abnormality is transmitted to the digital relay processing unit together with the current value.
In the digital relay processing section, when this abnormal signal is sent, the digital optical receiving circuit receives the above transmission data, separates the current value from the sensor abnormal information, and transmits it to the CPU if there is an abnormal sensor. I do. If the optical CT fails and receives an erroneous current value, a malfunction may occur. Therefore, when the CPU receives information on a sensor abnormality, the current value of the optical CT is invalidated and another CT
, The malfunction of the digital relay due to the malfunction of the optical CT is prevented.

As shown in FIG. 1, if the current detected by each optical CT is multiplexed and transmitted by one transmission fiber,
Although the length of the transmission fiber can be reduced, it is needless to say that some optical CT outputs may be directly transmitted to the digital relay processing unit without multiplexing depending on the arrangement of the measurement points. Absent. In addition, although the multiplexing uses the wavelength multiplexing method, it goes without saying that this may be a time division multiplexing method.

[0023]

According to the present invention, two signals obtained by amplifying AC signals separated from two light intensities to be detected at different amplification factors are formed, and these signals are A / D-converted. Even if the resolution of the D converter is not particularly increased, the measurement accuracy and the measurement range required for the protection relay processing can be secured. Further, since the current value of the optical CT and the presence or absence of the sensor abnormality are transmitted to the digital relay as transmission data, it is possible to prevent the digital relay from malfunctioning due to the malfunction of the optical CT. Also, there is no need to provide a means for synchronizing sampling with the digital relay on the optical CT side, and the protection relay processing can be performed with a current value having a small phase delay. Furthermore, since the current detected by each optical CT is multiplexed and transmitted by one transmission fiber, the laying length of the transmission fiber can be reduced. Further, since the transmission between the current detection processing unit and the digital relay processing unit is a system that can achieve both multiplexing and single transmission, the system is excellent in flexibility and expandability.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration example of a current detection processing unit which is a feature of the present invention.

FIG. 2 is a block diagram showing a configuration example of a protection relay system of the present invention.

FIG. 3 is a block diagram illustrating a configuration example of a digital relay processing unit which is a feature of the present invention.

[Explanation of symbols]

 1, 2, 3 conductor 4 optical wavelength multiplexing transmission processing unit 5 light transmission fiber 6 fiber coupler 7, 8, 9 optical wavelength separation transmission processing unit 10, 20, 30 optical CT sensor head 11, 21, 31 current detection processing unit 70, 80, 90 Digital relay processing section 71, 72, 73 Data receiving section 74 Sampling synchronization circuit 75 CPU 101 Sensor fiber 102 Polarizer 103 Analyzer 110 Light source 120, 130 Photodetector 121, 131 LPF 122, 132 BPF 123, 124, 133, 134 Amplifiers 125, 126, 135, 136 Divider 127, 128 Subtractor 140 A / D converter 150 Microcomputer 160 Digital optical transmission circuit 170 Clock generator 711 Digital optical receiving circuit 712 Latch circuit 713 Transmission delay correction circuit

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Yoshiyuki Kubota 7-2-1, Omika-cho, Hitachi City, Ibaraki Pref. Hitachi, Ltd. Power & Electricity Development Division (72) Inventor Tokio Yamagoku Hitachi, Ibaraki 1-1-1, Kokubucho, Kokubu Plant, Hitachi, Ltd. (72) Inventor Isamu Isane 7-2-1, Omikacho, Hitachi, Ibaraki Pref. Hitachi, Ltd. Power & Electricity Development Division (72) Inventor Masatomo Kobayashi 1-1-1, Kokubuncho, Hitachi City, Ibaraki Prefecture Inside Kokubu Plant, Hitachi, Ltd. (72) Inventor Jun Noro 1-1-1, Kokubuncho Town, Hitachi City, Ibaraki Prefecture, Kokubu Plant, Hitachi Ltd. (72) Inventor Kiyoshi Kurosawa 4-1 Egasakicho, Tsurumi-ku, Yokohama-shi, Kanagawa Prefecture Inside Tokyo Electric Power Company (72) Inventor Kazunori Yamashita E, Tsurumi-ku, Yokohama-shi, Kanagawa Prefecture Sakimachi fourth No. 1 Tokyo Electric Power Co., Ltd. in the F-term (reference) 2G025 AA05 AB14 AC09 CA05 CB02 CC01 2G035 AA04 AA15 AB08 AC16 AD19 AD20 AD25 AD28 AD37 AD61 AD65 5G042 BB02 BB07 BB13

Claims (6)

[Claims] A linear signal is propagated through a sensor fiber installed around a conductor, and a Faraday rotation angle of the propagated light is detected to obtain a current signal representing a current value flowing through the conductor. Is converted by an A / D converter into a digital signal and output. The A / D converter is provided with a first amplifier for amplifying the current signal, and A second amplifier having a large amplification factor, first and second A / D converters for digitizing output signals of the first and second amplifiers, respectively, according to the magnitude of the current signal Selecting means for selecting and outputting one output of the first or second A / D converter. 2. The photocurrent transformer according to claim 1, wherein a range of a current value in the conductor to be measured is divided into a low current range and a high current range by two, and the selecting means includes: The output of the first A / D converter is selected when the current value is in the high current range, and the output of the second A / D converter is selected when the current value is in the low current range. A photocurrent transformer characterized by having such a configuration. 3. A photocurrent transformer according to claim 1, which is provided for each measurement point, and a digital relay operation is performed using a current signal from the photocurrent transformer. A protection relay system comprising: digital relay processing means for performing a protection operation; and transmission means for transmitting a current signal from each of the photocurrent transformers to the digital relay processing means. 4. A first and a second A / A of the photocurrent transformer.
4. The protection relay system according to claim 3, wherein the D converter samples and digitizes the input current signal at least at a frequency 360 times the system frequency. 5. The protection relay system according to claim 3, wherein said digital relay processing means includes a correction means for correcting a transmission delay of a current signal transmitted through said transmission means. 6. The photocurrent transformer is provided with means for detecting an abnormal operation of the transformer, and means for transmitting a signal indicating the presence or absence of an abnormal operation together with the current signal. 4. The protection relay system according to claim 3, further comprising a function of discarding a current signal corresponding to the signal indicating that the signal is present and not using the signal.