JP7548799B2 - High-resistance ground fault detector for DC power lines - Google Patents

Description

The present invention relates to a ground fault detection device for DC feeders in electric railways, and in particular to technology that is effective for detecting high-resistance ground faults in DC feeders in substations.

In a feeding system using 1500V DC, the vehicle load current is on the order of several hundred to several thousand A. Normally, short circuits and ground faults in the feeding circuit are detected by monitoring the current at a substation and capturing a sudden increase in current, and are then cut off by a high-speed DC circuit breaker. However, if a ground fault occurs in a DC feeding line through a structure or other object with a large resistance value (several ohms to several tens of ohms) compared to the feeding circuit, the fault current will be on the order of several hundred A, making it difficult to distinguish it from the vehicle load current. This type of ground fault phenomenon is generally referred to as a high-resistance ground fault, and detecting high-resistance ground faults in DC feeding systems has been a major challenge for many years.

Conventionally, substations have provided protection against earth faults by installing an overcurrent detector (54F) that monitors the feeding current and trips a DC high-speed circuit breaker to cut off the current if the current exceeds a set value, and a ΔI type fault selection device (50F) that cuts off the current if the current fluctuation (ΔI/Δt) exceeds a set value. In addition, a DC earth fault detector (64P) that monitors the potential between the rail and the substation mesh ground, and a DC earth fault detector (64PB) that monitors the potential between the substation mesh ground and the reference ground are also provided to detect and protect against earth faults.
When a complete earth fault occurs, in which the feeder line hangs down and comes into contact with a support pole or the ground, causing a large earth fault current of several thousand amperes to flow to the ground, the detection device can detect this and activate a high-speed DC circuit breaker to cut off the current flowing through the feeder line.

However, when a high-resistance ground fault occurs, the ground fault current is only several hundred A, so it cannot be detected by the overcurrent detector (54F) or ΔI type fault selection device (50F) installed in the substation. In addition, when a high-resistance ground fault occurs, the change in rail potential and substation mesh potential is small, so it was found that the above-mentioned ground fault detector (64P, 64PB) cannot detect it either.
Conventionally, inventions relating to a detection system, detection device, and detection method for a high-resistance ground fault are proposed in, for example, Patent Documents 1 and 2.

JP 2009-247155 A JP 2018-36054 A

The invention described in Patent Document 1 detects high-resistance ground faults in high-voltage DC feeding cables by using a search coil to detect the difference current between the harmonic components of the current flowing through all high-voltage DC feeding cables connected to a rectifier and the harmonic components of the current flowing through all return DC feeding cables connected to the rectifier within an electric railway substation. However, the above invention targets high-resistance ground faults within the substation, and has the problem that it is difficult to detect high-resistance ground faults that occur outside the substation.

The earth fault detection device described in Patent Document 2 is composed of a potential difference detector that detects the potential difference between the rail potential and the ground potential, a current detector that detects the current value of the power supply circuit, a calculator that calculates a calculated value of the potential difference value/current value from the potential difference value detected by the potential difference detector and the current value detected by the current detector, and a comparator that compares the calculated value by the calculator with a predetermined threshold value and sends an abnormality detection signal if the calculated value exceeds the threshold value. Therefore, there are problems in that a current detector is required in addition to the potential difference detector, and since the potential difference value/current value must be calculated, the processing is complicated and it takes a long time to make a judgment.

The present invention was made in response to the above-mentioned problems, and its purpose is to provide a high-resistance ground fault detection device that can detect a high-resistance ground fault in a DC feeder that occurs outside a substation and interrupt the current at the substation with a relatively simple configuration and without complex calculations.

Prior to the invention, the inventors of the present invention conducted a study on the route of the ground fault current and the change in rail potential when a high-resistance ground fault occurs.
First, when a train is normally running, a DC voltage of 1500V is applied between the contact wire and the rail, and the load resistance of the vehicle is present on the feeding circuit, and the voltage on the feeding circuit is divided by the resistance of this vehicle. Then, where a train is present on the line, the voltage applied between the rail and ground is the feeding voltage of 1500V minus the voltage divided by the resistance when the train is powered, and the rail potential increases in the positive (positive) direction with respect to the ground.

As shown in Figure 4, there are two types of return routes for the load current from the train location to the substation: a route that flows through the rails and a route that flows through the ground. In the first route, part of the train load current flows from the rails to the substation. In the second route, the load current leaks to the ground because the rail potential near the train is more positive than the ground, and then travels through the ground and flows from ground to rail to substation near the substation. In the current route that flows through the ground to the substation, a negative voltage is applied to the rail near the substation with the ground as the reference. This is because when a load current flows through the ground, it always returns to the substation, which is the power source, so the ground becomes positive and the rail becomes negative.

Figure 5 shows the equivalent circuit of a ground fault. When a ground fault occurs, the rail potential becomes negative, as shown in Figure 6. This is because the application of a DC voltage to the earth causes the earth potential to rise, and an earth-fault current flows from the earth to the rail, causing the earth to become a positive potential and the rail to become a negative potential. As a result, the rail potential at the earth fault point and the substation changes in the negative direction (negative pole) when the earth is used as the reference. The earth-fault current flows through the leakage resistance between the earth and the rail to the substation. Some of this leakage current flows through the rail resistance to the substation, so the voltage between the earth and the rail decreases by the amount of the rail resistance.

In addition, the return current conductor is connected to the rail near the substation, and the rail resistance is low on the return route from the ground near the substation to the rail and back to the substation. Also, since the rail resistance is small near the substation, more ground fault current flows compared to the ground fault point, and the voltage between the ground and the rail becomes higher.
Furthermore, because the earth fault current near the substation is several tens to several hundreds of amperes, and because the rise of the earth fault current (ΔI/Δt) is not steep due to the reactance of the rail, it is difficult to detect based on the rate of change of current (ΔI/Δt). Therefore, we hypothesized that high-resistance earth faults with small earth fault currents can be detected by detecting fluctuations in the voltage between the ground and rail near the substation, rather than current fluctuations, and conducted verification. The details and results of this verification are explained below.

Earth fault voltage and current are related to the resistance and reactance of the feeder line and rail. Earth fault voltage is applied instantaneously to the feeding circuit, but because earth fault current takes time to flow to a steady state due to the reactance (L) on the feeder line (time constant τ = L/R), it is more effective to capture voltage fluctuations rather than fluctuations in earth fault current. If it is possible to distinguish rail potential fluctuations during an earth fault from rail potential fluctuations due to train load, it is believed that it will be possible to detect earth faults from rail-to-ground potential fluctuations (ΔV/Δt) over a certain period of time.

Therefore, the inventors measured rail potential fluctuations due to train loads at a substation, and found that, while the rail-to-ground potential fluctuations due to train loads are fairly small at 10 V or less, as shown by the solid line A in Fig. 7, in the event of a high-resistance ground fault, the rail-to-ground potential fluctuations are expected to be larger than the rail potential fluctuations due to train loads, as shown by the dashed line B in Fig. 7, and therefore it is possible to distinguish between the two.
The following Table 1 shows the maximum rail-to-ground potential fluctuation (ΔVmax) obtained by the inventors when they actually measured rail-to-ground potential fluctuations due to train loads over a one-day period at substations A, B, C, and D, with measurement sampling times of 10 ms and 50 ms (milliseconds).

8 shows, by solid lines, current changes measured at substations E and F, which are close to the location of a ground fault, when a high-resistance ground fault actually occurred in the past. Table 2 shows the measured current values before and after the occurrence of a high-resistance ground fault, and the difference between before and after, which is the amount of current change.

The inventors created a circuit model as shown in Figure 9, adjusted the ground fault point resistance so that the fault current when a high resistance ground fault occurs is 196A for E substation and 52A for F substation based on the results shown in Table 2 above, and performed simulation and analysis using a circuit simulator called EMTP (Electro Magnetic Transients Program). In Figure 9, SS represents the substation, Rs represents the internal resistance of each of the E, F, and H substations, Ls represents the substation inductance, IS represents the station premises, Rw and Lw represent the resistance and inductance components of the feeder line per km, Rf represents the ground fault point resistance, Rg represents the ground fault earth resistance, Rr and Lr represent the resistance and inductance components of the rail per km, Rl represents the leakage resistance, and Rlc represents the rail leakage characteristic resistance. UP represents the uplink side, and DW represents the downlink side. Table 3 shows the input conditions of the feeder circuit in the circuit model shown in Figure 9. The rail leakage characteristic resistance is a value expressed as √(R/G) (G: rail leakage conductance (s/m)).

The analysis results are shown in Table 4 and Figure 10. Comparing Table 2 with Table 4, the earth fault current values at substations E and F match the actual measured values to a certain extent, so it can be said that the analysis results are equivalent to the actual equipment environment. Furthermore, the negative rail potential fluctuation at Δt = 10 ms (milliseconds) at each substation is greater in the event of a high-resistance earth fault (-61 to 64 V) than the maximum rail-to-earth potential fluctuation (maximum -6.0 V) in Table 1. Therefore, it is possible to detect high-resistance earth faults by focusing on the rail potential fluctuation over a certain period of time (ΔV/Δt).

The present invention has been made based on the above findings,
a potential difference detection means for detecting a potential difference between a potential of the rail in the vicinity of the substation and a mesh ground potential of the substation;
and a processing means for detecting an occurrence of a high resistance ground fault in a DC feeder to which a current is supplied from a substation based on the potential difference detected by the potential difference detection means,
The arithmetic processing means
a voltage change calculation means for calculating a voltage change (ΔV/Δt) in a certain time (Δt) of the potential difference detected by the potential difference detection means;
a determination means for determining whether or not the voltage change (ΔV/Δt) exceeds a preset set value based on a maximum rail potential change amount in the negative pole direction detected in the substation during a predetermined period of time;
a command signal generating means for generating and outputting a command signal for opening a DC high-speed circuit breaker of a substation when the determining means determines that the voltage change (ΔV/Δt) has exceeded the set value;
The present invention is designed to provide the above.

According to the high resistance ground fault detection device having the above-mentioned configuration, when the voltage change (ΔV/Δt) exceeds a preset value based on the amount of negative rail potential change detected in the substation over a specified period of time, a command signal to open the substation's current breaker is generated and output, making it possible to detect a high resistance ground fault in a DC feeder and interrupt the current in the substation. In addition, with a relatively simple configuration and without complex calculations, it is possible to detect a high resistance ground fault in a DC feeder that has occurred outside the substation and interrupt the current in the substation.

Here, it is preferable that the certain time (Δt) can be set arbitrarily within the range of 1 to 100 milliseconds.
Also, preferably, the set value is a value obtained by multiplying a maximum amount of change in rail potential in the negative direction detected in the substation in a predetermined period by a safety factor.
This makes it possible to reliably detect a high resistance ground fault in the DC feeder without causing erroneous detection.

Further, preferably, the predetermined period is the past 30 days,
The set value for that day is determined by multiplying the maximum rail potential change in the negative direction during the 30 days from the previous day to the 30th day before by a safety factor.
With this configuration, the occurrence of a high-resistance ground fault can be accurately detected even if the leakage resistance of the rail changes due to the influence of weather or season, causing the ground fault current to change.

Also, preferably, the arithmetic processing means includes a signal sending means for sending the command signal for opening the DC high-speed circuit breaker, generated by the DC high-speed circuit breaker opening command signal generating means, to another substation.
With this configuration, a high-resistance ground fault outside the substation can be detected and the high-speed DC circuit breakers of the local substation and other adjacent substations can be opened, stopping the application of DC voltage to the feeder line where the high-resistance ground fault has occurred and preventing the ground fault current from continuing to flow and damaging or burning equipment around the track.

The high-resistance ground fault detection device of the present invention can detect high-resistance ground faults in DC feeders that occur at locations far from the substation. It also has the advantage of being able to detect high-resistance ground faults in DC feeders that occur outside the substation and cut off the current in the substation with a relatively simple configuration and without performing complex calculations.

1 is a system configuration diagram showing a schematic configuration of a ground fault detection system to which a high resistance ground fault detection device according to the present invention is applied. 1 is a block diagram showing a configuration example of a high resistance ground fault detection device according to an embodiment; 4 is a flowchart showing an example of a procedure of a high resistance ground fault detection process in the high resistance ground fault detection device of the embodiment. FIG. 2 is a diagram showing the current route of the load current of a running train and changes in rail potential. FIG. 2 is a circuit diagram showing an equivalent circuit of a ground fault. FIG. 2 is a diagram showing a current route and changes in rail potential when a ground fault occurs. 1 is a graph showing changes in load current of a running train and changes in earth fault current before and after a ground fault occurs. 1 is a graph showing changes in earth fault current measured at a substation when an actual earth fault occurs. FIG. 1 is a circuit diagram showing an example of a circuit model used in an analysis by an EPMT (circuit simulator). 1 is a graph showing changes in rail potential and changes in earth fault current at multiple substations calculated by analysis using EPMT.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of a high resistance ground fault detection device according to the present invention will be described in detail with reference to the drawings.
Fig. 1 is a diagram showing a schematic configuration of a ground fault detection system to which a high resistance ground fault detection device according to the present embodiment is applied. In Fig. 1, reference numeral 10 denotes a substation, W1 and W2 denote DC feeders to which DC power is supplied from the substation 10, and W3 denotes a return current wire connected to a rail R.
As shown in FIG. 1, a substation 10 is provided with disconnectors 11 (89B1, 89B2), power receiving circuit breakers 12 (52-1, 52-2), AC transformers 13 (SRTr1, SRTr2), rectifiers 14 (SR1, SR2), DC high-speed circuit breakers 15 (54-1, 54-2), a ground fault detection device 16 for detecting complete ground faults, and a high-resistance ground fault detection system 20.

The ground fault detection device 16 includes an earth fault detection device (64P) which monitors the potential difference between the rail R near the substation and the substation mesh ground MG to detect a complete earth fault on the feeder circuit, and an in-substation earth fault detection device (64PB) which monitors the potential difference between the substation mesh ground MG and the reference ground CG, and is configured to operate a DC high-speed circuit breaker to cut off the current sent to the DC feeders W1, W2 when an earth fault is detected.
When the earth fault detection device (64P) detects that the potential difference has exceeded a preset voltage (e.g., 500 V) and continued for a preset time (e.g., 400 ms), it activates the DC high-speed circuit breaker 15 (54-1, 54-2). Similarly, when the substation earth fault detection device (64PB) detects that the potential difference has exceeded a preset voltage and continued for a preset time, it activates the DC high-speed circuit breaker 15 (54-1, 54-2).

The high-resistance ground fault detection system 20 is composed of a potential difference detector 21 that detects the potential between the rail and the substation mesh ground at a specified sampling period, a high-resistance ground fault detection device 22 that calculates the rail potential fluctuation (ΔV/Δt) over a certain time based on the detected potential difference and compares it with a preset setting value to detect a high-resistance ground fault and generate and output a command signal to operate the DC high-speed circuit breaker 15 (54-1, 54-2), and a signal transceiver 23 that sends the command signal generated by the high-resistance ground fault detection device 22 to other substations via a transmission line installed between the substations and receives command signals from other substations.

2, the high resistance ground fault detection device 22 can be configured by a general computer device (PC) equipped with a programmable arithmetic processing device 31 such as a microprocessor (MPU), storage means such as a ROM (read only memory) 32 and a RAM (random access memory) 33, a user interface (user I/F) 34, an input device 35 such as a keyboard or a mouse, a display device 36 such as a liquid crystal display panel, a timer 37 for measuring time, etc. The timer 37 may be provided as hardware, but can also be configured as software.
The ROM 32 stores a high-resistance ground fault detection program executed by the arithmetic processing device 31. The arithmetic processing device 31 and the high-resistance ground fault detection program constitute a voltage change calculation means for calculating the rail potential fluctuation (ΔV/Δt) over a fixed period of time, a high-resistance ground fault determination means based on the calculation results, and a command signal generation means for operating a current breaker.

3 shows an example of a procedure for high resistance ground fault detection processing by the arithmetic processing device 31. The procedure for high resistance ground fault detection processing in FIG. 3 will be described below.
The following process according to the flowchart of FIG. 3 is performed by the arithmetic processing unit 31 executing a high resistance ground fault detection program stored in the memory (32 or 33) of the high resistance ground fault detection device 22.

When the high resistance ground fault detection process in FIG. 3 is started, the arithmetic processing device 31 first reads the current time from the timer 37 and also reads the potential difference between the rail and the substation mesh ground detected at a predetermined sampling period by the potential difference detector 21 (step S1). Then, based on the detected potential difference, it calculates the rail potential fluctuation (ΔV/Δt) over a certain time (Δt) (step S2).

Next, the maximum rail potential fluctuation value in the negative direction measured over a certain period of time is read (step S3). The maximum change amount thus extracted is then multiplied by a safety factor (e.g., "2") to determine the setpoint and store it in RAM 33 (step S4).

Then, the calculation processing device 31 proceeds to step S5, where it compares the rail potential fluctuation (ΔV/Δt) calculated in step S2 with the set value determined in step S4, and determines whether (ΔV/Δt) is greater than the set value. If (ΔV/Δt) is less than the set value (No), it determines that no high resistance ground fault has occurred, and returns to step S1.

On the other hand, if it is determined in step S5 that (ΔV/Δt) is greater than the set value (Yes), the process proceeds to step S6, where a command signal is generated to open the substation's DC high-speed circuit breaker 15 (54-1, 54-2) to cut off the current to the feeder, and the process ends. The generated command signal is also sent to other substations by the signal transceiver 23. This causes the DC high-speed circuit breakers of the local substation and other adjacent substations to open, stopping the application of DC voltage to the feeder where the high-resistance ground fault has occurred, and it is possible to prevent the ground fault current from continuing to flow and causing damage or burning of trackside equipment.
The arithmetic processing device 31 may be configured to output an alarm signal at the same time as opening the DC high-speed circuit breaker in step S6.

According to the above-mentioned procedure, it is possible to reliably detect high-resistance ground faults by distinguishing them from vehicle load currents. In addition, since the set value to be compared with the rail potential fluctuation (ΔV/Δt) in a certain time (Δt) is determined according to the maximum negative rail potential fluctuation measured for a certain period of time, it is possible to accurately detect high-resistance ground faults even if there are changes in the season, weather, train schedule, etc.
The certain time period (Δt) is not limited to 10 ms, but may be appropriately determined within the range of, for example, 1 ms to several hundred ms depending on the substation to which it is applied.

Although the embodiment of the present invention has been described above, the present invention is not limited to the above embodiment. For example, the set value may be determined by statistical processing, such as the moving average of the maximum value of the rail potential fluctuation (ΔV/Δt) in the previous week.

REFERENCE SIGNS LIST 10 Substation 11 Disconnector 12 Receiving circuit breaker 13 Rectifier transformer 14 Rectifier 15 DC high-speed circuit breaker 16 Earth fault detection device 20 High resistance earth fault detection system 21 Potential difference detector 22 High resistance earth fault detection device 23 Signal transmitter/receiver 31 Processing device W1, W2 DC feeder W3 Return current cable

Claims (5)

a potential difference detection means for detecting a potential difference between a potential of the rail in the vicinity of the substation and a mesh ground potential of the substation;
A calculation processing means for detecting an occurrence of a high resistance ground fault in a DC feeder to which a current is supplied from a substation based on the potential difference detected by the potential difference detection means,
The arithmetic processing means
a voltage change calculation means for calculating a voltage change (ΔV/Δt) in a certain time (Δt) of the potential difference detected by the potential difference detection means;
a determination means for determining whether or not the voltage change (ΔV/Δt) exceeds a preset set value based on a maximum rail potential change amount in the negative pole direction detected in the substation during a predetermined period of time;
a command signal generating means for generating and outputting a command signal for opening a DC high-speed circuit breaker of a substation when the determining means determines that the voltage change (ΔV/Δt) has exceeded the set value;
A high resistance ground fault detection device for a DC feeder line, comprising: The high-resistance ground fault detection device for DC power lines described in claim 1, characterized in that the fixed time (Δt) can be set arbitrarily between 1 and 100 milliseconds. The high resistance ground fault detection device for DC feeder according to claim 1 or 2, characterized in that the set value is a value obtained by multiplying the maximum amount of rail potential change in the negative direction detected in the substation during a specified period by a safety factor. The predetermined period is the past 30 days,
The high resistance ground fault detection device for a DC feeder according to claim 3, characterized in that the setting value for the day is a value obtained by multiplying a maximum rail potential change in the negative direction during the 30 days from the previous day to the 30th day before by a safety factor. The high resistance ground fault detection device for a DC feeder according to any one of claims 1 to 4, characterized in that the arithmetic processing means includes a signal sending means for sending the command signal for opening the DC high speed circuit breaker, generated by the DC high speed circuit breaker opening command signal generating means, to another substation.

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