JP2017159720A - Method for detecting ground fault in ac-side connection wire of rectifier for dc feeding - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for detecting a ground fault in an ac-side connection wire of a rectifier for DC feeding capable of reducing impacts on train operation in response to occurrence of a ground fault in an electric cable way (AC side) between a transformer for a rectifier in a substation for DC electric trains, by providing a method to detect the fault as well as to separate a position where the fault exists from a secondary side (DC side) of the rectifier, and by quickly searching and removing the fault point, to restore power generation at the substation.SOLUTION: A method for detecting a ground fault in an AC-side connection wire of a rectifier for DC feeding comprises: measuring a current flowing in a ground wire 10 with which a shield layer 9s of a connection wire 9 between a transformer 7 for a rectifier and a rectifier 8 at a substation 2 for DC electric trains; extracting a third harmonic component from harmonic components for a commercial frequency of the current; and detecting a ground fault in the connection wire 9 between the transformer 7 for the rectifier and the rectifier 8 at the substation 2 on the basis of a change in magnitude of the third harmonic component.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a method for detecting a ground fault in an AC side connection line of a DC feeder rectifier, and more particularly, to a ground fault in a connection line between a rectifier transformer and a rectifier in a DC railway substation. The present invention relates to a ground fault detection method for an AC side connection line of a DC feeding rectifier that detects a fault when it occurs.

  Conventionally, in a DC railway substation, when a ground fault of a DC bus occurs, a fault such as burning of the substation equipment occurs due to the large ground fault current. Therefore, as a result of diligent research, the present applicant, as shown in the following patent document (Japanese Patent Laid-Open No. 2010-42784), detects the voltage between the grounding mat of the substation and the return line, and shuts down the substation as quickly as possible. However, a DC high-voltage grounded relay that realizes a ground fault detection method that suppresses damage to substation equipment and protects the substation has been invented and put into practical use.

  FIG. 6 is a diagram showing a configuration of a conventional DC high-voltage grounded relay. A DC high-voltage grounding relay 90 shown in FIG. 6 is installed between a grounding mat 91 and a return line 92 of a substation, and has a potential difference measuring unit 93 that measures a potential difference therebetween, and the potential difference measuring unit 93 is greater than or equal to a threshold value. When the voltage is detected, a cut-off signal is sent to the AC breaker 95A and the DC high-speed breaker 95 to cut off the power supply to the DC bus 94. 96 is a rectifier transformer, 97 is a rectifier, 98 is a ground wire, 99 is a true ground, 96A is a connection line connecting the rectifier transformer 96 and the rectifier 97, 96B is a shielding layer of the connection line 96A, 98R is an insulation resistance between the connection line 96A and the shielding layer 96B.

  The ground fault detection method using the DC high-voltage ground relay 90 having the above-described configuration includes a potential difference measuring unit 93 that detects a voltage between the ground mat 91 and the return line 92, and the ground fault of the DC bus 94 in the substation. Detect failure. In other words, when a ground fault occurs in the DC bus 94, the grounding mat 91 has a positive (+) polarity potential with respect to the return line 92. Therefore, the potential difference measuring unit 93 detects this and interrupts the AC circuit breaker 95A. Output a signal. The AC circuit breaker 95A can quickly shut down the substation by protecting the power supply by this interruption signal, thereby protecting the substation equipment and the like.

JP 2010-42784 A

  However, in the conventional ground fault detection method for the DC high-voltage grounded relay 90, not only the ground fault of the secondary electric circuit (DC side) of the rectifier 97 of the DC substation substation, but also the rectifier transformer 96 and the rectifier 97 are provided. There is a problem that the operation is caused by a ground fault in the primary side electric circuit (AC side) between them, and these cannot be distinguished.

  As a background, in the DC high-voltage grounded relay 90 provided in the DC railway substation, the rectifier transformer 96 and the rectifier 97 are often arranged close to each other in terms of the arrangement of the substation equipment. Although it was often connected with a bare conductor such as a stranded wire, in recent years, it is less likely to be connected with a bare conductor for safety reasons, and it is now connected with a cable with a shielding layer 96B, etc. There is. For this reason, rainwater or the like may enter due to deterioration of the terminal treatment of the cable and the cable may cause insulation deterioration, which may lead to a ground fault. In addition, such a ground fault in the cable is harder to detect visually than in the case of a bare conductor, and it is difficult to quickly find the failure point.

  For this reason, when the DC high-voltage grounding relay 90 is operated, the worker in charge of restoration mainly searches for a ground fault in the DC circuit on the secondary side of the rectifier 97, so that the primary side circuit of the rectifier 97 is grounded. In the case of a fault, there is a problem that the above situation overlaps with the above situation, and it takes a lot of time to search for and remove the failure point and to recover the power at the substation, which greatly affects the operation of the train.

  FIG. 7 is a diagram showing harmonic components of the current flowing through the ground line 98 to which the shielding layer of the connection line between the rectifier transformer 96 and the rectifier 97 is connected in a healthy state. In a healthy state where no failure has occurred in a general three-phase alternating current such as a transmission / distribution line, almost no current flows through the grounding wire 98 if the three-phase collective grounding is performed, but this point is the return line 92 and the rectifier 97. The ground potential is a positive and negative asymmetric distortion waveform because it is a special grounding system that is electrically connected to the true ground via the diode. For this reason, even in a healthy state, the fundamental wave current, the fifth harmonic current, the seventh harmonic current, and the sixth harmonic current caused by the rectification ripple on the secondary side are caused by the primary side of the rectifier 97. Various currents such as double harmonic currents flow. In addition, since the substation equipment and the support hardware are influenced by induction from nearby electric circuits and the like, the current due to this also flows to the ground line in addition to the above.

  The present invention has been made in consideration of the above-mentioned matters, and the purpose of the present invention is the case where a ground fault occurs in the connection line between the rectifier transformer and the rectifier of the DC railway substation and the DC bus. DC power supply rectifiers that provide a method of isolating ground faults in the vehicle, facilitate the search for failure points, quickly implement power recovery at substations, and minimize the impact on train operation An object of the present invention is to provide a ground fault detection method for an AC side connection line.

  In order to solve the above-mentioned problem, the first invention measures the current flowing through the grounding line to which the electric line support of the connecting line between the rectifier transformer and the rectifier of the DC railway substation or the shielding layer of the connecting line is connected. Then, the third harmonic component is extracted from the harmonic components of the current with respect to the commercial frequency, and the rectifier transformer and the rectifier of the substation for the DC railway are changed by the change in the magnitude of the third harmonic component. A ground fault detection method for an AC side connection line of a DC feeding rectifier is provided. (Claim 1)

  In general, DC high-voltage grounded relays are intended to protect ground faults in the secondary side of the rectifier (DC side) in DC substations. It operates also by the ground fault of the primary side electric circuit (AC side).

  FIG. 8 is a diagram illustrating a flow of current that flows when a ground fault occurs in the primary side electric circuit (AC side) of the rectifier illustrated in FIG. 6. As shown in FIG. 8, when a ground fault occurs in the primary side electric circuit (AC side) of the rectifier 97, the grounding mat 91 and the grounding resistance 91R pass through the grounding resistance 98R ′ and the grounding wire 98. And the true ground 99, the rail leakage resistance 92R and the rail, the return line 92, and the circuit of the current returning to the rectifier 97 are configured. For this reason, since the grounding mat 91 has a positive (+) polarity potential from the direction of each rectifying element of the rectifier 97, there is a characteristic that the DC high-voltage grounding relay 90 operates even if there is a ground fault in the AC side circuit of the rectifier. .

  FIG. 9 shows the result of frequency analysis of the current flowing in the ground line 98 to which the shielding layer of the connection line between the rectifier transformer 96 and the rectifier 97 in FIG. 8 is connected. It can be seen that, in addition to the current of the commercial frequency (fundamental wave current), the current of the third harmonic component, the harmonic current associated with the rectifying action of the rectifier 97, and the like flow. As is clear from comparison with FIG. 7, the third harmonic current is almost nonexistent if there is no ground fault on the primary side of the rectifier.

  The ground fault detection method for the AC side connection line of the DC feeding rectifier of the first invention pays attention to the third harmonic component, and using the third harmonic component as an index, the primary side electric circuit (AC) of the rectifier This is used to detect a ground fault on the primary side of the rectifier, whereby the ground fault on the primary side of the rectifier can be determined with high accuracy.

  Measure the current flowing in the grounding line connected to the electrical circuit support of the connecting line between the transformer for rectifier and the rectifier or to the shielding layer of the connecting line, and change the magnitude of the third harmonic component of this current (threshold value) Therefore, a ground fault in the connection line between the rectifier transformer and the rectifier can be detected. In addition, it is possible to determine whether the cause of the operation of the DC high-voltage grounding relay is on the DC side of the rectifier or on the AC side (that is, the connection line between the rectifier transformer and the rectifier), so that the failure point search time can be determined. The power station can be shortened, the substation can be restored quickly, and the impact on train operation can be reduced. In addition, when a ground fault of the connection line between the rectifier transformer and the rectifier is detected by the ground fault detection method of the first invention, only the AC breaker on the primary side of the rectifier transformer is shut off, In addition, by configuring the interlock so that the interruption signal is transmitted earlier than the DC high-voltage grounding relay, train operation is possible because the power outage range at the time of the failure can be minimized and the substation can be locked. Can be kept to a minimum.

  The second aspect of the invention measures the current flowing through the grounding line to which the electric circuit support of the connecting line between the rectifier transformer and the rectifier of the DC railway substation or the shielding layer of the connecting line is connected, and the commercial frequency of this current In the connection line between the rectifier transformer and the rectifier of the substation for DC railway, by analyzing the content ratio of the at least one harmonic component with respect to the effective value of the current flowing in the ground line There is provided a ground fault detection method for an AC side connection line of a DC feeding rectifier characterized by detecting a ground fault. (Claim 2)

  2nd invention pays attention to the content rate of the harmonic component of the electric current which flows into the earthing line to which the electrical circuit support tool of the connection line between the transformer for rectifiers or the shield layer of the connection line was connected at the time of a ground fault, and this This is used to detect a ground fault in the primary side circuit (AC side) of the rectifier using the change in the content of harmonic components as an index. It can be determined with high accuracy.

  At least one harmonic component is measured by measuring the current flowing through the ground wire connected to the electrical circuit support of the connection line between the transformer for rectifier and the rectifier or the shield layer of the connection line, and analyzing the harmonic component of this current. It is possible to detect that a ground fault has occurred in the connection line between the rectifier transformer and the rectifier by the change in the content ratio with respect to the effective value of the current flowing in the ground line. In the healthy state, the content of the third harmonic component with respect to the effective value of the current flowing through the grounding wire is very small and the content of the sixth harmonic component is larger than the fundamental component, but when a ground fault occurs, Since the content ratio of the third harmonic component increases and the content ratio of the sixth harmonic component decreases, a ground fault in the connection line between the rectifier transformer and the rectifier is used by using the change in the content ratio. Can be detected. In addition, when a ground fault of the connection line between the rectifier transformer and the rectifier is detected by the ground fault detection method of the second invention, only the AC breaker on the primary side of the rectifier transformer is shut off, In addition, by configuring the interlock so that the interruption signal is transmitted earlier than the DC high-voltage grounding relay, train operation is possible because the power outage range at the time of the failure can be minimized and the substation can be locked. Can be kept to a minimum.

  As described above, according to the ground fault detection method for the AC side connection line of the DC feeding rectifier of the first invention, when the circuit has a ground fault in the primary side circuit (AC side) of the rectifier, It is possible to detect with high accuracy that a ground fault has occurred in the AC side circuit of the rectifier using a third harmonic component characteristically included in the ground fault current flowing in the ground line. This facilitates the search and removal of the fault point in the case of a ground fault in the primary side circuit of the rectifier, promptly recovers the substation, and minimizes the influence on the train operation.

  According to the ground fault detection method for the AC side connection line of the DC feeding rectifier of the second invention, the effective of the ground fault current of each harmonic component caused by the ground fault of the primary side circuit (AC side) of the rectifier. Since it is possible to accurately detect the occurrence of a ground fault in the connection line between the rectifier transformer and the rectifier by grasping the change in the content ratio with respect to the value, the fault in the ground fault in the AC side circuit of the rectifier This makes it easy to search for and remove points, quickly restore power at substations, and minimize the impact on train operations. In addition, when a ground fault in the connection line between the rectifier transformer and the rectifier is detected by the ground fault detection method of the first invention or the second invention, the fault detection information is transmitted to the distribution board of the substation. In addition, it is possible to incorporate control that takes this fault information into account for substation linkage. As a result, an early power recovery can be achieved if the interlocking configuration is performed so as not to suppress the power recovery operation for a healthy portion (for example, another rectifier circuit or the like).

It is a figure which shows the structure of the railway DC substation which implements the ground fault detection method of the alternating current side connection line of the rectifier for DC feeding of 1st Embodiment. It is a figure which shows the structure of the ground fault detection apparatus which implements the ground fault detection method of the alternating current side connection line of the DC feeding rectifier of 1st Embodiment. It is a figure explaining the ground-fault fault detection method of the alternating current side connection line of the rectifier for direct current feeding of 1st Embodiment. It is a figure which shows the structure of the ground fault detection apparatus which implements the ground fault detection method of the alternating current side connection line of the direct current feeding rectifier of 2nd Embodiment. It is a figure explaining the ground-fault fault detection method of the alternating current side connection line of the rectifier for direct current feeding of 2nd Embodiment. It is a figure which shows the structure of the substation for DC railways in which the conventional DC high voltage grounding relay is installed. It is a figure which shows the harmonic component of the electric current which flows into a ground line at the time of a healthy state body. (Shows the content of each high-frequency component with respect to the effective value of the ground line current.) It is a figure explaining the flow of an electric current when a ground fault has generate | occur | produced in the connection line (AC side) between the transformer for rectifiers of a DC railway substation, and a rectifier. It is a figure which shows the harmonic component of the electric current which flows into a ground line, when a ground fault has generate | occur | produced in the connection line (AC side) between the transformer for rectifiers of a DC railway substation, and a rectifier. (Shows the content of each harmonic component with respect to the effective value of the ground line current.)

  Hereinafter, a specific embodiment of the ground fault detection method for the AC side connection line of the DC feeding rectifier according to the first embodiment of the present invention will be described in detail with reference to the drawings using FIGS. Explained. As shown in FIG. 1, the DC high-voltage ground relay R is provided between the ground mat 3 and the return line 4 of the substation 2, and has a potential difference measuring unit 5 that measures the potential difference between the ground mat 3 and the return line 4. A ground fault determination output unit 6 that determines a ground fault using the measured potential difference is provided. 3r is a grounding resistance of the grounding mat 3, and 4r is a return line 4 and a rail leakage resistance between the rail and the true ground G.

  7 is a rectifier transformer, 7A is an AC circuit breaker that stops power supply to the rectifier transformer 7 when the ground fault determination output unit 6 determines a ground fault, 8 is a rectifier, and 9 is a rectifier. A connection line 10 between the transformer 7 and the rectifier 8 is a ground line to which the shielding layer 9s of the connection line 9 is connected. The connecting wire 9 includes a conductor serving as a core wire, a coating 9i made of an insulating material for protecting the conductor, the shielding layer 9s provided so as to cover the outside of the coating 9i, and a high level for protecting the shielding layer 9s. This is a cable provided with an outer sheath 9p made of a molecular material. Therefore, the conductor and the shielding layer 9s are connected via the large insulation resistance 10r by the covering 9i, but when a ground fault occurs in the connection line 9, the conductor and the shielding layer 9s have a smaller grounding resistance 10r. Connected by '.

  As shown in FIG. 2, the ground fault detection apparatus 1 according to the ground fault detection method for the AC side connection line of the DC feeding rectifier of the present invention includes a current measuring unit 11 that measures the current flowing through the ground line 10. A third harmonic extraction unit 12 composed of, for example, a filter circuit connected to the current measurement unit 11, an AC side ground fault determination output unit 13 connected to the third harmonic extraction unit 12, The AC side ground fault determination output unit 13 is connected to the AC side ground fault display unit 14, and each member 12 to 14 in the present embodiment is formed in one ground fault unit 1a. Further, 15 is a DC bus, and 16 is a DC high speed circuit breaker.

  As shown in FIG. 3, in the ground fault detection method for the AC side connection line of the DC feeding rectifier of this embodiment, first, the current flowing through the ground line 10 is measured by the current measuring unit 11 (step S <b> 1). The current measuring unit 11 is preferably formed using an AC current transformer, for example, and continuously measures current even if the following steps S2 to S2 are executed in time series. It is preferable.

  Next, the third harmonic component is extracted from the harmonic components for the commercial frequency of the current measured using the third harmonic extraction unit 12 (step S2). The third harmonic component is preferable because it can be performed in real time simultaneously with the current measurement by using hardware such as a filter circuit, for example. However, the measured current value is converted into a digital signal at one time to the arithmetic processing unit. The third harmonic extraction unit 12 may include an arithmetic processing unit and a third harmonic extraction program.

  Further, by detecting when the third harmonic component exceeds the threshold by the AC side ground fault determination output unit 13, the transformer for the rectifier of the substation 2 is detected by the change in the magnitude of the third harmonic component. A ground fault in the connection line 9 between the rectifier 7 and the rectifier 8 is detected (step S3). When it is determined in this step S3 that the third harmonic component is not equal to or greater than the threshold value, the process returns to the step S1. Steps S1 to S3 are repeated until the threshold value is exceeded. The processing in step S3 is also preferably performed simultaneously and continuously using hardware such as a comparator, but may be realized by software processing that can be executed by the arithmetic processing unit. The ground fault determination output unit 13 includes an arithmetic processing unit and an AC side ground fault determination output program.

  When it is determined in step S3 that the third harmonic component is equal to or greater than the threshold value, a ground fault on the primary side (AC side) of the rectifier is displayed on the AC side ground fault indicator 14 (step S4). In addition, it is preferable that the AC side ground fault indicator 14 can hold the display contents even when the control power of the substation is lost.

  As described above, a ground fault is detected on the primary side of the rectifier 8 (between the rectifier transformer 7 and the rectifier 8) by performing the ground fault detection method for the AC side connection line of the DC feeding rectifier. Since this can be displayed on the display 14, after the AC circuit breaker 7 </ b> A and the DC high-speed circuit breaker 16 are interrupted, the occurrence position of the ground fault causing the interruption is 1 of the rectifier 8. It can be confirmed that this is the secondary electric circuit.

  That is, when a ground fault occurs in the primary side circuit of the rectifier 8, a ground fault current flows to the ground mat 3 via the ground fault resistor 10r ′ and the ground line 10, and further true through the ground resistor 3r. Since a ground fault current flows to the ground G and through the circuit of the return line 4 and the rectifier 8 via the rail leakage resistance 4r, the potential difference measuring unit 5 connected between the grounding mat 3 and the return line 4 is grounded at both ends. Since the grounding mat 3 becomes a positive (+) polarity potential due to the impedance from the mat 3 to the return line 4, the DC high-voltage grounding relay R operates, so that the AC circuit breaker 7A and the DC high-speed circuit breaker 16 are cut off to transform the power. Power supply to the DC bus at station 2 stops.

  Further, since the third harmonic current is included in the ground fault current, when the third harmonic component exceeds a preset threshold, the AC side connecting line of the DC feeder rectifier of the present invention is used. The ground fault of the electric circuit (AC side) between the rectifier transformer and the rectifier is detected by the ground fault detection method of, and displayed on the AC side ground fault display unit 14. Therefore, when the operator who performs restoration checks the display on the AC side ground fault display unit 14, the ground fault occurs on the primary side of the rectifier 8 (between the transformer 7 and the rectifier 8, that is, the AC side). Therefore, early power recovery can be achieved.

  On the other hand, when the secondary side circuit (DC side) of the rectifier 8 is grounded, there is almost no third harmonic component current in the current measurement value by the current measurement unit, and the third harmonic extraction unit 12 is present. Therefore, the AC side ground fault determination output unit 13 does not perform the AC side ground fault determination, and the display on the AC side ground fault display unit 14 is not performed. Therefore, since the worker in charge of restoration does not have the display on the AC side ground fault display section 14, it can confirm that a ground fault has occurred on the secondary side (DC side) of the rectifier 8, and search for a fault in the DC side circuit. Can concentrate on.

  4 and 5 are diagrams for explaining a ground fault detection method for an AC side connection line of a DC feeding rectifier according to the second embodiment, and FIG. 4 is a DC feeding rectifier according to the second embodiment of the present invention. The figure which shows the structure of the ground fault detection apparatus 20 which implements the ground fault detection method of the AC side connection line of FIG. 5, FIG. 5 is the ground fault detection method of the AC side connection line of the rectifier for DC feeding of 2nd Embodiment. It is a figure explaining an example. In these drawings, members denoted by the same reference numerals as those in FIGS. 1 to 3 are the same or equivalent parts, and thus detailed description thereof is omitted.

  The ground fault detection device 20 shown in FIG. 4 includes an FFT unit (Fast Fourier Transform) 21 that analyzes the harmonic component of the current measured by the current measuring unit 11, and the harmonics analyzed by the FFT unit 21. An AC-side ground fault determination unit 22 that detects a change in the content ratio of the wave component with respect to the effective value of the ground line current and determines a ground fault in the electric circuit (AC side) between the rectifier transformer and the rectifier. These members 21, 22, and 14 constitute the ground fault determination unit 20a, and most of them may be realized by an arithmetic processing unit such as a one-chip microcomputer. In this case, for example, the FFT unit 21 and the AC side ground fault determination unit 22 are realized by an arithmetic processing unit and an AC side ground fault determination program that can be executed by the arithmetic processing unit.

  In FIG. 5, the current measured in step S1 clarifies the content of harmonic components by performing frequency analysis such as FFT (step S5). The present invention is not limited to FFT using a microcomputer or the like, but at least a third harmonic component that dramatically increases due to an AC side ground fault and / or a sixth harmonic that decreases due to an AC side ground fault. It is also conceivable to form it by hardware such as a filter circuit for extracting a wave component.

  Next, the occurrence of the AC side ground fault is detected depending on whether the content ratio of the analyzed harmonic component to the effective value of the ground line current shows a change that characterizes the AC side ground fault (step S6). ). If it is determined in step S6 that there is no change, the process returns to step S1, and the processes in steps S1, S5, and S6 are repeated. If it is determined that there is a change, the next step S4 is executed.

  In addition, various criteria can be considered. For example, when a ground fault occurs in the connection line on the AC side, the ground wave current has the largest fundamental wave component, and then the third harmonic component increases. Therefore, since the index is that both the contents of the fundamental wave component and the third harmonic component increase, or the ratio of the rectification ripple contained in the ground line current is relatively reduced, the third harmonic The content ratio of the component and the fifth harmonic component is larger than the content ratio of the sixth harmonic component, or the evaluation of the harmonic current content rate is not a ratio to the effective value of the ground line current. It is conceivable to carry out at a ratio to the fundamental wave component of the ground line current.

  As described above, it is possible to accurately determine the occurrence of the ground fault on the AC side even by the ground fault detection method for the AC side connection line of the DC feeding rectifier according to the second embodiment. Can contribute.

1,20 DC feeding rectifier ground fault detection device 2 Substation 3 Grounding mat 4 Return line 7 Rectifier transformer 8 Rectifier 9 Connection line 9s Shielding layer 10 Grounding line 11 Current measurement unit 12 Third harmonic extraction Part 14 AC side ground fault display part

Claims (2)

  Measure the current flowing through the grounding line connected to the circuit support of the connecting line or the shielding layer of the connecting line between the rectifier transformer and the rectifier of the DC railway substation, and the harmonic component of this current with respect to the commercial frequency Among them, the third harmonic component is extracted, and a ground fault in the connection line between the rectifier transformer and the rectifier of the DC railway substation is detected by the change in the magnitude of the third harmonic component. A ground fault detection method for an AC side connecting line of a DC feeding rectifier.   Measure the current flowing in the grounding line connected to the circuit support of the connection line between the rectifier transformer and the rectifier of the DC railway substation or the shield layer of the connection line, and determine the harmonic component of this current relative to the commercial frequency. By analyzing the frequency and changing the content ratio of the at least one harmonic component with respect to the effective value of the current flowing in the ground line, a ground fault in the connection line between the rectifier transformer and the rectifier of the substation for DC railways is detected. A method for detecting a ground fault in an AC side connection line of a rectifier for DC feeding, characterized by detecting the ground fault.

Images