JP4543007B2 - Current differential protection system - Google Patents

Description

  The present invention relates to a current differential protection system for protecting a transmission line or a device included in a protection target section of a power system.

  As a current differential protection system used for protecting an electric power system, a system of a system that obtains a differential current by connecting outputs of a plurality of optical sensors in cascade has been proposed in recent years. FIG. 4 is a configuration diagram showing a basic configuration example of a current differential protection system in which two photosensors are connected in series as an example of a current differential protection system in which the outputs of such photosensors are connected in cascade.

  In FIG. 4, optical sensors 31 and 32 are provided on the outer circumferences of the primary conductors 21 and 22 connected to both sides of the protection target facility 10, respectively, and the introduction of optical signals to these optical sensors 31 and 32 is performed. And the output are connected in a cascade by an optical fiber cable 40 having polarization plane holding ability. A signal processing unit 50 for emitting and receiving light is provided at the end of the optical fiber cable 40 on the optical sensor 31 side, and a mirror 60 is provided at the end of the optical sensor 32 side. The light emitted from the optical fiber cable 40 is transmitted through the optical fiber cable 40 and sent to the optical sensors 31 and 32, and is folded back by the mirror 60.

  The signal processing unit 50 also processes a light source 51, a coupler 52, a phase modulator 53, a detector 54 that detects an optical signal from the coupler 52 and converts it into an electrical signal, and an electrical signal. A signal processing circuit 55 for obtaining a difference current is included.

  The operation of the current differential protection system of FIG. 4 having such a configuration is as follows. First, system currents I1 and I2 flow through primary conductors 21 and 22 provided with optical sensors 31 and 32, respectively. In this case, the light propagating through the respective optical sensors 31 and 32 has an optical phase difference (θ1∝I1, θ2∝) proportional to the magnitude of the system currents I1 and I2 due to the Faraday effect (light-magnetic interaction). I2) occurs.

  The light is folded back by the mirror 60 provided at the end portion on the optical sensor 32 side. As a result, the light is detected by the detector 54 of the signal processing unit 50 and converted into an electric signal. Since the detected light amount changes in proportion to the phase difference (θ = θ1 + θ2) generated inside the optical sensor, the signal processing circuit 55 obtains the current value Id (= I1 + I2) from this light amount change amount. Using the differential current Id obtained in this way, the judgment of the accident of the protection target equipment is performed.

  Such a current differential protection system in which the outputs of the photosensors are connected in cascade has the advantage of being simple in configuration and excellent in reliability and maintainability, and therefore further development is desired.

  For example, in Patent Document 1, a differential relay that performs current differential protection using currents at both ends of an overhead line and a power cable mixed power cable, and a cable that obtains a differential current from a current amount at both ends of a cable section. A differential protection relay system composed of a differential relay for detecting an accident in a section has been proposed. This system obtains a differential current by connecting the outputs of optical sensors at both ends of a cable in cascade to detect an accident in a cable section.

  By the way, in particular, in order to detect a ground fault in a high resistance grounding system, a sensitivity of about 30 A is necessary as a system current, and in a system in which a normal load current flows as much as 3000 A, the relative error between the optical sensors. Strict accuracy of 1% or less is required.

On the other hand, an actual photosensor has an error of several percent, and the difference current obtained by connecting a plurality of photosensors in cascade includes an error due to a relative error between the photosensors. . For example, if the relative error between sensors is ε when the passing current of two sensors 31 and 32 connected in cascade as shown in FIG. 4 is Ith, the difference current Id generated by the passing current is expressed by the following equation: It is represented by (1).
Id = Ith × ε Expression (1)

  As described above, in order to realize the ground fault detection of the high resistance grounding system using the difference current Id including the error caused by the relative error between the optical sensors, in order to avoid malfunction due to the passing current. The ground fault detection sensitivity needs to be larger than the difference current Id in equation (1). This means that the sensitivity greatly depends on the magnitude of the passing current and the magnitude of the relative error.

  On the other hand, as a countermeasure against malfunction due to a passing current, for example, Patent Document 2 proposes a ratio differential relay device that takes in a current of an arbitrary one terminal in a protection section of a power system and uses it as a suppression amount.

JP2004-304915 JP 2004-336899 A

  As described above, the current differential protection system in which the outputs of the photosensors are connected in cascade has the advantage of being simple in structure and excellent in reliability and maintainability. There is a problem that it is not possible to obtain a sufficiently high sensitivity for detecting a tangled accident.

  For example, since the method described in Patent Document 1 is proposed on the assumption that the optical sensor has a high accuracy and a wide dynamic range, the cable section accident detection is performed by a simple differential method. However, an actual photosensor has an error of several percent, and the difference current obtained by connecting a plurality of photosensors in cascade includes an error due to a relative error between photosensors. There is a problem that high sensitivity cannot be expected only by the simple differential method.

  In addition, the technique described in Patent Document 2 focuses on countermeasures against malfunction caused by passing current, and is not intended for ground fault accident detection in a high resistance grounding system. It is insufficient to achieve high sensitivity.

  The present invention has been proposed to solve the above-described problems of the prior art, and its purpose is to mitigate and protect the influence of the difference current caused by the relative error between the photosensors connected in cascade. To provide a current differential protection system capable of detecting an accident in a target section with high sensitivity.

  In order to achieve the above object, the present invention corrects the differential current output of the optical sensor by the output of the current transformer, or outputs the current output and the output before a predetermined time as the differential current output. By obtaining the difference, the influence of the difference current caused by the relative error between the optical sensors connected in the cascade is reduced, and the accident in the protection target section can be detected with high sensitivity.

  That is, one current differential protection system of the present invention includes a differential current detection means for connecting a photosensor output in a cascade to detect a differential current in a protection target section and generating a differential current output of the photosensor, and a protection It has a correction signal generating means for generating a correction signal output for correcting the difference current output of the photosensor by the output of a current transformer provided at one terminal of the target section.

  ADVANTAGE OF THE INVENTION According to this invention, the influence of the difference electric current which arises by the relative error between the optical sensors connected to the cascade can be eased, and the current differential protection system which can detect the accident of a protection object area with high sensitivity can be provided. .

  Hereinafter, a plurality of embodiments of a current differential protection system according to the present invention will be specifically described with reference to the drawings. In addition, the same code | symbol is attached | subjected to the same part as the prior art shown in FIG.

[First Embodiment]
[Constitution]
FIG. 1 is a configuration diagram showing an outline of a current differential protection system that corrects a differential current output of an optical sensor by an output of a current transformer as a first embodiment of the present invention. In the system according to this embodiment, the normal difference current obtained by being connected to the cascade is determined in accordance with the fixed error and the proportional error generated from the normal load current. By paying attention to the relationship between the load current and the difference current that are sometimes flowing, the proportional error current generated from the load current is corrected.

  As shown in FIG. 1, a power transmission line and / or a device included in a protection target section of a power system is used as a protection target facility 10, and primary conductors connected to both sides of the protection target facility 10 and functioning as terminals respectively. Optical sensors 31 and 32 are provided on the outer peripheries of 21 and 22, respectively. The primary conductor 21 is provided with a core winding type current transformer or a photocurrent transformer as the current transformer 33. In FIG. 1, a two-terminal configuration is used from the viewpoint of simplifying the description, but a configuration with three or more terminals is also possible.

  Also, the introduction and output of the optical signals to the optical sensors 31 and 32 are connected in cascade by the optical fiber cable 40 having polarization plane maintaining property and led to the accident detection determination unit 70, but are different from FIG. The loop structure is reciprocated. Note that such a cascade configuration using the optical fiber cable 40 is merely an example, and a reflection configuration may be used in which the optical sensor unit at the end reflects the light from the mirror 60 in the same manner as the prior art in FIG.

  The accident detection / determination unit 70 is a part that detects and determines an accident by detecting the current flowing through the primary conductors 21 and 22 connected to the protection target facility 10, and includes a signal processing unit 71, a correction signal generation circuit 72, a determination A circuit 73 is included.

  The signal processing unit 71 sends an optical signal by the optical system, and at the same time, converts the optical signal of the current generated in the optical sensors 31 and 32 connected in cascade according to the current flowing through the primary conductors 21 and 22 into an electrical signal. As with the signal processing unit 50 in FIG. 4, it has a function of generating a differential current output Id of the protection target equipment 10.

  The correction signal generation circuit 72 generates a correction signal output Ia ′ for correcting the differential current output Id of the protection target equipment 10 from the output Ia of the current transformer 33 provided on the primary conductor 21 that is one terminal of the protection target section. Circuit.

  The determination circuit 73 combines the difference current output Id of the protection target facility 10 obtained from the signal processing unit 71 and the correction signal output Ia ′ obtained from the correction signal generation circuit 72 to determine whether or not an accident has occurred in the protection target facility 10. 74 is a determination result output generated by the determination circuit 73.

[Action]
The operation of the first embodiment having the above-described configuration is as follows.

  In the accident detection determination unit 70, the signal processing unit 71 outputs a difference current Id of the conversion current of the optical sensors 31 and 32 with respect to the current flowing through the protection target facility 10, and this difference current Id is output from the correction signal generation circuit 72. Input to the determination circuit 73.

  In the correction signal generation circuit 72, the normal relationship (K2) of these outputs Ia and Id is obtained from the output current Ia of the current transformer 33 and the difference current Id which is the output of the signal processing unit 71, and correction is performed from this relational expression. A signal output Ia ′ is generated and input to the determination circuit 73.

  In the determination circuit 73, the determination of the presence or absence of an accident in the protection target facility 10 is performed according to the presence or absence of voltage information. For example, when voltage information is given, an accident detection element such as undervoltage detection or ground fault overvoltage detection is created and determined, and when voltage information is not given, it is taken into the correction signal generation circuit 72. It is possible to determine an accident by performing overcurrent detection, ground fault overcurrent detection, and the like from the information of the current transformer 33. The fixed error can be obtained if different load current states are obtained.

  That is, when the load current is in the first state (time m1), the output Ia of the current transformer 33 and the difference current Id of the optical sensors 31, 32 are respectively Iam1 and Idm1, and the load current is in the second state (time m2). ), The output Ia of the current transformer 33 and the difference current Id of the optical sensors 31 and 32 are Iam2 and Idm2, respectively, and a fixed error Idk and a proportional error K2 are obtained.

K2 × Iam1 + Idk = Idm1
K2 × Iam2 + Idk = Idm2
Here, taking the difference between the two formulas,
K2 (Iam1-Iam2) = Idm1-Idm2
Therefore, the following formula (2) is obtained.

K2 = (Idm1-Idm2) / (Iam1-Iam2)
= Idm / Iam Formula (2)
However, Idm is a difference in normal current difference, and Iam is a normal system-side current difference.

In the correction signal generation circuit 72, K2 is obtained by the above equation (2), and the correction signal output Ia ′ is obtained by the following equation (3) using the obtained K2.
Ia ′ = K2 × Ia (3)
However, K2 is a correction coefficient vector.

The determination circuit 73 uses the difference current Id that is the output of the signal processing unit 71 and the correction signal output Ia ′ that is the output of the correction signal generation circuit 72, and is protected according to the following determination formulas (4) and (5). The presence or absence of an accident in the facility 10 is determined.
| Id | ≧ k0 Formula (4)
| Id−Ia ′ | ≧ k3 (5)
However, k0 and k3 are constants and are detection sensitivity setting values.

  In addition, the accident determination in the determination circuit 73 may determine that an accident has occurred in the protection target equipment when both the expressions (4) and (5) are satisfied, but may be determined only by the expression (5). .

[effect]
According to the first embodiment as described above, the effect of the difference current caused by the relative error between the photosensors connected in the cascade is reduced by correcting the difference current output of the photosensor by the output of the current transformer. Therefore, it is possible to detect an accident in the protected section with high sensitivity.

[Second Embodiment]
[Constitution]
FIG. 2 shows a second embodiment of the present invention, wherein the differential current output of the optical sensor is corrected by the output of the current transformer and the differential current output is generated from the output of the current transformer. It is a block diagram which shows the outline | summary of a system. As in the first embodiment, the system of this embodiment focuses on the relationship between the load current and the difference current that normally flows, corrects the proportional error current, and calculates the difference current from the output of the current transformer. An output suppression amount is generated and used for accident determination.

  As shown in FIG. 2, the current differential protection system according to the present embodiment includes a suppression amount / correction signal generation circuit instead of the correction signal generation circuit 72 and the determination circuit 73 of the accident detection determination unit 70 according to the first embodiment. 75, a determination circuit 76 is provided.

  Here, the suppression amount / correction signal generation circuit 75 corrects the difference current output Id of the protection target equipment 10 from the output Ia of the current transformer 33 provided in the primary conductor 21 that is one terminal of the protection target section. This is a circuit that generates a signal output Ia ′ and also generates a suppression current Ir of the differential current output from the output Ia of the current transformer 33.

  The determination circuit 76 combines the difference current output Id of the protection target facility 10 obtained from the signal processing unit 71, the correction signal output Ia ′ obtained from the suppression amount / correction signal generation circuit 75, and the suppression amount Ir of the difference current output. This is a circuit for determining whether or not an accident has occurred in the protection target facility 10.

[Action]
The operation of the second embodiment having the above configuration is as follows.

  In the accident detection determination unit 70, the signal processing unit 71 outputs a difference current Id of the conversion current of the optical sensors 31 and 32 with respect to the current flowing through the protection target facility 10, and this difference current Id is used to generate a suppression amount / correction signal. The signal is input to the circuit 75 and the determination circuit 76.

  The suppression amount / correction signal generation circuit 75 obtains the normal relationship (K2) between these outputs Ia and Id from the output current Ia of the current transformer 33 and the difference current Id that is the output of the signal processing unit 71. The correction signal output Ia ′ is generated from the relational expression, and the suppression amount Ir of the difference current output is generated from the output Ia of the current transformer 33. Then, the obtained correction signal output Ia ′ and the suppression amount Ir of the difference current output are input to the determination circuit 76.

  In this case, the method of generating the correction signal output Ia ′ is as described in the first embodiment. Moreover, the existing technique as described in Patent Document 2 can be applied to the generation of the suppression amount Ir.

  The determination circuit 76 uses the difference current Id that is the output of the signal processing unit 71, the correction signal output Ia ′ that is the output of the suppression amount / correction signal generation circuit 75, and the suppression amount Ir as follows. The presence or absence of an accident in the protection target facility 10 is determined by the determination formula (6) for performing the calculation and the determination formula (7) for performing the ratio differential calculation.

| Id ′ | ≧ k0 Formula (6)
| Id ′ | −k | Ir | ≧ k1 (7)
However, k0 is a constant, k is a suppression coefficient, and k1 is a constant.
In this case, Id ′ is a corrected difference current obtained by correcting the difference current Id with the correction signal output Ia ′, and is defined as follows.
Id ′ = | Id−Ia ′ |
However, Id is an output (difference current) of the signal processing unit 71, and Ia ′ is K2 × Ia.

  Note that the accident determination in the determination circuit 76 may determine that an accident has occurred in the protection target equipment when both the expressions (6) and (7) are satisfied, but only the expression (7) for performing the ratio differential calculation. You may judge by.

[effect]
According to the second embodiment as described above, in addition to obtaining the same effect as that of the first embodiment, further, the amount of suppression is generated by taking in the current of one terminal in the protection target section. By performing the accident determination by the ratio operation calculation using the suppression amount, the influence of the passing current that occurs at the time of the external accident can be reduced, so that the accident in the protection target section can be detected with higher sensitivity.

[ Reference example ]
[Constitution]
FIG. 3 is a configuration diagram showing an outline of a current differential protection system that obtains a difference between a current output and an output before a predetermined time as a differential current output of an optical sensor as a reference example of the present invention. In the system of this reference example , the normal difference current obtained by connecting to the cascade is determined according to the fixed error and the proportional error generated from the normal load current. By paying attention to the difference between the difference current between the hour and the normal time, the error caused by the load current is removed.

As shown in FIG. 3, the current differential protection system of the present embodiment, the correction signal generation circuit 72 of the fault detection determination unit 70 in the first embodiment, in place of the decision circuit 73, those provided with a determination circuit 77 It is. Here, the determination circuit 77 uses the differential current output of the protection target equipment 10 obtained from the signal processing unit 71 to obtain a difference between the current differential current output Id and the output Idn of a predetermined time before the protection target equipment. It is a circuit for determining whether or not an accident has occurred in the facility 10.

[Action]
The operation of the reference example having the above configuration is as follows.

  In the accident detection determination unit 70, the signal processing unit 71 outputs the difference current Id of the conversion current of the optical sensors 31 and 32 with respect to the current flowing through the protection target facility 10, and this difference current Id is input to the determination circuit 77. The

The determination circuit 77 uses the difference current that is the output of the signal processing unit 71 to obtain a difference between the current difference current output Id and a preset difference current output Idn before a predetermined time, and the value of the difference is constant. If it is equal to or greater than the value, it is determined that the accident is in the protection target facility 10.
The judgment formula in this case is expressed as follows.
| Id-Idn | ≧ k4
However, k4 is a detection sensitivity (setting value).

  Here, the difference current output Idn before a predetermined time is obtained by adding a fixed error (Idk) and a proportional error (K2 × Ian) caused by the load current. , A proportional error (K2 × (Idf + Ian)) resulting from the addition of the fixed error Idk, the accident current Idf, and the load current Ian.

That is, the current difference current output Id and the difference current output Idn a predetermined time ago are defined as follows.
Id = Idf + Idk + K2 × (Idf + Ian)
Idn = Idk + K2 × Ian

Further, the difference between the current difference current output Id and the difference current output Idn a predetermined time ago is defined as follows.
Id−Idn = Idf + K2 × Idf = (1 + K2) · Idf

  Therefore, by setting K2 to a value sufficiently smaller than 1 (for example, 0.03), it is possible to eliminate the influence of the error generated from the load current.

[effect]
According to the above reference example , as the difference current output, the difference between the current output and the output before a predetermined time is obtained, so that the influence of the difference current caused by the relative error between the photosensors connected to the cascade can be reduced. Mitigates and can detect accidents in protected areas with high sensitivity.

[Other Embodiments]
It should be noted that the present invention is not limited to the above-described embodiments, and various other variations can be implemented within the scope of the present invention. For example, the system configuration shown in the drawings is merely an example, and a specific configuration can be selected as appropriate.

The block diagram which shows the outline | summary of the current differential protection system which concerns on the 1st Embodiment of this invention. The block diagram which shows the outline | summary of the current differential protection system which concerns on the 2nd Embodiment of this invention. The block diagram which shows the outline | summary of the current differential protection system which concerns on the reference example of this invention. The block diagram which shows an example of the conventional current differential protection system which connected the output of the optical sensor in cascade.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Protection object equipment 21, 22 ... Primary conductor 31, 32 ... Optical sensor 33 ... Current transformer 40 ... Optical fiber cable 70 ... Accident detection judgment part 71 ... Signal processing part 72 ... Correction signal generation circuit 73, 76, 77 ... Determination circuit 74 ... determination result output 75 ... suppression amount / correction signal generation circuit

Claims (5)

In the current differential protection system that protects the transmission line or equipment included in the protection target section of the power system,
Differential current detection means for connecting the output of the optical sensor in a cascade to detect the differential current in the protection target section and generating the differential current output of the optical sensor;
A current differential protection system comprising correction signal generation means for generating a correction signal output for correcting a difference current output of the photosensor by an output of a current transformer provided at one terminal of the protection target section. 2. The current differential protection system according to claim 1, further comprising: a determination unit that determines whether there is an accident in the protection target section based on a difference current output of the photosensor and the correction signal output. The current differential protection system according to claim 1, wherein the correction signal generation unit is configured to generate a suppression amount of a difference current output of the photosensor from an output of the current transformer. 4. The apparatus according to claim 3, further comprising: a determination unit that performs a ratio differential operation using the difference current output of the optical sensor, the correction signal output, and the suppression amount to determine whether there is an accident in the protection target section. Current differential protection system as described in. 5. The current differential protection system according to claim 1, wherein the current transformer is an iron core winding type current transformer or a photocurrent transformer. 6.

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