A Phase-Selectable Station Power AC Ring Network Monitoring Device and Method

Abstract

This invention provides a station service AC ring network monitoring device with selectable phases, comprising a current and voltage acquisition unit, a change ratio calculation unit, and an AC ring network confirmation and phase selection unit. When a ground fault occurs in one or more station service transformers, the current and voltage acquisition unit acquires the zero-sequence current before and after the activation of the low-voltage side protection of two station service transformers, as well as the A, B, and C three-phase voltages after the protection activation. The change ratio calculation unit determines whether the zero-sequence current changes abruptly based on the zero-sequence current before and after the activation of the low-voltage side protection of the two station service transformers. If so, it calculates the change ratio between the voltage of each phase and the zero-sequence current on the low-voltage side of each station service transformer, combining the A, B, and C three-phase voltages. The AC ring network confirmation and phase selection unit compares all change ratios with preset thresholds to determine whether an AC ring network exists at the station service point. If so, it compares the change ratios of the same phase and selects the phase line where the ring network exists. Implementing this invention enables rapid monitoring and phase selection of the low-voltage side ring network operation.

Description

Technical Field

[0001] This invention relates to the field of power system technology, and in particular to a device and method for monitoring AC ring networks of station power with selectable phases. Background Technology

[0002] The substation auxiliary power supply system is used to supply power to the station's auxiliary loads. It is converted from 10kV or 20kV to 380V by the auxiliary transformer. When the high-voltage side (such as 10kV or 20kV) of the auxiliary transformer is operating separately, the low-voltage side (such as 380V) cannot be operated in parallel (i.e., in ring network operation). The main reason is that the low-voltage side will generate a large ring network current due to the voltage difference between the busbars at both ends of the ring network. This ring network current may cause the auxiliary power system to trip, resulting in a loss of voltage in the 380V system within the substation. In severe cases, it may cause equipment burnout and expand the scope of the accident.

[0003] However, there is currently a lack of effective monitoring devices for the operation of low-voltage side ring networks. Summary of the Invention

[0004] The technical problem to be solved by the embodiments of the present invention is to provide a station power AC ring network monitoring device and method with selectable phase, which can quickly monitor the operation of the low-voltage side ring network and select the phase.

[0005] To address the aforementioned technical problems, this invention provides a phase-selectable AC ring network monitoring device for station power supplies. This device is connected to two current transformers pre-installed on the grounding neutral lines of two station power supply transformers, and also to six voltage transformers pre-installed on the A, B, and C phase lines of the corresponding output low-voltage busbars of the two station power supply transformers. The device includes: a current and voltage acquisition unit, a change ratio calculation unit, and an AC ring network confirmation and phase selection unit.

[0006] The current and voltage acquisition unit is used to acquire, when a ground fault occurs in one or more station service transformers, the zero-sequence currents on the low-voltage side of the two station service transformers collected by the two current transformers before the protection is started and the zero-sequence currents on the low-voltage side of the two station service transformers collected by the two current transformers after the protection is started, and to acquire the three-phase A, B, and C voltages on the low-voltage side of the two station service transformers collected by the six voltage transformers after the protection is started.

[0007] The change ratio calculation unit is used to determine whether the zero-sequence current of the low-voltage side of each station service transformer has a sudden change based on the zero-sequence current of the two station service transformers before and after the protection is started. When it is determined that the zero-sequence current of at least one station service transformer has a sudden change, the unit combines the three-phase voltages (A, B, C) of the two station service transformers after the protection is started to calculate the change ratio between the voltage of each phase and the zero-sequence current on the low-voltage side of the same station service transformer.

[0008] The AC loop network confirmation and phase selection unit is used to compare all the calculated change ratios with preset thresholds, and determine whether the AC loop network for power supply to the station exists based on the comparison results. When it is determined that the AC loop network for power supply to the station exists, the change ratios between the same phases on the low-voltage side of the two station service transformers are compared to select the phase line where the AC loop network for power supply to the station exists.

[0009] The change rate calculation unit includes:

[0010] The current mutation calculation module is used to subtract the zero-sequence current before the protection starts from the zero-sequence current after the low-voltage side protection of each station transformer starts, and the difference is output as the current mutation.

[0011] The current mutation judgment module is used to determine that at least one station service transformer has experienced a mutation in its zero-sequence current on the low-voltage side when it is determined that at least one current mutation amount is greater than the preset mutation amount limit.

[0012] The change ratio calculation module is used to calculate the change ratio between the phase voltage and the zero-sequence current on the low-voltage side of the same station service transformer based on the obtained three-phase A, B, and C voltages on the low-voltage side of the two station service transformers after protection activation, and in combination with the obtained zero-sequence currents on the low-voltage side of the two station service transformers before and after protection activation.

[0013] Among them, through the formula Calculate the ratio of the change in voltage of each phase to the zero-sequence current on the low-voltage side of the #1 station service transformer; where R xa#1 R xb#1 and R xc#1 These are the ratios of change between phase A voltage and zero-sequence current on the low-voltage side of transformer #1, respectively; the ratios of change between phase B voltage and zero-sequence current; and the ratios of change between phase C voltage and zero-sequence current. a#1 U b#1 and U c#1 These are the A-phase, B-phase, and C-phase voltages on the low-voltage side of transformer #1 after protection activation; U a#2 U b#2 and U c#2 These are the A-phase, B-phase, and C-phase voltages on the low-voltage side of the #2 substation transformer after protection activation; I 0l#1 This refers to the zero-sequence current on the low-voltage side of the #1 substation transformer after protection activation; I 0l#10 This refers to the zero-sequence current on the low-voltage side of the #1 station service transformer before the protection is activated; the two station service transformers consist of the #1 station service transformer and the #2 station service transformer.

[0014] Through formula Calculate the ratio of the change in voltage of each phase to the zero-sequence current on the low-voltage side of the transformer at station #2; where R xa#2 R xb#2 and R xc#2 These are the ratios of change between phase A voltage and zero-sequence current on the low-voltage side of transformer #2, respectively; the ratios of change between phase B voltage and zero-sequence current; and the ratios of change between phase C voltage and zero-sequence current. 0l#2 This refers to the zero-sequence current on the low-voltage side of the transformer at station #2 after protection activation; I 0l#20 This refers to the zero-sequence current on the low-voltage side of the transformer used at station #2 before the protection is activated.

[0015] The AC ring network confirmation and phase selection unit includes:

[0016] The AC ring network judgment module is used to compare all calculated change ratios with a preset threshold and determine whether the station power AC ring network exists based on the comparison results; wherein, if it is determined that each calculated change ratio is less than the preset threshold, the station power AC ring network is determined to exist; or, if it is determined that at least one of the calculated change ratios is greater than the preset threshold, the station power AC ring network is determined not to exist.

[0017] The ring network phase selection module is used to compare the change ratios between the same phases on the low-voltage sides of the two station service transformers when it is determined that an AC ring network exists at the station. Specifically, if the difference in the change ratio between phase A on the low-voltage sides of the two station service transformers is within a first predetermined range, then phase A is selected as having an AC ring network. If the difference in the change ratio between phase B on the low-voltage sides of the two station service transformers is within a second predetermined range, then phase B is selected as having an AC ring network. If the difference in the change ratio between phase C on the low-voltage sides of the two station service transformers is within a third predetermined range, then phase C is selected as having an AC ring network.

[0018] This also includes:

[0019] The early warning unit is used to output an alarm indicating that an AC loop exists on the selected phase line when a phase line of the AC loop network for power supply to the candidate station is found.

[0020] This invention also provides a method for monitoring a selectable phase AC ring network of station power supply, implemented on the aforementioned selectable phase AC ring network monitoring device. This device is connected to two current transformers pre-installed on the grounding neutral lines of two station power supply transformers, and also to six voltage transformers pre-installed on the A, B, and C phase lines of the corresponding output low-voltage busbars of the two station power supply transformers. The method includes the following steps:

[0021] When a ground fault occurs in one or more station service transformers, the zero-sequence currents on the low-voltage side of the two station service transformers collected by the two current transformers before the protection is started and the zero-sequence currents on the low-voltage side of the two station service transformers collected by the two current transformers after the protection is started are obtained, and the three-phase A, B, and C voltages on the low-voltage side of the two station service transformers collected by the six voltage transformers after the protection is started are obtained.

[0022] Based on the zero-sequence currents of the low-voltage sides of the two station service transformers before and after the protection is started, it is determined whether there is a sudden change in the zero-sequence current of the low-voltage side of each station service transformer. When it is determined that there is a sudden change in the zero-sequence current of the low-voltage side of at least one station service transformer, the three-phase A, B, and C voltages of the low-voltage sides of the two station service transformers after the protection is started are combined to calculate the change ratio of each phase voltage and the zero-sequence current in the low-voltage side of the same station service transformer.

[0023] All calculated change ratios are compared with preset thresholds. Based on the comparison results, it is determined whether the AC loop network for power supply to the station exists. Once it is determined that the AC loop network for power supply to the station exists, the change ratios between the same phases on the low-voltage side of the two station service transformers are compared to select the phase line where the AC loop network for power supply to the station exists.

[0024] The step of determining whether the zero-sequence current on the low-voltage side of each station service transformer undergoes a sudden change based on the zero-sequence currents obtained before and after protection activation of the two station service transformers, and calculating the change ratio between the zero-sequence current and the zero-sequence current when at least one station service transformer's low-voltage side is determined to have undergone a sudden change, by combining the obtained A, B, C, and three-phase voltages on the low-voltage sides of the two station service transformers after protection activation, specifically includes:

[0025] Subtract the zero-sequence current before the protection starts from the zero-sequence current after the low-voltage side protection of each station is started, and output the difference as the current surge.

[0026] When it is determined that at least one current mutation exceeds the preset mutation limit, it is determined that at least one station service transformer has experienced a mutation in the zero-sequence current on the low-voltage side.

[0027] Based on the obtained A, B, and C three-phase voltages of the low-voltage side of the two station service transformers after protection activation, and combined with the obtained zero-sequence currents of the low-voltage side of the two station service transformers before and after protection activation, the change ratios of each phase voltage and the zero-sequence current on the low-voltage side of the same station service transformer are calculated.

[0028] Among them, through the formula Calculate the ratio of the change in voltage of each phase to the zero-sequence current on the low-voltage side of the #1 station service transformer; where Rxa#1 R xb#1 and R xc#1 These are the ratios of change between phase A voltage and zero-sequence current on the low-voltage side of transformer #1, respectively; the ratios of change between phase B voltage and zero-sequence current; and the ratios of change between phase C voltage and zero-sequence current. a#1 U b#1 and U c#1 These are the A-phase, B-phase, and C-phase voltages on the low-voltage side of transformer #1 after protection activation; U a#2 U b#2 and U c#2 These are the A-phase, B-phase, and C-phase voltages on the low-voltage side of the #2 substation transformer after protection activation; I 0l#1 This refers to the zero-sequence current on the low-voltage side of the #1 substation transformer after protection activation; I 0l#10 This refers to the zero-sequence current on the low-voltage side of the #1 station service transformer before the protection is activated; the two station service transformers consist of the #1 station service transformer and the #2 station service transformer.

[0029] Through formula Calculate the ratio of the change in voltage of each phase to the zero-sequence current on the low-voltage side of the transformer at station #2; where R xa#2 R xb#2 and R xc#2 These are the ratios of change between phase A voltage and zero-sequence current on the low-voltage side of transformer #2, respectively; the ratios of change between phase B voltage and zero-sequence current; and the ratios of change between phase C voltage and zero-sequence current. 0l#2 This refers to the zero-sequence current on the low-voltage side of the transformer at station #2 after protection activation; I 0l#20 This refers to the zero-sequence current on the low-voltage side of the transformer used at station #2 before the protection is activated.

[0030] The specific steps of comparing all calculated change ratios with preset thresholds, determining whether an AC loop network exists for outgoing power supply based on the comparison results, and comparing the change ratios between the same phases on the low-voltage sides of the two station service transformers to select the phase lines where the AC loop network exists, include:

[0031] If it is determined that each calculated change ratio is less than the preset threshold, then it is determined that the station power AC loop network exists; or, if it is determined that at least one of the calculated change ratios is greater than the preset threshold, then it is determined that the station power AC loop network does not exist.

[0032] Once the existence of the AC loop network for station power supply is confirmed, the change ratios between the same phases on the low-voltage sides of the two station service transformers are compared to select the phase lines where the AC loop network exists. Specifically, if the difference in the change ratio between phase A on the low-voltage sides of the two station service transformers is determined to be within a first predetermined range, then phase A is selected as having an AC loop network. If the difference in the change ratio between phase B on the low-voltage sides of the two station service transformers is determined to be within a second predetermined range, then phase B is selected as having an AC loop network. If the difference in the change ratio between phase C on the low-voltage sides of the two station service transformers is determined to be within a third predetermined range, then phase C is selected as having an AC loop network.

[0033] Implementing the embodiments of the present invention has the following beneficial effects:

[0034] In this invention, when a ground fault occurs in one or more substation transformers, the device determines whether the zero-sequence current changes abruptly by acquiring the zero-sequence current before and after the low-voltage side protection of the two substation transformers is activated. If so, the device acquires the three-phase voltages (A, B, and C) of the two substation transformers after the low-voltage side protection is activated, and calculates the change ratio between the voltage of the two substation transformers and the zero-sequence current by combining the aforementioned zero-sequence current. The change ratio is then compared with a preset threshold to determine whether a substation AC loop exists. If a loop exists, the corresponding phase line is selected, thereby enabling rapid monitoring and phase selection of the low-voltage side loop operation. Attached Figure Description

[0035] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, obtaining other drawings based on these drawings without creative effort still falls within the scope of the present invention.

[0036] Figure 1 A circuit connection diagram of a station power supply system with an A-phase AC ring network provided in an embodiment of the present invention;

[0037] Figure 2 A schematic diagram of a station power AC ring network monitoring device with selectable phase provided in an embodiment of the present invention;

[0038] Figure 3 for Figure 2 A schematic diagram of the structure of the change rate calculation unit;

[0039] Figure 4 for Figure 2 Schematic diagram of the AC ring network confirmation and phase selection unit;

[0040] Figure 5A flowchart illustrating the detection of an AC ring network in an application scenario of a station power AC ring network monitoring device with selectable phases provided in an embodiment of the present invention;

[0041] Figure 6 Another flowchart for detecting AC ring networks in an application scenario of a selectable phase station power AC ring network monitoring device provided in an embodiment of the present invention;

[0042] Figure 7 A flowchart illustrating a method for monitoring a station power AC ring network with selectable phases, provided in an embodiment of the present invention. Detailed Implementation

[0043] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings.

[0044] The inventor discovered that, such as Figure 1 As shown, when a loop load Rx exists in phase A between the low-voltage side busbars n1 and n2 of transformers #1 and #2, if a ground fault occurs in transformers #1 and / or #2, the voltage difference in phase A will cause the grounded neutral line to form a loop with the earth, resulting in a loop current I at the neutral point of both transformers. 0l Based on the principle that changes in voltage on both busbar sides will cause changes in current, and that the voltage-current change ratio is linear with the load connected to the low-voltage side of the station service transformer and the ring network load, the inventors proposed a device that can monitor and select phases for the operation of the low-voltage side ring network.

[0045] like Figure 2 As shown in the illustration, this invention provides a selectable phase AC ring network monitoring device for station power supply. This device can be installed in an AC switchgear cabinet of ATS1 or ATS2 (i.e., automatic transfer switchgear) and connected to two station power transformers (such as...). Figure 1 The two current transformers (such as those used in the grounding neutral line of the #1 and #2 substation transformers) Figure 1 Both CTs in the system are connected, and they are also connected to the corresponding low-voltage busbars of the two station service transformers (such as...). Figure 1 The A, B, and C phase lines of the intermediate busbars n1 and n2 (e.g.) Figure 1 The six voltage transformers (not shown) on both sides of the middle (a phase, b phase, c phase) are all connected, including: current and voltage acquisition unit 1, change ratio calculation unit 2, AC ring network confirmation and phase selection unit 3, and early warning unit 4.

[0046] At this time, the current and voltage acquisition unit 1 is used to acquire the zero-sequence current of the low-voltage side of the two station service transformers before the protection starts, collected by two current transformers, and the zero-sequence current of the low-voltage side of the two station service transformers after the protection starts, when a ground fault occurs in one or more station service transformers. It also acquires the three-phase A, B, and C voltages of the low-voltage side of the two station service transformers after the protection starts, collected by six voltage transformers. It should be noted that the zero-sequence current before the protection starts is the effective value of the zero-sequence current within a certain period of time (e.g., -100ms to -20ms) before the protection starts, and the zero-sequence current after the protection starts is the effective value of the zero-sequence current within a certain period of time (e.g., 20 to 100ms) after the protection starts. The three-phase A, B, and C voltages after the protection starts are the effective values ​​of the three phases A, B, and C within a certain period of time (e.g., 20 to 100ms) after the protection starts.

[0047] At this time, the change ratio calculation unit 2 is used to determine whether the zero-sequence current of the low-voltage side of each station service transformer has changed abruptly based on the zero-sequence current of the two station service transformers before and after the protection is started. When it is determined that the zero-sequence current of at least one station service transformer has changed abruptly, the unit combines the three-phase voltages (A, B, C) of the two station service transformers after the protection is started to calculate the change ratio between the voltage of each phase and the zero-sequence current on the low-voltage side of the same station service transformer.

[0048] Specifically, such as Figure 3 As shown, the change rate calculation unit 2 includes:

[0049] The current mutation calculation module 21 is used to subtract the zero-sequence current before the protection starts from the zero-sequence current after the low-voltage side protection of each station transformer starts, and the difference is output as the current mutation.

[0050] The current mutation judgment module 22 is used to determine that at least one station service transformer has a mutation in the zero-sequence current on the low-voltage side when it is determined that at least one current mutation is greater than the preset mutation limit.

[0051] The change ratio calculation module 23 is used to calculate the change ratio between the voltage of each phase and the zero-sequence current on the low-voltage side of the same station service transformer based on the obtained three-phase A, B, C voltages on the low-voltage side of the two station service transformers after the protection is started, and in combination with the obtained zero-sequence currents on the low-voltage side of the two station service transformers before and after the protection is started.

[0052] In one embodiment, the ratio of the change in voltage of each phase and the zero-sequence current on the low-voltage side of the #1 station service transformer is calculated using formula (1);

[0053]

[0054] Among them, Rxa#1 R xb#1 and R xc#1 These are the ratios of change between phase A voltage and zero-sequence current on the low-voltage side of transformer #1, respectively; the ratios of change between phase B voltage and zero-sequence current; and the ratios of change between phase C voltage and zero-sequence current. a#1 U b#1 and U c#1 These are the A-phase, B-phase, and C-phase voltages on the low-voltage side of transformer #1 after protection activation; U a#2 U b#2 and U c#2 These are the A-phase, B-phase, and C-phase voltages on the low-voltage side of the #2 substation transformer after protection activation; I 0l#1 This refers to the zero-sequence current on the low-voltage side of the #1 substation transformer after protection activation; I 0l#10 This refers to the zero-sequence current on the low-voltage side of the transformer at station #1 before the protection is activated.

[0055] Using formula (2), the ratio of the change in voltage of each phase and the zero-sequence current on the low-voltage side of the transformer at station #2 is calculated.

[0056]

[0057] Among them, R xa#2 R xb#2 and R xc#2 These are the ratios of change between phase A voltage and zero-sequence current on the low-voltage side of transformer #2, respectively; the ratios of change between phase B voltage and zero-sequence current; and the ratios of change between phase C voltage and zero-sequence current. 0l#2 This refers to the zero-sequence current on the low-voltage side of the transformer at station #2 after protection activation; I 0l#20 This refers to the zero-sequence current on the low-voltage side of the transformer used at station #2 before the protection is activated.

[0058] At this time, the AC ring network confirmation and phase selection unit 3 is used to compare all the calculated change ratios with the preset threshold, and determine whether the AC ring network for power supply to the station exists based on the comparison results. When it is determined that the AC ring network for power supply to the station exists, the change ratios between the same phases on the low-voltage side of the two station service transformers are compared to select the phase line where the AC ring network for power supply to the station exists.

[0059] Specifically, such as Figure 4 As shown, the AC ring network confirmation and phase selection unit 3 includes:

[0060] The AC ring network judgment module 31 is used to compare all the calculated change ratios with a preset threshold, and determine whether the AC ring network for power supply at the station exists based on the comparison results; wherein, if it is determined that each of the calculated change ratios is less than the preset threshold, the AC ring network for power supply at the station is determined to exist; or, if it is determined that at least one of the calculated change ratios is greater than the preset threshold, the AC ring network for power supply at the station is determined not to exist.

[0061] For example, if R xa#1 R xb#1 R xc#1 R xa#2 R xb#2 and R xc#2 If all values ​​are less than the preset threshold k, then the existence of the station's AC power loop network is confirmed; otherwise, if R... xa#1 R xb#1 R xc#1 R xa#2 R xb#2 and R xc#2 If any one of them is greater than the preset threshold k, then it is determined that the station's AC power ring network does not exist;

[0062] The ring network phase selection module 32 is used to compare the change ratios between the same phases on the low-voltage sides of the two station service transformers when it is determined that an AC ring network exists at the station. Specifically, if the difference in the change ratio between phase A on the low-voltage sides of the two station service transformers is within a first predetermined range, then phase A is selected as having an AC ring network. If the difference in the change ratio between phase B on the low-voltage sides of the two station service transformers is within a second predetermined range, then phase B is selected as having an AC ring network. If the difference in the change ratio between phase C on the low-voltage sides of the two station service transformers is within a third predetermined range, then phase C is selected as having an AC ring network. It is understood that the selection of phases for an AC ring network is not limited to single-phase, but can also include two-phase or three-phase, so the above determination conditions can be freely combined, which will not be elaborated here.

[0063] For example, if R xa#1 -R xa#2 If the difference lies within [-a1, a1], then there is an AC loop between the low-voltage sides of transformer #1 and transformer #2 on phase A; similarly, if R xb#1 -R xb#2 If the difference is within [-b1, b1], then there is an AC loop between phase B of the low-voltage side of transformer #1 and transformer #2; if R xc#1 -R xc#2 If the difference is within [-c1,c1], then there is an AC loop between the low-voltage sides of the transformers at stations #1 and #2 in phase C.

[0064] And so on, if Rxa#1 -R xa#2 The difference lies within [-a1, a1] and R xb#1 -R xb#2 If the difference is within [-b1, b1], then there are AC loops between phases A and B on the low-voltage side of both the #1 station transformer and the #2 station transformer.

[0065] It should be noted that in the ring network phase selection module 32, the phase lines of the selected station power AC ring network can also be determined based on the standard deviation formed by the current and voltage change rate after the current protection starts and the current and voltage change rate after the previous protection starts.

[0066] For example, the standard deviation of each phase line can be calculated using formula (3);

[0067]

[0068] Among them, R xai#1 R xbi#1 R xci#1 These represent the change ratios of phases A, B, and C during the i-th startup of the low-voltage side of transformer #1; R xai#2 R xbi#2 R xci#2 These represent the change ratios of phases A, B, and C during the i-th startup of the low-voltage side of transformer #2; R xa(i-1)#1 R xb(i-1)#1 R xc(i-1)#1 These represent the change ratios of phases A, B, and C during the (i-1)th startup of the low-voltage side of transformer #1; R xa(i-1)#2 R xb(i-1)#2 R xc(i-1)#2 These represent the change ratios of phases A, B, and C during the (i-1)th startup of the low-voltage side of transformer #2 at station service; This is the average ratio of current to voltage change.

[0069] At this time, the early warning unit 4, after the phase line of the selected station power AC ring network exists, will alarm and output that the selected phase line has an AC ring network.

[0070] like Figure 5 and Figure 6 As shown, the application scenario of a selectable phase station power AC ring network monitoring device for detecting AC ring networks in an embodiment of the present invention is further explained as follows:

[0071] exist Figure 5 First, determine the sudden change ΔI of the zero-sequence current used at station #1 or station #2. 0l Does ≥n satisfy the condition? If so, calculate the ratio R of the change between phase A voltage and zero-sequence current on the low-voltage side of transformer #1. xa#1The ratio R of the change between phase B voltage and zero-sequence current xb#1 and the ratio R of the change between the C-phase voltage and the zero-sequence current xc#1 The calculation is shown in formula (1); and the ratio R of the change between the phase A voltage and the zero-sequence current on the low-voltage side of the transformer at station #2 is calculated. xa#2 The ratio R of the change between phase B voltage and zero-sequence current xb#2 and the ratio R of the change between the C-phase voltage and the zero-sequence current xc#2 The calculation is shown in formula (2); next, determine R. xa#1 R xb#1 R xc#1 R xa#2 R xb#2 and R xc#2 Are all values ​​less than the preset threshold k? If so, then the existence of the station's AC power ring network is confirmed. Finally, based on R... xa#1 -R xa#2 Is the difference within [-a1, a1]? R xb#1 -R xb#2 Whether the difference lies within [-b1, b1] and R xc#1 -R xc#2 The difference is judged item by item to determine whether it is within [-c1,c1], in order to select whether there is an AC loop network between the low voltage side of the #1 station service transformer and the #2 station service transformer in the three phases A, B, and C.

[0072] exist Figure 6 First, determine the sudden change ΔI of the zero-sequence current used at station #1 or station #2. 0l Does ≥n satisfy the condition? If so, calculate the ratio R of the change between phase A voltage and zero-sequence current during the i-th and (i-1)-th startups of the low-voltage side of transformer #1. xa#1 The ratio R of the change between phase B voltage and zero-sequence current during the i-th start-up and the (i-1)-th start-up. xb#1 The ratio R of the change between phase C voltage and zero-sequence current during the i-th start and the (i-1)-th start. xc#1 See formula (1) for calculation; and calculate the ratio R of the change between phase A voltage and zero-sequence current during the i-th and i-1-th startups of the low-voltage side of the #2 station transformer. xa#2 The ratio R of the change between phase B voltage and zero-sequence current during the i-th and (i-1)-th startups xb#2 The ratio R of the change between phase C voltage and zero-sequence current during the i-th and (i-1)-th startups. xc#2 For calculation, please refer to formula (2); next, determine R. xa#1 R xb#1 R xc#1 R xa#2 R xb#2 and Rxc#2 Are all values ​​less than the preset threshold k? If so, then the existence of the station service AC loop network is confirmed. Then, calculate the standard deviation of the i-th change ratio and the (i-1)-th change ratio of the three phases A, B, and C on the low-voltage side of station service transformers #1 and #2 to obtain T. xai T xbi T xci The calculation is shown in formula (3); finally, according to T xai T xbi T xci Each item is judged individually to determine whether it is less than the threshold m, in order to select that there is an AC loop network between the low-voltage sides of the #1 station service transformer and the #2 station service transformer in the three phases A, B, and C.

[0073] like Figure 7 As shown in the illustration, a method for monitoring a selectable-phase AC ring network of station power supply is provided in an embodiment of the present invention. This method is implemented on a selectable-phase AC ring network monitoring device for station power supply, which is connected to two current transformers pre-installed on the grounding neutral lines of two station power transformers, and also to six voltage transformers pre-installed on the A, B, and C phase lines of the corresponding output low-voltage busbars of the two station power transformers. The method includes the following steps:

[0074] Step S1: When a ground fault occurs in one or more station service transformers, obtain the zero-sequence current of the low-voltage side of the two station service transformers before the protection is started, collected by the two current transformers, and the zero-sequence current of the low-voltage side of the two station service transformers after the protection is started, and obtain the three-phase A, B, and C voltages of the low-voltage side of the two station service transformers after the protection is started, collected by the six voltage transformers.

[0075] Step S2: Based on the zero-sequence currents of the low-voltage sides of the two station service transformers before and after the protection is started, determine whether there is a sudden change in the zero-sequence current of the low-voltage side of each station service transformer. When it is determined that there is a sudden change in the zero-sequence current of the low-voltage side of at least one station service transformer, combine the three-phase A, B, and C voltages of the low-voltage sides of the two station service transformers after the protection is started to calculate the change ratio between the voltage of each phase and the zero-sequence current on the low-voltage side of the same station service transformer.

[0076] Step S3: Compare all the calculated change ratios with the preset thresholds, and determine whether the AC ring network for outgoing power supply exists based on the comparison results. Once it is determined that the AC ring network for outgoing power supply exists, compare the change ratios between the same phases on the low-voltage side of the two station service transformers to select the phase lines where the AC ring network for outgoing power supply exists.

[0077] The specific process is as follows: In step S1, when a ground fault occurs in one or more station service transformers (such as station service transformer #1 or / and station service transformer #2), the zero-sequence currents of the low-voltage side of the two station service transformers collected by two current transformers before the protection is started and the zero-sequence currents of the low-voltage side of the two station service transformers collected by the two current transformers after the protection is started are obtained, and the three-phase A, B, and C voltages of the low-voltage side of the two station service transformers collected by six voltage transformers after the protection is started are obtained.

[0078] In step S2, firstly, the zero-sequence current before the protection starts is subtracted from the zero-sequence current after the low-voltage side protection of each station is started, and the difference is output as the current surge.

[0079] Secondly, when it is determined that at least one current change exceeds the preset change limit, it is determined that at least one station service transformer has experienced a change in zero-sequence current on the low-voltage side.

[0080] Finally, based on the obtained three-phase (A, B, C) voltages of the low-voltage side of the two station service transformers after protection activation, and combined with the obtained zero-sequence currents of the low-voltage side of the two station service transformers before and after protection activation, the change ratios of each phase voltage and the zero-sequence current on the low-voltage side of the same station service transformer are calculated.

[0081] Among them, through the formula Calculate the ratio of the change in voltage of each phase to the zero-sequence current on the low-voltage side of the #1 station service transformer; where R xa#1 R xb#1 and R xc#1 These are the ratios of change between phase A voltage and zero-sequence current on the low-voltage side of transformer #1, respectively; the ratios of change between phase B voltage and zero-sequence current; and the ratios of change between phase C voltage and zero-sequence current. a#1 U b#1 and U c#1 These are the A-phase, B-phase, and C-phase voltages on the low-voltage side of transformer #1 after protection activation; U a#2 U b#2 and U c#2 These are the A-phase, B-phase, and C-phase voltages on the low-voltage side of the #2 substation transformer after protection activation; I 0l#1 This refers to the zero-sequence current on the low-voltage side of the #1 substation transformer after protection activation; I 0l#10 This refers to the zero-sequence current on the low-voltage side of the #1 station service transformer before the protection is activated; the two station service transformers consist of the #1 station service transformer and the #2 station service transformer.

[0082] Through formula Calculate the ratio of the change in voltage of each phase to the zero-sequence current on the low-voltage side of the transformer at station #2; where R xa#2 R xb#2 and R xc#2 These are the ratios of change between phase A voltage and zero-sequence current on the low-voltage side of transformer #2, respectively; the ratios of change between phase B voltage and zero-sequence current; and the ratios of change between phase C voltage and zero-sequence current. 0l#2 This refers to the zero-sequence current on the low-voltage side of the transformer at station #2 after protection activation; I 0l#20 This refers to the zero-sequence current on the low-voltage side of the transformer used at station #2 before the protection is activated.

[0083] In step S3, firstly, if it is determined that each calculated change ratio is less than the preset threshold, then it is determined that the station power AC loop network exists; or, if it is determined that at least one of the calculated change ratios is greater than the preset threshold, then it is determined that the station power AC loop network does not exist.

[0084] Finally, once the existence of the AC loop network for the outgoing station power supply is confirmed, the change ratios between the same phases on the low-voltage sides of the two station service transformers are compared to select the phase lines where the AC loop network exists. Specifically, if the difference in the change ratio between phase A on the low-voltage sides of the two station service transformers is determined to be within a first predetermined range, then phase A is selected as having an AC loop network; if the difference in the change ratio between phase B on the low-voltage sides of the two station service transformers is determined to be within a second predetermined range, then phase B is selected as having an AC loop network; and if the difference in the change ratio between phase C on the low-voltage sides of the two station service transformers is determined to be within a third predetermined range, then phase C is selected as having an AC loop network.

[0085] Implementing the embodiments of the present invention has the following beneficial effects:

[0086] In this invention, when a ground fault occurs in one or more substation transformers, the device determines whether the zero-sequence current changes abruptly by acquiring the zero-sequence current before and after the low-voltage side protection of the two substation transformers is activated. If so, the device acquires the three-phase voltages (A, B, and C) of the two substation transformers after the low-voltage side protection is activated, and calculates the change ratio between the voltage of the two substation transformers and the zero-sequence current by combining the aforementioned zero-sequence current. The change ratio is then compared with a preset threshold to determine whether a substation AC loop exists. If a loop exists, the corresponding phase line is selected, thereby enabling rapid monitoring and phase selection of the low-voltage side loop operation.

[0087] It is worth noting that in the above device embodiments, the various device modules are divided according to functional logic, but are not limited to the above division, as long as the corresponding functions can be achieved; in addition, the specific names of each functional module are only for easy differentiation and are not used to limit the scope of protection of the present invention.

[0088] Those skilled in the art will understand that all or part of the steps in the methods of the above embodiments can be implemented by a program instructing related hardware. The program can be stored in a computer-readable storage medium, such as ROM / RAM, disk, optical disk, etc.

[0089] The above description discloses only preferred embodiments of the present invention and should not be construed as limiting the scope of the present invention. Therefore, equivalent variations made in accordance with the claims of the present invention are still within the scope of the present invention.

Claims

1. An optional phase station power AC ring network monitoring device, characterized in that, It is connected with two current transformers preset on the ground neutral line of two station transformers, and also connected with six voltage transformers preset on A, B and C phase lines of corresponding output low voltage bus bars of two station transformers, comprising: a current and voltage acquisition unit, a change ratio calculation unit and an AC ring network confirmation and phase selection unit; wherein, The current and voltage acquisition unit is configured to acquire zero sequence currents of low voltage sides of two station transformers before protection starting and zero sequence currents of low voltage sides of two station transformers after protection starting collected by the two current transformers, and acquire A, B and C three-phase voltages of low voltage sides of two station transformers after protection starting collected by the six voltage transformers when ground fault occurs in one or more station transformers; The change ratio calculation unit is configured to determine whether the zero sequence current of the low voltage side of each station transformer appears to be abrupt according to the obtained zero sequence currents of low voltage sides of two station transformers before and after protection starting, and calculate the change ratio of each phase voltage and zero sequence current in the low voltage side of the same station transformer according to the obtained A, B and C three-phase voltages of low voltage sides of two station transformers after protection starting when it is determined that the zero sequence current of at least one low voltage side of station transformer appears to be abrupt; The AC ring network confirmation and phase selection unit is configured to compare all the calculated change ratios with a preset threshold, and determine whether the AC ring network of station electricity exists according to the comparison result, and compare the change ratios between the same phases of low voltage sides of two station transformers to select the phase line in which the AC ring network of station electricity exists when it is determined that the AC ring network of station electricity exists.

2. The selectable phase station power AC ring monitoring device of claim 1, wherein, The change ratio calculation unit comprises: A current abruptness calculation module configured to subtract the zero sequence current before protection starting from the zero sequence current after protection starting of each low voltage side of station transformer, and output the difference as a current abruptness; A current abruptness judgment module configured to determine that the zero sequence current of at least one low voltage side of station transformer appears to be abrupt when it is determined that at least one current abruptness is greater than a preset abruptness limit value; A change ratio calculation module configured to calculate the change ratio of each phase voltage and zero sequence current in the low voltage side of the same station transformer according to the obtained A, B and C three-phase voltages of low voltage sides of two station transformers after protection starting, and in combination with the obtained zero sequence currents of low voltage sides of two station transformers before and after protection starting.

3. The selectable phase station power AC ring monitoring device of claim 2, wherein, Through the formula The change ratio of each phase voltage in the low voltage side of the transformer for #1 station with zero sequence current is calculated respectively; wherein, R xa#1 , R xb#1 and R xc#1 are respectively the change ratio of A phase voltage, the change ratio of B phase voltage and the change ratio of C phase voltage in the low voltage side of the transformer for #1 station with zero sequence current; U a#1 , U b#1 and U c#1 are respectively A phase voltage, B phase voltage and C phase voltage in the low voltage side of the transformer for #1 station after protection starting; U a#2 , U b#2 and U c#2 are respectively A phase voltage, B phase voltage and C phase voltage in the low voltage side of the transformer for #2 station after protection starting; I 0l#1 is zero sequence current in the low voltage side of the transformer for #1 station after protection starting; I 0l#10 is zero sequence current in the low voltage side of the transformer for #1 station before protection starting; the two station transformers are composed of the transformer for #1 station and the transformer for #2 station; Through the formula The change ratio of each phase voltage in the low voltage side of the transformer for #2 station with zero sequence current is calculated; wherein, R xa#2 , R xb#2 and R xc#2 are respectively the change ratio of A phase voltage in the low voltage side of the transformer for #2 station with zero sequence current, the change ratio of B phase voltage with zero sequence current and the change ratio of C phase voltage with zero sequence current; I 0l#2 is the zero sequence current in the low voltage side of the transformer for #2 station after the protection is started; and I 0l#20 is the zero sequence current in the low voltage side of the transformer for #2 station before the protection is started.

4. The phase-selective station power AC ring monitoring device of claim 3, wherein, The AC ring network confirmation and phase selection unit comprises: An AC ring network judgment module configured to compare all the calculated change ratios with a preset threshold, and determine whether the AC ring network of station electricity exists according to the comparison result; wherein, if it is determined that each calculated change ratio is less than the preset threshold, it is determined that the AC ring network of station electricity exists; or, if it is determined that at least one of the calculated change ratios is greater than the preset threshold, it is determined that the AC ring network of station electricity does not exist; The ring network phase selection module is configured to, when it is determined that the outgoing power AC ring network exists, compare the change ratios between the same phases of the low-voltage sides of the two outgoing power transformers to select the phase in which the outgoing power AC ring network exists; wherein, if the difference between the change ratios between the A phases of the low-voltage sides of the two outgoing power transformers is within a first predetermined range, it is determined that the A phase exists in the AC ring network; if the difference between the change ratios between the B phases of the low-voltage sides of the two outgoing power transformers is within a second predetermined range, it is determined that the B phase exists in the AC ring network; and if the difference between the change ratios between the C phases of the low-voltage sides of the two outgoing power transformers is within a third predetermined range, it is determined that the C phase exists in the AC ring network.

5. The selectable phase station power AC ring monitoring device of claim 4, wherein, Further comprising: A pre-warning unit configured to, after the phase in which the outgoing power AC ring network exists is selected, output an alarm that the selected phase has the AC ring network.

6. A method for monitoring an AC ring network for optional phase service, characterized by, The method is implemented on the optional-phase outgoing power AC ring network monitoring device as claimed in claim 5, which is connected to two current transformers preset on the ground neutral lines of two outgoing power transformers, and is also connected to six voltage transformers preset on the A, B and C phase lines of the corresponding outgoing power transformer low-voltage busbars of the two outgoing power transformers; the method comprises the following steps: When a ground fault occurs in one or more outgoing power transformers, the zero-sequence currents of the low-voltage sides of the two outgoing power transformers before protection startup collected by the two current transformers, the zero-sequence currents of the low-voltage sides of the two outgoing power transformers after protection startup collected by the two current transformers, and the A, B and C three-phase voltages of the low-voltage sides of the two outgoing power transformers after protection startup collected by the six voltage transformers are obtained; According to the obtained zero-sequence currents of the low-voltage sides of the two outgoing power transformers before and after protection startup, it is determined whether the zero-sequence current of each outgoing power transformer low-voltage side has a sudden change, and when it is determined that the zero-sequence current of at least one outgoing power transformer low-voltage side has a sudden change, the A, B and C three-phase voltages of the low-voltage sides of the two outgoing power transformers after protection startup are combined to calculate the change ratio formed by each phase voltage and the zero-sequence current in the same outgoing power transformer low-voltage side. After all the calculated change ratios are compared with a preset threshold value, and according to the comparison result, it is determined whether the outgoing power AC ring network exists, and when it is determined that the outgoing power AC ring network exists, the change ratios between the same phases of the low-voltage sides of the two outgoing power transformers are compared to select the phase in which the outgoing power AC ring network exists.

7. The phase-selective station power monitoring method of claim 6, wherein, The step of determining, according to the obtained zero-sequence currents of the low-voltage sides of the two outgoing power transformers before and after protection startup, whether the zero-sequence current of each outgoing power transformer low-voltage side has a sudden change, and when it is determined that the zero-sequence current of at least one outgoing power transformer low-voltage side has a sudden change, combining the A, B and C three-phase voltages of the low-voltage sides of the two outgoing power transformers after protection startup to calculate the change ratio formed by each phase voltage and the zero-sequence current in the same outgoing power transformer low-voltage side specifically comprises: The zero-sequence current of each outgoing power transformer low-voltage side after protection startup is subtracted by the zero-sequence current of the same outgoing power transformer low-voltage side before protection startup, and the obtained difference is output as a current sudden change variable. When it is determined that at least one current mutation value is greater than the preset mutation value limit, it is determined that at least one zero sequence current of the low-voltage side of the station transformer has a mutation; According to the obtained ABC three-phase voltages of the low-voltage sides of the two station transformers after the protection is started, and in combination with the obtained zero sequence currents of the low-voltage sides of the two station transformers before and after the protection is started, the change ratios respectively formed by each phase voltage and the zero sequence current of the low-voltage side of the same station transformer are calculated.

8. The method of claim 7, wherein the method further comprises: determining if the selected phase is the same as the previous selected phase; and if the selected phase is different than the previous selected phase, then updating the selected phase in the selected phase register. The formula is The change ratio of each phase voltage in the low voltage side of the transformer for #1 station with zero sequence current is calculated respectively; wherein, R xa#1 , R xb#1 and R xc#1 are respectively the change ratio of A phase voltage, the change ratio of B phase voltage and the change ratio of C phase voltage in the low voltage side of the transformer for #1 station with zero sequence current; U a#1 , U b#1 and U c#1 are respectively A phase voltage, B phase voltage and C phase voltage in the low voltage side of the transformer for #1 station after protection starting; U a#2 , U b#2 and U c#2 are respectively A phase voltage, B phase voltage and C phase voltage in the low voltage side of the transformer for #2 station after protection starting; I 0l#1 is zero sequence current in the low voltage side of the transformer for #1 station after protection starting; I 0l#10 is zero sequence current in the low voltage side of the transformer for #1 station before protection starting; the two station transformers are composed of the transformer for #1 station and the transformer for #2 station; The formula is The change ratio of each phase voltage in the low voltage side of the transformer for #2 station with zero sequence current is calculated, wherein R xa#2 , R xb#2 and R xc#2 are respectively the change ratio of A phase voltage in the low voltage side of the transformer for #2 station with zero sequence current, the change ratio of B phase voltage with zero sequence current and the change ratio of C phase voltage with zero sequence current; I 0l#2 is the zero sequence current in the low voltage side of the transformer for #2 station after the protection is started; and I 0l#20 is the zero sequence current in the low voltage side of the transformer for #2 station before the protection is started.

9. The method for monitoring a station power AC ring network with selectable phases as described in claim 8, characterized in that, The step of comparing all the calculated change ratios with the preset threshold value, and determining whether the station electricity AC loop network exists according to the comparison result, and comparing the change ratios between the same phases of the low-voltage sides of the two station transformers to select the phase line in which the station electricity AC loop network exists when it is determined that the station electricity AC loop network exists, specifically comprises: If it is determined that each calculated change ratio is less than the preset threshold value, it is determined that the station electricity AC loop network exists; or if it is determined that at least one of the calculated change ratios is greater than the preset threshold value, it is determined that the station electricity AC loop network does not exist; When it is determined that the station electricity AC loop network exists, the change ratios between the same phases of the low-voltage sides of the two station transformers are compared to select the phase line in which the station electricity AC loop network exists; wherein if it is determined that the difference between the change ratios of the A phases of the low-voltage sides of the two station transformers is within a first predetermined range, it is determined that the A phase exists the AC loop network; if it is determined that the difference between the change ratios of the B phases of the low-voltage sides of the two station transformers is within a second predetermined range, it is determined that the B phase exists the AC loop network; and if it is determined that the difference between the change ratios of the C phases of the low-voltage sides of the two station transformers is within a third predetermined range, it is determined that the C phase exists the AC loop network.

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