A method and device for identifying the presence of electric locomotive load current in feeder current

Abstract

The present invention belongs to the technical field of traction power supply for electrified railways, and specifically relates to a method and device for identifying the presence of electric locomotive load current in feeder current. The present invention uses mathematical morphology to separate the morphological harmonic waveform in the feeder current of a traction substation, counts the number of zero crossings of the morphological harmonic waveform in a quarter-cycle time window, and determines whether the feeder current contains the electric locomotive load current, which helps relay protection to take blocking or suppression measures based on the judgment result, improves the reliability and sensitivity of relay protection, and ensures the safe and reliable operation of the traction power supply system.

Description

Technical Field

[0001] The invention belongs to the technical field of electrified railway traction power supply, and in particular relates to a method and a device for identifying the presence of electric locomotive load current in feeder current. Background Art

[0002] When a short circuit fault occurs in the electrified railway traction network, if the voltage of the traction substation feeder is high and the current is low at the time of the fault, the distance protection configured as the main protection and the overcurrent protection and current increment protection configured as the backup protection of the traction substation may fail to operate. If the load current of the electric locomotive is too large, it may enter the protection action area and cause the protection to malfunction. At present, the traditional electrified railway feeder protection is configured with "second harmonic blocking" and "comprehensive harmonic suppression" functions to maximize the reliability and sensitivity of relay protection.

[0003] The "Second Harmonic Interlock" function assists in identifying the excitation surge current generated by the transformer after the electric locomotive is over-phased, preventing the distance protection element, overcurrent protection element and current increment protection element of the feeder protection from malfunctioning. When there are multiple electric locomotives on a single power supply arm of an electrified railway, if another electric locomotive is put into the traction transformer to cause an excitation surge current, the second harmonic content of the current collected by the traction substation feeder protection may be less than the set value, resulting in the failure of the second harmonic interlock function.

[0004] The 2nd, 3rd, and 5th low-order harmonics in the operation of "AC-DC" electric locomotives are relatively high. The traditional feeder protection configuration of the traction substation is based on the comprehensive harmonic suppression elements of the 2nd, 3rd, and 5th harmonic content to assist in identifying the load of the electric locomotive. The distance protection elements, overcurrent protection elements, and current increment protection elements of the feeder protection dynamically adjust the protection setting values ​​based on the size of the comprehensive harmonic content to reduce the protection misoperation caused by the load of the electric locomotive. Due to the widespread application of "AC-DC-AC" electric locomotives or EMUs, the locomotive load current contains various low-order harmonics and high-order harmonics, but the comprehensive harmonic content calculated based on the 2nd, 3rd, and 5th harmonics is relatively small, and the traditional comprehensive harmonic suppression function loses its meaning.

[0005] The document "Research on Analysis and Protection Setting of High-Resistance Grounding Faults in Traction Power Supply Systems" (Electrified Railway, Issue 5, 2020, pp. 36-38, p. 45) proposes to lower the current increment setting value to correctly identify the electric locomotive load and high-resistance grounding faults, but the frequent changes in the operating conditions of the electric locomotive will cause the current increment protection to malfunction.

[0006] In summary, the effective and correct identification of the electric locomotive load by the traction substation feeder protection can avoid or reduce the probability of false operation or refusal of relay protection. The traditional functions based on "second harmonic blocking" and "comprehensive harmonic suppression" have shortcomings. It is necessary to propose a method that can effectively identify whether the traction substation feeder current contains the electric locomotive load current, which will help improve the reliability and sensitivity of relay protection and ensure the safe and reliable operation of the traction power supply system. Summary of the invention

[0007] In order to solve the problem that the current traction substation feeder protection cannot effectively identify the feeder current as load current and fault current, which may lead to protection refusal or malfunction, the present invention provides a method for identifying the presence of electric locomotive load current in the feeder current, separates the morphological harmonic waveform in the traction substation feeder current by mathematical morphology, counts the number of zero crossings of the morphological harmonic waveform in a quarter-cycle time window, and judges whether the feeder current contains the electric locomotive load current, which helps the relay protection to take locking or suppression measures based on the judgment result, improves the reliability and sensitivity of the relay protection, and ensures the safe and reliable operation of the traction power supply system.

[0008] The technical solution adopted by the present invention is:

[0009] A method for identifying the presence of electric locomotive load current in feeder current comprises the following steps:

[0010] S1. Sample the feeder current to obtain a current sampling value i(k), where k is the sampling value sequence number;

[0011] S2, perform morphological calculation on the current sampling value after the feeder protection element is started, specifically, perform expansion operation and corrosion operation respectively to obtain i pz (k) and i fs (k);

[0012] S3. Calculate the morphological harmonic component i in the feeder current h (k):

[0013]

[0014] S4. Statistical Morphology Harmonics h (k) The number of zero crossings within a quarter of a cycle is N. The zero crossing determination method is: if the morphological harmonics satisfy or It is believed that the morphological harmonic i h (k) passes through zero once;

[0015] S5. Determine whether N ≥ a is established, where a is a determination threshold determined according to the current sampling frequency. If so, the identification result is that the feeder current contains the electric locomotive load current. Otherwise, the identification result is that the feeder current does not contain the electric locomotive load current.

[0016] Furthermore, the sampling frequency of sampling in S1 is 96 points / cycle.

[0017] Furthermore, the expansion operation method in S2 is:

[0018] i pz (k)=max{i(k-2),i(k-1),i(k)}

[0019] The erosion operation method is:

[0020] i fs (k)=min{i(k-2),i(k-1),i(k)}.

[0021] Further, according to the sampling frequency of 96 points / cycle, a=5 in S5.

[0022] The present invention also provides a device for identifying the presence of electric locomotive load current in feeder current, comprising an analog quantity acquisition module, a data operation module, and an analysis and decision module; the analog quantity acquisition module is used to sample the feeder current to obtain a current sampling value i(k), where k is the sampling value sequence number; the data operation module is used to perform morphological calculations on the obtained current sampling values, specifically, respectively performing expansion operations and corrosion operations to obtain i pz (k) and i fs (k), then calculate the morphological harmonic component i in the feeder current h (k):

[0023]

[0024] The final statistical morphology harmonics i h (k) The number of zero crossings within a quarter of a cycle is N. The zero crossing determination method is: if the morphological harmonics satisfy or It is believed that the morphological harmonic i h (k) passes through zero once;

[0025] The analysis and decision module is used to determine whether the feeder current has an electric locomotive load current. The specific method is to determine whether N≥5 is established. If so, the identification result is that the feeder current has an electric locomotive load current. Otherwise, the identification result is that the feeder current does not have an electric locomotive load current.

[0026] The beneficial effects of the present invention are as follows: the present invention provides a method and device for identifying whether there is a load current of an electric locomotive in a feeder current, wherein the feeder current is collected by an analog quantity collection module of a feeder protection device of a traction substation, the data operation module performs mathematical morphological filtering on the feeder current and performs short-time window zero-crossing statistics on the filtered morphological harmonic waveform, and the analysis and decision module identifies whether there is a load current of an electric locomotive in the feeder current according to the number of zero-crossing statistics. This helps relay protection to take blocking or suppression measures based on the judgment results, improve the reliability and sensitivity of relay protection, and ensure the safe and reliable operation of the traction power supply system. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 Schematic diagram of the logical structure of the device of the present invention.

[0028] Figure 2 This is the feeder current waveform containing unilateral excitation inrush current.

[0029] Figure 3 This is the zero-crossing frequency diagram of the morphological harmonic waveform of the feeder current containing unilateral excitation inrush current.

[0030] Figure 4 This is the feeder current waveform with symmetrical excitation inrush current.

[0031] Figure 5 This is the zero-crossing frequency diagram of the morphological harmonic waveform of the feeder current containing symmetrical excitation inrush current.

[0032] Figure 6 This is the feeder current waveform during the electric locomotive current increase process.

[0033] Figure 7 This is the zero-crossing frequency diagram of the morphological harmonic waveform of the feeder current during the electric locomotive current increase process.

[0034] Figure 8 This is the feeder current waveform of a high-resistance grounding fault.

[0035] Fig. 9 The figure shows the zero-crossing frequency of the harmonic waveform of the feeder current in a high-resistance grounding fault.

[0036] Fig.10 This is the feeder current waveform of the overhead contact network short-circuit test.

[0037] Fig.11 This is the zero-crossing frequency diagram of the morphological harmonic waveform of the feeder current in the overhead line short-circuit test. DETAILED DESCRIPTION

[0038] The technical solution of the present invention is described in detail below in conjunction with the accompanying drawings:

[0039] like Figure 1 As shown, the method for identifying the presence of electric locomotive load current in feeder current of the present invention is based on the feeder protection device of the electrified railway traction substation, and includes an analog quantity acquisition module, a data operation module, and an analysis and decision module. The traction substation feeder protection device is equipped with an analog quantity acquisition module for collecting feeder current. The data operation module completes mathematical morphological filtering and zero-crossing count of the morphological harmonic waveform based on the feeder current waveform. The analysis and decision module determines whether the feeder current contains the electric locomotive load current according to the zero-crossing count. The decision result can be used for the feeder protection to lock or inhibit the relay protection element.

[0040] Figure 1 As shown in , the analog quantity acquisition module is mainly used to collect the feeder current of the traction substation in real time and transmit it to the data operation module. The data operation module receives the feeder current data from the analog quantity acquisition module, performs mathematical morphological filtering on the feeder current waveform in real time, and counts the number of zero crossings of the filtered morphological harmonic waveform. The analysis and decision module determines whether there is electric locomotive load current in the feeder current based on the number of zero crossings.

[0041] Figure 1 As shown in , when the present invention is used, the traction substation feeder protection can lock or inhibit the relay protection element according to the identification result, thereby improving the reliability and sensitivity of the relay protection device.

[0042] The present invention comprises the following steps:

[0043] S1: Collect feeder current sampling value i(k) in the feeder protection device of the traction substation, with a sampling frequency of 96 points / cycle, where k is the sampling value sequence number, the same below.

[0044] S2: Morphological calculation of the feeder current waveform after the feeder protection element is activated: using i pz (k)=max{i(k-2),i(k-1),i(k)} performs expansion operation on the feeder current sampling value i(k), using i fs (k) = min{i(k-2),i(k-1),i(k)} performs corrosion operation on the feeder current sampling value i(k). pz (k) is the result of the expansion operation on the original waveform sampling value, i fs (k) is the result of corrosion operation on the feeder current sampling value, i(k) is the kth point of the original waveform sampling value, i(k-1) is the k-1th point of the original waveform sampling value, i(k-2) is the k-2th point of the original waveform sampling value, and the same below.

[0045] S3: Adoption Calculate the morphological harmonic components i in the feeder current h(k).

[0046] S4: If the morphological harmonics separated by mathematical morphology satisfy or It is believed that the morphological harmonic i h (k) Passing through zero once, within one quarter of a cycle, count the number of zero crossings N.

[0047] S5: If the number of zero crossings of the morphological harmonic waveform in the feeder current is N≥5, it is identified that the feeder current contains an electric locomotive load current. If N<5, it is identified that the feeder current waveform does not contain an electric locomotive load current.

[0048] The following five examples of normal operating conditions and short-circuit faults of electric locomotive loads collected from feeders of traction substations on electrified railways illustrate the effectiveness of the method proposed in the present invention.

[0049] 1. Feeder current waveform with unilateral excitation inrush current

[0050] like Figure 2 The waveform of the feeder current and morphological harmonics containing unilateral excitation inrush current is sampled at 96 points / cycle. Figure 3 The graph of the number of zero crossings N recursively calculated in a quarter-cycle time window versus time shows that the minimum number of zero crossings of the morphological harmonics is 8, which is greater than the set value of 5. The analysis and decision module identifies that the feeder current contains electric locomotive load current.

[0051] 2. Feeder current waveform with symmetrical magnetizing inrush current

[0052] like Figure 4 The waveform of the feeder current and morphological harmonics containing symmetrical excitation inrush current is sampled at 96 points / cycle. Figure 5 This is a graph of the number of zero crossings N recursively counted in a quarter-cycle time window versus time. It can be seen that the minimum number of morphological harmonic zero crossings is 9, which is greater than the set value of 5. The analysis and decision module identifies that the feeder current contains electric locomotive load current.

[0053] 3. Feeder current waveform during the electric locomotive current increase process

[0054] like Figure 6 The feeder current and morphological harmonic waveform of the electric locomotive current increase process, the sampling frequency is 96 points / cycle, such as Figure 7 This is a graph of the number of zero crossings N of the recursive quarter-cycle time window statistics changing with time. It can be seen that the minimum number of morphological harmonic zero crossings is 14, which is greater than the set value of 5. The analysis and decision module identifies that the feeder current contains electric locomotive load current.

[0055] 4. Feeder current waveform of high resistance ground fault

[0056] like Figure 8 The feeder current and morphological harmonic waveform of high-resistance grounding fault, the sampling frequency is 96 points / cycle, such as Fig. 9 The graph of the number of zero crossings N recursively calculated in a quarter-cycle time window versus time shows that the maximum number of zero crossings of the morphological harmonics is 2, which is less than the set value of 5. The analysis and decision module identifies that the feeder current does not contain the electric locomotive load current.

[0057] 5. Feeder current waveform of overhead line short circuit test

[0058] like Fig.10 The feeder current and morphological harmonic waveform of the overhead line short-circuit test, the sampling frequency is 96 points / cycle, such as Fig.11 The graph of the number of zero crossings N recursively calculated in a quarter-cycle time window versus time shows that the maximum number of zero crossings of the morphological harmonics is 1, which is less than the set value of 5. The analysis and decision module identifies that the feeder current does not contain the electric locomotive load current.

Claims

1. A method for identifying the presence of electric locomotive load current in feeder current, characterized in that: The following steps are involved: S1. Sample the feeder current to obtain a current sampling value i(k), where k is the sampling value sequence number; S2, perform morphological calculation on the current sampling value after the feeder protection element is started, specifically, perform expansion operation and corrosion operation respectively to obtain i pz (k) and i fs (k); S3. Calculate the morphological harmonic component i in the feeder current h (k): S4. Statistical Morphology Harmonics h (k) The number of zero crossings within a quarter of a cycle is N. The zero crossing determination method is: if the morphological harmonics satisfy or It is believed that the morphological harmonic i h (k) passes through zero once; S5. Determine whether N≥a is established, where a is a determination threshold determined according to the current sampling frequency. If so, the identification result is that the feeder current has an electric locomotive load current. Otherwise, the identification result is that the feeder current does not have an electric locomotive load current.

2. A method for identifying the presence of electric locomotive load current in feeder current according to claim 1, characterized in that: The sampling frequency of S1 is 96 points / cycle.

3. The method for identifying the presence of electric locomotive load current in feeder current according to claim 2, characterized in that: The expansion operation method in S2 is: i pz (k)=max{i(k-2),i(k-1),i(k)} The erosion operation method is: in fs (k) = min{i(k-2),i(k-1),i(k)}.

4. A method for identifying the presence of electric locomotive load current in feeder current according to claim 3, characterized in that: In S5, a=5.

5. A device for identifying the presence of electric locomotive load current in feeder current, characterized in that: It includes an analog quantity acquisition module, a data operation module, and an analysis and decision module; the analog quantity acquisition module is used to sample the feeder current to obtain a current sampling value i(k), where k is the sampling value sequence number; the data operation module is used to perform morphological calculations on the obtained current sampling values, specifically, performing expansion operations and corrosion operations to obtain i pz (k) and i fs (k), then calculate the morphological harmonic component i in the feeder current h (k): The final statistical morphology harmonics i h (k) The number of zero crossings within a quarter of a cycle is N. The zero crossing determination method is: if the morphological harmonics satisfy or It is believed that the morphological harmonic i h (k) passes through zero once; The analysis and decision module is used to determine whether the feeder current contains the electric locomotive load current. The specific method is to determine whether N≥a is established, where a is a judgment threshold determined according to the current sampling frequency. If so, the identification result is that the feeder current contains the electric locomotive load current. Otherwise, the identification result is that the feeder current does not contain the electric locomotive load current.

6. The device for identifying the presence of electric locomotive load current in feeder current according to claim 5, characterized in that: The sampling frequency of the analog acquisition module for sampling the feeder current is set to 96 points / cycle, and the expansion operation and corrosion operation are calculated in the data operation module to obtain i pz (k) and i fs (k) The method is: i pz (k)=max{i(k-2),i(k-1),i(k)} in fs (k)=min{i(k-2),i(k-1),i(k)} And in the analysis and decision module, the value of a is 5.

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